无法实例化活动:尝试调用虚拟方法 android.content.Context.getResources() [英] Unable to instantiate activity:Attempt to invoke virtual method android.content.Context.getResources()
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问题描述
我是初学者.
<块引用>首先说我看过以前的帖子但没有回答.
我尝试测试一个音频播放器，但是当我尝试运行该应用程序时，它会因为空对象引用而立即崩溃.
这是 Logcat:(此日志说:错误在 java 代码的第 28 行)
例外:主要进程:ir.pluto.mediaplayer，PID:19100java.lang.RuntimeException:无法实例化活动 ComponentInfo{ir.pluto.mediaplayer/ir.pluto.mediaplayer.MainActivity}:java.lang.NullPointerException:尝试调用虚拟方法 'android.content.res.Resources android.content.Context.getResources()' 在空对象引用上在 android.app.ActivityThread.performLaunchActivity(ActivityThread.java:3132)在 android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3415)在 android.app.ActivityThread.access$1100(ActivityThread.java:229)在 android.app.ActivityThread$H.handleMessage(ActivityThread.java:1821)在 android.os.Handler.dispatchMessage(Handler.java:102)在 android.os.Looper.loop(Looper.java:148)在 android.app.ActivityThread.main(ActivityThread.java:7325)在 java.lang.reflect.Method.invoke(Native Method)在 com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1230)在 com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1120)引起:java.lang.NullPointerException:尝试在空对象引用上调用虚拟方法android.content.res.Resources android.content.Context.getResources()"在 android.content.ContextWrapper.getResources(ContextWrapper.java:92)在 android.view.ContextThemeWrapper.getResources(ContextThemeWrapper.java:81)在 android.view.View.(View.java:4054)在 android.view.View.(View.java:4186)在 android.widget.ProgressBar.(ProgressBar.java:313)在 android.widget.AbsSeekBar.(AbsSeekBar.java:188)在 android.widget.SeekBar.(SeekBar.java:85)在 android.widget.SeekBar.(SeekBar.java:81)在 android.widget.SeekBar.(SeekBar.java:77)在 android.widget.SeekBar.(SeekBar.java:73)在 ir.pluto.mediaplayer.MainActivity.(MainActivity.java:28)在 java.lang.Class.newInstance(本机方法)在 android.app.Instrumentation.newActivity(Instrumentation.java:1096)在 android.app.ActivityThread.performLaunchActivity(ActivityThread.java:3122)在 android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3415)在 android.app.ActivityThread.access$1100(ActivityThread.java:229)在 android.app.ActivityThread$H.handleMessage(ActivityThread.java:1821)在 android.os.Handler.dispatchMessage(Handler.java:102)在 android.os.Looper.loop(Looper.java:148)在 android.app.ActivityThread.main(ActivityThread.java:7325)在 java.lang.reflect.Method.invoke(Native Method)在 com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1230)在 com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1120) 我的部分 java 代码是:
import android.app.Activity;导入 android.content.Intent;导入 android.media.MediaPlayer;导入 android.os.Bundle;导入 android.os.Handler;导入 android.view.View;导入 android.widget.ImageButton;导入 android.widget.SeekBar;导入 android.widget.TextView;导入 android.widget.Toast;导入 java.io.IOException;导入 java.util.ArrayList;导入 java.util.HashMap;导入 java.util.Random;公共类 MainActivity 扩展 Activity 实现 MediaPlayer.OnCompletionListener {ImageButton btnPlay;ImageButton btnForward;ImageButton btnBackward;ImageButton btnNext;ImageButton btnPrevious;ImageButton btnPlaylist;ImageButton btnRepeat;ImageButton btnShuffle;SeekBar songProgressBar=new SeekBar(this);TextView 歌曲标题标签；TextView songCurrentDurationLabel;TextView songTotalDurationLabel;//媒体播放器媒体播放器 mp;//用于更新 UI 计时器、进度条等的处理程序.Handler mHandler = new Handler();SongsManager 歌曲管理器；实用工具；int seekForwardTime = 5000;//5000 毫秒int seekBackwardTime = 5000;//5000 毫秒int currentSongIndex = 0;boolean isShuffle = false;boolean isRepeat = false;ArrayList>SongList = 新的 ArrayList<>();@覆盖protected void onCreate(Bundle savedInstanceState) {super.onCreate(savedInstanceState);setContentView(R.layout.activity_main);btnPlay = (ImageButton) findViewById(R.id.btnPlay);btnForward = (ImageButton) findViewById(R.id.btnForward);btnBackward = (ImageButton) findViewById(R.id.btnBackward);btnNext = (ImageButton) findViewById(R.id.btnNext);btnPrevious = (ImageButton) findViewById(R.id.btnPrevious);btnPlaylist = (ImageButton) findViewById(R.id.btnPlaylist);btnRepeat = (ImageButton) findViewById(R.id.btnRepeat);btnShuffle = (ImageButton) findViewById(R.id.btnShuffle);SongProgressBar = (SeekBar) findViewById(R.id.songProgressBar);SongTitleLabel = (TextView) findViewById(R.id.songTitle);songCurrentDurationLabel = (TextView) findViewById(R.id.songCurrentDurationLabel);songTotalDurationLabel = (TextView) findViewById(R.id.songTotalDurationLabel);//媒体播放器mp = 新媒体播放器()；歌曲管理器 = 新歌曲管理器()；utils = 新的实用程序()；//监听器SongProgressBar.setOnSeekBarChangeListener(new SeekBar.OnSeekBarChangeListener() {@覆盖public void onProgressChanged(SeekBar seekBar, int progress, boolean fromUser) {} ... 第 28 行是:
SeekBar songProgressBar=new SeekBar(this);感谢您的回答...
<块引用>通过@PavneetSingh 回答更新我的代码后，发生了同样的错误再次但这次是在第 70 行，它是:
songProgressBar.setOnSeekBarChangeListener(this);//重要的<块引用>
第一个回答编辑后的主要活动的完整代码是:
package ir.pluto.mediaplayer;导入 android.app.Activity;导入 android.content.Intent;导入 android.media.MediaPlayer;导入 android.os.Bundle;导入 android.os.Handler;导入 android.view.View;导入 android.widget.ImageButton;导入 android.widget.SeekBar;导入 android.widget.TextView;导入 android.widget.Toast;导入 java.io.IOException;导入 java.util.ArrayList;导入 java.util.HashMap;导入 java.util.Random;公共类 MainActivity 扩展 Activity 实现 MediaPlayer.OnCompletionListener,SeekBar.OnSeekBarChangeListener {ImageButton btnPlay;ImageButton btnForward;ImageButton btnBackward;ImageButton btnNext;ImageButton btnPrevious;ImageButton btnPlaylist;ImageButton btnRepeat;ImageButton btnShuffle;SeekBar songProgressBar;TextView 歌曲标题标签；TextView songCurrentDurationLabel;TextView songTotalDurationLabel;//媒体播放器媒体播放器 mp;//用于更新 UI 计时器、进度条等的处理程序.Handler mHandler = new Handler();SongsManager 歌曲管理器；实用工具；int seekForwardTime = 5000;//5000 毫秒int seekBackwardTime = 5000;//5000 毫秒int currentSongIndex = 0;boolean isShuffle = false;boolean isRepeat = false;ArrayList>SongList = 新的 ArrayList<>();@覆盖protected void onCreate(Bundle savedInstanceState) {super.onCreate(savedInstanceState);setContentView(R.layout.activity_main);btnPlay = (ImageButton) findViewById(R.id.btnPlay);btnForward = (ImageButton) findViewById(R.id.btnForward);btnBackward = (ImageButton) findViewById(R.id.btnBackward);btnNext = (ImageButton) findViewById(R.id.btnNext);btnPrevious = (ImageButton) findViewById(R.id.btnPrevious);btnPlaylist = (ImageButton) findViewById(R.id.btnPlaylist);btnRepeat = (ImageButton) findViewById(R.id.btnRepeat);btnShuffle = (ImageButton) findViewById(R.id.btnShuffle);SongProgressBar = (SeekBar) findViewById(R.id.songProgressBar);SongTitleLabel = (TextView) findViewById(R.id.songTitle);songCurrentDurationLabel = (TextView) findViewById(R.id.songCurrentDurationLabel);songTotalDurationLabel = (TextView) findViewById(R.id.songTotalDurationLabel);//媒体播放器mp = 新媒体播放器()；歌曲管理器 = 新歌曲管理器()；utils = 新的实用程序()；//监听器songProgressBar.setOnSeekBarChangeListener(this);//重要的mp.setOnCompletionListener(this);//重要的//获取所有歌曲列表songList = songManager.getPlayList();/*播放列表点击事件的按钮点击事件启动显示歌曲列表的列表活动*/btnPlaylist.setOnClickListener(new View.OnClickListener() {@覆盖公共无效 onClick(查看 arg0){Intent i = new Intent(getApplicationContext(), PlayListActivity.class);startActivityForResult(i, 100);}});/*前进按钮点击事件转发歌曲指定秒数*/btnForward.setOnClickListener(new View.OnClickListener() {@覆盖公共无效 onClick(查看 arg0){//获取当前歌曲位置int currentPosition = mp.getCurrentPosition();//检查seekForward 时间是否小于歌曲持续时间if(currentPosition + seekForwardTime <= mp.getDuration()){//转发歌曲mp.seekTo(currentPosition + seekForwardTime);}别的{//前进到结束位置mp.seekTo(mp.getDuration());}}});/*后退按钮点击事件将歌曲倒退到指定秒*/btnBackward.setOnClickListener(new View.OnClickListener() {@覆盖公共无效 onClick(查看 arg0){//获取当前歌曲位置int currentPosition = mp.getCurrentPosition();//检查seekBackward时间是否大于0秒if(currentPosition - seekBackwardTime >= 0){//转发歌曲mp.seekTo(currentPosition - seekBackwardTime);}别的{//回到起始位置mp.seekTo(0);}}});/*下一个按钮点击事件通过获取 currentSongIndex + 1 播放下一首歌曲*/btnNext.setOnClickListener(new View.OnClickListener() {@覆盖公共无效 onClick(查看 arg0){//检查下一首歌曲是否存在if(currentSongIndex < (songsList.size() - 1)){playSong(currentSongIndex + 1);currentSongIndex = currentSongIndex + 1;}别的{//播放第一首歌曲播放歌曲(0);当前歌曲索引 = 0;}}});/*返回按钮点击事件按 currentSongIndex - 1 播放上一首歌曲*/btnPrevious.setOnClickListener(new View.OnClickListener() {@覆盖公共无效 onClick(查看 arg0){如果(当前歌曲索引 > 0){playSong(currentSongIndex - 1);currentSongIndex = currentSongIndex - 1;}别的{//播放最后一首歌曲playSong(songsList.size() - 1);currentSongIndex = SongsList.size() - 1;}}});/** 重复按钮的按钮单击事件* 启用重复标志为真*/btnRepeat.setOnClickListener(new View.OnClickListener() {@覆盖公共无效 onClick(查看 arg0){如果(是重复){isRepeat = false;Toast.makeText(getApplicationContext(), "Repeat is OFF", Toast.LENGTH_LONG).show();btnRepeat.setImageResource(R.drawable.btn_repeat);}别的{//使重复为真isRepeat = true;Toast.makeText(getApplicationContext(), "Repeat is ON", Toast.LENGTH_LONG).show();//将 shuffle 设为 falseisShuffle = false;btnRepeat.setImageResource(R.drawable.btn_repeat);btnShuffle.setImageResource(R.drawable.btn_shuffle);}}});/** 随机播放按钮的按钮点击事件* 启用 shuffle 标志为真*/btnShuffle.setOnClickListener(new View.OnClickListener() {@覆盖公共无效 onClick(查看 arg0){如果(isShuffle){isShuffle = false;Toast.makeText(getApplicationContext(), "Shuffle is OFF", Toast.LENGTH_SHORT).show();btnShuffle.setImageResource(R.drawable.btn_shuffle);}别的{//使重复为真isShuffle=真；Toast.makeText(getApplicationContext(), "Shuffle is ON", Toast.LENGTH_SHORT).show();//将 shuffle 设为 falseisRepeat = false;btnShuffle.setImageResource(R.drawable.btn_shuffle);btnRepeat.setImageResource(R.drawable.btn_repeat);}}});}//************在onCreate()之外**************/*** 从播放列表视图接收歌曲索引* 并播放歌曲**/@覆盖protected void onActivityResult(int requestCode,int resultCode, Intent data) {super.onActivityResult(requestCode, resultCode, data);如果(结果代码 == 100){currentSongIndex = data.getExtras().getInt("songIndex");//播放选定的歌曲playSong(currentSongIndex);}}/*** 播放歌曲的功能* @param songIndex - 歌曲索引* */public void playSong(int songIndex){//播放歌曲尝试 {mp.reset();mp.setDataSource(songsList.get(songIndex).get("songPath"));mp.prepare();mp.start();//显示歌曲名称String songTitle = SongsList.get(songIndex).get("songTitle");SongTitleLabel.setText(songTitle);//更改按钮图像以暂停图像btnPlay.setImageResource(R.drawable.btn_pause);//设置进度条值SongProgressBar.setProgress(0);SongProgressBar.setMax(100);//更新进度条更新进度条()；} catch (IllegalArgumentException | IllegalStateException | IOException e) {e.printStackTrace();}}/*** 更新搜索栏上的计时器**/公共无效updateProgressBar(){mHandler.postDelayed(mUpdateTimeTask, 100);}/*** 后台可运行线程* */private Runnable mUpdateTimeTask = new Runnable() {公共无效运行(){long totalDuration = mp.getDuration();长 currentDuration = mp.getCurrentPosition();//显示总持续时间songTotalDurationLabel.setText(utils.milliSecondsToTimer(totalDuration));//显示播放完成的时间SongCurrentDurationLabel.setText(utils.milliSecondsToTimer(currentDuration));//更新进度条int progress = utils.getProgressPercentage(currentDuration, totalDuration);//Log.d("Progress", ""+progress);SongProgressBar.setProgress(progress);//100 毫秒后运行此线程mHandler.postDelayed(this, 100);}};/** 在歌曲播放完成* 如果重复打开再次播放同一首歌曲* 如果 shuffle 是 ON 播放随机歌曲*/@覆盖公共无效 onCompletion(MediaPlayer mp) {//检查repeat是ON还是OFF如果(是重复){//重复播放同一首歌曲playSong(currentSongIndex);} else if(isShuffle){//shuffle 开启 - 随机播放一首歌曲随机 rand = new Random();currentSongIndex = rand.nextInt((songsList.size() - 1) + 1);playSong(currentSongIndex);} 别的{//没有重复或随机播放 - 播放下一首歌曲if(currentSongIndex < (songsList.size() - 1)){playSong(currentSongIndex + 1);currentSongIndex = currentSongIndex + 1;}别的{//播放第一首歌曲播放歌曲(0);当前歌曲索引 = 0;}}}@覆盖public void onProgressChanged(SeekBar seekBar, int progress, boolean fromUser) {}/** 当用户开始移动进度处理器时*/@覆盖公共无效 onStartTrackingTouch(SeekBar seekBar) {//从更新进度条中删除消息处理程序mHandler.removeCallbacks(mUpdateTimeTask);}/** 当用户停止移动进度条时*/@覆盖公共无效 onStopTrackingTouch(SeekBar seekBar) {mHandler.removeCallbacks(mUpdateTimeTask);int totalDuration = mp.getDuration();int currentPosition = utils.progressToTimer(seekBar.getProgress(), totalDuration);//前进或后退到特定秒mp.seekTo(currentPosition);//再次更新定时器进度更新进度条()；}} <块引用>
完整的错误细节是(MainActivity.java:70):
例外:主要进程:ir.pluto.mediaplayer，PID:28285java.lang.RuntimeException: 无法启动活动 ComponentInfo{ir.pluto.mediaplayer/ir.pluto.mediaplayer.MainActivity}: java.lang.NullPointerException: 尝试调用虚拟方法 'void android.widget.SeekBar.setOnSeekBarChangeListener(android.widget.SeekBar$OnSeekBarChangeListener)' 在一个空对象引用上在 android.app.ActivityThread.performLaunchActivity(ActivityThread.java:3319)在 android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3415)在 android.app.ActivityThread.access$1100(ActivityThread.java:229)在 android.app.ActivityThread$H.handleMessage(ActivityThread.java:1821)在 android.os.Handler.dispatchMessage(Handler.java:102)在 android.os.Looper.loop(Looper.java:148)在 android.app.ActivityThread.main(ActivityThread.java:7325)在 java.lang.reflect.Method.invoke(Native Method)在 com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1230)在 com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1120)引起:java.lang.NullPointerException:尝试在空对象引用上调用虚方法void android.widget.SeekBar.setOnSeekBarChangeListener(android.widget.SeekBar$OnSeekBarChangeListener)"在 ir.pluto.mediaplayer.MainActivity.onCreate(MainActivity.java:70)在 android.app.Activity.performCreate(Activity.java:6904)在 android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1136)在 android.app.ActivityThread.performLaunchActivity(ActivityThread.java:3266)在 android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3415)在 android.app.ActivityThread.access$1100(ActivityThread.java:229)在 android.app.ActivityThread$H.handleMessage(ActivityThread.java:1821)在 android.os.Handler.dispatchMessage(Handler.java:102)在 android.os.Looper.loop(Looper.java:148)在 android.app.ActivityThread.main(ActivityThread.java:7325)在 java.lang.reflect.Method.invoke(Native Method)在 com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1230)在 com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1120)<块引用>
设计在这个文件下:
播放器.xml
<?xml version="1.0" encoding="utf-8"?><RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"android:layout_width="match_parent"android:layout_height="match_parent"android:background="@drawable/player_background"><!--另一个代码--><!-- 进度条/搜索栏 --><搜索栏android:id="@+id/songProgressBar"android:layout_width="match_parent"android:layout_height="wrap_content"android:layout_above="@id/player_footer_bg"机器人:layout_marginBottom="1dp"android:layout_marginLeft="20dp"android:layout_marginRight="20dp"机器人:paddingLeft =6dp"机器人:paddingRight="6dp"android:progressDrawable="@drawable/seekbar_progress"android:thumb="@drawable/seekbar_thumb"/><!--另一个代码--></相对布局>
解决方案
this 没有任何意义，因为在 onCreate 之前它会是 null> 因为 Activity 在 onCreate 被调用所以移动你的 songProgressBar=new SeekBar(this); 在 Oncreate
public class MainActivity extends Activity 实现 MediaPlayer.OnCompletionListener {//..SeekBar songProgressBar;//..@覆盖protected void onCreate(Bundle savedInstanceState) {super.onCreate(savedInstanceState);setContentView(R.layout.activity_main);songProgressBar=new SeekBar(this);更新:您正在使用 findViewById 从 XML 初始化 songProgressBar 引用，因此您根本不需要这部分
songProgressBar=new SeekBar(this);这样做
public class MainActivity extends Activity 实现 MediaPlayer.OnCompletionListener {//.. 代码SeekBar songProgressBar;//.. 代码@覆盖protected void onCreate(Bundle savedInstanceState) {super.onCreate(savedInstanceState);setContentView(R.layout.activity_main);//.. 代码SongProgressBar = (SeekBar) findViewById(R.id.songProgressBar);//.. 代码更新 2 : 使用 setContentView(R.layout.Player); 而不是 setContentView(R.layout.activity_main); 虽然你必须重命名 XML 文件转成小写
i am a beginner.
First of all say that I have read previous posts but did not answer.
I try to test a audio player,But when I try to run the app, it instantly crashes because of a null object reference.
This is Logcat: (this log say: Error is in Line 28 of java code)
EXCEPTION: main
Process: ir.pluto.mediaplayer, PID: 19100
java.lang.RuntimeException: Unable to instantiate activity ComponentInfo{ir.pluto.mediaplayer/ir.pluto.mediaplayer.MainActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'android.content.res.Resources android.content.Context.getResources()' on a null object reference
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:3132)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3415)
at android.app.ActivityThread.access$1100(ActivityThread.java:229)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1821)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:148)
at android.app.ActivityThread.main(ActivityThread.java:7325)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1230)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1120)
Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'android.content.res.Resources android.content.Context.getResources()' on a null object reference
at android.content.ContextWrapper.getResources(ContextWrapper.java:92)
at android.view.ContextThemeWrapper.getResources(ContextThemeWrapper.java:81)
at android.view.View.<init>(View.java:4054)
at android.view.View.<init>(View.java:4186)
at android.widget.ProgressBar.<init>(ProgressBar.java:313)
at android.widget.AbsSeekBar.<init>(AbsSeekBar.java:188)
at android.widget.SeekBar.<init>(SeekBar.java:85)
at android.widget.SeekBar.<init>(SeekBar.java:81)
at android.widget.SeekBar.<init>(SeekBar.java:77)
at android.widget.SeekBar.<init>(SeekBar.java:73)
at ir.pluto.mediaplayer.MainActivity.<init>(MainActivity.java:28)
at java.lang.Class.newInstance(Native Method)
at android.app.Instrumentation.newActivity(Instrumentation.java:1096)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:3122)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3415)
at android.app.ActivityThread.access$1100(ActivityThread.java:229)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1821)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:148)
at android.app.ActivityThread.main(ActivityThread.java:7325)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1230)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1120)
And part of my java code is:
import android.app.Activity;
import android.content.Intent;
import android.media.MediaPlayer;
import android.os.Bundle;
import android.os.Handler;
import android.view.View;
import android.widget.ImageButton;
import android.widget.SeekBar;
import android.widget.TextView;
import android.widget.Toast;
import java.io.IOException;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.Random;
public class MainActivity extends Activity implements MediaPlayer.OnCompletionListener {
ImageButton btnPlay;
ImageButton btnForward;
ImageButton btnBackward;
ImageButton btnNext;
ImageButton btnPrevious;
ImageButton btnPlaylist;
ImageButton btnRepeat;
ImageButton btnShuffle;
SeekBar songProgressBar=new SeekBar(this);
TextView songTitleLabel;
TextView songCurrentDurationLabel;
TextView songTotalDurationLabel;
// Media Player
MediaPlayer mp;
// Handler to update UI timer, progress bar etc,.
Handler mHandler = new Handler();
SongsManager songManager;
Utilities utils;
int seekForwardTime = 5000; // 5000 milliseconds
int seekBackwardTime = 5000; // 5000 milliseconds
int currentSongIndex = 0;
boolean isShuffle = false;
boolean isRepeat = false;
ArrayList<HashMap<String, String>> songsList = new ArrayList<>();
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
btnPlay = (ImageButton) findViewById(R.id.btnPlay);
btnForward = (ImageButton) findViewById(R.id.btnForward);
btnBackward = (ImageButton) findViewById(R.id.btnBackward);
btnNext = (ImageButton) findViewById(R.id.btnNext);
btnPrevious = (ImageButton) findViewById(R.id.btnPrevious);
btnPlaylist = (ImageButton) findViewById(R.id.btnPlaylist);
btnRepeat = (ImageButton) findViewById(R.id.btnRepeat);
btnShuffle = (ImageButton) findViewById(R.id.btnShuffle);
songProgressBar = (SeekBar) findViewById(R.id.songProgressBar);
songTitleLabel = (TextView) findViewById(R.id.songTitle);
songCurrentDurationLabel = (TextView) findViewById(R.id.songCurrentDurationLabel);
songTotalDurationLabel = (TextView) findViewById(R.id.songTotalDurationLabel);
// Media player
mp = new MediaPlayer();
songManager = new SongsManager();
utils = new Utilities();
// Listeners
songProgressBar.setOnSeekBarChangeListener(new SeekBar.OnSeekBarChangeListener() {
@Override
public void onProgressChanged(SeekBar seekBar, int progress, boolean fromUser) {
}...
and line 28 is:
SeekBar songProgressBar=new SeekBar(this);
Thank you for your answers ...
After Update my code by @PavneetSingh answer,The same error occurred again but this time on line 70 and it is:
songProgressBar.setOnSeekBarChangeListener(this); // Important
Complete code of Main Activty after edit by first answer is:
package ir.pluto.mediaplayer;
import android.app.Activity;
import android.content.Intent;
import android.media.MediaPlayer;
import android.os.Bundle;
import android.os.Handler;
import android.view.View;
import android.widget.ImageButton;
import android.widget.SeekBar;
import android.widget.TextView;
import android.widget.Toast;
import java.io.IOException;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.Random;
public class MainActivity extends Activity implements MediaPlayer.OnCompletionListener,SeekBar.OnSeekBarChangeListener {
ImageButton btnPlay;
ImageButton btnForward;
ImageButton btnBackward;
ImageButton btnNext;
ImageButton btnPrevious;
ImageButton btnPlaylist;
ImageButton btnRepeat;
ImageButton btnShuffle;
SeekBar songProgressBar;
TextView songTitleLabel;
TextView songCurrentDurationLabel;
TextView songTotalDurationLabel;
// Media Player
MediaPlayer mp;
// Handler to update UI timer, progress bar etc,.
Handler mHandler = new Handler();
SongsManager songManager;
Utilities utils;
int seekForwardTime = 5000; // 5000 milliseconds
int seekBackwardTime = 5000; // 5000 milliseconds
int currentSongIndex = 0;
boolean isShuffle = false;
boolean isRepeat = false;
ArrayList<HashMap<String, String>> songsList = new ArrayList<>();
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
btnPlay = (ImageButton) findViewById(R.id.btnPlay);
btnForward = (ImageButton) findViewById(R.id.btnForward);
btnBackward = (ImageButton) findViewById(R.id.btnBackward);
btnNext = (ImageButton) findViewById(R.id.btnNext);
btnPrevious = (ImageButton) findViewById(R.id.btnPrevious);
btnPlaylist = (ImageButton) findViewById(R.id.btnPlaylist);
btnRepeat = (ImageButton) findViewById(R.id.btnRepeat);
btnShuffle = (ImageButton) findViewById(R.id.btnShuffle);
songProgressBar = (SeekBar) findViewById(R.id.songProgressBar);
songTitleLabel = (TextView) findViewById(R.id.songTitle);
songCurrentDurationLabel = (TextView) findViewById(R.id.songCurrentDurationLabel);
songTotalDurationLabel = (TextView) findViewById(R.id.songTotalDurationLabel);
// Media player
mp = new MediaPlayer();
songManager = new SongsManager();
utils = new Utilities();
// Listeners
songProgressBar.setOnSeekBarChangeListener(this); // Important
mp.setOnCompletionListener(this); // Important
// Getting all songs list
songsList = songManager.getPlayList();
/*
Button Click event for Play list click event
Launches list activity which displays list of songs
*/
btnPlaylist.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View arg0) {
Intent i = new Intent(getApplicationContext(), PlayListActivity.class);
startActivityForResult(i, 100);
}
});
/*
Forward button click event
Forwards song specified seconds
*/
btnForward.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View arg0) {
// get current song position
int currentPosition = mp.getCurrentPosition();
// check if seekForward time is lesser than song duration
if(currentPosition + seekForwardTime <= mp.getDuration()){
// forward song
mp.seekTo(currentPosition + seekForwardTime);
}else{
// forward to end position
mp.seekTo(mp.getDuration());
}
}
});
/*
Backward button click event
Backward song to specified seconds
*/
btnBackward.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View arg0) {
// get current song position
int currentPosition = mp.getCurrentPosition();
// check if seekBackward time is greater than 0 sec
if(currentPosition - seekBackwardTime >= 0){
// forward song
mp.seekTo(currentPosition - seekBackwardTime);
}else{
// backward to starting position
mp.seekTo(0);
}
}
});
/*
Next button click event
Plays next song by taking currentSongIndex + 1
*/
btnNext.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View arg0) {
// check if next song is there or not
if(currentSongIndex < (songsList.size() - 1)){
playSong(currentSongIndex + 1);
currentSongIndex = currentSongIndex + 1;
}else{
// play first song
playSong(0);
currentSongIndex = 0;
}
}
});
/*
Back button click event
Plays previous song by currentSongIndex - 1
*/
btnPrevious.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View arg0) {
if(currentSongIndex > 0){
playSong(currentSongIndex - 1);
currentSongIndex = currentSongIndex - 1;
}else{
// play last song
playSong(songsList.size() - 1);
currentSongIndex = songsList.size() - 1;
}
}
});
/*
* Button Click event for Repeat button
* Enables repeat flag to true
*/
btnRepeat.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View arg0) {
if(isRepeat){
isRepeat = false;
Toast.makeText(getApplicationContext(), "Repeat is OFF", Toast.LENGTH_LONG).show();
btnRepeat.setImageResource(R.drawable.btn_repeat);
}else{
// make repeat to true
isRepeat = true;
Toast.makeText(getApplicationContext(), "Repeat is ON", Toast.LENGTH_LONG).show();
// make shuffle to false
isShuffle = false;
btnRepeat.setImageResource(R.drawable.btn_repeat);
btnShuffle.setImageResource(R.drawable.btn_shuffle);
}
}
});
/*
* Button Click event for Shuffle button
* Enables shuffle flag to true
*/
btnShuffle.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View arg0) {
if(isShuffle){
isShuffle = false;
Toast.makeText(getApplicationContext(), "Shuffle is OFF", Toast.LENGTH_SHORT).show();
btnShuffle.setImageResource(R.drawable.btn_shuffle);
}else{
// make repeat to true
isShuffle= true;
Toast.makeText(getApplicationContext(), "Shuffle is ON", Toast.LENGTH_SHORT).show();
// make shuffle to false
isRepeat = false;
btnShuffle.setImageResource(R.drawable.btn_shuffle);
btnRepeat.setImageResource(R.drawable.btn_repeat);
}
}
});
}
//************Outside of onCreate()**************
/**
* Receiving song index from playlist view
* and play the song
**/
@Override
protected void onActivityResult(int requestCode,int resultCode, Intent data) {
super.onActivityResult(requestCode, resultCode, data);
if(resultCode == 100){
currentSongIndex = data.getExtras().getInt("songIndex");
// play selected song
playSong(currentSongIndex);
}
}
/**
* Function to play a song
* @param songIndex - index of song
* */
public void playSong(int songIndex){
// Play song
try {
mp.reset();
mp.setDataSource(songsList.get(songIndex).get("songPath"));
mp.prepare();
mp.start();
// Displaying Song title
String songTitle = songsList.get(songIndex).get("songTitle");
songTitleLabel.setText(songTitle);
// Changing Button Image to pause image
btnPlay.setImageResource(R.drawable.btn_pause);
// set Progress bar values
songProgressBar.setProgress(0);
songProgressBar.setMax(100);
// Updating progress bar
updateProgressBar();
} catch (IllegalArgumentException | IllegalStateException | IOException e) {
e.printStackTrace();
}
}
/**
* Update timer on seekbar
**/
public void updateProgressBar() {
mHandler.postDelayed(mUpdateTimeTask, 100);
}
/**
* Background Runnable thread
* */
private Runnable mUpdateTimeTask = new Runnable() {
public void run() {
long totalDuration = mp.getDuration();
long currentDuration = mp.getCurrentPosition();
// Displaying Total Duration time
songTotalDurationLabel.setText(utils.milliSecondsToTimer(totalDuration));
// Displaying time completed playing
songCurrentDurationLabel.setText(utils.milliSecondsToTimer(currentDuration));
// Updating progress bar
int progress = utils.getProgressPercentage(currentDuration, totalDuration);
//Log.d("Progress", ""+progress);
songProgressBar.setProgress(progress);
// Running this thread after 100 milliseconds
mHandler.postDelayed(this, 100);
}
};
/*
* On Song Playing completed
* if repeat is ON play same song again
* if shuffle is ON play random song
*/
@Override
public void onCompletion(MediaPlayer mp) {
// check for repeat is ON or OFF
if(isRepeat){
// repeat is on play same song again
playSong(currentSongIndex);
} else if(isShuffle){
// shuffle is on - play a random song
Random rand = new Random();
currentSongIndex = rand.nextInt((songsList.size() - 1) + 1);
playSong(currentSongIndex);
} else{
// no repeat or shuffle ON - play next song
if(currentSongIndex < (songsList.size() - 1)){
playSong(currentSongIndex + 1);
currentSongIndex = currentSongIndex + 1;
}else{
// play first song
playSong(0);
currentSongIndex = 0;
}
}
}
@Override
public void onProgressChanged(SeekBar seekBar, int progress, boolean fromUser) {
}
/*
* When user starts moving the progress handler
*/
@Override
public void onStartTrackingTouch(SeekBar seekBar) {
// remove message Handler from updating progress bar
mHandler.removeCallbacks(mUpdateTimeTask);
}
/*
* When user stops moving the progress hanlder
*/
@Override
public void onStopTrackingTouch(SeekBar seekBar) {
mHandler.removeCallbacks(mUpdateTimeTask);
int totalDuration = mp.getDuration();
int currentPosition = utils.progressToTimer(seekBar.getProgress(), totalDuration);
// forward or backward to certain seconds
mp.seekTo(currentPosition);
// update timer progress again
updateProgressBar();
}
}
And complete error detail is(MainActivity.java:70):
EXCEPTION: main
Process: ir.pluto.mediaplayer, PID: 28285
java.lang.RuntimeException: Unable to start activity ComponentInfo{ir.pluto.mediaplayer/ir.pluto.mediaplayer.MainActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.SeekBar.setOnSeekBarChangeListener(android.widget.SeekBar$OnSeekBarChangeListener)' on a null object reference
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:3319)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3415)
at android.app.ActivityThread.access$1100(ActivityThread.java:229)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1821)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:148)
at android.app.ActivityThread.main(ActivityThread.java:7325)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1230)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1120)
Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.SeekBar.setOnSeekBarChangeListener(android.widget.SeekBar$OnSeekBarChangeListener)' on a null object reference
at ir.pluto.mediaplayer.MainActivity.onCreate(MainActivity.java:70)
at android.app.Activity.performCreate(Activity.java:6904)
at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1136)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:3266)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3415)
at android.app.ActivityThread.access$1100(ActivityThread.java:229)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1821)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:148)
at android.app.ActivityThread.main(ActivityThread.java:7325)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1230)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1120)
Design is under this File:
Player.xml
<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:background="@drawable/player_background">
<!--another codes-->
<!-- Progress Bar/Seek bar -->
<SeekBar
android:id="@+id/songProgressBar"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:layout_above="@id/player_footer_bg"
android:layout_marginBottom="1dp"
android:layout_marginLeft="20dp"
android:layout_marginRight="20dp"
android:paddingLeft="6dp"
android:paddingRight="6dp"
android:progressDrawable="@drawable/seekbar_progress"
android:thumb="@drawable/seekbar_thumb" />
<!--another codes-->
</RelativeLayout
>
解决方案
this doesn't mean anything because before onCreate it will be null because Activity gets it's context(which you are referring as this ) from Application when onCreate get called so move your songProgressBar=new SeekBar(this); inside Oncreate
public class MainActivity extends Activity implements MediaPlayer.OnCompletionListener {
//..
SeekBar songProgressBar;
//..
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
songProgressBar=new SeekBar(this);
Update : you are initializing the songProgressBar reference from XML using findViewById so you don't need this part at all
songProgressBar=new SeekBar(this);
so do this
public class MainActivity extends Activity implements MediaPlayer.OnCompletionListener {
// .. code
SeekBar songProgressBar;
// .. code
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
// .. code
songProgressBar = (SeekBar) findViewById(R.id.songProgressBar);
// .. code
Update 2 : Use setContentView(R.layout.Player); instead of setContentView(R.layout.activity_main); although it's you must rename XML file to lowercase letters
这篇关于无法实例化活动:尝试调用虚拟方法 android.content.Context.getResources()的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！
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