从Android的为什么getActionBar（）得到空值在TabHost？ [英] Why getActionBar() getting null value in TabHost from Android?
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问题描述
我试图写一个code在Android中，向下滚动事件中隐藏动作条。我有一个网格10X50。所以，当我向下滚动操作栏应隐藏。我得到的滚动状态导致日志猫正确所以，每当我申请getActionBar（），躲起来，我得到的NullPointerException错误。
I am trying to write a code in Android , to hide the Actionbar during scroll down event. I have a grid 10x50. So when i am scrolling down the action bar should hide. I am getting scroll state result in the Log Cat correctly so , whenever i am applying for getActionBar().hide , i am getting NullPointerException error.
我的code：
package com.example.complexdatepicker;
import android.app.TabActivity;
import android.content.Intent;
import android.os.Bundle;
import android.widget.TabHost;
import android.widget.TabHost.TabSpec;
public class MainActivity extends TabActivity
{
@Override
protected void onCreate(Bundle savedInstanceState)
{
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
TabHost tabHost = getTabHost();
TabSpec tab1 = tabHost.newTabSpec("Home");
tab1.setIndicator("Home");
Intent photosIntent = new Intent(this, Home.class);
tab1.setContent(photosIntent);
tabHost.addTab(tab1);
}
}
Home.java
package com.example.complexdatepicker;
import java.util.ArrayList;
import android.os.Bundle;
import android.support.v7.app.ActionBarActivity;
import android.widget.GridView;
public class Home extends ActionBarActivity
{
ArrayList<String> abc;
TestGrid tg;
GridView gv;
int mLastFirstVisibleItem;
int mLastVisibleItemCount;
@Override
protected void onCreate(Bundle savedInstanceState)
{
super.onCreate(savedInstanceState);
setContentView(R.layout.home);
gv = (GridView) findViewById(R.id.gridView1);
abc = new ArrayList<String>();
for(int i=0;i<500;i++)
{
abc.add(String.valueOf(i));
}
tg = new TestGrid(Home.this,Home.this,abc);
gv.setAdapter(tg);
getSupportActionBar().hide(); /// Getting Error at this point..
/*
gv.setOnScrollListener(new AbsListView.OnScrollListener() {
public void onScroll(AbsListView view, int firstVisibleItem, int visibleItemCount, int totalItemCount) {
if (mLastFirstVisibleItem > firstVisibleItem) {
Log.e(getClass().toString(), "scrolling up");
getActionBar().show();
} else if (mLastFirstVisibleItem < firstVisibleItem) {
Log.e(getClass().toString(), "scrolling down");
getActionBar().hide();
} else if (mLastVisibleItemCount < visibleItemCount) {
Log.e(getClass().toString(), "scrolling down");
getActionBar().hide();
} else if (mLastVisibleItemCount > visibleItemCount) {
Log.e(getClass().toString(), "scrolling up");
getActionBar().show();
}
mLastFirstVisibleItem = firstVisibleItem;
mLastVisibleItemCount = visibleItemCount;
}
public void onScrollStateChanged(AbsListView listView, int scrollState) {
}
});
*/
}
}
TestGrid.java
package com.example.complexdatepicker;
import java.util.ArrayList;
import java.util.Calendar;
import android.annotation.SuppressLint;
import android.app.DatePickerDialog;
import android.app.Dialog;
import android.content.Context;
import android.content.SharedPreferences;
import android.content.SharedPreferences.Editor;
import android.graphics.Color;
import android.os.Bundle;
import android.support.v4.app.DialogFragment;
import android.support.v4.app.FragmentActivity;
import android.util.Log;
import android.view.Gravity;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.view.View.OnClickListener;
import android.widget.BaseAdapter;
import android.widget.DatePicker;
import android.widget.TextView;
import android.widget.Toast;
public class TestGrid extends BaseAdapter
{
private ArrayList<String> abc;
private FragmentActivity activity;
private Context context;
String text;
int c = 0;
int x = 0;
SelectDateFragment newFragment;
public TestGrid(FragmentActivity activity , Context cont,ArrayList<String> abc)
{
super();
this.activity=activity;
this.context = cont;
this.abc = abc;
}
@Override
public int getCount()
{
return abc.size();
}
@Override
public Object getItem(int in)
{
return abc.get(in);
}
@Override
public long getItemId(int arg0)
{
return 0;
}
public class ViewHolder
{
public TextView txt;
}
@Override
public View getView(final int arg0, View arg1, ViewGroup arg2)
{
final SharedPreferences pref = context.getApplicationContext().getSharedPreferences("TestDate", 0);
ViewHolder view;
LayoutInflater inflator = activity.getLayoutInflater();
if(arg1==null)
{
view = new ViewHolder();
arg1 = inflator.inflate(R.layout.test_grid, null);
view.txt = (TextView) arg1.findViewById(R.id.txt);
arg1.setTag(view);
}
else
{
view = (ViewHolder) arg1.getTag();
}
View.OnClickListener alert = new OnClickListener()
{
public void onClick(View v)
{
Toast.makeText(activity.getApplicationContext(), abc.get(arg0)+" - Clicked ", Toast.LENGTH_SHORT).show();
newFragment = new SelectDateFragment();
Bundle args = new Bundle();
newFragment.setArguments(args);
newFragment.setOnDateSetListener(new DatePickerDialog.OnDateSetListener()
{
@Override
public void onDateSet(DatePicker view, int yy, int mm, int dd)
{
String saved_date = pref.getString("SavedDate", null);
Toast.makeText(activity.getApplicationContext(), "SavedDate : "+saved_date,Toast.LENGTH_LONG).show();
}
});
newFragment.show(activity.getSupportFragmentManager(), "DatePicker");
}
};
view.txt.setOnClickListener(alert);
text = String.valueOf(abc.get(arg0));
view.txt.setBackgroundResource(R.drawable.txtbk);
view.txt.setTextSize(18);
view.txt.setTextColor(Color.BLACK);
view.txt.setGravity(Gravity.CENTER);
view.txt.setText(text);
return arg1;
}
@SuppressLint({ "ValidFragment", "NewApi" })
public class SelectDateFragment extends DialogFragment implements DatePickerDialog.OnDateSetListener
{
private DatePickerDialog.OnDateSetListener externalListener;
public void setOnDateSetListener(DatePickerDialog.OnDateSetListener listener)
{
this.externalListener = listener;
}
@Override
public Dialog onCreateDialog(Bundle savedInstanceState)
{
final Calendar calendar = Calendar.getInstance();
int yy = calendar.get(Calendar.YEAR);
int mm = calendar.get(Calendar.MONTH);
int dd = calendar.get(Calendar.DAY_OF_MONTH);
return new DatePickerDialog(getActivity(), this, yy, mm, dd);
}
public void onDateSet(DatePicker view, int yy, int mm, int dd)
{
SharedPreferences pref = context.getApplicationContext().getSharedPreferences("TestDate", 0);
Editor et = pref.edit();
et.putString("SavedDate", String.valueOf(dd+"/"+mm+"/"+yy));
et.commit();
Log.d("SavedDate : ", String.valueOf(dd+"/"+mm+"/"+yy));
if(externalListener != null)
externalListener.onDateSet(view, yy, mm, dd);
}
public void onFinishEditDialog(String inputText)
{
}
}
}
AndroidManifest.xml中
<manifest
xmlns:android="http://schemas.android.com/apk/res/android"
package="com.example.complexdatepicker"
android:versionCode="1"
android:versionName="1.0" >
<uses-sdk
android:minSdkVersion="14"
android:targetSdkVersion="17" />
<application
android:allowBackup="true"
android:icon="@drawable/ic_launcher"
android:label="@string/app_name"
android:theme="@style/Theme.AppCompat" >
<activity
android:name="com.example.complexdatepicker.MainActivity"
android:label="@string/app_name" >
<intent-filter>
<action android:name="android.intent.action.MAIN" />
<category android:name="android.intent.category.LAUNCHER" />
</intent-filter>
</activity>
<activity
android:name="com.example.complexdatepicker.Home"
android:label="@string/app_name" ></activity>
</application>
Style.xml
<resources>
<!--
Base application theme, dependent on API level. This theme is replaced
by AppBaseTheme from res/values-vXX/styles.xml on newer devices.
-->
<style name="AppBaseTheme" parent="android:Theme.Light">
<!--
Theme customizations available in newer API levels can go in
res/values-vXX/styles.xml, while customizations related to
backward-compatibility can go here.
-->
</style>
<!-- Application theme. -->
<style name="AppTheme" parent="AppBaseTheme">
<!-- All customizations that are NOT specific to a particular API-level can go here. -->
</style>
</resources>
错误图片：
错误：
05-25 11:10:37.374: E/AndroidRuntime(872): FATAL EXCEPTION: main
05-25 11:10:37.374: E/AndroidRuntime(872): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.complexdatepicker/com.example.complexdatepicker.MainActivity}: java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.complexdatepicker/com.example.complexdatepicker.Home}: java.lang.NullPointerException
05-25 11:10:37.374: E/AndroidRuntime(872): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2211)
05-25 11:10:37.374: E/AndroidRuntime(872): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2261)
05-25 11:10:37.374: E/AndroidRuntime(872): at android.app.ActivityThread.access$600(ActivityThread.java:141)
05-25 11:10:37.374: E/AndroidRuntime(872): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1256)
05-25 11:10:37.374: E/AndroidRuntime(872): at android.os.Handler.dispatchMessage(Handler.java:99)
05-25 11:10:37.374: E/AndroidRuntime(872): at android.os.Looper.loop(Looper.java:137)
05-25 11:10:37.374: E/AndroidRuntime(872): at android.app.ActivityThread.main(ActivityThread.java:5103)
05-25 11:10:37.374: E/AndroidRuntime(872): at java.lang.reflect.Method.invokeNative(Native Method)
05-25 11:10:37.374: E/AndroidRuntime(872): at java.lang.reflect.Method.invoke(Method.java:525)
05-25 11:10:37.374: E/AndroidRuntime(872): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:737)
05-25 11:10:37.374: E/AndroidRuntime(872): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:553)
05-25 11:10:37.374: E/AndroidRuntime(872): at dalvik.system.NativeStart.main(Native Method)
05-25 11:10:37.374: E/AndroidRuntime(872): Caused by: java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.complexdatepicker/com.example.complexdatepicker.Home}: java.lang.NullPointerException
05-25 11:10:37.374: E/AndroidRuntime(872): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2211)
05-25 11:10:37.374: E/AndroidRuntime(872): at android.app.ActivityThread.startActivityNow(ActivityThread.java:2054)
05-25 11:10:37.374: E/AndroidRuntime(872): at android.app.LocalActivityManager.moveToState(LocalActivityManager.java:135)
05-25 11:10:37.374: E/AndroidRuntime(872): at android.app.LocalActivityManager.startActivity(LocalActivityManager.java:347)
05-25 11:10:37.374: E/AndroidRuntime(872): at android.widget.TabHost$IntentContentStrategy.getContentView(TabHost.java:749)
05-25 11:10:37.374: E/AndroidRuntime(872): at android.widget.TabHost.setCurrentTab(TabHost.java:413)
05-25 11:10:37.374: E/AndroidRuntime(872): at android.widget.TabHost.addTab(TabHost.java:240)
05-25 11:10:37.374: E/AndroidRuntime(872): at com.example.complexdatepicker.MainActivity.onCreate(MainActivity.java:42)
05-25 11:10:37.374: E/AndroidRuntime(872): at android.app.Activity.performCreate(Activity.java:5133)
05-25 11:10:37.374: E/AndroidRuntime(872): at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1087)
05-25 11:10:37.374: E/AndroidRuntime(872): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2175)
05-25 11:10:37.374: E/AndroidRuntime(872): ... 11 more
05-25 11:10:37.374: E/AndroidRuntime(872): Caused by: java.lang.NullPointerException
05-25 11:10:37.374: E/AndroidRuntime(872): at android.support.v7.app.ActionBarImplICS.hide(ActionBarImplICS.java:289)
05-25 11:10:37.374: E/AndroidRuntime(872): at com.example.complexdatepicker.Home.onCreate(Home.java:50)
05-25 11:10:37.374: E/AndroidRuntime(872): at android.app.Activity.performCreate(Activity.java:5133)
05-25 11:10:37.374: E/AndroidRuntime(872): at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1087)
05-25 11:10:37.374: E/AndroidRuntime(872): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2175)
05-25 11:10:37.374: E/AndroidRuntime(872): ... 21 more
这些均高于codeS和错误的详细信息，请让我知道我可以使用 getActionBar（）在 TabWidget 。
These are all above codes and error details , please let me know how can i use getActionBar() in TabWidget.
请给我建议一些好的解决方案。
Please suggest me some good solution.
推荐答案
您首页活动必须扩展 ActionBarActivity 而不是对 FragmentActivity 这样你就可以调用 getActionBar（）方法。
Your Home Activity must extend ActionBarActivity instead of FragmentActivity so you can call getActionBar() method.
ActionBarActivity 扩展 FragmentActivity 。此外，你应该使用 getSupportActionBar（），而不是 getActionBar（）的，因为最新的要求API级别11。
ActionBarActivity extends FragmentActivity. Also, you should use getSupportActionBar() instead of getActionBar() because the latest requires API level 11.
另外请注意，您需要导入V4支持库，以便能够调用 getSupportActionBar（）和支持V7库使用 ActionBarActivity 。
Also note that you need to import v4 support library to be able to call getSupportActionBar() and support v7 library to use ActionBarActivity.
这篇关于从Android的为什么getActionBar（）得到空值在TabHost？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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