NullPointerException - 尝试获取空数组的长度 (readDirectory()) [英] NullPointerException - Attempt to get length of null array (readDirectory())
本文介绍了NullPointerException - 尝试获取空数组的长度 (readDirectory())的处理方法，对大家解决问题具有一定的参考价值，需要的朋友们下面随着小编来一起学习吧！
问题描述
我有此处显示的代码.我的问题是 files.length 处的 NullPointerException
for(int i=0; i 这是因为我在
有一个fail readDirectory() errno=13"File[] files = f.listFiles();但是为什么我在路径好的情况下会出现 readDirectory 失败?
package com.example.androidexplorer;导入 java.io.File;导入 java.util.ArrayList;导入 java.util.List;导入 android.os.Bundle;导入 android.os.Environment;导入 android.app.AlertDialog;导入 android.app.ListActivity;导入 android.util.Log;导入 android.view.View;导入 android.widget.ArrayAdapter;导入 android.widget.ListView;导入 android.widget.TextView;公共类 MainActivity 扩展 ListActivity {私人列表<字符串>项目 = 空；私人列表<字符串>路径 = 空；私有字符串根；私人 TextView myPath;@覆盖public void onCreate(Bundle savedInstanceState) {super.onCreate(savedInstanceState);setContentView(R.layout.activity_main);myPath = (TextView)findViewById(R.id.path);root = Environment.getExternalStorageDirectory().getPath();获取目录(根)；}私有无效getDir(字符串dirPath){myPath.setText("位置:" + dirPath);item = new ArrayList();path = new ArrayList();File f = new File(dirPath);Log.v("路径:", dirPath);Log.v("BEFORE", "读取失败前...");File[] 文件 = f.listFiles();Log.v("AFTER", "读取失败后...");if(!dirPath.equals(root)){item.add(root);路径.添加(根)；item.add("../");path.add(f.getParent());}Log.v("崩溃", "崩溃前 1 行");for(int i=0; i 文件列表 =new ArrayAdapter(this, R.layout.row, item);setListAdapter(fileList);}@覆盖protected void onListItemClick(ListView l, View v, int position, long id) {//TODO 自动生成的方法存根File file = new File(path.get(position));如果 (file.isDirectory()){if(file.canRead()){getDir(path.get(position));}别的{新的 AlertDialog.Builder(this).setIcon(R.drawable.ic_launcher).setTitle("[" + file.getName() + "] 文件夹无法读取！").setPositiveButton("OK", null).show();}}别的 {新的 AlertDialog.Builder(this).setIcon(R.drawable.ic_launcher).setTitle("[" + file.getName() + "]").setPositiveButton("OK", null).show();}}} LogCat:
<块引用>>04-23 15:35:34.084:D/ResourcesManager(20672):创建新的>AssetManager 并设置为>/data/app/com.example.androidexplorer-1/base.apk 04-23 15:35:34.104:>I/art(20672):创建应用空间>/data/dalvik-cache/arm/data@app@com.example.androidexplorer-1@base.apk@classes.dex.art>在 0x76eb0000~0x76f15ff8 04-23 15:35:34.104:I/art(20672):加载的艺术>文件:>/data/dalvik-cache/arm/data@app@com.example.androidexplorer-1@base.apk@classes.dex.art>04-23 15:35:34.194: V/BitmapFactory(20672):>DecodeImagePath(decodeResourceStream3) :>res/drawable-xxhdpi-v4/ic_ab_back_holo_dark_am.png 04-23 15:35:34.204:>V/BitmapFactory(20672): DecodeImagePath(decodeResourceStream3) :>res/drawable-xxhdpi-v4/sym_def_app_icon.png 04-23 15:35:34.234:>D/AbsListView(20672): 获取 MotionRecognitionManager 04-23 15:35:34.244:>V/BitmapFactory(20672): DecodeImagePath(decodeResourceStream3) :>res/drawable-xhdpi-v4/ic_launcher.png 04-23 15:35:34.254:>V/Path:(20672):/storage/emulated/0 04-23 15:35:34.254:>V/BEFORE(20672): 阅读失败前... 04-23 15:35:34.254:>E/File(20672): 失败 readDirectory() errno=13 04-23 15:35:34.254:>V/AFTER(20672): 读取失败后... 04-23 15:35:34.254:>V/CRASH(20672): 崩溃前 1 行 04-23 15:35:34.254:>D/AndroidRuntime(20672):关闭 VM 04-23 15:35:34.254:>E/AndroidRuntime(20672): 致命异常: main 04-23 15:35:34.254:>E/AndroidRuntime(20672):进程:com.example.androidexplorer，PID:>20672 04-23 15:35:34.254: E/AndroidRuntime(20672):>java.lang.RuntimeException:无法启动活动>组件信息{com.example.androidexplorer/com.example.androidexplorer.MainActivity}:>java.lang.NullPointerException:尝试获取空数组的长度>04-23 15:35:34.254:E/AndroidRuntime(20672):在>android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2658)>04-23 15:35:34.254:E/AndroidRuntime(20672):在>android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2725)>04-23 15:35:34.254:E/AndroidRuntime(20672):在>android.app.ActivityThread.access$900(ActivityThread.java:172) 04-23>15:35:34.254:E/AndroidRuntime(20672):在>android.app.ActivityThread$H.handleMessage(ActivityThread.java:1422)>04-23 15:35:34.254:E/AndroidRuntime(20672):在>android.os.Handler.dispatchMessage(Handler.java:102) 04-23>15:35:34.254:E/AndroidRuntime(20672):在>android.os.Looper.loop(Looper.java:145) 04-23 15:35:34.254:>E/AndroidRuntime(20672):在>android.app.ActivityThread.main(ActivityThread.java:5834) 04-23>15:35:34.254:E/AndroidRuntime(20672):在>java.lang.reflect.Method.invoke(Native Method) 04-23 15:35:34.254:>E/AndroidRuntime(20672):在>java.lang.reflect.Method.invoke(Method.java:372) 04-23 15:35:34.254:>E/AndroidRuntime(20672):在>com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1388)>04-23 15:35:34.254:E/AndroidRuntime(20672):在>com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1183) 04-23>15:35:34.254:E/AndroidRuntime(20672):由:>java.lang.NullPointerException:尝试获取空数组的长度>04-23 15:35:34.254:E/AndroidRuntime(20672):在>com.example.androidexplorer.MainActivity.getDir(MainActivity.java:57)>04-23 15:35:34.254:E/AndroidRuntime(20672):在>com.example.androidexplorer.MainActivity.onCreate(MainActivity.java:31)>04-23 15:35:34.254:E/AndroidRuntime(20672):在>android.app.Activity.performCreate(Activity.java:6221) 04-23>15:35:34.254:E/AndroidRuntime(20672):在>android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1119)>04-23 15:35:34.254:E/AndroidRuntime(20672):在>android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2611)>04-23 15:35:34.254: E/AndroidRuntime(20672): ... 10 更多更新
错误出现在我的权限清单中.我一开始就拥有:
<申请机器人:allowBackup =真"android:icon="@drawable/ic_launcher"android:label="@string/app_name"android:theme="@style/AppTheme"android:name="android.permission.READ_EXTERNAL_STORAGE"><活动android:name=".MainActivity"android:label="@string/app_name" ><意图过滤器><action android:name="android.intent.action.MAIN"/><category android:name="android.intent.category.LAUNCHER"/></意图过滤器></活动><activity android:name=".sysinfo"></activity><activity android:name=".daten"></activity><activity android:name=".storage"></activity><activity android:name="org.achartengine.GraphicalActivity"></活动></应用程序></清单>并更新:
<uses-permission android:name="android.permission.READ_EXTERNAL_STORAGE"/><申请机器人:allowBackup =真"android:icon="@drawable/ic_launcher"android:label="@string/app_name"android:theme="@style/AppTheme"><活动android:name=".MainActivity"android:label="@string/app_name" ><意图过滤器><action android:name="android.intent.action.MAIN"/><category android:name="android.intent.category.LAUNCHER"/></意图过滤器></活动><activity android:name=".sysinfo"></activity><activity android:name=".daten"></activity><activity android:name=".storage"></activity><activity android:name="org.achartengine.GraphicalActivity"></活动></应用程序></清单> 解决方案
f.listFiles()如果路径不存在则返回null.
请检查您的路径.
更新
Android 还需要获得读取某些文件的权限.也许您需要将此添加到您的清单中:
<uses-permission android:name="android.permission.READ_EXTERNAL_STORAGE"/>更多信息:
http://developer.android.com/reference/android/Manifest.permission.html
I have the code as shown here. My Problem is a NullPointerException at files.length
for(int i=0; i < files.length; i++){
It is caused because i have a "fail readDirectory() errno=13" at
File[] files = f.listFiles();
But why do I have a readDirectory fail when the path is good?
package com.example.androidexplorer;
import java.io.File;
import java.util.ArrayList;
import java.util.List;
import android.os.Bundle;
import android.os.Environment;
import android.app.AlertDialog;
import android.app.ListActivity;
import android.util.Log;
import android.view.View;
import android.widget.ArrayAdapter;
import android.widget.ListView;
import android.widget.TextView;
public class MainActivity extends ListActivity {
private List<String> item = null;
private List<String> path = null;
private String root;
private TextView myPath;
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
myPath = (TextView)findViewById(R.id.path);
root = Environment.getExternalStorageDirectory().getPath();
getDir(root);
}
private void getDir(String dirPath)
{
myPath.setText("Location: " + dirPath);
item = new ArrayList<String>();
path = new ArrayList<String>();
File f = new File(dirPath);
Log.v("Path: ", dirPath);
Log.v("BEFORE", "Before Reading Fail...");
File[] files = f.listFiles();
Log.v("AFTER", "After Reading Fail...");
if(!dirPath.equals(root))
{
item.add(root);
path.add(root);
item.add("../");
path.add(f.getParent());
}
Log.v("CRASH", "1 Line before crash");
for(int i=0; i < files.length; i++){
Log.v("AFTER CRASH", "1 Line after crash");
File file = files[i];
if(!file.isHidden() && file.canRead()){
path.add(file.getPath());
if(file.isDirectory()){
item.add(file.getName() + "/");
}else{
item.add(file.getName());
}
}
}
ArrayAdapter<String> fileList =
new ArrayAdapter<String>(this, R.layout.row, item);
setListAdapter(fileList);
}
@Override
protected void onListItemClick(ListView l, View v, int position, long id) {
// TODO Auto-generated method stub
File file = new File(path.get(position));
if (file.isDirectory())
{
if(file.canRead()){
getDir(path.get(position));
}else{
new AlertDialog.Builder(this)
.setIcon(R.drawable.ic_launcher)
.setTitle("[" + file.getName() + "] folder can't be read!")
.setPositiveButton("OK", null).show();
}
}else {
new AlertDialog.Builder(this)
.setIcon(R.drawable.ic_launcher)
.setTitle("[" + file.getName() + "]")
.setPositiveButton("OK", null).show();
}
}
}
LogCat:
> 04-23 15:35:34.084: D/ResourcesManager(20672): creating new > AssetManager and set to > /data/app/com.example.androidexplorer-1/base.apk 04-23 15:35:34.104: > I/art(20672): Created application space > /data/dalvik-cache/arm/data@app@com.example.androidexplorer-1@base.apk@classes.dex.art > at 0x76eb0000~0x76f15ff8 04-23 15:35:34.104: I/art(20672): Loaded art > file: > /data/dalvik-cache/arm/data@app@com.example.androidexplorer-1@base.apk@classes.dex.art > 04-23 15:35:34.194: V/BitmapFactory(20672): > DecodeImagePath(decodeResourceStream3) : > res/drawable-xxhdpi-v4/ic_ab_back_holo_dark_am.png 04-23 15:35:34.204: > V/BitmapFactory(20672): DecodeImagePath(decodeResourceStream3) : > res/drawable-xxhdpi-v4/sym_def_app_icon.png 04-23 15:35:34.234: > D/AbsListView(20672): Get MotionRecognitionManager 04-23 15:35:34.244: > V/BitmapFactory(20672): DecodeImagePath(decodeResourceStream3) : > res/drawable-xhdpi-v4/ic_launcher.png 04-23 15:35:34.254: > V/Path:(20672): /storage/emulated/0 04-23 15:35:34.254: > V/BEFORE(20672): Before Reading Fail... 04-23 15:35:34.254: > E/File(20672): fail readDirectory() errno=13 04-23 15:35:34.254: > V/AFTER(20672): After Reading Fail... 04-23 15:35:34.254: > V/CRASH(20672): 1 Line before crash 04-23 15:35:34.254: > D/AndroidRuntime(20672): Shutting down VM 04-23 15:35:34.254: > E/AndroidRuntime(20672): FATAL EXCEPTION: main 04-23 15:35:34.254: > E/AndroidRuntime(20672): Process: com.example.androidexplorer, PID: > 20672 04-23 15:35:34.254: E/AndroidRuntime(20672): > java.lang.RuntimeException: Unable to start activity > ComponentInfo{com.example.androidexplorer/com.example.androidexplorer.MainActivity}: > java.lang.NullPointerException: Attempt to get length of null array > 04-23 15:35:34.254: E/AndroidRuntime(20672): at > android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2658) > 04-23 15:35:34.254: E/AndroidRuntime(20672): at > android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2725) > 04-23 15:35:34.254: E/AndroidRuntime(20672): at > android.app.ActivityThread.access$900(ActivityThread.java:172) 04-23 > 15:35:34.254: E/AndroidRuntime(20672): at > android.app.ActivityThread$H.handleMessage(ActivityThread.java:1422) > 04-23 15:35:34.254: E/AndroidRuntime(20672): at > android.os.Handler.dispatchMessage(Handler.java:102) 04-23 > 15:35:34.254: E/AndroidRuntime(20672): at > android.os.Looper.loop(Looper.java:145) 04-23 15:35:34.254: > E/AndroidRuntime(20672): at > android.app.ActivityThread.main(ActivityThread.java:5834) 04-23 > 15:35:34.254: E/AndroidRuntime(20672): at > java.lang.reflect.Method.invoke(Native Method) 04-23 15:35:34.254: > E/AndroidRuntime(20672): at > java.lang.reflect.Method.invoke(Method.java:372) 04-23 15:35:34.254: > E/AndroidRuntime(20672): at > com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1388) > 04-23 15:35:34.254: E/AndroidRuntime(20672): at > com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1183) 04-23 > 15:35:34.254: E/AndroidRuntime(20672): Caused by: > java.lang.NullPointerException: Attempt to get length of null array > 04-23 15:35:34.254: E/AndroidRuntime(20672): at > com.example.androidexplorer.MainActivity.getDir(MainActivity.java:57) > 04-23 15:35:34.254: E/AndroidRuntime(20672): at > com.example.androidexplorer.MainActivity.onCreate(MainActivity.java:31) > 04-23 15:35:34.254: E/AndroidRuntime(20672): at > android.app.Activity.performCreate(Activity.java:6221) 04-23 > 15:35:34.254: E/AndroidRuntime(20672): at > android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1119) > 04-23 15:35:34.254: E/AndroidRuntime(20672): at > android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2611) > 04-23 15:35:34.254: E/AndroidRuntime(20672): ... 10 more
UPDATE
Error was in my manifest with the permissions. What I had at the beginning:
<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
package="com.spicysoftware.infoid"
android:versionCode="1"
android:versionName="1.0" >
<uses-sdk
android:minSdkVersion="15"
android:targetSdkVersion="15" />
<application
android:allowBackup="true"
android:icon="@drawable/ic_launcher"
android:label="@string/app_name"
android:theme="@style/AppTheme"
android:name="android.permission.READ_EXTERNAL_STORAGE">
<activity
android:name=".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=".sysinfo"></activity>
<activity android:name=".daten"></activity>
<activity android:name=".storage"></activity>
<activity android:name="org.achartengine.GraphicalActivity"> </activity>
</application>
</manifest>
And Updated:
<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
package="com.spicysoftware.infoid"
android:versionCode="1"
android:versionName="1.0" >
<uses-sdk
android:minSdkVersion="15"
android:targetSdkVersion="15" />
<uses-permission android:name="android.permission.READ_EXTERNAL_STORAGE" />
<application
android:allowBackup="true"
android:icon="@drawable/ic_launcher"
android:label="@string/app_name"
android:theme="@style/AppTheme">
<activity
android:name=".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=".sysinfo"></activity>
<activity android:name=".daten"></activity>
<activity android:name=".storage"></activity>
<activity android:name="org.achartengine.GraphicalActivity"> </activity>
</application>
</manifest>
解决方案
f.listFiles()
will return null if the path does not exist.
Please check your path.
Update
Android will also require a permission to read certain files. Maybe you need to add this to your manifest:
<uses-permission android:name="android.permission.READ_EXTERNAL_STORAGE" />
More information:
http://developer.android.com/reference/android/Manifest.permission.html
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