NullPointerException与ListView

我正在玩与使用导航抽屉ListView。 Eclipse不会给我任何错误，但是当我在模拟器中启动代码时，它会说：“不幸的是，DrunKingz已经停止了。”NullPointerException与ListView

MainActivity.java：

package de.pascalborker.drunkingz; 
 

 
import android.app.ListActivity; 
 
import android.content.res.Configuration; 
 
import android.os.Bundle; 
 
import android.support.v4.app.ActionBarDrawerToggle; 
 
import android.support.v4.widget.DrawerLayout; 
 
import android.view.MenuItem; 
 
import android.view.View; 
 
import android.view.View.OnClickListener; 
 
import android.widget.AdapterView; 
 
import android.widget.AdapterView.OnItemClickListener; 
 
import android.widget.ArrayAdapter; 
 
import android.widget.ListView; 
 
import android.widget.Toast; 
 

 
public class MainActivity extends ListActivity implements OnClickListener{ 
 
\t 
 

 
\t private DrawerLayout DrawerLayout; 
 
\t private ActionBarDrawerToggle ActionBarDrawerToggle; 
 
\t 
 
\t public ListView drawerlist; 
 
\t public String[] listentext = {"DrunKingz","Songs","Kontakt"}; 
 

 
\t @Override 
 
\t protected void onCreate(Bundle savedInstanceState) { 
 
\t \t super.onCreate(savedInstanceState); 
 
\t \t //setContentView(R.layout.activity_main); 
 

 
\t \t DrawerLayout = (DrawerLayout) findViewById(R.id.dlDrawerLayout); 
 
\t \t ActionBarDrawerToggle = new ActionBarDrawerToggle(this, DrawerLayout, R.drawable.icon_drawer, R.string.open, R.string.close); 
 
\t \t DrawerLayout.setDrawerListener(ActionBarDrawerToggle); 
 

 
\t \t getActionBar().setDisplayHomeAsUpEnabled(true); 
 
\t \t getActionBar().setHomeButtonEnabled(true); 
 
\t \t 
 
\t \t // ListView 
 
\t \t // ------ 
 
\t \t // ------ 
 
\t \t 
 
\t \t drawerlist = (ListView) findViewById(R.id.drawerliste); 
 
\t \t ArrayAdapter<String> drawerlistadapter = new ArrayAdapter<String>(this, android.R.layout.simple_list_item_1, listentext); 
 
\t \t drawerlist.setAdapter(drawerlistadapter); 
 
\t \t drawerlist.setOnItemClickListener(new OnItemClickListener() { 
 

 
\t \t \t @Override 
 
\t \t \t public void onItemClick(AdapterView<?> parent, View view, 
 
\t \t \t \t \t int position, long id) { 
 
\t \t \t \t 
 
\t \t \t \t switch (drawerlist.getPositionForView(view)) { 
 
\t \t \t \t case 0: { 
 
\t \t \t \t \t Toast.makeText(getApplicationContext(), "DrunKingz", Toast.LENGTH_SHORT).show(); 
 
\t \t \t \t \t break; 
 
\t \t \t \t \t \t } 
 
\t \t \t \t 
 
\t \t \t \t case 1: { 
 
\t \t \t \t \t Toast.makeText(getApplicationContext(), "Songs", Toast.LENGTH_SHORT).show(); 
 
\t \t \t \t \t break; 
 
\t \t \t \t \t \t } 
 
\t \t \t \t 
 
\t \t \t \t case 2: { 
 
\t \t \t \t \t Toast.makeText(getApplicationContext(), "Kontakt", Toast.LENGTH_SHORT).show(); 
 
\t \t \t \t \t break; 
 
\t \t \t \t \t \t } 
 
\t \t \t \t \t 
 

 
\t \t \t \t } 
 
\t \t \t \t 
 
\t \t \t } 
 
\t \t }); 
 
\t \t 
 
\t } 
 

 
\t @Override 
 
\t protected void onPostCreate(Bundle savedInstanceState) { 
 
\t \t super.onPostCreate(savedInstanceState); 
 

 
\t \t ActionBarDrawerToggle.syncState(); 
 
\t } 
 

 
\t @Override 
 
\t public void onConfigurationChanged(Configuration newConfig) { 
 
\t \t super.onConfigurationChanged(newConfig); 
 

 
\t \t ActionBarDrawerToggle.onConfigurationChanged(newConfig); 
 
\t } 
 

 
\t @Override 
 
\t public boolean onOptionsItemSelected(MenuItem item) { 
 

 
\t \t if (ActionBarDrawerToggle.onOptionsItemSelected(item)) { 
 
\t \t \t return true; 
 
\t \t } 
 

 
\t \t return super.onOptionsItemSelected(item); 
 
\t } 
 

 
\t @Override 
 
\t public void onClick(View v) { 
 
\t \t Toast.makeText(getApplicationContext(), "Test", Toast.LENGTH_SHORT).show(); 
 
\t } 
 

 
}

activity_main.xml中：

<android.support.v4.widget.DrawerLayout xmlns:android="http://schemas.android.com/apk/res/android" 
 
    android:id="@+id/dlDrawerLayout" 
 
    android:layout_width="match_parent" 
 
    android:layout_height="match_parent" > 
 

 
    <!-- Content --> 
 
    <RelativeLayout 
 
      android:id="@+id/rlContent" 
 
      android:layout_width="match_parent" 
 
      android:layout_height="match_parent"> 
 

 
     <TextView 
 
       android:layout_width="match_parent" 
 
       android:layout_height="wrap_content" 
 
       android:layout_centerInParent="true" 
 
       android:text="@string/hauptansicht" 
 
       android:gravity="center"/> 
 

 

 
    </RelativeLayout> 
 
    <!-- Menu --> 
 
    <RelativeLayout 
 
      android:id="@+id/rlDrawer" 
 
      android:layout_width="240dp" 
 
      android:layout_height="match_parent" 
 
      android:layout_gravity="start" 
 
      android:background="#111"> 
 
     
 
     <TextView 
 
       android:layout_width="match_parent" 
 
       android:layout_height="wrap_content" 
 
       android:layout_centerInParent="true" 
 
       android:text="@string/menuansicht" 
 
       android:gravity="center"/> 
 
     
 
     <ListView 
 
      android:id="@+id/drawerliste" 
 
      android:layout_width="match_parent" 
 
      android:layout_height="match_parent" 
 
      
 
      
 
      ></ListView> 
 

 
    </RelativeLayout> 
 
</android.support.v4.widget.DrawerLayout>

logcat的：

09-20 21:37:02.920: E/AndroidRuntime(827): FATAL EXCEPTION: main 
 
09-20 21:37:02.920: E/AndroidRuntime(827): java.lang.RuntimeException: Unable to start activity ComponentInfo{de.pascalborker.drunkingz/de.pascalborker.drunkingz.MainActivity}: java.lang.NullPointerException 
 
09-20 21:37:02.920: E/AndroidRuntime(827): \t at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1956) 
 
09-20 21:37:02.920: E/AndroidRuntime(827): \t at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:1981) 
 
09-20 21:37:02.920: E/AndroidRuntime(827): \t at android.app.ActivityThread.access$600(ActivityThread.java:123) 
 
09-20 21:37:02.920: E/AndroidRuntime(827): \t at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1147) 
 
09-20 21:37:02.920: E/AndroidRuntime(827): \t at android.os.Handler.dispatchMessage(Handler.java:99) 
 
09-20 21:37:02.920: E/AndroidRuntime(827): \t at android.os.Looper.loop(Looper.java:137) 
 
09-20 21:37:02.920: E/AndroidRuntime(827): \t at android.app.ActivityThread.main(ActivityThread.java:4424) 
 
09-20 21:37:02.920: E/AndroidRuntime(827): \t at java.lang.reflect.Method.invokeNative(Native Method) 
 
09-20 21:37:02.920: E/AndroidRuntime(827): \t at java.lang.reflect.Method.invoke(Method.java:511) 
 
09-20 21:37:02.920: E/AndroidRuntime(827): \t at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:784) 
 
09-20 21:37:02.920: E/AndroidRuntime(827): \t at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:551) 
 
09-20 21:37:02.920: E/AndroidRuntime(827): \t at dalvik.system.NativeStart.main(Native Method) 
 
09-20 21:37:02.920: E/AndroidRuntime(827): Caused by: java.lang.NullPointerException 
 
09-20 21:37:02.920: E/AndroidRuntime(827): \t at de.pascalborker.drunkingz.MainActivity.onCreate(MainActivity.java:33) 
 
09-20 21:37:02.920: E/AndroidRuntime(827): \t at android.app.Activity.performCreate(Activity.java:4465) 
 
09-20 21:37:02.920: E/AndroidRuntime(827): \t at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1049) 
 
09-20 21:37:02.920: E/AndroidRuntime(827): \t at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1920) 
 
09-20 21:37:02.920: E/AndroidRuntime(827): \t ... 11 more 
 
09-20 21:39:05.640: A/BatteryStatsImpl(77): problem reading network stats 
 
09-20 21:39:05.640: A/BatteryStatsImpl(77): java.lang.IllegalStateException: problem parsing idx 1 
 
09-20 21:39:05.640: A/BatteryStatsImpl(77): \t at com.android.internal.net.NetworkStatsFactory.readNetworkStatsDetail(NetworkStatsFactory.java:300) 
 
09-20 21:39:05.640: A/BatteryStatsImpl(77): \t at com.android.internal.net.NetworkStatsFactory.readNetworkStatsDetail(NetworkStatsFactory.java:250) 
 
09-20 21:39:05.640: A/BatteryStatsImpl(77): \t at com.android.internal.os.BatteryStatsImpl.getNetworkStatsDetailGroupedByUid(BatteryStatsImpl.java:5734) 
 
09-20 21:39:05.640: A/BatteryStatsImpl(77): \t at com.android.internal.os.BatteryStatsImpl.access$100(BatteryStatsImpl.java:76) 
 
09-20 21:39:05.640: A/BatteryStatsImpl(77): \t at com.android.internal.os.BatteryStatsImpl$Uid.computeCurrentTcpBytesReceived(BatteryStatsImpl.java:2457) 
 
09-20 21:39:05.640: A/BatteryStatsImpl(77): \t at com.android.internal.os.BatteryStatsImpl$Uid.getTcpBytesReceived(BatteryStatsImpl.java:2446) 
 
09-20 21:39:05.640: A/BatteryStatsImpl(77): \t at com.android.internal.os.BatteryStatsImpl.writeSummaryToParcel(BatteryStatsImpl.java:5437) 
 
09-20 21:39:05.640: A/BatteryStatsImpl(77): \t at com.android.internal.os.BatteryStatsImpl.writeLocked(BatteryStatsImpl.java:4836) 
 
09-20 21:39:05.640: A/BatteryStatsImpl(77): \t at com.android.internal.os.BatteryStatsImpl.writeAsyncLocked(BatteryStatsImpl.java:4818) 
 
09-20 21:39:05.640: A/BatteryStatsImpl(77): \t at com.android.server.am.ActivityManagerService.updateCpuStatsNow(ActivityManagerService.java:1652) 
 
09-20 21:39:05.640: A/BatteryStatsImpl(77): \t at com.android.server.am.ActivityManagerService$3.run(ActivityManagerService.java:1534) 
 
09-20 21:39:05.640: A/BatteryStatsImpl(77): Caused by: java.io.FileNotFoundException: /proc/net/xt_qtaguid/stats: open failed: ENOENT (No such file or directory) 
 
09-20 21:39:05.640: A/BatteryStatsImpl(77): \t at libcore.io.IoBridge.open(IoBridge.java:406) 
 
09-20 21:39:05.640: A/BatteryStatsImpl(77): \t at java.io.FileInputStream.<init>(FileInputStream.java:78) 
 
09-20 21:39:05.640: A/BatteryStatsImpl(77): \t at com.android.internal.net.NetworkStatsFactory.readNetworkStatsDetail(NetworkStatsFactory.java:269) 
 
09-20 21:39:05.640: A/BatteryStatsImpl(77): \t ... 10 more 
 
09-20 21:39:05.640: A/BatteryStatsImpl(77): Caused by: libcore.io.ErrnoException: open failed: ENOENT (No such file or directory) 
 
09-20 21:39:05.640: A/BatteryStatsImpl(77): \t at libcore.io.Posix.open(Native Method) 
 
09-20 21:39:05.640: A/BatteryStatsImpl(77): \t at libcore.io.BlockGuardOs.open(BlockGuardOs.java:110) 
 
09-20 21:39:05.640: A/BatteryStatsImpl(77): \t at libcore.io.IoBridge.open(IoBridge.java:390) 
 
09-20 21:39:05.640: A/BatteryStatsImpl(77): \t ... 12 more 
 
09-20 21:48:39.280: E/AndroidRuntime(868): FATAL EXCEPTION: main 
 
09-20 21:48:39.280: E/AndroidRuntime(868): java.lang.RuntimeException: Unable to start activity ComponentInfo{de.pascalborker.drunkingz/de.pascalborker.drunkingz.MainActivity}: java.lang.NullPointerException 
 
09-20 21:48:39.280: E/AndroidRuntime(868): \t at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1956) 
 
09-20 21:48:39.280: E/AndroidRuntime(868): \t at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:1981) 
 
09-20 21:48:39.280: E/AndroidRuntime(868): \t at android.app.ActivityThread.access$600(ActivityThread.java:123) 
 
09-20 21:48:39.280: E/AndroidRuntime(868): \t at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1147) 
 
09-20 21:48:39.280: E/AndroidRuntime(868): \t at android.os.Handler.dispatchMessage(Handler.java:99) 
 
09-20 21:48:39.280: E/AndroidRuntime(868): \t at android.os.Looper.loop(Looper.java:137) 
 
09-20 21:48:39.280: E/AndroidRuntime(868): \t at android.app.ActivityThread.main(ActivityThread.java:4424) 
 
09-20 21:48:39.280: E/AndroidRuntime(868): \t at java.lang.reflect.Method.invokeNative(Native Method) 
 
09-20 21:48:39.280: E/AndroidRuntime(868): \t at java.lang.reflect.Method.invoke(Method.java:511) 
 
09-20 21:48:39.280: E/AndroidRuntime(868): \t at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:784) 
 
09-20 21:48:39.280: E/AndroidRuntime(868): \t at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:551) 
 
09-20 21:48:39.280: E/AndroidRuntime(868): \t at dalvik.system.NativeStart.main(Native Method) 
 
09-20 21:48:39.280: E/AndroidRuntime(868): Caused by: java.lang.NullPointerException 
 
09-20 21:48:39.280: E/AndroidRuntime(868): \t at de.pascalborker.drunkingz.MainActivity.onCreate(MainActivity.java:33) 
 
09-20 21:48:39.280: E/AndroidRuntime(868): \t at android.app.Activity.performCreate(Activity.java:4465) 
 
09-20 21:48:39.280: E/AndroidRuntime(868): \t at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1049) 
 
09-20 21:48:39.280: E/AndroidRuntime(868): \t at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1920) 
 
09-20 21:48:39.280: E/AndroidRuntime(868): \t ... 11 more

任何人都知道可能是什么原因造成的？

来源

2014-09-20 thetigerhay

为什么'setContentView（R.layout.activity_main）;'注释掉了？你需要这个。 – 2014-09-20 21:59:27

由于你在玩耍：[什么是空指针异常，以及如何解决它？]（http://stackoverflow.com/questions/218384/what-is-a-null-pointer-exception-and-我如何解决它）。我正在“玩耍”意味着你正在学习它。 – jww 2014-09-20 22:23:16

在你的onCreate（）

//setContentView(R.layout.activity_main); 

DrawerLayout = (DrawerLayout) findViewById(R.id.dlDrawerLayout);

如果您没有设置内容视图与布局，然后findViewById将返回null，并且

DrawerLayout.setDrawerListener(ActionBarDrawerToggle);

这将引发NullPointerException异常。

取消注释该行

来源

2014-09-20 22:17:58

我认为解决了这个问题。但我有另外一个：LogCat告诉我“你的内容必须有一个ListView的id属性是'android.R.id.list'。这是什么意思？对不起，我在这方面是全新的。 – thetigerhay 2014-09-20 23:34:54

@thetigerhay ListActivity预计你可能只是想要一个常规的Activity，也就是'MainActivity extends Activity'。 – 2014-09-20 23:43:52

这意味着你的布局需要一个ListView Widget，它的id属性设置为：android.R.id.list。为什么那么因为你在扩展ListViewActivity而不是普通的Activity类ListViewActivity希望在里面有一个列表视图，其中指向的ID是我在你的activity_main.xml布局中看到没有列表视图被添加。更改父Activity类，或者如果您真的需要添加ListView。 – 2014-09-21 13:25:49

NullPointerException与ListView

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