Android SDK空指针异常

Question

我想创建一个音板，所以当您点击按钮时，它会播放声音。

@Override 
protected void onCreate(Bundle savedInstanceState) { 
    // TODO Auto-generated method stub 
    super.onCreate(savedInstanceState); 
    setContentView(R.layout.akali); 

    Button b = (Button) findViewById(R.id.akaliJokeButton); 
    b.setOnClickListener(new OnClickListener() { 


     public void onClick(View v) { 
      MediaPlayer mp = MediaPlayer.create(Akali.this, R.raw.akalijoke); 
      mp.start(); 
     } 
    }); 

} 

这是我到目前为止的代码。但我得到一个没有指针异常错误

07-25 14:36:47.919: DEBUG/AndroidRuntime(1079): >>>>>> AndroidRuntime START com.android.internal.os.RuntimeInit <<<<<< 
07-25 14:36:47.919: DEBUG/AndroidRuntime(1079): CheckJNI is ON 
07-25 14:36:48.529: DEBUG/AndroidRuntime(1079): Calling main entry com.android.commands.pm.Pm 
07-25 14:36:48.560: DEBUG/AndroidRuntime(1079): Shutting down VM 
07-25 14:36:48.569: DEBUG/dalvikvm(1079): GC_CONCURRENT freed 101K, 71% free 297K/1024K, external 0K/0K, paused 1ms+1ms 
07-25 14:36:48.579: DEBUG/dalvikvm(1079): Debugger has detached; object registry had 1 entries 
07-25 14:36:48.599: INFO/dalvikvm(1079): JNI: AttachCurrentThread (from ???.???) 
07-25 14:36:48.599: INFO/AndroidRuntime(1079): NOTE: attach of thread 'Binder Thread #3' failed 
07-25 14:36:48.989: DEBUG/AndroidRuntime(1089): >>>>>> AndroidRuntime START com.android.internal.os.RuntimeInit <<<<<< 
07-25 14:36:48.989: DEBUG/AndroidRuntime(1089): CheckJNI is ON 
07-25 14:36:49.579: DEBUG/AndroidRuntime(1089): Calling main entry com.android.commands.am.Am 
07-25 14:36:49.609: INFO/ActivityManager(61): Starting: Intent { act=android.intent.action.MAIN cat=[android.intent.category.LAUNCHER] flg=0x10000000 cmp=com.reg.lolsoundboard/.Main } from pid 1089 
07-25 14:36:49.829: DEBUG/AndroidRuntime(1089): Shutting down VM 
07-25 14:36:49.849: DEBUG/dalvikvm(1089): GC_CONCURRENT freed 102K, 69% free 320K/1024K, external 0K/0K, paused 1ms+1ms 
07-25 14:36:49.849: DEBUG/jdwp(1089): Got wake-up signal, bailing out of select 
07-25 14:36:49.849: DEBUG/dalvikvm(1089): Debugger has detached; object registry had 1 entries 
07-25 14:36:49.879: INFO/ActivityManager(61): Start proc com.reg.lolsoundboard for activity com.reg.lolsoundboard/.Main: pid=1099 uid=10036 gids={} 
07-25 14:36:49.931: INFO/AndroidRuntime(1089): NOTE: attach of thread 'Binder Thread #3' failed 
07-25 14:36:50.839: DEBUG/dalvikvm(1099): GC_EXTERNAL_ALLOC freed 49K, 53% free 2557K/5379K, external 2002K/2137K, paused 54ms 
07-25 14:36:51.250: INFO/ActivityManager(61): Displayed com.reg.lolsoundboard/.Main: +1s426ms (total +8m29s588ms) 
07-25 14:36:52.179: INFO/ActivityManager(61): Starting: Intent { cmp=com.reg.lolsoundboard/.Akali } from pid 1099 
07-25 14:36:52.299: DEBUG/AndroidRuntime(1099): Shutting down VM 
07-25 14:36:52.299: WARN/dalvikvm(1099): threadid=1: thread exiting with uncaught exception (group=0x40015560) 
07-25 14:36:52.309: ERROR/AndroidRuntime(1099): FATAL EXCEPTION: main 
07-25 14:36:52.309: ERROR/AndroidRuntime(1099): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.reg.lolsoundboard/com.reg.lolsoundboard.Akali}: java.lang.NullPointerException 
07-25 14:36:52.309: ERROR/AndroidRuntime(1099):  at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1647) 
07-25 14:36:52.309: ERROR/AndroidRuntime(1099):  at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:1663) 
07-25 14:36:52.309: ERROR/AndroidRuntime(1099):  at android.app.ActivityThread.access$1500(ActivityThread.java:117) 
07-25 14:36:52.309: ERROR/AndroidRuntime(1099):  at android.app.ActivityThread$H.handleMessage(ActivityThread.java:931) 
07-25 14:36:52.309: ERROR/AndroidRuntime(1099):  at android.os.Handler.dispatchMessage(Handler.java:99) 
07-25 14:36:52.309: ERROR/AndroidRuntime(1099):  at android.os.Looper.loop(Looper.java:123) 
07-25 14:36:52.309: ERROR/AndroidRuntime(1099):  at android.app.ActivityThread.main(ActivityThread.java:3683) 
07-25 14:36:52.309: ERROR/AndroidRuntime(1099):  at java.lang.reflect.Method.invokeNative(Native Method) 
07-25 14:36:52.309: ERROR/AndroidRuntime(1099):  at java.lang.reflect.Method.invoke(Method.java:507) 
07-25 14:36:52.309: ERROR/AndroidRuntime(1099):  at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:839) 
07-25 14:36:52.309: ERROR/AndroidRuntime(1099):  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:597) 
07-25 14:36:52.309: ERROR/AndroidRuntime(1099):  at dalvik.system.NativeStart.main(Native Method) 
07-25 14:36:52.309: ERROR/AndroidRuntime(1099): Caused by: java.lang.NullPointerException 
07-25 14:36:52.309: ERROR/AndroidRuntime(1099):  at com.reg.lolsoundboard.Akali.onCreate(Akali.java:19) 
07-25 14:36:52.309: ERROR/AndroidRuntime(1099):  at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1047) 
07-25 14:36:52.309: ERROR/AndroidRuntime(1099):  at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1611) 
07-25 14:36:52.309: ERROR/AndroidRuntime(1099):  ... 11 more 
07-25 14:36:52.319: WARN/ActivityManager(61): Force finishing activity com.reg.lolsoundboard/.Akali 
07-25 14:36:52.329: WARN/ActivityManager(61): Force finishing activity com.reg.lolsoundboard/.Main 
07-25 14:36:52.839: WARN/ActivityManager(61): Activity pause timeout for HistoryRecord{406fa098 com.reg.lolsoundboard/.Akali} 
07-25 14:36:54.199: INFO/Process(1099): Sending signal. PID: 1099 SIG: 9 
07-25 14:36:54.209: INFO/ActivityManager(61): Process com.reg.lolsoundboard (pid 1099) has died. 
07-25 14:36:54.209: INFO/WindowManager(61): WIN DEATH: Window{40761880 com.reg.lolsoundboard/com.reg.lolsoundboard.Main paused=true} 
07-25 14:36:54.299: WARN/InputManagerService(61): Got RemoteException sending setActive(false) notification to pid 1099 uid 10036 

XML文件

<?xml version="1.0" encoding="utf-8"?> 
    <LinearLayout 
     xmlns:android="http://schemas.android.com/apk/res/android" 
     android:orientation="vertical" 
     android:layout_width="match_parent" 
     android:layout_height="match_parent" 
     android:background="@drawable/akalibg" android:weightSum="1"> 
     <RelativeLayout android:layout_width="match_parent" android:id="@+id/relativeLayout1" android:layout_height="wrap_content" android:layout_weight="0.33"> 

      <Button android:layout_height="wrap_content" android:layout_width="wrap_content" android:layout_alignParentTop="true" android:layout_centerHorizontal="true" android:id="@+id/akaliLaugh1" android:text="Laugh 1"></Button> 
      <Button android:layout_height="wrap_content" android:layout_width="wrap_content" android:layout_alignParentTop="true" android:layout_alignParentRight="true" android:text="Laugh 2" android:id="@+id/akaliLaugh2"></Button> 
      <Button android:text="Laugh 3" android:id="@+id/akaliLaugh3" android:layout_height="wrap_content" android:layout_width="wrap_content" android:layout_alignTop="@+id/akaliLaugh4" android:layout_alignLeft="@+id/akaliJokeButton"></Button> 
      <Button android:id="@+id/akaliLaugh4" android:layout_height="wrap_content" android:keepScreenOn="false" android:layout_width="wrap_content" android:layout_centerVertical="true" android:layout_alignLeft="@+id/akaliLaugh1" android:text="Laugh 4"></Button> 
      <Button android:layout_height="wrap_content" android:layout_width="wrap_content" android:layout_alignBottom="@+id/akaliLaugh4" android:layout_alignParentRight="true" android:id="@+id/akaliTaunt" android:layout_alignLeft="@+id/akaliLaugh2" android:text="Taunt 1"></Button> 
      <Button android:id="@+id/button1" android:layout_height="wrap_content" android:layout_width="wrap_content" android:layout_alignParentTop="true" android:layout_alignParentLeft="true" android:layout_alignRight="@+id/akaliLaugh3" android:text="Joke 1"></Button> 

      </RelativeLayout> 
     <RelativeLayout android:layout_width="match_parent" android:id="@+id/relativeLayout2" android:layout_height="wrap_content"> 
     </RelativeLayout> 


    </LinearLayout> 

初始主屏幕，以获得实际的音板

package com.reg.lolsoundboard; 

import android.app.Activity; 
import android.content.Intent; 
import android.os.Bundle; 
import android.view.View; 
import android.view.View.OnClickListener; 
import android.widget.ImageButton; 


public class Main extends Activity { 
    /** Called when the activity is first created. */ 
    @Override 
    public void onCreate(Bundle savedInstanceState) { 
     super.onCreate(savedInstanceState); 
     setContentView(R.layout.main); 


     ImageButton b = (ImageButton) findViewById(R.id.akaliButton); 
     b.setOnClickListener(new OnClickListener() { 

     @Override 
     public void onClick(View arg0) { 
      startActivity(new Intent(Main.this, Akali.class)); 

     } 
    }); 
    } 
} 

Answer 1

似乎你不会有一个按钮ID“akaliJokeButton”