AlertDialog.Builder错误

我将此代码复制到我现有的文件中。

if (mSensorX >= 5){ 


     AlertDialog.Builder builder1 = new AlertDialog.Builder(context); 
     builder1.setMessage("Write your message here."); 
     builder1.setCancelable(true); 
     builder1.setPositiveButton("Yes", 
       new DialogInterface.OnClickListener() { 
      public void onClick(DialogInterface dialog, int id) { 
       dialog.cancel(); 
      } 
     }); 
     builder1.setNegativeButton("No", 
       new DialogInterface.OnClickListener() { 
      public void onClick(DialogInterface dialog, int id) { 
       dialog.cancel(); 
      } 
     }); 

     AlertDialog alert11 = builder1.create(); 
     alert11.show(); 
    }

这是代码：

package de.example.baum_projekt_5_punkt_fix; 


import android.app.AlertDialog; 
import android.content.Context; 
import android.content.DialogInterface; 
import android.graphics.Bitmap; 
import android.graphics.BitmapFactory; 
import android.graphics.BitmapFactory.Options; 
import android.graphics.Canvas; 
import android.hardware.Sensor; 
import android.hardware.SensorEvent; 
import android.hardware.SensorEventListener; 
import android.hardware.SensorManager; 
import android.view.Display; 
import android.view.Surface; 
import android.view.View; 
import android.view.WindowManager; 

public class SimulationView extends View implements SensorEventListener { 

private SensorManager mSensorManager; 
private Sensor mAccelerometer; 
private Display mDisplay; 

private Bitmap mGrass; 
private Bitmap mHole; 
private Bitmap mBitmap; 
private static final int BALL_SIZE = 32; 
private static final int HOLE_SIZE = 40; 

private float mXOrigin; 
private float mYOrigin; 

private float mHorizontalBound; 
private float mVerticalBound;  

private float mSensorX; 
private float mSensorY; 
private float mSensorZ; 
private long mSensorTimeStamp; 

private Particle mBall = new Particle(); 
private Context context; 
private int onlyonetime; 

public SimulationView(Context context) { 
    super(context); 

    WindowManager mWindowManager = (WindowManager)            
    context.getSystemService(Context.WINDOW_SERVICE); 
    mDisplay = mWindowManager.getDefaultDisplay(); 

    mSensorManager = (SensorManager) context.getSystemService(Context.SENSOR_SERVICE); 
    mAccelerometer = mSensorManager.getDefaultSensor(Sensor.TYPE_ACCELEROMETER); 

    Bitmap ball = BitmapFactory.decodeResource(getResources(), R.drawable.ball); 
    mBitmap = Bitmap.createScaledBitmap(ball, BALL_SIZE, BALL_SIZE, true); 

    Bitmap hole = BitmapFactory.decodeResource(getResources(), R.drawable.hole); 
    mHole = Bitmap.createScaledBitmap(hole, HOLE_SIZE, HOLE_SIZE, true); 

    Options opts = new Options(); 
    opts.inDither = true; 
    opts.inPreferredConfig = Bitmap.Config.RGB_565; 
    mGrass = BitmapFactory.decodeResource(getResources(), R.drawable.wald, opts);   
} 

public void startSimulation() { 
    mSensorManager.registerListener(this, mAccelerometer, SensorManager.SENSOR_DELAY_UI); 
} 

public void stopSimulation() { 
    mSensorManager.unregisterListener(this); 
} 

@Override 
public void onSensorChanged(SensorEvent event) { 
    if (event.sensor.getType() != Sensor.TYPE_ACCELEROMETER) 
     return; 

    switch (mDisplay.getRotation()) { 
    case Surface.ROTATION_0: 
     mSensorX = event.values[0]; 
     mSensorY = event.values[1]; 
     break; 
    case Surface.ROTATION_90: 
     mSensorX = -event.values[1]; 
     mSensorY = event.values[0]; 
     break; 
    case Surface.ROTATION_180: 
     mSensorX = -event.values[0]; 
     mSensorY = -event.values[1]; 
     break; 
    case Surface.ROTATION_270: 
     mSensorX = event.values[1]; 
     mSensorY = -event.values[0]; 
     break; 
    } 
    mSensorZ = event.values[2]; 
    mSensorTimeStamp = event.timestamp; 


    if (mSensorX >= 5){ 


     AlertDialog.Builder builder1 = new AlertDialog.Builder(context); 
     builder1.setMessage("Write your message here."); 
     builder1.setCancelable(true); 
     builder1.setPositiveButton("Yes", 
       new DialogInterface.OnClickListener() { 
      public void onClick(DialogInterface dialog, int id) { 
       dialog.cancel(); 
      } 
     }); 
     builder1.setNegativeButton("No", 
       new DialogInterface.OnClickListener() { 
      public void onClick(DialogInterface dialog, int id) { 
       dialog.cancel(); 
      } 
     }); 

     AlertDialog alert11 = builder1.create(); 
     alert11.show(); 
    } 

} 

@Override 
public void onAccuracyChanged(Sensor sensor, int accuracy) { 

} 

@Override 
protected void onSizeChanged(int w, int h, int oldw, int oldh) { 
    mXOrigin = w * 0.5f; 
    mYOrigin = h * 0.5f; 

    mHorizontalBound = (w - BALL_SIZE) * 0.5f; 
    mVerticalBound = (h - BALL_SIZE) * 0.5f; 
} 

@Override 
protected void onDraw(Canvas canvas) { 
    super.onDraw(canvas); 

    canvas.drawBitmap(mGrass, 0, 0, null); 
    canvas.drawBitmap(mHole, 100+mXOrigin - HOLE_SIZE/2, 100+ mYOrigin - HOLE_SIZE/2, null); 

    mBall.updatePosition(mSensorX, mSensorY, mSensorZ, mSensorTimeStamp); 
    mBall.resolveCollisionWithBounds(mHorizontalBound, mVerticalBound); 

    canvas.drawBitmap(mBitmap, 100+(mXOrigin - BALL_SIZE/2) + mBall.mPosX, 100+(mYOrigin - BALL_SIZE/2) - mBall.mPosY, null); 

    invalidate(); 
} 

}

而且在MainActivity：

package de.example.baum_projekt_5_punkt_fix; 

import android.app.Activity; 
import android.media.MediaPlayer; 
import android.os.Bundle; 


public class MainActivity extends Activity { 

private static final String TAG = "appsrox.example.accelerometer.MainActivity"; 
private MediaPlayer mp; 
int media_length; 

//private WakeLock mWakeLock; 
private SimulationView mSimulationView; 

@Override 
protected void onCreate(Bundle savedInstanceState) { 
    super.onCreate(savedInstanceState); 
    mp = MediaPlayer.create(this, R.raw.bgmusic); 
    //PowerManager mPowerManager = (PowerManager) getSystemService(POWER_SERVICE); 
    //mWakeLock = mPowerManager.newWakeLock(PowerManager.SCREEN_BRIGHT_WAKE_LOCK, TAG); 
    mp.seekTo(0); 
    mp.start(); 
    mSimulationView = new SimulationView(this); 
    setContentView(mSimulationView); 
} 

@Override 
protected void onResume() { 
    super.onResume(); 
    //mWakeLock.acquire(); 
    mSimulationView.startSimulation(); 
    mp.seekTo(0); 
    mp.start(); 

} 

@Override 
protected void onPause() { 
    super.onPause(); 
    mSimulationView.stopSimulation(); 
    media_length = mp.getCurrentPosition(); 
    mp.pause(); 
    //mWakeLock.release(); 
} 

@Override 
protected void onDestroy() { 

    mp.release(); 

    super.onDestroy(); 
    //mWakeLock.release(); 
} 
}

应用程序崩溃，我得到这个logcat的：

02-06 21:50:06.515: E/AndroidRuntime(3314): FATAL EXCEPTION: main 
02-06 21:50:06.515: E/AndroidRuntime(3314): Process: de.example.baum_projekt_5_punkt_fix, PID: 3314 
02-06 21:50:06.515: E/AndroidRuntime(3314): java.lang.NullPointerException 
02-06 21:50:06.515: E/AndroidRuntime(3314):  at  android.app.AlertDialog.resolveDialogTheme(AlertDialog.java:143) 
02-06 21:50:06.515: E/AndroidRuntime(3314):  at android.app.AlertDialog$Builder.<init>(AlertDialog.java:360) 
02-06 21:50:06.515: E/AndroidRuntime(3314):  at de.example.baum_projekt_5_punkt_fix.SimulationView.onSensorChanged(SimulationView.java:106) 
02-06 21:50:06.515: E/AndroidRuntime(3314):  at android.hardware.SystemSensorManager$SensorEventQueue.dispatchSensorEvent(SystemSensorManager.java:474) 
02-06 21:50:06.515: E/AndroidRuntime(3314):  at android.os.MessageQueue.nativePollOnce(Native Method) 
02-06 21:50:06.515: E/AndroidRuntime(3314):  at android.os.MessageQueue.next(MessageQueue.java:138) 
02-06 21:50:06.515: E/AndroidRuntime(3314):  at android.os.Looper.loop(Looper.java:123) 
02-06 21:50:06.515: E/AndroidRuntime(3314):  at android.app.ActivityThread.main(ActivityThread.java:5356) 
02-06 21:50:06.515: E/AndroidRuntime(3314):  at java.lang.reflect.Method.invokeNative(Native Method) 
02-06 21:50:06.515: E/AndroidRuntime(3314):  at java.lang.reflect.Method.invoke(Method.java:515) 
02-06 21:50:06.515: E/AndroidRuntime(3314):  at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1265) 
02-06 21:50:06.515: E/AndroidRuntime(3314):  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1081) 
02-06 21:50:06.515: E/AndroidRuntime(3314):  at dalvik.system.NativeStart.main(Native Method)

有任何人的想法？我认为“上下文”有问题，但我不知道如何解决它。

忠实的

来源

2015-02-06 Ma Tze

这点指向你正确的方向：在de.example.baum_projekt_5_punkt_fix.SimulationView.onSensorChanged（SimulationView.java:106）第106行的东西是空的？哪条线？ – Melquiades 2015-02-06 21:17:08

您并未初始化您的本地“上下文”变量。由于您使用本地上下文初始化构建器，因此构建器实例为空，无法正确使用。在构造函数中添加：

this.context = context;

这应该照顾它。

来源

2015-02-06 21:19:05 aProperFox

感谢您的帮助。这是一个愚蠢的问题，我知道。但我是一个初学者;-) – 2015-02-08 17:10:41

不用担心！我们都犯愚蠢的错误:) – aProperFox 2015-02-12 17:00:35

AlertDialog.Builder错误

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