应用程序在关闭/重新打开时崩溃，然后按下按钮

Question

我正在运行eclipse并诚实地教导自己了解android编程的基础知识。我想我会开始一个简单的手电筒应用程序，所以我可以更好地了解这是如何工作的。该应用程序本身工作正常，并启动相机闪光灯。

我的问题是，当我按主页按钮，然后回到应用程序，然后按下按钮打开手电筒，应用程序崩溃。我一直在阅读很多，我猜这是因为我没有“onResume”，但我可能是错的。任何帮助是极大的赞赏。

import android.app.Activity; 
    import android.content.Context; 
    import android.content.pm.PackageManager; 
    import android.hardware.Camera; 
    import android.hardware.Camera.Parameters; 
    import android.os.Bundle; 
    import android.util.Log; 
    import android.view.View; 
    import android.view.View.OnClickListener; 
    import android.widget.Button; 
    import com.pmm.lettherebe.R; 

    public class MainActivity extends Activity { 

//flag to detect flash is on or off 
private boolean isLighOn = false; 

private Camera camera; 

private Button button; 

@Override 
protected void onPause() { 
    super.onPause(); 

    if (camera != null) { 
     camera.release();; 
    } 
} 




@Override 
public void onCreate(Bundle savedInstanceState) { 
    super.onCreate(savedInstanceState); 
    setContentView(R.layout.activity_main); 

    button = (Button) findViewById(R.id.buttonFlashlight); 

    Context context = this; 
    PackageManager pm = context.getPackageManager(); 

    // if device support camera? 
    if (!pm.hasSystemFeature(PackageManager.FEATURE_CAMERA)) { 
     Log.e("err", "Device has no camera!"); 
     return; 
    } 

    camera = Camera.open(); 
    final Parameters p = camera.getParameters(); 

    button.setOnClickListener(new OnClickListener() { 

     @Override 
     public void onClick(View arg0) { 

      if (isLighOn) { 
       Log.i("info", "torch is turn off!"); 

       p.setFlashMode(Parameters.FLASH_MODE_OFF); 
       camera.setParameters(p); 
       camera.stopPreview(); 
       isLighOn = false; 


      } else { 

       Log.i("info", "torch is turn on!"); 
       p.setFlashMode(Parameters.FLASH_MODE_TORCH); 

       camera.setParameters(p); 
       camera.startPreview(); 
       isLighOn = true; 

      } 

     } 
    }); 

} 
    } 

这里是logcat的错误：

07-02 20:32:19.680: D/OpenGLRenderer(14897): Enabling debug mode 0 
07-02 20:32:21.121: I/info(14897): torch is turn on! 
07-02 20:32:22.553: I/info(14897): torch is turn off! 
07-02 20:32:23.363: I/info(14897): torch is turn on! 
07-02 20:32:23.964: I/info(14897): torch is turn off! 
07-02 20:32:29.090: I/info(14897): torch is turn on! 
07-02 20:32:29.090: D/AndroidRuntime(14897): Shutting down VM 
07-02 20:32:29.090: W/dalvikvm(14897): threadid=1: thread exiting 
withuncaught   exception (group=0x41b46930) 
07-02 20:32:29.090: E/AndroidRuntime(14897): FATAL EXCEPTION: main 
07-02 20:32:29.090: E/AndroidRuntime(14897): java.lang.RuntimeException: Method 
alled after release() 
07-02 20:32:29.090: E/AndroidRuntime(14897):  at 
android.hardware.Camera.native_setParameters(Native Method) 
07-02 20:32:29.090: E/AndroidRuntime(14897):  at 
android.hardware.Camera.setParameters(Camera.java:1496) 
07-02 20:32:29.090: E/AndroidRuntime(14897):  at 
com.pmm.lettherebe.MainActivity$1.onClick(MainActivity.java:74) 
07-02 20:32:29.090: E/AndroidRuntime(14897):  at 
android.view.View.performClick(View.java:4204) 
07-02 20:32:29.090: E/AndroidRuntime(14897):  at 
android.view.View$PerformClick.run(View.java:17355) 
07-02 20:32:29.090: E/AndroidRuntime(14897):  at 
android.os.Handler.handleCallback(Handler.java:725)  
07-02 20:32:29.090: E/AndroidRuntime(14897):  at 
android.os.Handler.dispatchMessage(Handler.java:92) 
07-02 20:32:29.090: E/AndroidRuntime(14897):  at 
android.os.Looper.loop(Looper.java:137) 
07-02 20:32:29.090: E/AndroidRuntime(14897):  at 
android.app.ActivityThread.main(ActivityThread.java:5195) 
07-02 20:32:29.090: E/AndroidRuntime(14897):  at 
java.lang.reflect.Method.invokeNative(Native Method) 
07-02 20:32:29.090: E/AndroidRuntime(14897):  at 
java.lang.reflect.Method.invoke(Method.java:511) 
07-02 20:32:29.090: E/AndroidRuntime(14897):  at 
com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:795) 
07-02 20:32:29.090: E/AndroidRuntime(14897):  at 
com.android.internal.os.ZygoteInit.main(ZygoteInit.java:562) 
07-02 20:32:29.090: E/AndroidRuntime(14897):  at 
dalvik.system.NativeStart.main(Native Method) 
07-02 20:32:31.222: I/Process(14897): Sending signal. PID: 14897 SIG: 9 

Answer 1

看来，你的活动被调用，而你释放相机 - 这是件好事。但是，你永远不会重新初始化它。

Android开发人员指南有this exact example。

基本上，你需要做这样的事情：

@Override 
protected void onPause() { 
    super.onPause(); 

    if (camera != null) { 
     camera.release(); 
     camera = null; 
    } 
} 

@Override 
protected void onResume() { 
    super.onResume(); 

    if (camera == null) { 
     initializeCamera(); 
    } 
} 

然后你把所有的相机初始化代码从onCreate到一个新的initializeCamera方法。

请注意，您不应该在onCreate中初始化摄像头，因为它在onResume中完成（即使在第一次加载时也会调​​用该摄像头）。