java - Android - 应用程序仅在第一次启动时崩溃，但第二次运行

Question

我的 Android 手电筒应用程序有问题。当我在应用程序打开然后恢复时尝试按设备的主页按钮时应用程序崩溃(通过单击主屏幕上的应用程序图标而不是最近的应用程序按钮)。在我从最近的应用程序列表中终止该应用程序然后再次打开后，它不再使用上面的相同指令崩溃。

请看下面的代码。

public class MainActivity extends Settings {

public Camera camera;
public Camera.Parameters parameters;
public ImageButton flashLightButton;
boolean isFlashLightOn = false;
MediaPlayer mySound;



@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    flashLightButton = (ImageButton)findViewById(R.id.flashlight_button);
    flashLightButton.setOnClickListener(new FlashOnOffListener());


    registerReceiver(mBatInfoReceiver, new IntentFilter(Intent.ACTION_BATTERY_CHANGED));

    mySound = MediaPlayer.create(this, R.raw.balloon_snap);

    if (isFlashSupported()) {
        camera = Camera.open();
        parameters = camera.getParameters();
    } else {
        showNoFlashAlert();
    }

    Settings.active = false;

    //super.onCreate(savedInstanceState);
    //Set layout we created
    //setContentView(R.layout.activity_main);
    //Register the receiver which triggers event
    //when battery charge is changed



}

public void settings(View view)
{

    Intent intent = new Intent(MainActivity.this, Settings.class);
    startActivity(intent);
    this.finish();
}


private BroadcastReceiver mBatInfoReceiver = new BroadcastReceiver() {
    @Override
    //When Event is published, onReceive method is called
    public void onReceive(Context c, Intent i) {
        //Get Battery %
        int level = i.getIntExtra("level", 0);
        //Find the progressbar creating in main.xml
        ProgressBar pb = (ProgressBar) findViewById(R.id.progressbar);
        //Set progress level with battery % value
        pb.setProgress(level);
        //Find textview control created in main.xml
        TextView tv = (TextView) findViewById(R.id.textfield);
        //Set TextView with text
        tv.setText("" + Integer.toString(level) + "");
    }

};

public class FlashOnOffListener implements View.OnClickListener{


    SharedPreferences sharedPrefs = getSharedPreferences("VibrateSettings", MODE_PRIVATE);
    Boolean vibration = sharedPrefs.getBoolean("VibrateSet", false);

    SharedPreferences sharedPrefs2 = getSharedPreferences("SoundSettings", MODE_PRIVATE);
    Boolean sound = sharedPrefs2.getBoolean("SoundSet", false);

    @Override
    public void onClick(View v) {

        if(isFlashLightOn){
            flashLightButton.setImageResource(R.drawable.flashlight_off);
            parameters.setFlashMode(Parameters.FLASH_MODE_OFF);
            camera.setParameters(parameters);
            camera.stopPreview();
            isFlashLightOn = false;

            if(vibration == true){
                // Get instance of Vibrator from current Context
                Vibrator vib = (Vibrator) getSystemService(Context.VIBRATOR_SERVICE);
                // Vibrate for 400 milliseconds
                vib.vibrate(20);
            }
            else {
                // Get instance of Vibrator from current Context
                Vibrator vib = (Vibrator) getSystemService(Context.VIBRATOR_SERVICE);
                // Vibrate for 400 milliseconds
                vib.vibrate(00);
        }
            if (sound == true){
                mySound.start();
            }

        }else{
            flashLightButton.setImageResource(R.drawable.flashlight_on);
            parameters.setFlashMode(Parameters.FLASH_MODE_TORCH);
            camera.setParameters(parameters);
            camera.startPreview();
            isFlashLightOn = true;

            if(vibration == true){
                // Get instance of Vibrator from current Context
                Vibrator vib = (Vibrator) getSystemService(Context.VIBRATOR_SERVICE);
                // Vibrate for 400 milliseconds
                vib.vibrate(20);
            }
            else {
                // Get instance of Vibrator from current Context
                Vibrator vib = (Vibrator) getSystemService(Context.VIBRATOR_SERVICE);
                // Vibrate for 400 milliseconds
                vib.vibrate(00);
            }
            if (sound == true){
                mySound.start();
            }

        }

    }

}

private void showNoFlashAlert() {
    new AlertDialog.Builder(this)
            .setMessage("Your device hardware does not support flashlight!")
            .setIcon(android.R.drawable.ic_dialog_alert).setTitle("Error")
            .setPositiveButton("Ok", new OnClickListener() {

                @Override
                public void onClick(DialogInterface dialog, int which) {
                    dialog.dismiss();
                    finish();
                }
            }).show();
}

private boolean isFlashSupported() {
    PackageManager pm = getPackageManager();
    return pm.hasSystemFeature(PackageManager.FEATURE_CAMERA_FLASH);
}



@Override
protected void onDestroy() {
    if(camera != null){
        camera.stopPreview();
        camera.release();
        camera = null;
    }
    super.onDestroy();
}}

AndroidManifest.xml

<uses-sdk
    android:minSdkVersion="14"
    android:targetSdkVersion="19" />

<uses-permission android:name="android.permission.CAMERA" />
<uses-feature android:name="android.hardware.camera" />
<uses-permission android:name="android.permission.BATTERY_STATS"/>
<uses-permission android:name="android.permission.BROADCAST_STICKY"/>
<uses-permission android:name="android.permission.VIBRATE"/>

<application
    android:allowBackup="true"
    android:icon="@drawable/btn_switch_on"
    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=".Settings"
        android:label="@string/app_name">
    </activity>

</application>

日志

E/AndroidRuntime(22941): FATAL EXCEPTION: main

E/AndroidRuntime(22941): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.johncarlo.flashlight/com.example.johncarlo.flashlight.MainActivity}: java.lang.RuntimeException: Fail to connect to camera service

E/AndroidRuntime(22941):    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2186)

E/AndroidRuntime(22941):    at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2236)

E/AndroidRuntime(22941):    at android.app.ActivityThread.access$600(ActivityThread.java:145)

E/AndroidRuntime(22941):    at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1238)

E/AndroidRuntime(22941):    at android.os.Handler.dispatchMessage(Handler.java:99)

E/AndroidRuntime(22941):    at android.os.Looper.loop(Looper.java:137)

E/AndroidRuntime(22941):    at android.app.ActivityThread.main(ActivityThread.java:5099)

E/AndroidRuntime(22941):    at java.lang.reflect.Method.invokeNative(Native Method)

E/AndroidRuntime(22941):    at java.lang.reflect.Method.invoke(Method.java:511)

E/AndroidRuntime(22941):    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:803)

E/AndroidRuntime(22941):    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:570)

E/AndroidRuntime(22941):    at dalvik.system.NativeStart.main(Native Method)

E/AndroidRuntime(22941): Caused by: java.lang.RuntimeException: Fail to connect to camera service

E/AndroidRuntime(22941):    at android.hardware.Camera.native_setup(Native Method)

E/AndroidRuntime(22941):    at android.hardware.Camera.<init>(Camera.java:365)

E/AndroidRuntime(22941):    at android.hardware.Camera.open(Camera.java:338)

E/AndroidRuntime(22941):    at com.example.johncarlo.flashlight.MainActivity.onCreate(MainActivity.java:49)

E/AndroidRuntime(22941):    at android.app.Activity.performCreate(Activity.java:5117)

E/AndroidRuntime(22941):    at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1081)

E/AndroidRuntime(22941):    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2150)

E/AndroidRuntime(22941):    ... 11 more

W/ActivityManager(  786):   Force finishing activity com.example.johncarlo.flashlight/.MainActivity

Answer 1

将onCreate下面一行去掉，写入onResume中，这样可能不会崩溃。

@Override
protected void onResume() {
    super.onResume();
    registerReceiver(mBatInfoReceiver, new IntentFilter(Intent.ACTION_BATTERY_CHANGED));
}