Question

我正在尝试在手机背景上运行摄像机。但是出现以下错误：

java.lang.NullPointerException: Attempt to invoke virtual method 'void android.hardware.Camera.stopPreview()' on a null object reference
    at android.app.ActivityThread.handleServiceArgs(ActivityThread.java:3230)
    at android.app.ActivityThread.-wrap17(ActivityThread.java)
    at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1590)
    at android.os.Handler.dispatchMessage(Handler.java:111)
    at android.os.Looper.loop(Looper.java:207)
    at android.app.ActivityThread.main(ActivityThread.java:5737)
    at java.lang.reflect.Method.invoke(Native Method)
    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:789)
    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:679)
 Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.hardware.Camera.stopPreview()' on a null object reference
    at bd.org.rain.lostphonefinder.CameraService.handleStopRecordingCommand(CameraService.java:241)
    at bd.org.rain.lostphonefinder.CameraService.onStartCommand(CameraService.java:104)
    at android.app.ActivityThread.handleServiceArgs(ActivityThread.java:3213)
    at android.app.ActivityThread.-wrap17(ActivityThread.java) 
    at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1590) 
    at android.os.Handler.dispatchMessage(Handler.java:111) 
    at android.os.Looper.loop(Looper.java:207) 
    at android.app.ActivityThread.main(ActivityThread.java:5737) 
    at java.lang.reflect.Method.invoke(Native Method) 
    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:789) 
    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:679)

相机服务类代码：

https://pastebin.com/WKKPafD3

清单：

<uses-feature android:name="android.hardware.camera2.full" />
<uses-feature android:name="android.hardware.camera2.front" android:required="false" />
<uses-permission android:name="android.permission.CAMERA" />
<uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE" />
<uses-permission android:name="android.permission.RECORD_AUDIO" />
<uses-permission android:name="android.permission.SYSTEM_ALERT_WINDOW" />

请帮助！

Answer 1

您的问题是 mCamera 对象为空。简单的解决方法是：

private void handleStopRecordingCommand(Intent intent) {
    ResultReceiver resultReceiver = intent.getParcelableExtra(RESULT_RECEIVER);

    if (!mRecording) {
        // have not recorded
        resultReceiver.send(RECORD_RESULT_NOT_RECORDING, null);
        return;
    }

    try {
        mMediaRecorder.stop();
        mMediaRecorder.release();
    } catch (RuntimeException e) {
        mMediaRecorder.reset();
        resultReceiver.send(RECORD_RESULT_UNSTOPPABLE, new Bundle());
        return;
    } finally {
        mMediaRecorder = null;
        if(mCamera != null) {// This will prevent null pointer exception
            mCamera.stopPreview();
            mCamera.release();
        }
        mRecording = false;
    }

    Bundle b = new Bundle();
    b.putString(VIDEO_PATH, mRecordingPath);
    resultReceiver.send(RECORD_RESULT_OK, b);

    Log.d(TAG, "recording is finished.");
}

Answer 2

只需尝试一下...

Camera mcamera = Camera.open(0);

尝试在空对象引用上调用虚拟方法'void android.hardware.Camera.stopPreview（）'

2 个答案: