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

Question

我正试图在手机背景上运行摄像机。但是得到以下错误：

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) 

摄像头服务等级代码：

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" />

请帮忙！

Answer 1

您需要获得Camera 实现Detlex库的权限

implementation 'com.karumi:dexter:4.2.0'

然后采取低于的置换

Dexter.withActivity(this)
.withPermissions(
android.Manifest.permission.CAMERA,
android.Manifest.permission.VIBRATE,
android.Manifest.permission.READ_PHONE_STATE)
.withListener(new MultiplePermissionsListener() {
@Override
public void onPermissionsChecked(MultiplePermissionsReport report) {
// check if all permissions are granted
if (report.areAllPermissionsGranted()) {
// do you work now
}
// check for permanent denial of any permission
if (report.isAnyPermissionPermanentlyDenied()) {
// permission is denied permenantly, navigate user to app settings
}
}
@Override
public void onPermissionRationaleShouldBeShown(List<PermissionRequest> permissions, PermissionToken token) {
token.continuePermissionRequest();
}
})
.onSameThread()
.check();

还将权限粘贴到清单中

<uses-permission android:name="android.permission.CAMERA" />
<uses-permission android:name="android.permission.READ_PHONE_STATE" />
<uses-permission android:name="android.permission.INTERNET" />
<uses-permission android:name="android.permission.RECEIVE_BOOT_COMPLETED" />
<uses-permission android:name="android.permission.ACCESS_NETWORK_STATE" />
<uses-permission android:name="android.permission.VIBRATE" />
<uses-feature android:name="android.hardware.camera" />
<uses-feature android:name="android.hardware.camera.autofocus" />
<permission
android:name="android.permission.FLASHLIGHT"
android:permissionGroup="android.permission-group.HARDWARE_CONTROLS" />
enter code here

Answer 2

您的问题是mCamera对象为null。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 3

试试这个。。。

Camera mcamera = Camera.open(0);