如果设备中没有摄像头，则在android上显示黑色背景色

Question

最近我使用了闭路电视摄像头应用程序，但如果设备中没有摄像头，则显示此logcat和应用程序已死亡

java.lang.RuntimeException: Unable to start activity ComponentInfo{kr.co.iosystem.blackeyeonandroid/kr.co.iosystem.blackeyeonandroid.BlackEyeActivity}: java.lang.NullPointerException
    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2184)
    at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2233)
    at android.app.ActivityThread.access$800(ActivityThread.java:135)
    at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1196)
    at android.os.Handler.dispatchMessage(Handler.java:102)
    at android.os.Looper.loop(Looper.java:136)
    at android.app.ActivityThread.main(ActivityThread.java:5001)
    at java.lang.reflect.Method.invokeNative(Native Method)
    at java.lang.reflect.Method.invoke(Method.java:515)
    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:785)
    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:601)
    at dalvik.system.NativeStart.main(Native Method)
 Caused by: java.lang.NullPointerException
    at org.webrtc.PeerConnectionFactory.createVideoSource(PeerConnectionFactory.java:111)
    at kr.co.iosystem.blackeyeonandroid.BlackEyeActivity.onCreate(MainActivity.java:235)
    at android.app.Activity.performCreate(Activity.java:5231)
    at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1087)
    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2148)
    at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2233) 
    at android.app.ActivityThread.access$800(ActivityThread.java:135) 
    at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1196) 
    at android.os.Handler.dispatchMessage(Handler.java:102) 
    at android.os.Looper.loop(Looper.java:136) 
    at android.app.ActivityThread.main(ActivityThread.java:5001) 
    at java.lang.reflect.Method.invokeNative(Native Method) 
    at java.lang.reflect.Method.invoke(Method.java:515) 
    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:785) 
    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:601) 
    at dalvik.system.NativeStart.main(Native Method) 

和我的来源 MainActivity.java

@Override
protected void onCreate(final Bundle savedInstanceState) {
   super.onCreate(savedInstanceState);
   setContentView(R.layout.activity_main);
   String nameOfFrontFacingDevice = VideoCapturerAndroid.getNameOfFrontFacingDevice();
   String nameOfBackFacingDevice = VideoCapturerAndroid.getNameOfBackFacingDevice();
   VideoCapturerAndroid capturer = VideoCapturerAndroid.create(nameOfFrontFacingDevice);
   . 
   . 
   . 
   }

如果没有相机。capturer返回null因此，我输入test

if (capturer == null || capturer.equals("") == true) {
   try {
      rebootProcess = Runtime.getRuntime().exec(new String[]{"su", "-c", "reboot"});
   } catch (IOException e) {
      e.printStackTrace();
    }
 }

和我执行应用程序。我重启了我的设备，但我想如果没有相机，显示黑色背景

如果连接到摄像头，则显示GLSurfaceView

glview = (GLSurfaceView) findViewById(R.id.glview);
VideoRendererGui.setView(glview, null) ;
try {
     . . . .
} catch {
}

也许，我用片段?请给我一些建议。我想

if (capturer == null || capturer.equals("") == true) {
   // showing black background ??..
  } 

但是我不知道显示黑色背景部分。

谢谢。

@update

MainActivity.java (full oncreate)

@Override
protected void onCreate(final Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    String nameOfFrontFacingDevice = VideoCapturerAndroid.getNameOfFrontFacingDevice();
    if (nameOfFrontFacingDevice != null) {
        VideoCapturerAndroid capturer = VideoCapturerAndroid.create(nameOfFrontFacingDevice);
        MediaConstraints videoConstraints = new MediaConstraints();
        VideoSource videoSource = peerConnectionFactory.createVideoSource(capturer, videoConstraints);
        localVideoTrack = peerConnectionFactory.createVideoTrack(VIDEO_TRACK_ID, videoSource);
        glview =(GLSurfaceView) findViewById.(R.id.showing);
        VideoRendererGui.setView(glview, null);
        try {
            renderer = VideoRendererGui.createGui(0,0,100,100, VideoRendererGui.ScalingType.SCALE_ASPECT_FILL, true);
            localVideoTrack.addRenderer(renderer);
        } catch (Exception e) {
             e.printStackTrace();
        }
        mediaStream = peerConnectionFactory.createLocalMediaStream(LOCAL_MEDIA_STREAM_ID);
        mediaStream.addTrack(localVideoTrack);
    } else {
        //space
    }

我改变了我的来源你的建议。但出现nullpointerException

在其他部分。我怎么能编程?

Answer 1

如果这是一个你使用摄像头的应用程序，那么这个应用程序不应该安装在没有这个功能的手机上。在您的清单中:

<uses-feature android:name="android.hardware.camera"
    required="true" />

[编辑]

根据VideoCapturerAndroid源，如果不存在相机，下面一行将返回null:

String nameOfFrontFacingDevice = VideoCapturerAndroid.getNameOfFrontFacingDevice();

所以，在你的例子中，这个本身必须为空。但是，您要将名称传递给create。我认为这就是NPE的来源:

VideoCapturerAndroid capturer = VideoCapturerAndroid.create(nameOfFrontFacingDevice); // name might be null

所以，你应该在这里设置一个空检查:

if (nameOfFrontFacingDevice != null) {
    VideoCapturerAndroid capturer = VideoCapturerAndroid.create(nameOfFrontFacingDevice);
} else {
    // Other stuff
}

[编辑2]

对于没有相机的设备，您的捕获器仍然会出现null，这将导致调用peerConnectionFactory.createVideoSource(capturer, videoConstraints)的问题。因此，我们可以确保只有当我们拥有相机并避免NPE时才调用它。现在，我们在活动onResume()的glview.onResume()调用中遇到另一个问题。我们必须在检查camera之前初始化它。检查下面的代码以获得建议的修复:

        String nameOfFrontFacingDevice = VideoCapturerAndroid.getNameOfFrontFacingDevice();
        String nameOfBackFacingDevice = VideoCapturerAndroid.getNameOfBackFacingDevice();
        Log.i(TAG, "VideoCapturerAndroid.getNameOfFrontFacingDevice() = " + nameOfFrontFacingDevice);
        Log.i(TAG, "VideoCapturerAndroid.getNameOfBackFacingDevice() = " + nameOfBackFacingDevice);
        VideoCapturerAndroid capturer = VideoCapturerAndroid.create(nameOfFrontFacingDevice);
        // Initialising the glview here
        glview = (GLSurfaceView) findViewById(R.id.glview);
        VideoRendererGui.setView(glview, null);
        MediaConstraints videoConstraints = new MediaConstraints();
        if (capturer == null || capturer.equals("")) {
            Log.d(TAG, "not camera");
        }
        // Doing further processing only if capturer is not null
        else {
            VideoSource videoSource = peerConnectionFactory.createVideoSource(capturer, videoConstraints);
            localVideoTrack = peerConnectionFactory.createVideoTrack(VIDEO_TRACK_ID, videoSource);
            try {
                renderer = VideoRendererGui.createGui(0, 0, 100, 100, VideoRendererGui.ScalingType.SCALE_ASPECT_FILL, true);
                renderer_sub = VideoRendererGui.createGui(72, 72, 25, 25, VideoRendererGui.ScalingType.SCALE_ASPECT_FILL, true);
                localVideoTrack.addRenderer(renderer_sub);
                localVideoTrack.addRenderer(renderer);
            } catch (Exception e) {
                e.printStackTrace();
            }
            mediaStream = peerConnectionFactory.createLocalMediaStream(LOCAL_MEDIA_STREAM_ID);
            mediaStream.addTrack(localVideoTrack);
            ImageButton imageButton = (ImageButton) findViewById(R.id.backbutton);
            imageButton.setOnClickListener(new View.OnClickListener() {
                @Override
                public void onClick(View v) {
                    moveTaskToBack(true);
                    finish();
                    android.os.Process.killProcess(android.os.Process.myPid());
                }
            });
        }