Android相机应用程序在关闭时崩溃(Android camera application crashes on closing)

 我写了一个相机应用程序。 它在“onCreate”中创建了一个无限循环，每秒拍摄一张照片： 
 
    Runnable mRunnable = new Runnable() {
        @Override
        public void run() {
            camera.takePicture(null, null, mPicture);
            mHandler.postDelayed(this, 1000);
        }
    };
    mHandler.postDelayed(mRunnable,1000);
 
 之后，它运行基于caffe的分类器。 但是，当我在某个时候退出应用程序时，我总是会收到错误消息： 
 
"App has been stopped"
 
 同时我在Android Monitor收到以下错误消息： 
 
E/AndroidRuntime: FATAL EXCEPTION: main
             Process: com.myUsername.myAppName, PID: 25490
             java.lang.NullPointerException: Attempt to invoke virtual method 'void android.hardware.Camera.takePicture(android.hardware.Camera$ShutterCallback, android.hardware.Camera$PictureCallback, android.hardware.Camera$PictureCallback)' on a null object reference
                 at com.myUsername.myAppName.MainActivity$1.run(MainActivity.java:178)
                 at android.os.Handler.handleCallback(Handler.java:746)
                 at android.os.Handler.dispatchMessage(Handler.java:95)
                 at android.os.Looper.loop(Looper.java:135)
                 at android.app.ActivityThread.main(ActivityThread.java:5343)
                 at java.lang.reflect.Method.invoke(Native Method)
                 at java.lang.reflect.Method.invoke(Method.java:372)
                 at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:907)
                 at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:702)
 
 有谁知道如何避免这个错误？ 在完成结束无限循环的应用程序或明确关闭在预览模式下运行的相机时，是否需要调用一些特殊功能？ 

I have written a camera application. It has an infinite loop created inside "onCreate" that takes a picture every second:
 
    Runnable mRunnable = new Runnable() {
        @Override
        public void run() {
            camera.takePicture(null, null, mPicture);
            mHandler.postDelayed(this, 1000);
        }
    };
    mHandler.postDelayed(mRunnable,1000);
 
After that it runs a classifier based on caffe. However when I exit the application at some point I always get an error saying: 
 
"App has been stopped"
 
At the same time I get the following error message in Android Monitor: 
 
E/AndroidRuntime: FATAL EXCEPTION: main
             Process: com.myUsername.myAppName, PID: 25490
             java.lang.NullPointerException: Attempt to invoke virtual method 'void android.hardware.Camera.takePicture(android.hardware.Camera$ShutterCallback, android.hardware.Camera$PictureCallback, android.hardware.Camera$PictureCallback)' on a null object reference
                 at com.myUsername.myAppName.MainActivity$1.run(MainActivity.java:178)
                 at android.os.Handler.handleCallback(Handler.java:746)
                 at android.os.Handler.dispatchMessage(Handler.java:95)
                 at android.os.Looper.loop(Looper.java:135)
                 at android.app.ActivityThread.main(ActivityThread.java:5343)
                 at java.lang.reflect.Method.invoke(Native Method)
                 at java.lang.reflect.Method.invoke(Method.java:372)
                 at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:907)
                 at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:702)
 
Does anyone have an idea how to avoid this error? Do I need to call some special functions when finishing the app that end the infinite loop or explicitly shut down the camera which runs in preview mode?

原文：https://stackoverflow.com/questions/39100468