Android 相机每次在 onResume 或 onRestart 时都会崩溃

Question

我从android camera example 构建了一个相机应用程序。它正在工作，但每次我的应用程序从 onPause 和 onStop 恢复或重新启动时，我的应用程序都会崩溃。我已经尝试过这两个link1、link2，但没有任何改变。我应该如何解决它？

logcat 显示此消息：

2169-2169/com.exshinigami.theremembrance E/AndroidRuntime﹕ FATAL EXCEPTION: main
Process: com.exshinigami.theremembrance, PID: 2169
java.lang.NullPointerException
        at com.exshinigami.theremembrance.CameraPreview.surfaceCreated(CameraPreview.java:35)
        at android.view.SurfaceView.updateWindow(SurfaceView.java:572)
        at android.view.SurfaceView.onWindowVisibilityChanged(SurfaceView.java:232)
        at android.view.View.dispatchWindowVisibilityChanged(View.java:8004)
        at android.view.ViewGroup.dispatchWindowVisibilityChanged(ViewGroup.java:1077)
        at android.view.ViewGroup.dispatchWindowVisibilityChanged(ViewGroup.java:1077)
        at android.view.ViewGroup.dispatchWindowVisibilityChanged(ViewGroup.java:1077)
        at android.view.ViewGroup.dispatchWindowVisibilityChanged(ViewGroup.java:1077)
        at android.view.ViewGroup.dispatchWindowVisibilityChanged(ViewGroup.java:1077)
        at android.view.ViewRootImpl.performTraversals(ViewRootImpl.java:1237)
        at android.view.ViewRootImpl.doTraversal(ViewRootImpl.java:1000)
        at android.view.ViewRootImpl$TraversalRunnable.run(ViewRootImpl.java:5670)
        at android.view.Choreographer$CallbackRecord.run(Choreographer.java:761)
        at android.view.Choreographer.doCallbacks(Choreographer.java:574)
        at android.view.Choreographer.doFrame(Choreographer.java:544)
        at android.view.Choreographer$FrameDisplayEventReceiver.run(Choreographer.java:747)
        at android.os.Handler.handleCallback(Handler.java:733)
        at android.os.Handler.dispatchMessage(Handler.java:95)
        at android.os.Looper.loop(Looper.java:136)
        at android.app.ActivityThread.main(ActivityThread.java:5017)
        at java.lang.reflect.Method.invokeNative(Native Method)
        at java.lang.reflect.Method.invoke(Method.java:515)
        at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:779)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:595)
        at dalvik.system.NativeStart.main(Native Method)

Answer 1

我按照@Kevin Crain 所说的做了，我将这行代码添加到我的surefaceCreated 中，它现在可以工作了。

如果（mCamera == null）返回；

我的 CameraPreview 类：

import java.io.IOException;
import android.content.Context;
import android.hardware.Camera;
import android.util.Log;
import android.view.SurfaceHolder;
import android.view.SurfaceView;

/** A basic Camera preview class */
public class CameraPreview extends SurfaceView implements SurfaceHolder.Callback {
    private SurfaceHolder mHolder;
    private Camera mCamera;
    private static final String TAG = "------MyCamera------";

    public CameraPreview(Context context, Camera camera) {
        super(context);
        mCamera = camera;

        // Install a SurfaceHolder.Callback so we get notified when the
        // underlying surface is created and destroyed.
        mHolder = getHolder();
        mHolder.addCallback(this);
        // deprecated setting, but required on Android versions prior to 3.0
        mHolder.setType(SurfaceHolder.SURFACE_TYPE_PUSH_BUFFERS);
    }

    public void surfaceCreated(SurfaceHolder holder) {
        // The Surface has been created, now tell the camera where to draw the preview.
        if(mCamera == null) return;
        try {
            mCamera.setPreviewDisplay(holder);
            mCamera.startPreview();
        } catch (IOException e) {
            Log.d(TAG, "Error setting camera preview: " + e.getMessage());
        }
    }

    public void surfaceDestroyed(SurfaceHolder holder) {
        // empty. Take care of releasing the Camera preview in your activity.
        if (mCamera != null) {
            mCamera.stopPreview();
            mCamera.setPreviewCallback(null);
            mCamera.release();
            mCamera = null;
        }
    }

    public void surfaceChanged(SurfaceHolder holder, int format, int w, int h) {
        // If your preview can change or rotate, take care of those events here.
        // Make sure to stop the preview before resizing or reformatting it.

        if (mHolder.getSurface() == null) {
            // preview surface does not exist
            return;
        }

        // stop preview before making changes
        try {
            mCamera.stopPreview();
        } catch (Exception e) {
            // ignore: tried to stop a non-existent preview
        }

        // set preview size and make any resize, rotate or
        // reformatting changes here

        // start preview with new settings
        try {
            mCamera.setPreviewDisplay(mHolder);
            //mCamera.setDisplayOrientation(180);
            mCamera.startPreview();

        } catch (Exception e) {
            Log.d(TAG, "Error starting camera preview: " + e.getMessage());
        }
    }
}

在我的 MainActivity 中：

    @Override
        protected void onStop() {
            super.onStop();
            if (mPreview != null) {
                FrameLayout preview = (FrameLayout) findViewById(R.id.camera_preview);
                preview.removeView(mPreview);
                mPreview = null;
            }

        }

  @Override
    protected void onRestart() {
        super.onRestart();
        mCamera = getCameraInstance();    //Open rear camer
        mPreview = new CameraPreview(this, mCamera);
        preview = (FrameLayout) findViewById(R.id.camera_preview);
        preview.addView(mPreview);
    }