java - Surface View with Camera 在 Android API 23 (android 6+) 上无法运行

Question

我想在 SurfaceView 上使用相机制作背景，并且我在低于 23 的 android API 上取得了成功。虽然我之前在 API 23 上的应用程序中请求相机许可，但我的 Nexus 5 和 Android 6 上仍然出现以下错误:

java.lang.NullPointerException:尝试在空对象引用上调用虚拟方法“void android.hardware.Camera.setPreviewDisplay(android.view.SurfaceHolder)” 在 com.package.name.CameraPreview.surfaceCreated(CameraPreview.java:31)

我的代码是:

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

import java.io.IOException;

/** A basic Camera preview class */
public class CameraPreview extends SurfaceView implements SurfaceHolder.Callback {
    private SurfaceHolder mHolder;
    private Camera mCamera;

    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 activity_hologram where to draw the preview.
        try {
            mCamera.setPreviewDisplay(holder);
            mCamera.startPreview();
            mCamera.setDisplayOrientation(90);
        } catch (IOException e) {
            Log.d("", "Error setting activity_hologram preview: " + e.getMessage());
        }
    }

    public void surfaceDestroyed(SurfaceHolder holder) {
        // empty. Take care of releasing the Camera preview in your activity.
    }

    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.startPreview();

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

}

错误跳转到mCamera.setPreviewDisplay(holder);

我的主要 Activity 代码:

public class MainActivity extends AppCompatActivity {

private static Context mContext;

private Camera mCamera;
private CameraPreview mPreview;

private FrameLayout layout;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    mContext = getApplicationContext();

    layout = (FrameLayout) findViewById(R.id.camera_preview);

    mCamera = getCameraInstance();
    mPreview = new CameraPreview(this, mCamera);
    layout.addView(mPreview);
}


/** A safe way to get an instance of the Camera object. */
public static Camera getCameraInstance(){
    Camera c = null;
    try {
        c = Camera.open(); // attempt to get a Camera instance
    }
    catch (Exception e){
        // Camera is not available (in use or does not exist)
    }
    return c; // returns null if activity_hologram is unavailable
}

}

我的 list 有:

<uses-feature android:name="android.hardware.camera" />
<uses-permission android:name="android.permission.CAMERA" />

有什么想法可以解决 Android 6 上的这个问题吗？

谢谢你的时间，干杯。

Answer 1

建立在@Fildor 的回答之上，它为我指明了正确的方向。相机对象为空。 API 23及以上版本，进入app info -> permissions，开启camera权限，即可成功获取camera对象。