相机无法在Android API 23上运行的Surface View(android 6+)

Question

我想在SurfaceView上使用相机制作背景,并且我在低于23的Android API成功.Altough我以前在API 23上的应用程序中请求相机权限,以下错误仍出现在我的Android 6的Nexus 5上:

java.lang.NullPointerException:尝试在com.package.name.CameraPreview.surfaceCreated(CameraPreview.java:31)的空对象引用上调用虚方法'void android.hardware.Camera.setPreviewDisplay(android.view.SurfaceHolder)'

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);

我的主要活动代码:

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
}

}

我的清单得到了:

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

有什么想法在Android 6上解决这个问题吗？

谢谢你的时间,欢呼.

Answer 1

建立@Fildor的答案,指出了我正确的方向.相机对象为空.在API 23及更高版本中,进入应用信息 - >权限并启用相机权限以成功获取相机对象.

Answer 2

有问题的地方我在评论里标出了：

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)
// >>> HERE is your problem! Do not swallow exceptions silently!
    }
    return c; // returns null if activity_hologram is unavailable
}

看起来getCameraInstance返回 null。这可能有两个原因：

1. Camera.Open()回报null
2. 有一个例外你不会意识到，因为你只是默默地接受它并继续前进。

另一点：

此类在 API 级别 21 中已弃用。
我们建议对新应用程序使用新的 android.hardware.camera2 API。

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