android 可以修复打开相机时的错误吗？

Question

您好，我编写了一个应用程序，在部署时显示 mCamera=Camera.open(); 行错误 其中mCamera是Camera的引用。

请问如何解决？

谢谢

Answer 1

您需要首先检查并调用释放函数是否有其他应用程序正在使用相机。

我使用了以下代码，效果很好。它捕获图像并将其保存到媒体卡上。不要忘记将权限放入清单文件中。

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

代码：

//Surface View for displaying the content

package my.custom.cam;

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

public class CameraPreview1 extends SurfaceView implements SurfaceHolder.Callback {
    private SurfaceHolder mHolder;
    private Camera mCamera;

    public CameraPreview1(Context context, Camera camera) {
        super(context);
        Log.i("#####","constructor is getting called");
        mCamera = camera;
//      mCamera = CustomCameraActivity.getCameraInstance();

        // 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.
        Log.i("*****", "Surface created.....");
        try {
            if(holder == null) { Log.i("%%%%%%%%%","Holder is null"); return; }
            mCamera.setPreviewDisplay(holder);
            mCamera.startPreview();
        } catch (IOException e) {
            Log.d("********", "Error setting camera preview: " + e.getMessage());
        }
    }

    public void surfaceDestroyed(SurfaceHolder holder) {

        Log.i("*****", "Surface destroyed.....");
        mCamera.release();
        // 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.
        Log.i("*****", "Surface changed.....");

        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 camera preview: " + e.getMessage());
        }
    }
}


// Activity to use

package my.custom.cam;

import java.io.File;
import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.IOException;
import java.text.SimpleDateFormat;
import java.util.Date;

import android.app.Activity;
import android.hardware.Camera;
import android.hardware.Camera.PictureCallback;
import android.net.Uri;
import android.os.Bundle;
import android.os.Environment;
import android.util.Log;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;
import android.widget.FrameLayout;

public class CustomCameraActivity extends Activity {
    /** Called when the activity is first created. */

    private Camera mCamera;
    private CameraPreview1 mPreview;
    private PictureCallback mPicture ;

    @Override
    public void onCreate(Bundle savedInstanceState) 
    {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);

        // Create an instance of Camera
        mCamera = getCameraInstance();

        // Create our Preview view and set it as the content of our activity.
        mPreview = new CameraPreview1(this, mCamera);
        FrameLayout preview = (FrameLayout) findViewById(R.id.camera_preview);
        preview.addView(mPreview);

        Button clickButton = (Button) findViewById(R.id.button_capture);
        clickButton.setOnClickListener(new OnClickListener() {

            @Override
            public void onClick(View v) {
                // TODO Auto-generated method stub

                mCamera.takePicture(null, null, mPicture);
            }
        });

        mPicture = new PictureCallback() {

            @Override
            public void onPictureTaken(byte[] data, Camera camera) {

                File pictureFile = getOutputMediaFile(MEDIA_TYPE_IMAGE);
                if (pictureFile == null){
                    Log.d("********", "Error creating media file, check storage permissions: ");

                    return;
                }

                try {
                    FileOutputStream fos = new FileOutputStream(pictureFile);
                    fos.write(data);
                    fos.close();
                    Log.i("$$$$$", "file saved successfully....");
                } catch (FileNotFoundException e) {
                    Log.e("********", "File not found: " + e.getMessage());
                } catch (IOException e) {
                    Log.e("********", "Error accessing file: " + e.getMessage());
                }
            }
        };
    }

    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 camera is unavailable
    }

    public static final int MEDIA_TYPE_IMAGE = 1;
    public static final int MEDIA_TYPE_VIDEO = 2;

    /** Create a file Uri for saving an image or video */
    private static Uri getOutputMediaFileUri(int type){
        return Uri.fromFile(getOutputMediaFile(type));
    }

    /** Create a File for saving an image or video */
    private static File getOutputMediaFile(int type){
        // To be safe, you should check that the SDCard is mounted
        // using Environment.getExternalStorageState() before doing this.

        File mediaStorageDir = new File(Environment.getExternalStoragePublicDirectory(
                  Environment.DIRECTORY_PICTURES), "MyCameraApp");
        // This location works best if you want the created images to be shared
        // between applications and persist after your app has been uninstalled.

        // Create the storage directory if it does not exist
        if (! mediaStorageDir.exists()){
            if (! mediaStorageDir.mkdirs()){
                Log.d("MyCameraApp", "failed to create directory");
                return null;
            }
        }

        // Create a media file name
        String timeStamp = new SimpleDateFormat("yyyyMMdd_HHmmss").format(new Date());
        File mediaFile;
        if (type == MEDIA_TYPE_IMAGE){
            mediaFile = new File(mediaStorageDir.getPath() + File.separator +
                    "IMG_"+ timeStamp + ".jpg");
        } else if(type == MEDIA_TYPE_VIDEO) {
            mediaFile = new File(mediaStorageDir.getPath() + File.separator +
                    "VID_"+ timeStamp + ".mp4");
        } else {
            return null;
        }

        return mediaFile;
    }
}