Android-相机预览不起作用

Question

I'm trying to write a camera app for android, but I'm having trouble with getting the preview to work. I tried to follow the steps that android gives here , but it doesn't work, the app keeps crashing. I'm not sure what I'm doing wrong, but I'm pretty sure that I followed the steps right.

Here is what I have so far: Camera Activity class

public class CameraActivity extends Activity
{
    private CameraPreview mPreview = null;
    private Camera mCamera = null;


    @Override
    protected void onCreate(Bundle savedInstanceState)
    {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_camera);

        mCamera = getCameraInstance();

        mPreview = new CameraPreview(this, mCamera);
        FrameLayout preview = (FrameLayout) findViewById(R.id.camera_preview);
        preview.addView(mPreview);

    }
    public static Camera getCameraInstance()
    {
        Camera c = null;

        try
        {
            //attempt to get a Camera instance
            c = Camera.open();
        }
        catch(Exception e)
        {
            //Camera is not available(in use or does not exist)
        }
        return c;//returns null if camera is unavailable
    }


    public void onPause()
    {
        super.onPause();
        mCamera.stopPreview();
        releaseCamera();
    }


    private void releaseCamera()
    {
        if(mCamera != null)
        {
            mCamera.release();
            mCamera = null;
        }
    }

    @Override
    public boolean onCreateOptionsMenu(Menu menu)
    {
        // Inflate the menu; this adds items to the action bar if it is present.
        getMenuInflater().inflate(R.menu.camera, menu);
        return true;
    }
}

Camera Preview class

public class CameraPreview extends SurfaceView implements SurfaceHolder.Callback
{
    private final String TAG = "CameraPreview";
    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 camera where to draw the preview
            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
    }

    public void surfaceChanged(SurfaceHolder holder, int format, int width, int height)
    {
        //if your preview can change or rotate, take care of those events here.
        //make sure to stop the preview before resizing of 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
        try
        {
            //start preview with new settings
            mCamera.setPreviewDisplay(mHolder);
            mCamera.startPreview();
        }
        catch(Exception e)
        {
            Log.d(TAG, "Error starting camera preview: " + e.getMessage());
        }
    }
}

and this is my .xml for the camera activity:

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:orientation="vertical"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent"
    >

    <FrameLayout
        android:id="@+id/camera_preview"
        android:layout_width="fill_parent"
        android:layout_height="fill_parent"
        android:layout_weight="1"
        />


    <Button
        android:id="@+id/button_capture"
        android:text="Capture"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_gravity="center"
        />
</LinearLayout> 

As far as I can tell, I followed the guide correctly and it should work. Since the next part has to do with recording I figured all the steps until then should produce a working preview, but it doesn't work. Can anyone see something wrong that I need to change? Thanks

Edit: Added my manifest manifest.xml

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
package="com.ics466.project.warpwalker"
android:versionCode="1"
android:versionName="1.0" >

<uses-sdk
    android:minSdkVersion="8"
    android:targetSdkVersion="17" />

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

<application
    android:allowBackup="true"
    android:icon="@drawable/ic_launcher"
    android:label="@string/app_name"
    android:theme="@style/AppTheme" >
    <activity
        android:name="com.ics466.project.warpwalker.WarpIntro"
        android:label="@string/app_name" >
        <intent-filter>
            <action android:name="android.intent.action.MAIN" />

            <category android:name="android.intent.category.LAUNCHER" />
        </intent-filter>
            </activity>
            <activity
            android:name="com.ics466.project.warpwalker.CameraActivity"
            android:label="@string/title_activity_camera" >
        </activity>
    </application>

</manifest>

Answer 1

android:minSdkVersion="8" should be android:minSdkVersion="9"

if you have used some functions which are added in API 9

and Read this link How To Enable Camera in Android Emulator

Or test this app in a Real Device which has a camera.

Answer 2

On most devices, the default orientation of the camera preview is landscape.

Try adding android:orientation="horizontal" in to your .xml file's LinearLayout.

Answer 3

try this
Give the CameraId as integer
Camera.open(0);
http://developer.android.com/reference/android/hardware/Camera.html#open(int)