Android 如何将顶部有网络摄像头层的surfaceview保存为图像？

我已经在android上开发了一个非常简单的应用程序，可以在surfaceView上获取网络摄像头屏幕，现在我想将surfaceView作为图像捕获到SD卡上，但我只在保存了下面的图片后才得到一个黑屏，这是我的完整应用程序，可以在surfaceView上获取网络摄像头屏幕，还可以从surfaceView捕获图像：

imported packages 
import android.app.Activity;
import android.content.pm.ActivityInfo;
import android.graphics.Bitmap;
import android.graphics.Canvas;
import android.graphics.PixelFormat;
import android.hardware.Camera;
import android.os.Bundle;
import android.os.Environment;
import android.util.Log;
import android.view.*;
import android.widget.Button;
import android.widget.Toast;

import java.io.File;
import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.IOException;

在surfaceview上获取网络摄像头屏幕的方法

Camera camera;
SurfaceView surfaceView;
SurfaceHolder surfaceHolder;
boolean previewing = false;

private String mScreenshotPath = Environment.getExternalStorageDirectory() + "/myimages";
//private ArrayList<Element> mElements = new ArrayList<Element>();

private Button takePicture;
/** Called when the activity is first created. */
@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.main);
    setRequestedOrientation(ActivityInfo.SCREEN_ORIENTATION_LANDSCAPE);

    getWindow().setFormat(PixelFormat.UNKNOWN);
    surfaceView = (SurfaceView)findViewById(R.id.camerapreview);
    surfaceHolder = surfaceView.getHolder();
    surfaceHolder.addCallback(this);
    surfaceHolder.setType(SurfaceHolder.SURFACE_TYPE_PUSH_BUFFERS);
    surfaceView.setDrawingCacheEnabled(true);


    LayoutInflater controlInflater = LayoutInflater.from(getBaseContext());
    View viewControl = controlInflater.inflate(R.layout.control, null);
    ViewGroup.LayoutParams layoutParamsControl = new ViewGroup.LayoutParams(ViewGroup.LayoutParams.FILL_PARENT
            ,ViewGroup.LayoutParams.FILL_PARENT);
    this.addContentView(viewControl,layoutParamsControl);
    takePicture = (Button) findViewById(R.id.takepicture);
    takePicture.setOnClickListener(this);


}



@Override
public void surfaceChanged(SurfaceHolder holder, int format, int width,
                           int height) {
    // TODO Auto-generated method stub
    if(previewing){
        camera.stopPreview();
        previewing = false;
    }

    if (camera != null){
        try {
            camera.setPreviewDisplay(surfaceHolder);
            camera.startPreview();
            previewing = true;
        } catch (IOException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
    }
}

@Override
public void surfaceCreated(SurfaceHolder holder) {
    // TODO Auto-generated method stub
    camera = Camera.open();
}

@Override
public void surfaceDestroyed(SurfaceHolder holder) {
    // TODO Auto-generated method stub
    camera.stopPreview();
    camera.release();
    camera = null;
    previewing = false;
}

布局：

//main.xml
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
              android:orientation="vertical"
              android:layout_width="fill_parent"
              android:layout_height="fill_parent"
        >
    <SurfaceView
            android:id="@+id/camerapreview"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_gravity="center"
            />

</LinearLayout>


//control.xml
<?xml version="1.0" encoding="utf-8"?>

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
              android:layout_width="fill_parent"
              android:layout_height="fill_parent"
              android:orientation="vertical"
              android:layout_gravity="bottom"
        >
    <Button android:id="@+id/takepicture"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="Take picture"
            android:layout_gravity="right"
            android:layout_margin="10dp"

            />

</LinearLayout>

//main.xml
//control.xml

正如您所见，我能够在位图对象中捕获surfaceView，但我的问题是，在将其保存到位图对象中时，surfaceView上没有任何网络摄像头屏幕的线索

---

我怎样才能有一个持久化的surfaceView，这样我就不会错过网络摄像头屏幕？

我有一个类似的东西，我需要用一个覆盖来保存我的图像。我实现了这一点，首先保存捕获的图像，然后将其放回视图，然后将其保存为位图。它对我所需要的足够好了

//main.xml
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
              android:orientation="vertical"
              android:layout_width="fill_parent"
              android:layout_height="fill_parent"
        >
    <SurfaceView
            android:id="@+id/camerapreview"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_gravity="center"
            />

</LinearLayout>


//control.xml
<?xml version="1.0" encoding="utf-8"?>

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
              android:layout_width="fill_parent"
              android:layout_height="fill_parent"
              android:orientation="vertical"
              android:layout_gravity="bottom"
        >
    <Button android:id="@+id/takepicture"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="Take picture"
            android:layout_gravity="right"
            android:layout_margin="10dp"

            />

</LinearLayout>