Android:从后台服务中获取网页的 'screenshot'？

Question

我有一个网页的 URL，我想在后台截取该网页的“屏幕截图”，例如。在服务中，不向用户显示 UI。

我尝试在我的服务中创建一个 WebView，然后使用 capturePicture() 方法在页面加载完成时获取屏幕截图，但是创建的 Picture(以及我从中创建的 Bitmap)始终为空。 (这在正常 Activity 中完美运行，但在我的后台服务中却不行)。

有什么方法可以让它工作，或者有一种替代方法可以在没有 UI 的情况下获取网页的“屏幕截图”？

Answer 1

注意:这个答案是旧的 - 我试过的最新 Android 版本是 4.4，其他 Android 版本或设备上的 YMMV 我没有测试过... 这也是一个 super 笨拙的 hack - 现在我建议为此使用网络服务/API。

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想通了，我必须设置 WebView 的“大小”，这样生成的“屏幕截图”就不是 0 x 0 大小。然后我必须直接从 WebView 的绘图缓存获取位图，因为 capturePicture() 在这里似乎不起作用。

package com.example.screenshot;

import android.app.*;
import android.content.*;
import android.widget.*;
import android.util.*;
import android.webkit.*;
import android.graphics.*;
import java.io.*;
import android.view.View.*;
import android.os.*;
import android.os.Process;

//this is an example of how to take a screenshot in a background service
//not very elegant, but it works (for me anyway)


public class ScreenshotService extends Service {
private Looper mServiceLooper;
private ServiceHandler mServiceHandler;
private Message msg;

private WebView webview;

// Handler that receives messages from the thread
private final class ServiceHandler extends Handler {
    public ServiceHandler(Looper looper) {
        super(looper);
    }
    @Override
    public void handleMessage(Message msg) {

        webview = new WebView(ScreenshotService.this);

        //without this toast message, screenshot will be blank, dont ask me why...
        Toast.makeText(ScreenshotService.this, "Taking screenshot...", Toast.LENGTH_SHORT).show();


        // This is the important code :)   
        webview.setDrawingCacheEnabled(true);

        //width x height of your webview and the resulting screenshot
        webview.measure(600, 400);
        webview.layout(0, 0, 600, 400); 


        webview.loadUrl("http://stackoverflow.com");

        webview.setWebViewClient(new WebViewClient() {

                @Override
                public void onReceivedError(WebView view, int errorCode, String description, String failingUrl) {
                    //without this method, your app may crash...
                }

                @Override
                public void onPageFinished(WebView view, String url) {
                    new takeScreenshotTask().execute();
                    stopSelf();


                }
            });


    }
}

private class takeScreenshotTask extends AsyncTask<Void, Void, Void> {

    @Override
    protected Void doInBackground(Void[] p1) {

        //allow the webview to render
        synchronized (this) {try {wait(350);} catch (InterruptedException e) {}}

        //here I save the bitmap to file
        Bitmap b = webview.getDrawingCache();

        File file = new File("/sdcard/example-screenshot.png");
        OutputStream out;


        try {
            out = new BufferedOutputStream(new FileOutputStream(file));
            b.compress(Bitmap.CompressFormat.PNG, 100, out);
            out.close();

        } catch (IOException e) {
            Log.e("ScreenshotService", "IOException while trying to save thumbnail, Is /sdcard/ writable?");

            e.printStackTrace();
        }

        Toast.makeText(ScreenshotService.this, "Screenshot taken", Toast.LENGTH_SHORT).show();




        return null;
    }
}

//service related stuff below, its probably easyer to use intentService...

@Override
public void onCreate() {

    HandlerThread thread = new HandlerThread("ServiceStartArguments", Process.THREAD_PRIORITY_BACKGROUND);
    thread.start();

    // Get the HandlerThread's Looper and use it for our Handler 
    mServiceLooper = thread.getLooper();
    mServiceHandler = new ServiceHandler(mServiceLooper);
}

@Override
public int onStartCommand(Intent intent, int flags, int startId) {


    // For each start request, send a message to start a job and deliver the
    // start ID so we know which request we're stopping when we finish the job
    msg = mServiceHandler.obtainMessage();
    msg.arg1 = startId;
    mServiceHandler.sendMessage(msg);

    // If we get killed, after returning from here, restart
    return START_STICKY;
}

@Override
public IBinder onBind(Intent intent) {
    // We don't provide binding, so return null
    return null;
}

@Override
public void onDestroy() {

}


}