webview threads running

Hello,

I have the following problem with a WebView Control. I have the following code:

public class MyWebView extends Activity {
private WebView webview;
...

@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.mywebview);
...
webview = new WebView(getApplicationContext());
webview.setWebChromeClient(new WebChromeClient() { ... });
webview.setWebViewClient(new WebViewClient() { ... });
...
webview.loadUrl("http://www.google.de");
}

The Webpage is opened, but if close the Activity on Back-Button pressed and go back to my main-menue, the WebView is not closed and the http-threads keep running.
If I open about 10 several pages one after another, the Webpages are not nonger loadet, but "Webpage not available" is displayd in the WebView.

I tried to close the thread by adding the code:
webview.destroy();
webview = null;
and
myLinearLayout = null;
and
Method op = Class.forName("android.webkit.WebView").getMethod("onPause",(Class[]) null);
op.invoke(webview, (Object[]) null);

But there is no change - the http-threads are still running.
What is wrong? How to close the WebView in the right way?

Thanx a lot for any suggestions!

In the onPause-method of the activity i call the onPause of the webview as shown below. There occours NO error, but the treads (http0, http1, http2, http3) are still running (not paused). Maybee you can give me a working code-sample what to do in the onPause-method of the activity?

protected void onPause(){
super.onPause();
webview.clearCache(true);
webview.pauseTimers();
if(isFinishing()){
webview.loadUrl("about:blank");
}

try {
Method method = WebView.class.getMethod("onPause");
method.invoke(webview);
} catch (IllegalArgumentException e) {
e.printStackTrace();
} catch (SecurityException e) {
e.printStackTrace();
} catch (IllegalAccessException e) {
e.printStackTrace();
} catch (InvocationTargetException e) {
e.printStackTrace();
} catch (NoSuchMethodException e) {
e.printStackTrace();
}

CookieSyncManager.getInstance().stopSync();
}

The onPause of a webview is hidden, so I need this implicite call.

I have Android 2.1, SDK 7. But I built a project with the same code for Android 2.2 and 2.3. Nothing changed, so this can't cause the problem.

But I'm note sure if the running http-threads cause my problem, that the message "web page not available" is displayd after opening of several webpages.
Maybee this has an other reason?