webview添加cookie有时失效

public class WebViewActivity extends Activity {   WebView myWebView; 	private final static String TAG = "WebView"; 	@Override	protected void onCreate(Bundle savedInstanceState) {				super.onCreate(savedInstanceState); 		setContentView(R.layout.webview); 		myWebView = (WebView) findViewById(R.id.webview);                           new WebViewTask().execute();        }         private class WebViewTask extends AsyncTask<Void, Void, Boolean> {		String sessionCookie;		CookieManager cookieManager; 	        @Override		protected void onPreExecute() {			CookieSyncManager.createInstance(WebViewActivity.this);			cookieManager = CookieManager.getInstance();                        			sessionCookie = new PersistentConfig(getApplicationContext()).getCookieString();			if (sessionCookie != null) {                                /* delete old cookies */				cookieManager.removeSessionCookie(); 			}			super.onPreExecute();		}		protected Boolean doInBackground(Void... param) {                        /* this is very important - THIS IS THE HACK */			SystemClock.sleep(1000);			return false;		}		@Override		protected void onPostExecute(Boolean result) {			if (sessionCookie != null) {				cookieManager.setCookie("yourdomain.com", sessionCookie);				CookieSyncManager.getInstance().sync();			}			WebSettings webSettings = myWebView.getSettings();			webSettings.setJavaScriptEnabled(true);			webSettings.setBuiltInZoomControls(true);			myWebView.setWebViewClient(new WebViewClient() {				@Override				public boolean shouldOverrideUrlLoading(WebView view, String url) {					return super.shouldOverrideUrlLoading(view, url);				}							});			myWebView.loadUrl("https://yourdomain.com/anything");		}	}