you need to read this explanation:
http://groups.google.com/group/Google-Web-Toolkit/browse_thread/thread/faca1575f306ba0f
It talks specifically about RPC, but it is relevant to all
Asynchronous calls.
-jason
On Oct 2, 2008, at 6:47 PM, slow wrote:
>
> Thank you Jason for your help. That was a bad mistake. Anywhere I used
> other code and it worked. The problem i have is that I have conficting
> results. One statement tells me I have the data and the other says the
> same data is null. Worse enough, if I call the same statement twice i
> get different results. for example, passing the same string to
> window.alert twice brings null and some correct string. I want to
> later plot the received data using canvas. Here is the code.
>
> package com.daq.client;
>
> import com.google.gwt.core.client.EntryPoint;
> import com.google.gwt.user.client.ui.Button;
> import com.google.gwt.user.client.ui.ClickListener;
> import com.google.gwt.user.client.ui.DialogBox;
> import com.google.gwt.user.client.ui.Image;
> import com.google.gwt.user.client.ui.RootPanel;
> import com.google.gwt.user.client.ui.VerticalPanel;
> import com.google.gwt.user.client.ui.Widget;
> import com.google.gwt.http.client.*;
> import com.google.gwt.user.client.ui.Label;
> import com.google.gwt.http.client.RequestCallback;
> import com.google.gwt.user.client.Window;
>
>
>
> /**
> * Entry point classes define <code>onModuleLoad()</code>.
> */
> public class thesis implements EntryPoint {
>
> public static final int STATUS_CODE_OK = 200;
> static String recvd_data;
> private VerticalPanel mainPanel = new VerticalPanel();
> DialogBox diagbox = new DialogBox();
> Button button = new Button("Click Me");
> Label testLabel = new Label();
> static String my_data;
> //String[] formated_data;
>
> public static String doGet(String url) {
> RequestBuilder builder = new RequestBuilder(RequestBuilder.GET,
> url);
>
> try {
> Request response = builder.sendRequest(null, new
> RequestCallback() {
> public void onError(Request request, Throwable exception) {
> recvd_data = "Unable to reach the server";
> Window.alert(recvd_data);
> //responseText(recvd_data);
> }
>
> public void onResponseReceived(Request request, Response
> response) {
> // Code omitted for clarity
> //String recvd_data;
> if(response.getStatusCode() == STATUS_CODE_OK)
> {
> recvd_data = response.getText();
> }
> else
> recvd_data = response.getStatusText();
> recvd_data = recvd_data.trim();
> //responseText(recvd_data);
> //Window.alert(recvd_data);
> }
> });
>
> } catch (RequestException e) {
> recvd_data = "Unresolved Error";
> //responseText(recvd_data);
> Window.alert(recvd_data);
> return recvd_data;
> }
> return recvd_data;
> }
>
> /**********************************************************
> * get the string received from the http response
> *********************************************************/
>
> public static void responseText(String resp_text)
> {
> my_data = resp_text;
> //Window.alert(my_data);
> }
>
>
>
>
> public void onModuleLoad() {
>
> recvd_data = doGet("sw.csv"); //it seems that null is
> returned in
> this case
> /*line 82 *///Window.alert(recvd_data);
>
> /*if u uncomment line 82, it will print null on a window and the
> correct text will display by line 93
> * however when u leave it commented, line 93 has no effect */
>
> mainPanel.setTitle("Main Panel");
> mainPanel.setBorderWidth(300);
> mainPanel.add(button);
> //mainPanel.setVisible(true);
>
> //formated_data = my_data.split(",");
> /* line 93*/ testLabel.setText(recvd_data);
>
>
> diagbox.setTitle("Dialog Box");
> diagbox.setWidth("100%");
> diagbox.setHeight("20%");
> diagbox.setText(recvd_data);
>
> RootPanel.get().add(testLabel);
> //RootPanel.get().add(diagbox);
> //RootPanel.get().add(mainPanel);
> }
> }
>
>
>
> >
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