Vaadin 7 : RPC call from Server to Client - vaadin

Question

I would like to create custom image component .So I followed step by step from Integrating with Server-side. For basic or first-step , I created for the test Server to Client RPC call as following steps.
MyComponentWidget.java
public class MyComponentWidget extends HTML {
public MyComponentWidget() {
getElement().setAttribute("class", "thumbnail");
}
public final void createCustomImage(final String url) {
getElement().setInnerHTML("<div class='delete-block'></div><img src=" + url + " />");
}
}
MyComponentState.java
public class MyComponentState extends AbstractComponentState {
private String url;
private String html;
public final String getUrl() {
return url;
}
public final void setUrl(final String url) {
this.url = url;
}
public final String getHtml() {
return html;
}
public final void setHtml(final String html) {
this.html = html;
}
}
MyComponentConnector.java
public class MyComponentConnector extends AbstractComponentConnector {
public MyComponentConnector() {
registerRpc(MyComponentClientRpc.class, new MyComponentClientRpc() {
#Override
public void getMessage() {
// never reach to this place
System.err.println("Reach Here !");
getState().setHtml(getWidget().getHTML());
}
});
}
#Override
public final MyComponentWidget getWidget() {
return (MyComponentWidget) super.getWidget();
}
#Override
public final MyComponentState getState() {
return (MyComponentState) super.getState();
}
#OnStateChange("url")
final void updateText() {
getWidget().createCustomImage(getState().getUrl());
}
}
MyComponentClientRpc.java
import com.vaadin.shared.communication.ClientRpc;
public interface MyComponentClientRpc extends ClientRpc {
void getMessage();
}
MyComponent.java
public class MyComponent extends AbstractComponent {
public MyComponent(final String url) {
getState().setUrl(url);
}
public final MyComponentState getState() {
return (MyComponentState) super.getState();
}
public final String getHTML() {
getRpcProxy(MyComponentClientRpc.class).getMessage();
return getState().getHtml();
}
}
and call as
MyComponent image = new MyComponent("myImageUrl");
System.out.println(image.getHTML());
My problem is why I always get null value at my console ? I can see the image at browser but System.out.println(image.getHTML()); produces null. What am I missing ?

Answer 1

To make a rpc call from client to server, you must extend the ServerRpc interface, for example:
package com.example.client.MyServerRpc
public interface MyServerRpc extends com.vaadin.shared.communication.ServerRpc {
void sendHTML(String html);
}
In your connector your register the rpc:
private MyServerRpc rpc = RpcProxy.create(MyServerRpc.class, this);
And then you can send a value by using the registered rpc in your connector:
rpc.sendHTML(html);
To receive the value on your component's or extension's server-side class, you must create an instance of the rpc interface:
private MyServerRpc rpc = new MyServerRpc() {
#Override
public void sendHTML(String html) {
// this method will be called!
}
};
and register that in the constructor:
registerRpc(rpc);
After these steps RPC from client to server should work.