Automatic 'loading' indicator when calling an async function

Question

I am looking for a way to automate showing and hiding a \'loading\' message when calling an async service, so instead of doing this:

showLoadingWidget();

se         


        

Answer 1

You could wrap the call itself in an object that handles displaying the loading message, maybe retrying a few times on errors or whatever. Something like this:

public abstract class AsyncCall implements AsyncCallback {

    /** Call the service method using cb as the callback. */
    protected abstract void callService(AsyncCallback cb);

    public void go(int retryCount) {
        showLoadingMessage();
        execute(retryCount);
    }

    private void execute(final int retriesLeft) {
        callService(new AsyncCallback() {
            public void onFailure(Throwable t) {
                GWT.log(t.toString(), t);
                if (retriesLeft <= 0) {
                    hideLoadingMessage();
                    AsyncCall.this.onFailure(t);
                } else {
                    execute(retriesLeft - 1);
                }
            }
            public void onSuccess(T result) {
                hideLoadingMessage();
                AsyncCall.this.onSuccess(result);
            }
        });
    }

    public void onFailure(Throwable t) {
        // standard error handling
    }
    ...
}

To make the call do something like this:

new AsyncCall() {
    protected void callService(AsyncCallback cb) {
        DemoService.App.get().someService("bla", cb);
    }
    public void onSuccess(DTO result) {
        // do something with result
    }
}.go(3); // 3 retries

You could extend this with code to detect calls that are taking a long time and display a busy indicator of some kind etc.