(applications)

Custom Error Handling

The application (ProjX) implements the IExceptionListener interface and registers itself as listener:

protected void initApplication(UILauncher pLauncher) throws Throwable
{
    ExceptionHandler.addExceptionListener(this);
 
    ...
}

All exceptions will be handled in the listener method:

public void handleException(Throwable pThrowable)
{}

So, it's very easy to change the default error handling which shows a popup dialog:

with the error message and some details (stack trace).

As an example of a custom error handling, we'll show the exceptions directly in the workscreens. So, every workscreen should be able to show error messages. To make this possible, we introduce the following interface:

public interface IErrorHandler 
{
    public void showErrorMessage(String pMessage);
}

and all our workscreens should implement the interface, e.g.:

public class FirstWorkScreen extends DataSourceWorkScreen implements IErrorHandler
{
    /** labelMain. */
    private UILabel.labelMain = new UILabel();
 
    private void initializeUI() throws Throwable
    {
        labelMain.setText("ErrorArea");
        labelMain.setForeground(UIColor.red);
 
        ...
 
        add(labelMain, UIBorderLayout.SOUTH);
    }
 
    public void onLoad() throws Throwable
    {
        super.onLoad();
 
        labelMain.setVisible(false);
    }
 
    public void showErrorMessage(String pMessage)
    {
        labelMain.setText(pMessage);
        labelMain.setVisible(true);
    }
}

So, our workscreen example contains a new label in the SOUTH area (the bottom of the screen). The label will be hidden initially in onLoad().
Our screen is now ready to show error messages, but our application must be changed. To do this, we need a custom application.

Our application contains the following code:

MyCustomApplication.java

public class MyCustomApplication extends ProjX 
{
    private List<Throwable> liErrors = null;
 
    public MyCustomApplication(UILauncher pLauncher) throws Throwable 
    {
        super(pLauncher);
    }
 
    public void handleException(Throwable pThrowable)
    {
        if (liErrors == null)
        {
            liErrors = new ArrayUtil<Throwable>();
 
            invokeLater(this, "showErrorMessage");
        }
 
        liErrors.add(pThrowable);
    }    
 
    public void showErrorMessage()
    {
        String message = ExceptionUtil.getRootCause(liErrors.get(0)).getMessage();
 
        for (IWorkScreen screen : getWorkScreens())
        {
            if (screen instanceof IErrorHandler)
            {
                ((IErrorHandler)screen).showErrorMessage(message);
            }
        }
 
        liErrors = null;
    }
}

We collect all occurred exceptions in a list - liErrors - and show one message at the end, see showErrorMessages.

In showErrorMessages, we iterate through all opened workscreens and check if our interface is implemented. In our example, every workscreen has to implement the interface IErrorHandler. A better solution would be a custom workscreen base class, e.g.

public class MyCustomWorkScreen extends DataSourceWorkScreen implements IErrorHandler
{
}

and all our workscreens should extend this base screen:

public class FirstWorkScreen extends MyCustomWorkScreen

And the result will look like the following:

Custom Error Handling picture_as_pdf

Custom Error Handling