Differences

This shows you the differences between two versions of the page.

--- applications:custom_errorhandling [2019/08/05 21:35]
admin created
+++ applications:custom_errorhandling [2020/07/08 13:14] (current)
cduncan articles
@@ Line 1: / Line 1: @@
 ~~NOTRANS~~
-~~Title: Custom error handling~~
+~~Title: Custom Error Handling~~
-...
+The application (ProjX) implements the **IExceptionListener** interface and registers itself as listener:
+<file java>
+protected void initApplication(UILauncher pLauncher) throws Throwable
+{
+    ExceptionHandler.addExceptionListener(this);
+    ...
+}
+</file>
+All exceptions will be handled in the listener method:
+<file java>
+public void handleException(Throwable pThrowable)
+{}
+</file>
+So, it's very easy to change the default error handling which shows a popup dialog:
+{{:applications:error_dialog.png?nolink|}}
+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:
+<file java>
+public interface IErrorHandler
+{
+    public void showErrorMessage(String pMessage);
+}
+</file>
+and all our workscreens should implement the interface, e.g.:
+<file java>
+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);
+    }
+}
+</file>
+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 [[vaadin:customize_application|custom application]].
+Our application contains the following code:
+<file java 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;
+    }
+}
+</file>
+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.
+<file java>
+public class MyCustomWorkScreen extends DataSourceWorkScreen implements IErrorHandler
+{
+}
+</file>
+and all our workscreens should extend this base screen:
+<file java>
+public class FirstWorkScreen extends MyCustomWorkScreen
+</file>
+And the result will look like the following:
+{{:applications:error_screen.jpg?nolink|}}