SWT-MessageDialog-外壳

Question

I have an operations class that has no gui. The class basically does data management. The class is called from a method in my Main GUI. The problem I am having is with displaying messages to the user if something fails. I am using MessageDialog , but it keeps failing at runtime. I think the issue is with Shell. When I try to use null as the shell.

MessageDialog.openError(null, "Printer Error Message", "Error getting print reply file.");

The error is null pointer exception

MessageDialog.openError(Display.getCurrent().getActiveShell() etc

The error is null pointer exception

MessageDialog.openError(Display.getDefault().getActiveShell()

The error is invalid thread access

1. Being this is not a GUI class, do I have to pass in the shell from the GUI parent?
2. Can I just create a shell in the class and then use that?

Answer 1

You can fix the ERROR_THREAD_INVALID_ACCESS error with Display.syncExec or Display.asyncExec . Try with:

Display.syncExec(new Runnable() {
    void run() {
        MessageDialog.openError(Display.getDefault().getActiveShell()...
    }
}

Answer 2

This will do what you want:

MessageDialog.openError(new Shell(), "Printer Error Message", "Error getting print reply file.");

Just create a new Shell and pass it to the MessageDialog .

Answer 3

Few important points to consider.

1. First of all, do not mix Data Management classes(models) with UI.
2. Have a utility class and methods to show errors/info messages.
3. always access UI widgets in UI thread. Use Display.getDefault().asyncExec() or syncExce()
4. Check Display.getDefault().getActiveShell() to pass it to the dialog first, if it is null, create one and pass it.