Java：文本字段FocusListener focusGained执行两次，为什么？

Question

I have a text box and I would like to show a dialog box when text box is focus gain. So I wrote following codes. But when dialog box disposed the dialog box appears again. I tried to debug and check with line break. That time it does not execute multiple time but in normal mode it executes multiple time so dialog box appears two times...

txt1.addFocusListener(new FocusListener(){

    @Override
    public void focusGained(FocusEvent e) {

        myform f = new myform(null,true);
        f.setLocationRelativeTo(null);
        f.setVisible(true);
        if("OK".equals(f.button_state)){
            txt2.requestFocus();   
        }
    }

    @Override
    public void focusLost(FocusEvent e) {                
    }

});

If I place the txt2.requestFocus() before the dialog box visible then multiple execution does not happen. But I am not convinced. Because I required to keep the cursor in txt1 .

Have you any idea..>

Answer 1

• FocusListener isn't proper place for code where is created of modifyied container

• Focus is quite asynchronous, then there any some guarantee with proper ordering of methods

• Swing GUI creations must be wrapped into invokeLater, more see in Oracle tutorial - Initial Thread

• only this code snipped will be works in FocusListener

. wrapped into invokeLater

if("OK".equals(f.button_state)){
     txt2.requestFocus();   
}

• or setVisible(true); for myform wrapped into invokLater , but I think that must be prepared before (every JComponents are added, initialized, used and applied LayoutManager , packed ), otherwise nothing guarantee anything, there you can call only

. wrapped into invokeLater

f.setVisible(true);
if("OK".equals(f.button_state)){
      txt2.requestFocus();   
}