How to call a class using jToggleButton?

Question

I am developing a small screen capture application in java.i found a example to select rectangular area from here.(this is that question).i used another jframe and add a toggle button to call the Rectangular selection class.i create a object of Rectangular selection class when the toggle button is selected . Now i have to questions,

I used following code to create the selection class object But if the selection object is exists it create a new object. How to stop this ?
```
 if (sn == null) {   
    if (btn_selection.isSelected()) {
        sn = new SnipIt();
    } else {
        sn.frame.dispose();
    }
}
```

2.to close the selection class it use this code line,

    SwingUtilities.getWindowAncestor(sl).dispose();

So i created a method called closeSelection and insert above code line.but when i call this method returns a nullpointexception,

public void closeSelection() {
        SelectionPane sl=new SelectionPane();
        SwingUtilities.getWindowAncestor(sl).dispose();

    }

I know my code has many mistakes. So please show those and give me a solution.Highly appreciate your help ☺

score 1 · Accepted Answer · edited Oct 07 '15 at 13:56

1

For example by adding a simple condition if (sn == null) sn = new SnipIt();. null is the value when an object "does not exist".
You have to use a reference to the actual sn Object from your first code snippet. Maybe store a reference to it in a field. Your attempt fails because:
- it's an entirely different thing you try to get rid of (you make a new one just to dispose of it).
- it's not attached to the actual view hierarchy so it doesn't have a window.

edited Oct 07 '15 at 13:56

Andrew Thompson

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answered Oct 07 '15 at 12:36

zapl

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thanks.but i tried to dispose the jframe in that class.same exception? – stack questions Oct 07 '15 at 13:02
@stackquestions Is `sn` added to the window somewhere? I.e. can you see the pane when you run the program? If not then it has no window either. – zapl Oct 07 '15 at 13:05
Now,but there is a jframe in the class? – stack questions Oct 07 '15 at 13:07
@stackquestions swing does not care whether there are other things in the class. You'll have to add them http://stackoverflow.com/questions/10086936/java-adding-components-to-jframe to the frame – zapl Oct 07 '15 at 13:10
OK thanks a lot.i'll try that or i'll try to change the class file :-). – stack questions Oct 07 '15 at 13:12

How to call a class using jToggleButton?

1 Answers1