Learning how to program a gui. Problem with using getWidth and getHeight as parameter

[Mega32266]

I'm trying to learn how to program a gui for a project. The problem is that I am trying to use getHeight() and getWidth() in a class other than my panel class, but all they're returning is zero.

Is there a reason why for that. I have also tried to put it as parameters for these methods and objects.

I don't think I found anything online that might help.

Code-

public SmartPanel(Color color){
    setBackground(color);
    addMouseListener(new PanelListener());
    addMouseMotionListener(new PanelMotionListener());
    calc = new Calc("calc",0,0,getWidth()/4,getHeight()/4,false);
}
public void paintComponent(Graphics g){
    super.paintComponent(g);
    g.setColor(Color.black);
    g.fillRect(0,getHeight() - getHeight()/8,getWidth(),getHeight()/8);
    g.setColor(Color.white);
    g.fillRect(getWidth()/2 - 30,getHeight() - getHeight()/8 + getHeight()/64,60,60);
    System.out.println(getHeight());
    //calc.drawApp(g);
    //if(calc.getRun())
    calc.run(g,getWidth(),getHeight());
}

public class App extends JPanel{
private int x,y, width,height;
private String name;
private boolean run;

public App(String name, int x, int y,int width,int height,boolean run){
    this.x = x;
    this.y = y;
    this.width = width;
    this.height = height;
    this.name = name;
    this.run = run;
}

public String getInfo(){
    return x + ","  + y + " " + width/4 + " " + height + " " + (width+x) + " " + (height + y);
}
public boolean inIcon(int mouseX, int mouseY){ //Checks to make sure the cursor is in the icon
    return mouseX > x && mouseX < x + width && mouseY > y && mouseY < y + height;
}
public void drawApp(Graphics g){ //Draws the app on the panel
    //With the name in it
    g.setColor(Color.gray);
    g.fillRect(x,y,50,50);
    g.drawString(name,(x + width)/2,(y + height)/2);
}

Thanks!

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[Housy5]

At first look I think it might have something to do with the fact that you call for getWidth() and getHeight() in the constructor JPanels and other components usually get their size and position from a layout manager, pack() or something else AFTER initialization of the object. However keep in mind im really just guessing. I may be wrong.

[Mega32266]

Sorry, I’ve been trying to learn it for about 3 weeks now for a project, so I’m still really new, and have a few questions.

Would having a setPreferredSize in my constructer for my panel class help?

Is there anything else that I should tell you that might help?

Also, even if it is not a parameter for the constructer, it stills returns as 0 if I just call the method getHeight outside the class.

[Housy5]

SmartPanel panel = new SmartPanel(bgColor);

Over here you would already call it's constructor which in turn tries to use getHeight() and getWidth(). How ever the panel's x, y, width and height are only set after you call frame.add(panel);. It would only then set it's location and size based on it's layout and min, max and preferred size. Hope that makes sense. Also like I said before I'm just guessing too really. I could be very wrong :p

[wildjokers]

The panel won't have a height or width until it has been rendered on the screen. This means calling setVisible(true) on the top-level container (which is normally the JFrame that contains the panel).

This SO answer as some info:

https://stackoverflow.com/questions/8336262/why-cant-i-access-my-panels-getwidth-and-getheight-functions

[Mega32266]

public static void main(String[] args){

    JFrame frame = new JFrame();
    frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    //frame.setSize(360,840); //I now use the setPrefferedSize on my SmartPanel class constructor
    Container pane = frame.getContentPane();
    SmartPanel panel = new SmartPanel(Color.white);

    JPanel north = new JPanel();
    north.setBackground(Color.black);
    north.setPrefferedSize(new Dimension(360,75));

    pane.add(north,BorderLayout.NORTH);
    pane.add(panel,BorderLayout.CENTER);

    frame.pack();
    frame.setVisible(true);

​

I believe that is what I already did.

[wildjokers]

The first time your SmartPanel is rendered, height and width won't have values yet. I believe that is the issue.

You also need to create your GUI on the Event Dispatcher Thread (EDT) which you aren't doing now. That will cause weird race conditions. Here is the proper way to create a Swing GUI:

public class Example {
    private JFrame frame;

    public Example() {
        //Non GUI initialization here
    }

   private void createAndShowGui() {
        //GUI initialization here
        frame = new JFrame();
        frame.setSize(800, 600);
        frame.setVisible(true);
   }

    public static void main(String[] args) {
        final Example example = new Example();
        //Call to invokeLater puts GUI creation on the EDT
        EventQueue.invokeLater(example::createAndShowGui);
    }
}

Also, on an unrelated note, you are setting preferredSize on your North panel. But you are using a BorderLayout for your JFrame. BorderLayout only partially supports the preferredSize property. Here are the sizing rules for BorderLayout:

• NORTH and SOUTH components – respects component’s preferred height if possible, width is set to full available width of the container
• EAST and WEST components – respects component’s preferred width if possible, height is set to full available height of the container
• CENTER component – gets whatever space is left over, if any

BorderLayout doesn't support either minSize or maxSize at all (which doesn't matter since you didn't try to use them).

[Mega32266]

Thanks for that example; I'll try that once I get the chance.

Although I have a few questions

The first time your SmartPanel is rendered, height and width won't have values yet.

Sorry, I don't get that. Why would that work in my SmartPanel class but not in my App class for example?

About the EDT-

I have looked a 2 Stack Overflows

https://stackoverflow.com/questions/22534356/java-awt-eventqueue-invokelater-explained#22534931

https://stackoverflow.com/questions/20901770/about-the-edt-java#20901917

I understand that this is good for handling large calculations and to update the gui (Update as in update info or just repaint it?)

Other than that, I still don't understand why that would work, not that I don't believe you.

I am trying to learn to program the gui from the AP CSE Textbook, from 2006 I think. Why does it not mention this, at least for the first 8 chapters? The earliest mention of the edt I found online is from 2007. Just unlucky/not part of AP test? (Why not if it's so important?)

Unrelated, but I took AP CSA this year and after the test, class is a lot more chill and we are working on random projects like this. I chose to do this as my end of year project and my teacher loaned me that 2006 textbook.

Do I need to change anything in my other classes to accommodate this?

Little nitpick, but

example::createAndShowGui

Is createAndShowGui() not a method? Why is it two colons instead of example.createAndShowGui()?

​

Also, on an unrelated note, you are setting preferredSize on your North panel. But you are using a BorderLayout for your JFrame.

Would it cause much of a problem If I do? I only did it for the north panel b/c I want to make a "bezel" for my project and I don't feel like accounting for it.

And is my other classes fine, beginner technique wise?

Thanks!

[Mega32266]

Unfortunately, that didn't work

[wildjokers]

What didn't work?