CODEWITHSUNDEEP
javaswt
Wietlol
Wietlol

Reputation: 1071

SWT GridLayout inside ScrolledComposite messing up the size of the components

I have a window that must show a list of buttons all below each other. All buttons must be square of a specific size (size can change while running).

This simple example works as in it shows all the buttons.

public class Main
{
    public static void main(String[] args)
    {
        Display display = new Display();
        Shell shell = new Shell(display);
        shell.setLayout(new FillLayout());

        val scrollPanel = new ScrolledComposite(shell, SWT.V_SCROLL);
        scrollPanel.setLayoutData(new GridData(SWT.FILL, SWT.FILL, true, true));
        scrollPanel.setLayout(new FillLayout());

        val gridPanel = new Composite(scrollPanel, SWT.NONE);
        val gridLayout = new GridLayout(1, false);
        gridPanel.setLayoutData(new GridData(SWT.FILL, SWT.FILL, true, true));
        gridPanel.setLayout(gridLayout);
        scrollPanel.setContent(gridPanel);

        val blue = display.getSystemColor(SWT.COLOR_BLUE);
        val red = display.getSystemColor(SWT.COLOR_RED);
        scrollPanel.setBackground(blue);
        gridPanel.setBackground(red);

        val exitButton = new Button(gridPanel, SWT.PUSH);
        exitButton.setText("Exit");
        exitButton.addListener(SWT.Selection, touchEvent -> shell.dispose());

        for (int i = 1; i <= 10; i++)
        {
            val button = new Button(gridPanel, SWT.PUSH);
            button.setText("Item: " + i);
            button.setSize(60, 60);
            gridPanel.setSize(gridPanel.computeSize(SWT.DEFAULT, SWT.DEFAULT));
        }

        shell.setSize(100, 700);

        shell.open();
        while (!shell.isDisposed())
            if (!display.readAndDispatch())
                display.sleep();
        display.dispose();
    }
}

However, whenever I do the gridPanel.computeSize(), the buttons lose their size that is set by button.setSize().

When I remove the gridPanel.setSize() after adding a button, the size will be 0 and the gridPanel is never shown at all.

When I set the gridLayout on the scrollPanel and add the buttons to that, then only one button is shown. (The last button if I use setContent() and the second (for whatever reason) if I do not use setContent() and just rely on the constructor of the buttons.)

At this moment, I am quite out of my options so if anyone can clear something up of this scenario, then please go ahead.

Upvotes: 1

Views: 185

Answers (2)

R&#252;diger Herrmann
R&#252;diger Herrmann

Reputation: 20985

If you use a layout (which you should), you must not use setSize() or otherwise interfere with the layout.

Use widthHint and heightHint of GridData instead to control the size of the buttons.

For example:

GridData gridData = new GridData( SWT.BEGINNING, SWT.CENTER, false, false );
gridData.widthHint = 60;
gridData.heightHint = 60;
button.setLayoutData( gridData );

Upvotes: 2

Loris Securo
Loris Securo

Reputation: 7638

First of all, setSize is only going to work properly when you are not using layouts (absolute positioning).

If you are using a layout, it will automatically set the components size based on the layout itself and how you define the layout data of the components.

In general, it is highly recommended to use layouts over absolute positioning.

In case of GridLayout, you can specify a component size via widthHint and heightHint in its GridData, for example:

Button button = new Button(gridPanel, SWT.PUSH);
button.setText("Item: " + i);
GridData buttonLayoutData = new GridData();
buttonLayoutData.widthHint = 60;
buttonLayoutData.heightHint = 60;
button.setLayoutData(buttonLayoutData);

Other observations:

  • to make the ScrollComposite work properly you should add these lines:

    scrollPanel.setExpandHorizontal(true);
scrollPanel.setExpandVertical(true);
scrollPanel.setMinSize(gridPanel.computeSize(SWT.DEFAULT, SWT.DEFAULT));

    in particular, setMinSize will tell the ScrollComposite at what size it should make the scrollbar appear.

  • if the parent layout is a FillLayout you should not set layout data on its children. It won't do anything since it is not expected. So you should remove the setLayoutData from scrollPanel and gridPanel.

  • if you want to change the button size at a later moment, just get its layout data, modify the hints and ask the component to layout (also don't forget to notify the scrollbar of the change with setMinSize):

    GridData buttonLayoutData = (GridData) button.getLayoutData();
buttonLayoutData.widthHint = 40;
buttonLayoutData.heightHint = 40;
button.requestLayout();
scrollPanel.setMinSize(gridPanel.computeSize(SWT.DEFAULT, SWT.DEFAULT));

Upvotes: 1

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