swt canvas.redraw doesn't work for clicking button

[purplepare]

the code is :
import org.eclipse.swt.SWT;
import org.eclipse.swt.events.PaintEvent;
import org.eclipse.swt.events.PaintListener;
import org.eclipse.swt.events.SelectionAdapter;
import org.eclipse.swt.events.SelectionEvent;
import org.eclipse.swt.layout.GridData;
import org.eclipse.swt.layout.GridLayout;
import org.eclipse.swt.widgets.Button;
import org.eclipse.swt.widgets.Canvas;
import org.eclipse.swt.widgets.Display;
import org.eclipse.swt.widgets.Shell;
public class caseButton {
private Shell shell;
public static void main(String[] args) {
try {
caseButton window = new caseButton();
window.open();
} catch (Exception e) {
e.printStackTrace();
}
}

/**
* Open the window.
*/
public void open() {
Display display = Display.getDefault();
createContents();
shell.open();
shell.layout();
while (!shell.isDisposed()) {
if (!display.readAndDispatch()) {
display.sleep();
}
}
}
/**
* Create contents of the window.
*/
protected void createContents() {
shell = new Shell();
shell.setText("SWT Application");
GridLayout gridLayout = new GridLayout();
gridLayout.numColumns = 1;
gridLayout.marginWidth = 0;
gridLayout.marginHeight = 0;
gridLayout.verticalSpacing = 4;
gridLayout.makeColumnsEqualWidth=false;
shell.setLayout(gridLayout);

GridData gridData=new GridData();
gridData.verticalSpan = 0;
gridData.horizontalSpan = 3;
gridData.verticalAlignment = GridData.FILL;
gridData.grabExcessVerticalSpace= true;
gridData.horizontalAlignment = GridData.FILL;
gridData.grabExcessHorizontalSpace = true;

final Button button = new Button(shell, SWT.PUSH);
button.setText("draw Rectangle");

final Canvas canvas = new Canvas(shell, SWT.NONE);
canvas.setLayoutData(gridData);

canvas.addPaintListener(new PaintListener() {
public void paintControl(PaintEvent e) {
e.gc.drawRoundRectangle(10, 10, 180, 80, 10, 10);
}
});
button.addSelectionListener(new SelectionAdapter() {
@Override
public void widgetSelected(SelectionEvent e) {
System.out.println("buttton_start ");
canvas.redraw(); // it can' work
System.out.println("buttton_end ");

}
});
}

}

the question is : when I click this button, it will print "buttton_start" and "buttton_end", the "canvas.redraw()" can't work. I don't know the reason , who can help me? thanks

[jim829]

Please edit your post and place the code between [code][/code] tags. And just curious as to why you are using SWT?

Regards,
Jim

[purplepare]

Please edit your post and place the code between [code][/code] tags. And just curious as to why you are using SWT?

Regards,
Jim

Sorry, i don't find the place which is "edit".And do you think which is better than "SWT".and do you know how to change this code to let it work?

[jim829]

First, if your post is too old, you can't edit it. There are two ways to add the code tags. One is simply type them in.
The other is to go the advanced editor, highlight your code and then click on '#'.

Now, I finally got your code to compile and run. I am not familiar with the SWT API. I am more familiar with Swing
and a little familiar with AWT (which I don't use anymore). Read about them here --> Standard Widget Toolkit - Wikipedia, the free encyclopedia.

So your program prints out as you describe and draws a rounded rectangle. What exactly is it supposed
to do? (Note: I may not be able to help you but providing that information will allow someone else to since they
would probably request the same information).

Edit: Your program seems to work as designed. Try this:
1. Declare two int instance fields, w and h and set them to the initial width and height of the rectangle.
2. Replace the two constants of width and height where you draw the rectangle with w and h.
3. In your button listener, simply put h += 10 and w += 10 somewhere in the widgetSelected method.
4. Now each time you click the button your rectangle will grow in width and height by 10 pixels.


Regards,
Jim

[purplepare]

First, if your post is too old, you can't edit it. There are two ways to add the code tags. One is simply type them in.
The other is to go the advanced editor, highlight your code and then click on '#'.

Now, I finally got your code to compile and run. I am not familiar with the SWT API. I am more familiar with Swing
and a little familiar with AWT (which I don't use anymore). Read about them here --> Standard Widget Toolkit - Wikipedia, the free encyclopedia.

So your program prints out as you describe and draws a rounded rectangle. What exactly is it supposed
to do? (Note: I may not be able to help you but providing that information will allow someone else to since they
would probably request the same information).

Edit: Your program seems to work as designed. Try this:
1. Declare two int instance fields, w and h and set them to the initial width and height of the rectangle.
2. Replace the two constants of width and height where you draw the rectangle with w and h.
3. In your button listener, simply put h += 10 and w += 10 somewhere in the widgetSelected method.
4. Now each time you click the button your rectangle will grow in width and height by 10 pixels.


Regards,
Jim

thanks you very much,jim. that function cann't work, because, i don't update the heigh and width. when i update them ,they can work, thanks again.