How to update a ScriptUIGraphics object?

Question

Hello,
I've been able to use ScriptUIGraphics, but as far as I've seen there's no way to update / change any object, nor it seems possible to call the onDraw() handler but once if it contains either fillPath() or strokePath() - which usually does.
For instance, the following test script pops up a panel with a red square in it. Fine. When you click the "Try" button, the onDraw() is fired again and should draw a smaller square, but stops with a very informative "cannot execute" error at some point within the onDraw():
// ScriptUI graphics update issue
// resource string
var winRes = "dialog {  \
    text: 'ScriptUI Graphics test',  \
    margins: 15, \
    alignChildren: 'row', \
    canvas: Panel {  \
        preferredSize: [200, 200], \
        properties: {borderStyle: 'black'} , \
    buttonsGroup: Group{ \
        cancelButton: Button { text: 'Cancel', properties:{name:'cancel'} }, \
        tryButton: Button { text: 'Try', properties:{name:'try'},size: [40,24], alignment:['right', 'center'] }, \
// Window
var win = new Window(winRes);
// define the graphic property
canvasGraphics = win.canvas.graphics
// do the drawing
win.canvas.onDraw = function() {
          // creates a red filled square
          canvasGraphics.newPath()
          canvasGraphics.rectPath(10, 10, 200, 200)
          canvasGraphics.fillPath(canvasGraphics.newBrush(canvasGraphics.BrushType.SOLID_COLOR, [1,0,0,1], 1)) // HERE
win.buttonsGroup.tryButton.onClick = function() {
          win.canvas.onDraw.call()
win.show()
When you run it, it works as expected; if you click the Try button, an error is fired when the script gets to the line ("HERE" in the code), that is: when it comes to fill the path.
Strangely enough! Because it doesn't seem to be a problem with the onDraw second call (apparently the second square path is constructed, but can't be filled).
Am I doing something wrong here? Should I first delete the original square (how?!), or somehow initialize it again? Are ScriptUIGraphics immutable somehow?
--- Update ---
Further experiments led me to understand that onDraw() (so the whole drawing) seem to be called just once - when the Window is shown. I've tried to remove and rebuild the canvas Panel altogether, but its own new onDraw() is never called - nor an explicit call works. Apparently you can't invoke win.show() again, nor hide and show it. Ouch!
Thanks in advance for any suggestion
Davide

Answer 1

Sorry, I do not understand what do you really want (because of my bad english)
Try to change the bg color of the panel in the dialog box by clicking on button? Something like this?
// ScriptUI graphics update issue
// resource string
var winRes = "dialog {  \
    text: 'ScriptUI Graphics test',  \
    margins: 15, \
    alignChildren: 'row', \
    canvas: Panel {  \
        preferredSize: [200, 200], \
        properties: {borderStyle: 'black'} , \
    buttonsGroup: Group{ \
        cancelButton: Button { text: 'Cancel', properties:{name:'cancel'} }, \
        tryButton: Button { text: 'Try', properties:{name:'try'},size: [40,24], alignment:['right', 'center'] }, \
// Window
var win = new Window(winRes);
// define the graphic property
win.canvas.graphics.backgroundColor = win.canvas.graphics.newBrush (win.canvas.graphics.BrushType.SOLID_COLOR, [1,0,0],1);
win.buttonsGroup.tryButton.onClick = function() { // change the graphic background property by click on Button [try]
win.canvas.graphics.backgroundColor = win.canvas.graphics.newBrush (win.canvas.graphics.BrushType.SOLID_COLOR, [0,0,1],1);
win.show()