Android Question How to draw on a canvas in Android

saeed10051 · Apr 18, 2020

Hi all
i have seen on code from Erel where following code is executed on B4J side to draw on a canvas

Sub cvs_MouseDragged (EventData As MouseEvent)
cvs.DrawCircle(EventData.X, EventData.Y, 30dip, fx.Colors.From32Bit(Rnd(0xFF000000, -1)), True, 0)
End Sub

Here as we see that MouseDragged sub is using MouseEvent to draw. However if i want to use the same sub in B4A, i am unable to find an event which i can use to draw. I am trying to create an app in which on dragging my finger on the screen i can draw on the screen.

aeric · Apr 18, 2020

klaus said:
In B4X XUI, a Canvas must be linked to a Panel (B4A, B4i) or a Pane (B4J) with the B4XCanvas1.Initialize method.
You may need to call B4XCanvas1.Invalidate to make the drawing active.
This is different from B4A and B4i where you need to Invalidate the Panel.
You may have a look at the B4X Graphics and B4X XUI booklets.

[B4X] [XUI] Drawing with B4XCanvas

B4XCanvas is the cross platform version of Canvas. Steps to using B4XCanvas: 1. Initialize and pass the target view. In most cases it will be a Panel (or Pane). It must be a Pane in B4J. 2. Make the drawings. 3. Call Invalidate to commit the drawings. 4. If the target view is resized then you...

www.b4x.com

saeed10051 · Apr 18, 2020

Hi Aeric
thanks for the reply
however i am missing one point here, the examples given here refer to drawing something grammatically and displaying it on the canvas. I want to draw by dragging my finger on the screen. how to capture that event. When i see the code by Erel in B4J (as given in my original question) he has used the mouse drag to draw something, how to capture that event while working with B4A , as here we do not have a mouse we just drag our finger on the screen.

angel_ · Apr 18, 2020

Try this

[B4X] [XUI] AS Draw (FabricView and CanvasView)

Hello, 2 years ago i already had the idea of this view, but I failed in some places, but now I have taken up the challenge and the result is impressive. Inspired by @Johan Schoeman FabricView and CanvasView. Features cross-platform compatible set a background image draw, erase or draw lines...

www.b4x.com

saeed10051 · Apr 18, 2020

Thanks Angel
Impressive work there.
I need some extra effort to understand the code

saeed10051 · Apr 19, 2020

Hi Angel
i have reviewed the code, however i am unable to catch that in which event are you writing the code to draw the lines. There is a Sub ASDraw1_Touch (Action As Int, XY As Map)
but within the sub all the code is commented.
can you please explain.

klaus · Apr 19, 2020

Didn't you have a look HERE !?

Android Question How to draw on a canvas in Android

saeed10051

Active Member

aeric

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[B4X] [XUI] Drawing with B4XCanvas

saeed10051

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angel_

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[B4X] [XUI] AS Draw (FabricView and CanvasView)

saeed10051

Active Member

saeed10051

Active Member

klaus

Expert

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