iOS Question Canvas

[jamesnz]

I have a canvas (c) which is declared in main and initialised in my start routine for a separate module

Public Sub StartShow
    If pg.IsInitialized = False Then
        pg.Initialize("pg")
        pg.RootPanel.LoadLayout("Show")
    End If
    Main.NavControl.ShowPage(pg)
    interimList.Initialize
    parseSegmentsIntoObjects
    gmap.Initialize("gmap", ApiKey)
    addmap
    Main.c.Initialize(ChartPanelx)  '<==
    initialsetupchart
End Sub

What is the recommended method of clearing the canvas c.release and c.initialize do not clear it, if I return to the screen it has drawn one canvas over the top of the previous unless I restart the entire application

I have tried declaring the canvas in main , habe tried removing the canvas panel from the root panel, but even when re added it contains the old canvas data

 

[JanPRO]

Hi,

before initializing the canvas new, set it to Null. This will deallocate the object (ARC):

Sub ClearCanvas(C As Canvas)
    Dim V As View = C.View 'be sure Canvas.Release wasn't called before
    V.RemoveViewFromParent
    C = Null
    Dim C As Canvas
    C.Initialize(V)
    C.Refresh
End Sub

Jan

 

[jamesnz]

thanks will try this soon.

 

[klaus]

You may try this:
Move this two lines
Main.c.Initialize(ChartPanelx) '<==
initialsetupchart
insides the If / Then so you initialize the canvas only once.

Public Sub StartShow
    If pg.IsInitialized = False Then
        pg.Initialize("pg")
        pg.RootPanel.LoadLayout("Show")
        Main.c.Initialize(ChartPanelx)  '<==
        initialsetupchart
    End If
    Main.NavControl.ShowPage(pg)
    interimList.Initialize
    parseSegmentsIntoObjects
    gmap.Initialize("gmap", ApiKey)
    addmap
End Sub

 

[jamesnz]

OK I have moved these lines into the ISInitialized test and added Jans clear canvas method (thanks Jan) but the canvas plots still persists.
In my process_globals I have
Dim C As Canvas
Private ChartPanelx As Panel (made with designer)
have nothing in my page appear disappear or resize ( tried running canvasclear in pg_disappear, no difference)

Sub ClearCanvas(Cv As Canvas)
   
    Dim V As View = Cv.View 'be sure Canvas.Release wasn't called before
    V.RemoveViewFromParent
    Cv = Null
    Dim Cv As Canvas
    Cv.Initialize(V)
    Cv.Refresh
    'pg.RootPanel.AddView(C,0,0,50%x,50%y)
End Sub

Public Sub StartShow
   
    If pg.IsInitialized = False Then
        pg.Initialize("pg")
        pg.RootPanel.LoadLayout("Show")
    C.Initialize(ChartPanelx)   
    End If
   
    Main.NavControl.ShowPage(pg)
    interimList.Initialize
    parseSegmentsIntoObjects
    gmap.Initialize("gmap", ApiKey)
    addmap
    initialsetupchart
End Sub

The clue perhaps is that if I just initialising the canvas onto ChartPanelx , it won't show it at all, Instead I have to add Chartpanel x through the sub initialsetupchart (4th line) ***

Sub initialsetupchart
   
    Log("setting up chart")
    ClearCanvas(C)
   *** pg.RootPanel.AddView(ChartPanelx,0,pg.RootPanel.height/2,pg.RootPanel.Width,pg.RootPanel.Height/2)
   'if I leave the above line out I get no chart at all, yet it's added in the designer
    left=0
   
    Log ( "size of interim list = " & interimList.Size)
    For Each section As segment In interimList
        plotrectangle(interimList.Size, section.averageSpeed)
    Next
   
    C.refresh
    Log("finished drawing chart")
End Sub

 

[klaus]

Can you post a small project showing the problem so we can see what exactly you have done and test it in the same conditions as you do.

 

[jamesnz]

Thanks, yes, Will do this first thing in morning

 

[jamesnz]

apologies for delay, press the go button on screen1, the canvas will appear, note the size of the initial plots too.
Go back to screen 1 , press button again and note the canvas keeps the old plot values and draws new ones over the top of the old.

 

[jamesnz]

I think somewhere in the background it's actually taking a screenshot of the canvas . The reason I say this is if I put a red button on top of the canvaspanelx , when I redraw the canvas a copy of the button remains in the same position.

 

[Erel]

Why are you adding the panel in your code if it was already added in the layout file:

pg.RootPanel.AddView(ChartPanelx,0,pg.RootPanel.height/2,pg.RootPanel.Width,pg.RootPanel.Height/2)

?

 

[jamesnz]

If I comment that line out I get nothing, just a blank panel.
This has me confused also because in the smaller demo project I uploaded a post ago I don't need to add it programatically.
I have tried rebuilding the layout, renaming the panels, re ordering the panels in the designer,
Ive also tried initialising them in the Main Module as well as the Showx module

 

[klaus]

Attached you find a modified version.
To clear the canvas I draw a white color on it c.DrawColor(Colors.White).

 

[jamesnz]

Attached you find a modified version.
To clear the canvas I draw a white color on it c.DrawColor(Colors.White).

lol, thanks, I'd never thought of doing that.