Android Question Max height of panel with canvas in scrollview

[MartinR]

I am trying to display some rows of information. Each row has a row number followed by numbers, e.g.

...
123 4 5 6 7 8 1 2 3
124 4 6 5 8 7 2 1 3
...

There could be up to 6000 rows and I want to be able to scroll up and down.
I've implemented this in VB6 using a fixed picture and drawing just 30 rows to the picture at a time, with a vertical scrollbar controlling which 30 rows are displayed.

I thought I would be able to draw all 6000 rows to a canvas on a scrollview panel of the requisite height, and just scroll the view up and down, but I seem to be limited to 100 or 200 rows.

I don't get any error messages when trying, say, a 300-row data set, but get nothing displayed apart from a dark grey scrollview with a little indicator on the right hand side of the screen sliding up and down.

The following code illustrates the issue:

Sub Globals
Dim scv1 As ScrollView
Dim cvs1 As Canvas
End Sub

Sub Activity_Create(FirstTime As Boolean)
scv1.Initialize(0)
Activity.AddView(scv1,0,0,100%x,100%y)
scv1.Panel.Width=scv1.Width
scv1.Panel.Height=scv1.Height * 7 'OK with * 6
Dim panelcolor As ColorDrawable
panelcolor.Initialize(Colors.RGB(255,255,192),10)
scv1.Panel.Background=panelcolor
cvs1.Initialize(scv1.Panel)
Dim row As Int
For row = 1 To 2000
cvs1.DrawText(row,0,row * 20,Typeface.DEFAULT,12,Colors.Red,"LEFT")
Next
scv1.Panel.Invalidate
scv1.Invalidate
Activity.Invalidate
End Sub

If I make the scrollview panel 6 times the screen height this works OK, but get a blank display for 7 times.

B4A 5.8. Target is BLU ENERGY DIAMOND phone, Android 6

 

[ronell]

 

[Jeffrey Cameron]

Is there a specific reason why you're drawing the text manually onto the panel's canvas rather than just adding labels containing your text?

 

[ronell]

Is there a specific reason why you're drawing the text manually onto the panel's canvas rather than just adding labels containing your text?

yeah .. use label . measure the height, then your good
i guess

 

[MartinR]

Is there a specific reason why you're drawing the text manually onto the panel's canvas rather than just adding labels containing your text?

Yes, I should have explained...
The horizontal positioning of each digit corresponds to some timing associated with that digit and needs the drawtext facility for this. Also, I will want to draw lines through the paths of each digit from one row to the next, together with small, carefully positioned coloured rectangles.

The background to this is bell-ringing, and the app is to highlight errors in the rhythm (striking) of each ringer.

Apologies for pasting the code as text rather than using the correct facility.

Martin

 

[Jeffrey Cameron]

Creating bitmaps this large can be problematic, especially if you haven't locked the device to one specific orientation and your users tips the phone back-and-forth repeatedly (you'll run out of memory fairly quickly).

I would suggest you see if you can construct your layout using the standard label controls (remember, you can make a "line" by having a blank label and setting its background color and position/size).

 

[MartinR]

The kind of display I am trying to create is like the attached screenshot from the VB6 version.

Following your replies I am reassured that I am not doing anything wrong in terms of code, but am facing memory limitations.

I will take the approach of creating and displaying a relatively small bitmap representing just a few (30 or so) rows of ringing in response to a seekbar event and effectively scroll through the available striking data that way.

Many thanks for your help.

 

[Jeffrey Cameron]

That would be my suggestion as well, after seeing your desired result.

 

[MartinR]

Am I right: seekbars only work horizontally!? I want to scroll the display up and down so would like vertical action.
Perhaps some code involving _touch event on a designated panel?

 

[Jeffrey Cameron]

Yes, stock seekbars are horizontal only. You could code your own control, or use an existing library, such as: https://www.b4x.com/android/forum/threads/class-vertical-horizontal-and-circle-seekbars.19444/