Android Question How do you write multi-threaded applications?

[John H. Guillory]

I got a feeling I may know the answer. I have a feeling it's one of two things, but reading an article about making the main activity as small as possible and using multi-threaded applications to not bog down the application leads me to ask just in case. From what I read, it appears that Android supports multi-threaded applications running, so suppose I have an application with Thread1 and Thread2, and a subroutine called Job1 that calls both, how do I code it such that Thread1 and Thread2 run at the same time, and how would I check to see when they have finished? I've got a sneaky feeling that I need to create a service for this.

 

[Erel]

Basic4android takes care of running common long tasks (neworking, camera, ...) in the background. It is handled inside the libraries.

Your code should generally run in the main thread. Can you explain your specific requirements?

 

[John H. Guillory]

Just when drawing a bunch of lines, and some other task, the phone got bogged down, so I thought I could speed it up if I had it draw part in one thread, then part in another thread. It sounds like what I might have to do is build a library in Java, and write the threads in java and call the threads from a java class....

 

[thedesolatesoul]

Stuff like drawing etc that is related to the UI is all done on the same thread even in java, if i am not mistaken.

 

[Erel]

Can you post your drawing code?

 

[John H. Guillory]

I found an article on mulithreaded apps, and downloaded the library. I used it on a few routines. Strangely enough the one that bogged down the most was when I convert a classic Basic routine to display a bunch of random circles on the screen... Eg. I have 2 threads each basically like this:

Sub C1a
Dim X,Y, r, T,C1 As Int

For T = 1 To 500
X = Rnd(0,Panel1.Width)
Y = Rnd(0,Panel1.Height)
r = Rnd(0,Panel1.Width / 2)
C1 = Colors.ARGB(Rnd(50,255),Rnd(0,255),Rnd(0,255),Rnd(0,255))
c.drawcircle(X,Y,r,C1,True,1.0)
Next
End Sub

The other thread is Sub C2a ... That's the one that seems to bog it down the most. I originally was trying to do 32000 circles, I broke it down into 2 threads each doing 16000 random circles. I tried using doevents and sleep, I tried doing an Activity.Invalidate to have it update the screen... Either way, with a loop of at least 1000 or so, I get the phone kinda bogged down for a few seconds not showing anything till it's completely done drawing, then it shows the menu bar and the circles... On the multi-threaded, the second thread finishes a few seconds later and more circles appear.

Then I do a moire pattern, and a circle pattern, and generate random boxes (each on their own activity). The moire pattern shows instantly, no problems with it:

Sub M1a
For T = 0 To X Step 2
c.DrawLine(T,0,X-T,Y,Colors.Cyan,1.0)
Next
End Sub

Sub M2a
For T = 0 To Y Step 2
c.DrawLine(0,T,X,Y-T,Colors.Cyan,1.0)
Next
End Sub

M1a and M2a are 2 threads for the demo. Each thread runs at the same time, so it draws the Horizontal and Vertical parts at the same time. Very fast too!

Sub chaser
Dim T As Int
x = 0
y = 0
For T = 1 To 20000
Lx = x
Ly = y
x = Rnd(0,Panel1.Width)
y = Rnd(0,Panel1.Height)
c.DrawLine(x,y,Lx,Ly,Colors.ARGB(255,0,T,0),5)
Next
End Sub

On Chaser, I tried to use a delay and erase the previous line. I'd love to have it draw the line, delay, erase, re-draw a new line. But using the delay command someone else posted, it either delays too quickly, or delays far too long. I either get no line (erasing it instantaneous) or I get draw a line, pause 3-4 minutes, draw another line... So I went with this... Instantaneous... And yup, I tried invalidate on that too....

 

[John H. Guillory]

BTW, the app is available on the Google Playstore as Android Graphics Demo. The APK package name is org.roachguts.graphdemo
If you want to go to it directly, it's ID would be equal to that...