Use handler to update the android UI

Original post link: http://rayleung.javaeye.com/blog/411860

 

When I first came into contact with Android Thread Programming, I used to be like Java and tried to solve the problem using the following code.

Java code

1. New thread (New runnable (){
2. Public void run (){
3. Myview. invalidate ();
4. }
5. }). Start ();

 

However, this is not possible because it violates the single-threaded model: Android UI operations are not thread-safe and must be executed in the UI thread. After reading the document and apidemo, I found that the commonly used method is to use handler to update the UI thread.

 

The function of the following code is very simple: Draw a circle, every 0.1 seconds, the circle moves 10 pixels to 10. However, the process of updating the UI using handler is clearly displayed.

 

 

 

First, create a simple view. The Code is as follows:

Java code

1. Package com. Ray. Handler;
3. Import Android. content. context;
4. Import Android. Graphics. Canvas;
5. Import Android. Graphics. color;
6. Import Android. Graphics. paint;
7. Import Android. Graphics. Point;
8. Import Android. Graphics. drawable. drawable;
9. Import Android. View. view;
11. Public class bounceview extends view {
12. Float x = 40;
14. Public bounceview (context ){
15. Super (context );
16. }
18. @ Override
19. Protected void ondraw (canvas ){
20. X + = 10;
21. Paint mpaint = new paint ();
22. Mpaint. setantialias (true );
23. Mpaint. setcolor (color. Green );
24. Canvas. drawcircle (x, 40, 40, mpaint );
25. }
26. }

 

The code for creating an activity is as follows:

Java code

1. Package com. Ray. Handler;
3. Import Android. App. activity;
4. Import Android. content. context;
5. Import Android. Graphics. Canvas;
6. Import Android. Graphics. color;
7. Import Android. Graphics. paint;
8. Import Android. OS. Bundle;
9. Import Android. OS. Handler;
10. Import Android. OS. message;
11. Import Android. View. view;
12. Import Android. View. window;
14. Public class testhandler extends activity {
15. Protected static final int guiupdateidentifier = 0x101;
17. Thread myrefreshthread = NULL;
18. Bounceview mybounceview = NULL;
20. Handler myhandler = new handler (){
21. Public void handlemessage (Message MSG ){
22. Switch (msg. What ){
23. Case testhandler. guiupdateidentifier:
24. Mybounceview. invalidate ();
25. Break;
26. }
27. Super. handlemessage (MSG );
28. }
29. };
30. Public void oncreate (bundle savedinstancestate ){
31. Super. oncreate (savedinstancestate );
32. This. requestwindowfeature (window. feature_no_title );
34. This. mybounceview = new bounceview (this );
35. This. setcontentview (this. mybounceview );
36. New thread (New mythread (). Start ();
37. }
39. Class mythread implements runnable {
40. Public void run (){
41. While (! Thread. currentthread (). isinterrupted ()){
43. Message message = new message ();
44. Message. What = testhandler. guiupdateidentifier;
46. Testhandler. This. myhandler. sendmessage (Message );
47. Try {
48. Thread. Sleep (100 );
49. } Catch (interruptedexception e ){
50. Thread. currentthread (). Interrupt ();
51. }
52. }
53. }
54. }
55. }