使用雙緩沖技術實現Android畫板應用

什麼是雙緩沖技術？雙緩沖技術就是當用戶操作界面完成後，會有一個緩沖區保存用戶操作的結果。

為什麼要使用雙緩沖技術？拿Android 游戲開發來說，界面貞每次都是全部重畫的，也就說畫了新的，舊的就沒了，所以需要使用雙緩沖技術保存之前的內容。

如何實現雙緩沖？使用一個Bitmap對象保留之前的畫布即可。

1. package com.example.phonegaptest;
3. import android.content.Context;
4. import android.graphics.Bitmap;
5. import android.graphics.Bitmap.Config;
6. import android.graphics.Canvas;
7. import android.graphics.Color;
8. import android.graphics.Paint;
9. import android.graphics.Path;
10. import android.util.AttributeSet;
11. import android.view.MotionEvent;
12. import android.view.View;
14. public class DrawView extends View {
15. float preX;
16. float preY;
17. private Path path;
18. public Paint paint = null;
19. final int VIEW_WIDTH = 320;
20. final int VIEW_HEIGHT = 480;
21. Bitmap cacheBitmap = null;
22. Canvas cacheCanvas = null;
24. public DrawView(Context context, AttributeSet set) {
25. super(context, set);
26. cacheBitmap = Bitmap.createBitmap(VIEW_WIDTH, VIEW_HEIGHT,
27. Config.ARGB_8888);
28. cacheCanvas = new Canvas();
30. path = new Path();
31. cacheCanvas.setBitmap(cacheBitmap);
33. paint = new Paint(Paint.DITHER_FLAG);
34. paint.setColor(Color.RED);
35. paint.setStyle(Paint.Style.STROKE);
36. paint.setStrokeWidth(1);
37. paint.setAntiAlias(true);
38. paint.setDither(true);
39. }
41. @Override
42. public boolean onTouchEvent(MotionEvent event) {
43. float x = event.getX();
44. float y = event.getY();
46. switch (event.getAction()) {
47. case MotionEvent.ACTION_DOWN:
48. path.moveTo(x, y);
49. preX = x;
50. preY = y;
51. break;
52. case MotionEvent.ACTION_MOVE:
53. path.quadTo(preX, preY, x, y);
54. preX = x;
55. preY = y;
56. break;
57. case MotionEvent.ACTION_UP:
58. cacheCanvas.drawPath(path, paint);
59. path.reset();
60. break;
61. }
62. invalidate();
63. return true;
64. }
66. @Override
67. protected void onDraw(Canvas canvas) {
68. super.onDraw(canvas);
69. Paint bmpPaint = new Paint();
70. canvas.drawBitmap(cacheBitmap, 0, 0, bmpPaint);
71. canvas.drawPath(path, paint);
72. }
74. }