Android教程：高仿launcher和墨跡左右拖動效果

有這樣的想法，做出一個模仿launcher的效果。自己也曾從網上搜過很多資料，也思考過怎麼實現，最終還是參考了別人的資料實現了此效果，也解決了我這半個多月的冥思苦想，再次感謝，今天把代碼貼出來供大家學習，因為這方面做得比較好的資料缺失比較少（因為本人搜了很多資料都不能達到效果），如果大家覺得還不錯，請頂起。

更多Android相關信息見Android 專題頁面 http://www.linuxidc.com/topicnews.aspx?tid=11

首先自定義一個 ViewGroup：

1. public class MyScrollLayout extends ViewGroup{
3. private VelocityTracker mVelocityTracker; // 用於判斷甩動手勢
4. private static final int SNAP_VELOCITY = 600;
5. private Scroller mScroller; // 滑動控制器
6. private int mCurScreen;
7. private int mDefaultScreen = 0;
8. private float mLastMotionX;
9. // private int mTouchSlop;
11. private OnViewChangeListener mOnViewChangeListener;
13. public MyScrollLayout(Context context) {
14. super(context);
15. // TODO Auto-generated constructor stub
16. init(context);
17. }
18. public MyScrollLayout(Context context, AttributeSet attrs) {
19. super(context, attrs);
20. // TODO Auto-generated constructor stub
21. init(context);
22. }
24. public MyScrollLayout(Context context, AttributeSet attrs, int defStyle) {
25. super(context, attrs, defStyle);
26. // TODO Auto-generated constructor stub
27. init(context);
28. }
30. private void init(Context context)
31. {
32. mCurScreen = mDefaultScreen;
33. // mTouchSlop = ViewConfiguration.get(getContext()).getScaledTouchSlop();
34. mScroller = new Scroller(context);
36. }
38. @Override
39. protected void onLayout(boolean changed, int l, int t, int r, int b) {
40. // TODO Auto-generated method stub
41. if (changed) {
42. int childLeft = 0;
43. final int childCount = getChildCount();
44. for (int i=0; i<childCount; i++) {
45. final View childView = getChildAt(i);
46. if (childView.getVisibility() != View.GONE) {
47. final int childWidth = childView.getMeasuredWidth();
48. childView.layout(childLeft, 0,
49. childLeft+childWidth, childView.getMeasuredHeight());
50. childLeft += childWidth;
51. }
52. }
53. }
54. }
56. @Override
57. protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
58. // TODO Auto-generated method stub
59. super.onMeasure(widthMeasureSpec, heightMeasureSpec);
60. final int width = MeasureSpec.getSize(widthMeasureSpec);
61. final int widthMode = MeasureSpec.getMode(widthMeasureSpec);
63. final int count = getChildCount();
64. for (int i = 0; i < count; i++) {
65. getChildAt(i).measure(widthMeasureSpec, heightMeasureSpec);
66. }
67. scrollTo(mCurScreen * width, 0);
68. }
70. public void snapToDestination() {
71. final int screenWidth = getWidth();
72. final int destScreen = (getScrollX()+ screenWidth/2)/screenWidth;
73. snapToScreen(destScreen);
74. }
76. public void snapToScreen(int whichScreen) {
77. // get the valid layout page
78. whichScreen = Math.max(0, Math.min(whichScreen, getChildCount()-1));
79. if (getScrollX() != (whichScreen*getWidth())) {
80. final int delta = whichScreen*getWidth()-getScrollX();
81. mScroller.startScroll(getScrollX(), 0,
82. delta, 0, Math.abs(delta)*2);
84. mCurScreen = whichScreen;
85. invalidate(); // Redraw the layout
86. if (mOnViewChangeListener != null)
87. {
88. mOnViewChangeListener.OnViewChange(mCurScreen);
89. }
90. }
91. }
93. @Override
94. public void computeScroll() {
95. // TODO Auto-generated method stub
96. if (mScroller.computeScrollOffset()) {
97. scrollTo(mScroller.getCurrX(), mScroller.getCurrY());
98. postInvalidate();
99. }
100. }
102. @Override
103. public boolean onTouchEvent(MotionEvent event) {
104. // TODO Auto-generated method stub
105. final int action = event.getAction();
106. final float x = event.getX();
107. final float y = event.getY();
109. switch (action) {
110. case MotionEvent.ACTION_DOWN:
111. Log.i("", "onTouchEvent ACTION_DOWN");
112. if (mVelocityTracker == null) {
113. mVelocityTracker = VelocityTracker.obtain();
114. mVelocityTracker.addMovement(event);
115. }
116. if (!mScroller.isFinished()){
117. mScroller.abortAnimation();
118. }
119. mLastMotionX = x;
120. break;
122. case MotionEvent.ACTION_MOVE:
123. int deltaX = (int)(mLastMotionX - x);
124. if (IsCanMove(deltaX))
125. {
126. if (mVelocityTracker != null)
127. {
128. mVelocityTracker.addMovement(event);
129. }
130. mLastMotionX = x;
131. scrollBy(deltaX, 0);
132. }
134. break;
135. case MotionEvent.ACTION_UP:
136. int velocityX = 0;
137. if (mVelocityTracker != null)
138. {
139. mVelocityTracker.addMovement(event);
140. mVelocityTracker.computeCurrentVelocity(1000);
141. velocityX = (int) mVelocityTracker.getXVelocity();
142. }
143. if (velocityX > SNAP_VELOCITY && mCurScreen > 0) {
144. // Fling enough to move left
145. snapToScreen(mCurScreen - 1);
146. } else if (velocityX < -SNAP_VELOCITY
147. && mCurScreen < getChildCount() - 1) {
148. // Fling enough to move right
149. snapToScreen(mCurScreen + 1);
150. } else {
151. snapToDestination();
152. }
154. if (mVelocityTracker != null) {
155. mVelocityTracker.recycle();
156. mVelocityTracker = null;
157. }
158. // mTouchState = TOUCH_STATE_REST;
159. break;
160. }
161. return true;
162. }
164. private boolean IsCanMove(int deltaX)
165. {
166. if (getScrollX() <= 0 && deltaX < 0 ){
167. return false;
168. }
169. if (getScrollX() >= (getChildCount() - 1) * getWidth() && deltaX > 0){
170. return false;
171. }
172. return true;
173. }
175. public void SetOnViewChangeListener(OnViewChangeListener listener)
176. {
177. mOnViewChangeListener = listener;
178. }
179. }