名字随便取吧
2013-11-26 14:28
采纳率: 20%
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android ScrollView实现原理,求助!

能解释下ScrollView滚动显示的原理吗?就比如说你的ScollView有LinearLayout然后LinearLayout内有100个Button(id=1,2,3,4......),创建初,屏幕显示id=1~10的Button,当你向下拖的时候如何重新绘制控件,显示id=3~12的Button,我看ScrollView的源代码,并没有找到这部分功能,不知道能否解释下到底是怎么实现的,在哪里实现的?多谢!!

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  • 枫晨曦Aaron 2013-11-27 01:19
    已采纳

    01.package com.ql.view;

    02.

    03.import android.content.Context;

    04.import android.os.Handler;

    05.import android.os.Message;

    06.import android.util.AttributeSet;

    07.import android.view.MotionEvent;

    08.import android.view.View;

    09.import android.widget.ScrollView;

    10.

    11.public class LazyScrollView extends ScrollView{

    12. private static final String tag="LazyScrollView";

    13. private Handler handler;

    14. private View view;

    15. public LazyScrollView(Context context) {

    16. super(context);

    17. // TODO Auto-generated constructor stub

    18. }

    19. public LazyScrollView(Context context, AttributeSet attrs) {

    20. super(context, attrs);

    21. // TODO Auto-generated constructor stub

    22. }

    23. public LazyScrollView(Context context, AttributeSet attrs, int defStyle) {

    24. super(context, attrs, defStyle);

    25. // TODO Auto-generated constructor stub

    26. }

    27. //这个获得总的高度

    28. public int computeVerticalScrollRange(){

    29. return super.computeHorizontalScrollRange();

    30. }

    31. public int computeVerticalScrollOffset(){

    32. return super.computeVerticalScrollOffset();

    33. }

    34. private void init(){

    35.

    36. this.setOnTouchListener(onTouchListener);

    37. handler=new Handler(){

    38. @Override

    39. public void handleMessage(Message msg) {

    40. // process incoming messages here

    41. super.handleMessage(msg);

    42. switch(msg.what){

    43. case 1:

    44. if(view.getMeasuredHeight() <= getScrollY() + getHeight()) {

    45. if(onScrollListener!=null){

    46. onScrollListener.onBottom();

    47. }

    48.

    49. }else if(getScrollY()==0){

    50. if(onScrollListener!=null){

    51. onScrollListener.onTop();

    52. }

    53. }

    54. else{

    55. if(onScrollListener!=null){

    56. onScrollListener.onScroll();

    57. }

    58. }

    59. break;

    60. default:

    61. break;

    62. }

    63. }

    64. };

    65.

    66. }

    67.

    68. OnTouchListener onTouchListener=new OnTouchListener(){

    69.

    70. @Override

    71. public boolean onTouch(View v, MotionEvent event) {

    72. // TODO Auto-generated method stub

    73. switch (event.getAction()) {

    74. case MotionEvent.ACTION_DOWN:

    75. break;

    76. case MotionEvent.ACTION_UP:

    77. if(view!=null&&onScrollListener!=null){

    78. handler.sendMessageDelayed(handler.obtainMessage(1), 200);

    79. }

    80. break;

    81.

    82. default:

    83. break;

    84. }

    85. return false;

    86. }

    87.

    88. };

    89.

    90. /**
    91. * 获得参考的View,主要是为了获得它的MeasuredHeight,然后和滚动条的ScrollY+getHeight作比较。
    92. /

    93. public void getView(){

    94. this.view=getChildAt(0);

    95. if(view!=null){

    96. init();

    97. }

    98. }

    99.

    100. /
    *
    101. * 定义接口
    102. * @author admin
    103. *
    104. */

    105. public interface OnScrollListener{

    106. void onBottom();

    107. void onTop();

    108. void onScroll();

    109. }

    110. private OnScrollListener onScrollListener;

    111. public void setOnScrollListener(OnScrollListener onScrollListener){

    112. this.onScrollListener=onScrollListener;

    113. }

    114.}

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