android自定义View-垂直滚动的TextView
自定义垂直滚动的TextView，主要是用来学习Scroller的使用。关于ScrollTextView的实现，可以看下面的介绍和源码。
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package
com.orgcent.demo.view
;
import android.content.Context ; import android.util.AttributeSet ; import android.view.MotionEvent ; import android.view.VelocityTracker ; import android.view.ViewConfiguration ; import android.view.animation.DecelerateInterpolator ; import android.widget.Scroller ; import android.widget.TextView ; /** * 配置android:scrollbars="vertical"，启用垂直滚动条 * * 实现水平滚动就是修改mScrollX，可参考HorizontalScrollView * * 滚动原理： 在绘制前对画布进行偏移操作 * * 下面是View的绘制机制： * |- view.computeScroll() --用来对mScrollX/Y进行修改。由于在绘制前调用，可调用invalite()来触发 * |- canvas.translate(-mScrollX,-mScrollY) --偏移画布 * |- view.draw() --绘制 * * 上述内容可以在View.buildDrawingCache()或ViewGroup.dispatchDraw()->drawChild()中找到.直接查看方法名即可 * * 滚动帮助类： * Scroller --用来计算滚动后的偏移值.具体请参考ScrollView和HorizontalScrollView * VelocityTracker --速度计算类。根据fling时的按下、抬起动作，计算滚动初速度 * * ScrollTextView--流程解析： * 1、onTouchEvent() --使用Scroller来计算滚动偏移值 * 2、重写computeScroll() --对View的mScrollY进行修改， 此处控制滚动范围 * * 滚动范围： * 最小值：0 * 最大值：所有文本高度+内边距-View高度。也就是超出屏幕的文本高度 */ public class ScrollTextView extends TextView { private Scroller mScroller ; private int mTouchSlop ; private int mMinimumVelocity ; private int mMaximumVelocity ; private float mLastMotionY ; private boolean mIsBeingDragged ; private VelocityTracker mVelocityTracker ; private int mActivePointerId = INVALID_POINTER ; private static final int INVALID_POINTER = - 1 ; public ScrollTextView ( Context context, AttributeSet attrs, int defStyle ) { super (context, attrs, defStyle ) ; initView ( ) ; } public ScrollTextView ( Context context, AttributeSet attrs ) { super (context, attrs ) ; initView ( ) ; } public ScrollTextView ( Context context ) { super (context ) ; initView ( ) ; } private void initView ( ) { final Context cx = getContext ( ) ; //设置滚动减速器，在fling中会用到 mScroller = new Scroller (cx, new DecelerateInterpolator (0.5f ) ) ; final ViewConfiguration configuration = ViewConfiguration. get (cx ) ; mTouchSlop = configuration. getScaledTouchSlop ( ) ; mMinimumVelocity = configuration. getScaledMinimumFlingVelocity ( ) ; mMaximumVelocity = configuration. getScaledMaximumFlingVelocity ( ) ; } /** * 此方法为最后机会来修改mScrollX,mScrollY. * 这方法后将根据mScrollX,mScrollY来偏移Canvas已实现内容滚动 */ @Override public void computeScroll ( ) { super. computeScroll ( ) ; final Scroller scroller = mScroller ; if (scroller. computeScrollOffset ( ) ) { //正在滚动，让view滚动到当前位置 int scrollY = scroller. getCurrY ( ) ; final int maxY = (getLineCount ( ) * getLineHeight ( ) + getPaddingTop ( ) + getPaddingBottom ( ) ) - getHeight ( ) ; boolean toEdge = scrollY < 0 || scrollY > maxY ; if (scrollY < 0 ) scrollY = 0 ; else if (scrollY > maxY ) scrollY = maxY ; /* *下面等同于： * mScrollY = scrollY; * awakenScrollBars(); //显示滚动条，必须在xml中配置。 * postInvalidate(); */ scrollTo ( 0, scrollY ) ; if (toEdge ) //移到两端，由于位置没有发生变化，导致滚动条不显示 awakenScrollBars ( ) ; } } public void fling ( int velocityY ) { final int maxY = (getLineCount ( ) * getLineHeight ( ) + getPaddingTop ( ) + getPaddingBottom ( ) ) - getHeight ( ) ; mScroller. fling (getScrollX ( ), getScrollY ( ), 0, velocityY, 0, 0, 0, Math. max ( 0, maxY ) ) ; //刷新，让父控件调用computeScroll() invalidate ( ) ; } @Override public boolean onTouchEvent (MotionEvent ev ) { /* * 事件处理方式：先自己处理后交给父类处理。 * PS:方式不同，可能导致效果不同。请根据需求自行修改。 */ boolean handled = false ; final int contentHeight = getLineCount ( ) * getLineHeight ( ) ; if (contentHeight > getHeight ( ) ) { handled = processScroll (ev ) ; } return handled | super. onTouchEvent (ev ) ; } private boolean processScroll (MotionEvent ev ) { boolean handled = false ; if (mVelocityTracker == null ) { mVelocityTracker = VelocityTracker. obtain ( ) ; } mVelocityTracker. addMovement (ev ) ; //帮助类，用来在fling时计算移动初速度 final int action = ev. getAction ( ) ; switch (action ) { case MotionEvent. ACTION_DOWN : { if ( !mScroller. isFinished ( ) ) { mScroller. forceFinished ( true ) ; } mLastMotionY = ev. getY ( ) ; mActivePointerId = ev. getPointerId ( 0 ) ; mIsBeingDragged = true ; handled = true ; break ; } case MotionEvent. ACTION_MOVE : { final int pointerId = mActivePointerId ; if (mIsBeingDragged && INVALID_POINTER != pointerId ) { final int pointerIndex = ev. findPointerIndex (pointerId ) ; final float y = ev. getY (pointerIndex ) ; int deltaY = ( int ) (mLastMotionY - y ) ; if ( Math. abs (deltaY ) > mTouchSlop ) { //移动距离(正负代表方向)必须大于ViewConfiguration设置的默认值 mLastMotionY = y ; /* * 默认滚动时间为250ms，建议立即滚动，否则滚动效果不明显 * 或者直接使用scrollBy(0, deltaY); */ mScroller. startScroll (getScrollX ( ), getScrollY ( ), 0, deltaY, 0 ) ; invalidate ( ) ; handled = true ; } } break ; } case MotionEvent. ACTION_UP : { final int pointerId = mActivePointerId ; if (mIsBeingDragged && INVALID_POINTER != pointerId ) { final VelocityTracker velocityTracker = mVelocityTracker ; velocityTracker. computeCurrentVelocity ( 1000, mMaximumVelocity ) ; int initialVelocity = ( int ) velocityTracker. getYVelocity (pointerId ) ; if ( Math. abs (initialVelocity ) > mMinimumVelocity ) { fling ( -initialVelocity ) ; } mActivePointerId = INVALID_POINTER ; mIsBeingDragged = false ; if (mVelocityTracker != null ) { mVelocityTracker. recycle ( ) ; mVelocityTracker = null ; } handled = true ; } break ; } } return handled ; } } |
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