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*/    @Overridepublic 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();    }

    @Overridepublic 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;   }    }

转: http://orgcent.com/android-custom-vertical-scroll-textview/