横向滑动view , 实现 HorizontalScrollView 的效果

activity_layout.xml

...
    <HorizontalScrollLayout
        android:background="@drawable/border_shape"
        android:layout_width="300dp"
        android:layout_height="300dp"
        android:orientation="horizontal">
        <LinearLayout
            android:layout_width="3000dp"
            android:layout_height="match_parent"
            android:background="@drawable/long_picture">

        </LinearLayout>

    </HorizontalScrollLayout>


...

HorizontalScrollLayout.java

package com.python.cat.needwork.widgets.measure;

import android.content.Context;
import android.os.SystemClock;
import android.util.AttributeSet;
import android.view.MotionEvent;
import android.view.VelocityTracker;
import android.view.View;
import android.view.ViewConfiguration;
import android.view.ViewGroup;
import android.widget.LinearLayout;
import android.widget.OverScroller;

import com.apkfuns.logutils.LogUtils;
import com.python.cat.needwork.widgets.ViewUtils;

public class HorizontalScrollLayout extends LinearLayout {


    private int touchSlop;
    private OverScroller mOverScroller;
    private int tapTimeout;
    private float downX;
    private float downY;
    private long downTime;
    private boolean isMoving;
    private int leftBorder;
    private int rightBorder;
    private int selfWidth;
    private VelocityTracker velocityTracker;
    private ViewConfiguration configuration;
    private int minimumFlingVelocity;
    private int maximumFlingVelocity;

    public HorizontalScrollLayout(Context context) {
        super(context);
        init();
    }

    public HorizontalScrollLayout(Context context, AttributeSet attrs) {
        super(context, attrs);
        init();
    }


    public HorizontalScrollLayout(Context context, AttributeSet attrs, int defStyleAttr) {
        super(context, attrs, defStyleAttr);
        init();
    }

    public HorizontalScrollLayout(Context context, AttributeSet attrs, int defStyleAttr, int defStyleRes) {
        super(context, attrs, defStyleAttr, defStyleRes);
        init();
    }

    @Override
    protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
        LogUtils.i(ViewUtils.logMeasureSpec(widthMeasureSpec, "LogLayout.width"));
        LogUtils.i(ViewUtils.logMeasureSpec(heightMeasureSpec, "LogLayout.height"));
        super.onMeasure(widthMeasureSpec, heightMeasureSpec);
    }

    @Override
    protected void onSizeChanged(int w, int h, int oldw, int oldh) {
        super.onSizeChanged(w, h, oldw, oldh);
        LogUtils.e("real width=%s,height=%s", w, h);
        View childAt = getChildAt(0);
        ViewGroup.MarginLayoutParams params = (MarginLayoutParams) childAt.getLayoutParams();
        leftBorder = params.leftMargin;
        rightBorder = params.width - params.rightMargin;
        selfWidth = getWidth() - getPaddingLeft() - getPaddingRight();
        LogUtils.e("leftBorder=%s,rightBorder=%s,selfWidth=%s",
                leftBorder, rightBorder, selfWidth);
    }


    private void init() {
        configuration = ViewConfiguration.get(getContext());
        touchSlop = configuration.getScaledTouchSlop();
        tapTimeout = ViewConfiguration.getTapTimeout();
        minimumFlingVelocity = configuration.getScaledMinimumFlingVelocity();
        maximumFlingVelocity = configuration.getScaledMaximumFlingVelocity();
        mOverScroller = new OverScroller(getContext());
        LogUtils.e("touchSlop=%s,tapTimeout=%s,minFlingV=%s,maxiFlingV=%s",
                touchSlop, tapTimeout, minimumFlingVelocity, maximumFlingVelocity);
    }

    @Override
    public boolean performClick() {
        return super.performClick();
    }

    @Override
    public boolean onTouchEvent(MotionEvent event) {
        if (velocityTracker == null) {
            velocityTracker = VelocityTracker.obtain();
        }
        velocityTracker.addMovement(event);
        switch (event.getAction()) {
            case MotionEvent.ACTION_DOWN: {
                downTime = SystemClock.elapsedRealtime();
                downX = event.getX();
                downY = event.getY();
                LogUtils.d("down--- %s,%s", downX, downY);
            }
            break;
            case MotionEvent.ACTION_MOVE: {
                float moveX = event.getX();
                float moveY = event.getY();
                float diffX = moveX - downX;
                float diffY = moveY - downY;
                LogUtils.i("touchSlop=%s, diffX=%s,diffY=%s", touchSlop, diffX, diffY);
                if (!isMoving && Math.abs(diffX) > Math.abs(diffY)
                        && Math.abs(diffX) > touchSlop) {
                    isMoving = true;
                    LogUtils.w("can move dx= %s, scrollX=%s", diffX, getScrollX());
                    if (diffX > 0 && getScrollX() <= leftBorder) {
                        // don't move, want to move to left
                        LogUtils.e("不要滑动了。。。left " + getScrollX());
                    } else if (diffX < 0 && getScrollX() + selfWidth >= rightBorder) {
                        // don/t move, want to move to right
                        LogUtils.e("不要滑动了。。。right " + (getScrollX() + selfWidth));
                    } else if (diffX < 0
                            && getScrollX() + Math.abs(diffX) + selfWidth > rightBorder) {
                        scrollTo(rightBorder - selfWidth, 0);
                    } else if (diffX > 0 && getScrollX() - Math.abs(diffX) < leftBorder) {
                        scrollTo(leftBorder, 0);
                    } else {
                        scrollBy((int) -diffX, 0);
                    }
                } else if (isMoving) {
                    // 这个逻辑的目的是，在连续滑动的过程中，每次滑动距离可以非常小
                    LogUtils.w("can move dx= %s, scrollX=%s", diffX, getScrollX());

                    if (diffX > 0 && getScrollX() <= leftBorder) {
                        // don't move, want to move to left
                        LogUtils.e("不要滑动了。。。left " + getScrollX());
                    } else if (diffX < 0 && getScrollX() + selfWidth >= rightBorder) {
                        // don/t move, want to move to right
                        LogUtils.e("不要滑动了。。。right " + (getScrollX() + selfWidth));
                    } else if (diffX < 0
                            && getScrollX() + Math.abs(diffX) + selfWidth > rightBorder) {
                        scrollTo(rightBorder - selfWidth, 0);
                    } else if (diffX > 0 && getScrollX() - Math.abs(diffX) < leftBorder) {
                        scrollTo(leftBorder, 0);
                    } else {
                        scrollBy((int) -diffX, 0);
                    }
                }
                downX = moveX;
                downY = moveY;
            }
            break;
            case MotionEvent.ACTION_UP: {
                isMoving = false;
                velocityTracker.computeCurrentVelocity(1000, maximumFlingVelocity);
                int xVelocity = Math.round(velocityTracker.getXVelocity());
                float upX = event.getX();
                float upY = event.getY();
                float diffX = upX - downX;
                float diffY = upY - downY;
                if (Math.abs(diffX) < touchSlop
                        && Math.abs(diffY) < touchSlop
                        && SystemClock.elapsedRealtime() - downTime < tapTimeout) {
                    performClick();
                    LogUtils.e("is a click event");
                } else {
                    LogUtils.e("up----l %s, %s ", getScrollX(), rightBorder - selfWidth - getScrollX());
                    // 强制结束 mScroller 未完成的动画
                    mOverScroller.forceFinished(true);
                    final boolean canFling = (getScaleX() > 0 || xVelocity > 0) &&
                            (getScrollX() < getScrollRange() || xVelocity < 0);
                    if (canFling && Math.abs(xVelocity) > minimumFlingVelocity) {
                        int width = getWidth() - getPaddingLeft() - getPaddingRight();
                        int right = getChildAt(0).getWidth();
                        // 参考：android.widget.ScrollView.fling() 方法完成
                        mOverScroller.fling(getScrollX(), getScrollY(), -xVelocity, 0,
                                0, Math.max(0, right - width),
                                0, 0, 0, width / 2);
                    }
                    // 滚动到最左边 ok
                    // mOverScroller.startScroll(scrollX, getScrollY(), leftBorder - scrollX, getScrollY());
                    // 滚动到最右边 ok
                    // mOverScroller.startScroll(scrollX, getScrollY(), rightBorder - selfWidth - scrollX, getScrollY());
                    //  scrollBy(rightBorder - selfWidth - scrollX, 0); // ok
                    // 让 View 重绘
                    invalidate(); // 一定要调用，否则有时候不触发，如果是使用 Scroller 的话！


                }
                velocityTracker.clear();
                velocityTracker.recycle();
                velocityTracker = null;
            }
            break;
            case MotionEvent.ACTION_CANCEL: {
                isMoving = false;
                LogUtils.e("action--- cancel");
                velocityTracker.recycle();
            }
            break;
            default:
                LogUtils.e("action--- " + event.getAction());
                break;
        }
        return true; // 不true 的话，只有 down 能接收到
    }

    /**
     * 参考：android.widget.ScrollView#getScrollRange
     */
    private int getScrollRange() {
        int scrollRange = 0;
        if (getChildCount() > 0) {
            View child = getChildAt(0);
            scrollRange = Math.max(0,
                    child.getWidth() - (getWidth() - getPaddingLeft() - getPaddingRight()));
        }
        return scrollRange;
    }

    @Override
    public void computeScroll() {
        // 第三步，重写computeScroll()方法，并在其内部完成平滑滚动的逻辑
        if (mOverScroller.computeScrollOffset()) {
            scrollTo(mOverScroller.getCurrX(), mOverScroller.getCurrY());
            postInvalidate();
        }
    }


}