项目中我们经常有上拉、下拉刷新的需求，几乎所有的listView、RecyclerView都会伴随着上拉、下拉刷新的需求，如果我们使用一些开源控件，换了控件我们就要更新，现在我们自己撸起袖子写一个通用的刷新控件

思路：

写一个继承RelativeLayout的RefreshLayout
添加头尾控件作为刷新控件
通过事件分发来进行刷新操作
通过动画来控制控件移动
目的：让他的所有子控件都可以使用，哪怕是一个TextView

public class RefreshLayout extends RelativeLayout {

/**
 * 滑动控件时拉去的速度比例
 */
private final int V_REFRESH = 2;
/**
 * 是否是刷新过程
 * true 是
 * false 不是
 * 为false的时候才可以进行刷新
 */
private boolean mIsRefreshDuring;
/**
 * 可以进下拉刷新
 */
private boolean mCanDownPull;
/**
 * 可以进行上拉刷新
 */
private boolean mCanUpPull;
/**
 * 判断触摸后是否是初次移动
 */
private boolean mIsFirstMove;
/**
 * y轴呢平移的距离
 */
private int mDistanceY;
/**
 * 刷新接口对象
 */
private OnRefresh mOnRefresh;
/**
 * 用于控制事件拦截的变量
 */
private boolean mCanIntercept;
private int mTouchSlop;
private int mDistance;
private LayoutParams mHeaderParams;
private View mHeaderView;
private View mFootView;
private int mHeaderMaxHeight;
private int mStartY;
private LayoutParams mFootParams;
private int mFootMaxHeight;
private PullCallBack mCallBack;
private View mChildView;
private ObjectAnimator mAnimator;

public RefreshLayout(Context context) {
    super(context);
    initData();
}

public RefreshLayout(Context context, AttributeSet attrs) {
    super(context, attrs);
    initData();
}

public RefreshLayout(Context context, AttributeSet attrs, int defStyleAttr) {
    super(context, attrs, defStyleAttr);
    initData();
}

/**
 * 必须让头尾控件实现的接口
 */
public interface HeadAndFootCallBack {
    //设置属性
    void setAttribute();

    //开始刷新
    void startPull();

    //停止刷新
    void stopPull();
}

/**
 * 必须让被拖动的控件子类实现
 */
public interface PullCallBack {
    boolean canDownPull();

    boolean canUpPull();
}

private void initData() {
    //不调用该方法不能进行绘制
    setWillNotDraw(false);
}

/**
 * 下拉刷新完成后必须使用该方法
 */
public void downPullFinish() {
    mAnimator.setFloatValues(mChildView.getTranslationY(), 0);
    mAnimator.start();
    ((HeadAndFootCallBack) mHeaderView).stopPull();
}

/**
 * 上拉完成后必须调用该方法
 */
public void upPullFinish() {
    mAnimator.setFloatValues(mChildView.getTranslationY(), 0);
    mAnimator.start();
    ((HeadAndFootCallBack) mFootView).stopPull();
}

/**
 * 自动下拉刷新
 */
public void autoDownPullForHead() {
    postDelayed(new Runnable() {
        @Override
        public void run() {
            mCanDownPull = true;
            mCanUpPull = false;
            mAnimator.setFloatValues(10, mHeaderMaxHeight);
            mAnimator.start();
            ((HeadAndFootCallBack) mHeaderView).startPull();
            mOnRefresh.onDownPullRefresh();
        }
    }, 500);
}

/**
 * 自动下拉刷新
 */
public void autoUpPullForHead() {
    postDelayed(new Runnable() {
        @Override
        public void run() {
            mCanDownPull = false;
            mCanUpPull = true;
            mAnimator.setFloatValues(0, mFootMaxHeight);
            mAnimator.start();
            ((HeadAndFootCallBack) mFootView).startPull();
            mOnRefresh.onUpPullRefresh();
        }
    }, 500);
}

@Override
public boolean onInterceptTouchEvent(MotionEvent ev) {
    return mCanIntercept;
}

@Override
public boolean onTouchEvent(MotionEvent event) {
    return true;
}

@Override
public boolean dispatchTouchEvent(MotionEvent event) {
    Log.e("shen", "mIsRefreshDuring=" + mIsRefreshDuring);
    if (mIsRefreshDuring)/*如果正在进行刷新将不会获取MotionEvent*/ {
        return super.dispatchTouchEvent(event);
    }
    switch (event.getAction()) {
        case MotionEvent.ACTION_DOWN:
            mStartY = (int) event.getY();
            initPull();
            break;
        case MotionEvent.ACTION_MOVE:
            if (event.getPointerCount() == 1) {
                int moveY = (int) event.getY();
                mDistanceY = (moveY - mStartY) / V_REFRESH;
                if (!mIsFirstMove && mDistanceY != 0 && mDistanceY < mTouchSlop) {
                    mCanDownPull = mDistanceY > 0;
                    mCanUpPull = !mCanDownPull;
                    mIsFirstMove = true;
                }
                if (mCanDownPull && mCallBack.canDownPull()) {
                    upDataForDownPull();//下拉刷新
                    mChildView.setEnabled(false);
                    mCanIntercept = true;
                }
                if (mCanUpPull && mCallBack.canUpPull()) {
                    upDataForUpPull();//上拉加载
                    mChildView.setEnabled(false);
                    mCanIntercept = true;
                }
                mStartY = moveY;
            }
            break;
        case MotionEvent.ACTION_UP:
            mIsRefreshDuring = true;
            mIsFirstMove = false;
            if (mHeaderParams.height >= mHeaderMaxHeight)/*可以下拉刷新*/ {
                ((HeadAndFootCallBack) mHeaderView).startPull();
                mOnRefresh.onDownPullRefresh();
            } else if (mFootParams.height >= mFootMaxHeight)/*可以上拉刷新*/ {
                ((HeadAndFootCallBack) mFootView).startPull();
                mOnRefresh.onUpPullRefresh();
            } else if (mHeaderParams.height > 0 && mHeaderParams.height < mHeaderMaxHeight)/*不能进行下拉刷新，收回*/ {
                releaseForDownFinished();
            } else if (mFootParams.height > 0 && mFootParams.height < mFootMaxHeight)/*不能进行下拉刷新，收回*/ {
                releaseForUpFinished();
            } else {
                mIsRefreshDuring = false;
                mCanIntercept = false;
            }
            break;
    }
    super.dispatchTouchEvent(event);
    return true;
}

/**
 * 每次进行触摸都需要进行初始化
 */
private void initPull() {
    mCanDownPull = false;
    mCanUpPull = false;
}

/**
 * 不需要进行上拉刷新
 */
private void releaseForUpFinished() {
    mAnimator.setFloatValues(mChildView.getTranslationY(), 0);
    mAnimator.start();
}

/**
 * 不需要进行下拉刷新
 */
private void releaseForDownFinished() {
    mAnimator.setFloatValues(mChildView.getTranslationY(), 0);
    mAnimator.start();
}

/**
 * 上拉时处理手势
 */
private void upDataForUpPull() {
    if (mDistanceY != 0) {
        mFootParams.height -= mDistanceY;
        if (mFootParams.height <= 0) {
            mFootParams.height = 0;
        }
        if (mFootParams.height >= mFootMaxHeight) {
            mFootParams.height = mFootMaxHeight;
        }
        mChildView.setTranslationY(-mFootParams.height);
        mFootView.requestLayout();
    }
}

/**
 * 下拉时处理手势
 */
private void upDataForDownPull() {
    if (mDistanceY != 0) {
        mHeaderParams.height += mDistanceY;
        if (mHeaderParams.height >= mHeaderMaxHeight) { //最大
            mHeaderParams.height = mHeaderMaxHeight;
        }
        if (mHeaderParams.height <= 0) { //最小
            mHeaderParams.height = 0;
        }
        mChildView.setTranslationY(mHeaderParams.height);
        mHeaderView.requestLayout();
    }
}

@Override
protected void onAttachedToWindow() {
    super.onAttachedToWindow();
}

@Override
protected void onFinishInflate() {
    super.onFinishInflate();
    //加载头
    mHeaderView = getChildAt(0);
    if (!(mHeaderView instanceof HeadAndFootCallBack)) {
        new IllegalStateException("HeaderView必须实现HeadAndFootCallBack接口");
    }
    ((HeadAndFootCallBack) mHeaderView).setAttribute();
    mHeaderParams = (LayoutParams) mHeaderView.getLayoutParams();
    mHeaderParams.addRule(RelativeLayout.ALIGN_PARENT_TOP);

    //加载尾
    mFootView = getChildAt(2);
    if (!(mFootView instanceof HeadAndFootCallBack)) {
        new IllegalStateException("FootView必须实现HeadAndFootCallBack接口");
    }
    ((HeadAndFootCallBack) mFootView).setAttribute();
    mFootParams = (LayoutParams) mFootView.getLayoutParams();
    mFootParams.addRule(RelativeLayout.ALIGN_PARENT_BOTTOM);

    mChildView = getChildAt(1);
    if (!(mChildView instanceof HeadAndFootCallBack)) {
        new IllegalStateException("ChildView必须实现PullCallBack接口");
    }
    mCallBack = (PullCallBack) getChildAt(1);

    //设置动画
    mAnimator = ObjectAnimator.ofFloat(mChildView, "translationY", 0);
    mAnimator.setInterpolator(new DecelerateInterpolator());
    mAnimator.addUpdateListener(new ValueAnimator.AnimatorUpdateListener() {
        @Override
        public void onAnimationUpdate(ValueAnimator animation) {
            int translationY = (int) mChildView.getTranslationY();
            if (mCanUpPull) { //从移动到的位置往下滑
                mFootParams.height = Math.abs(translationY);
                mFootView.requestLayout();
            } else if (mCanDownPull) {
                mHeaderParams.height = Math.abs(translationY);
                mHeaderView.requestLayout();
            }
            Log.e("shen", "translationY=" + translationY);
            Log.e("shen", "mHeaderParams.height=" + mHeaderParams.height);
            if (translationY == 0) {
                mChildView.setEnabled(true);
                mDistanceY = 0; //重置
                mIsRefreshDuring = false; //重置
                mCanIntercept = false;
            } else {
                mIsRefreshDuring = true;
            }
        }
    });
}

@Override
protected void onSizeChanged(int w, int h, int oldw, int oldh) {
    super.onSizeChanged(w, h, oldw, oldh);
    mTouchSlop = ViewConfiguration.get(getContext()).getScaledTouchSlop();
    mDistance = mTouchSlop * 5;
    //设置下拉头初始属性
    mHeaderMaxHeight = mHeaderParams.height;
    mHeaderParams.height = 0;
    mHeaderView.requestLayout();
    //设置上拉尾初始属性
    mFootMaxHeight = mFootParams.height;
    mFootParams.height = 0;
    mFootView.requestLayout();
}

/**
 * 下拉/上拉事件监听
 */
public interface OnRefresh {
    /**
     * 下拉刷新
     */
    void onDownPullRefresh();

    /**
     * 上拉加载
     */
    void onUpPullRefresh();
}

public void setOnRefresh(OnRefresh onRefresh) {
    mOnRefresh = onRefresh;
}

给他添加三个控件，头尾就是刷新头、尾，第二个就是正常显示的控件。必须让头尾实现HeadAndFootCallBack接口，来设置属性，通知开始刷新、结束刷新

难点： 现在来说下开发时遇到的难点

由于判断在dispatchTouchEvent中，导致如果该控件以及子控件都不消费该事件的话，就会造成事件不会发送到它，因为如果不消费DOWN事件的话，之后所有的事件都不会在进行接收。解决方式，让该控件onTouchEvent方法消返回true，当子控件不进行事件消费的话，就会返回由该控件消费，不会造成因DOWN事件不消费而无法接收到事件，导致dispatchTouchEvent也不消费事件
动画，动画就是我的伤痛，最近在学习估值器
这个控件自认为写的不错，通过他可以帮我们学习事件分发、动画、接口回调，也是有一定的学习意义