sidhu眼中的CoordinatorLayout.Behavior（三）

摘要：好了，关于的使用我就先介绍到这了图片上传中如果觉得这篇文章对你有帮助，点个赞鼓励一下吧

看过前两篇文章的同学
sidhu眼中的CoordinatorLayout.Behavior（一）
sidhu眼中的CoordinatorLayout.Behavior（二）
应该知道今天要讲的内容了——Behavior的布局依赖
其实这个内容挺少的，我都想直接贴代码然大家自己体会了……额，开玩笑的，不过内容真的少，我也不浪费大家时间了，疑问我不提了，直入主题

（有木有直入主题，哈哈~）
我将上次的例子做了下修改
xml：

相比于之前的布局我们可以看到，就多了一个小方块在布局里面，至于我想实现的效果可以看下面效果图

让小方块可以随着上面的head做同步的位移
就如我上篇所说的，使用原理还是实现NestedScrollingChild接口，废话不多说，上代码（没错，我就是这样的人，一言不合就上代码）

package com.mintmedical.mybehaviordemo;

import android.animation.ValueAnimator;
import android.content.Context;
import android.support.design.widget.CoordinatorLayout;
import android.support.v4.view.NestedScrollingChild;
import android.support.v4.view.NestedScrollingChildHelper;
import android.util.AttributeSet;
import android.view.View;

/**
 * Created by SidHu on 2016/8/17.
 */
public class HideHeadBehavior extends CoordinatorLayout.Behavior implements NestedScrollingChild {

    private boolean isHeadHide = false;
    private boolean isAnimating = false;
    private final int SCROOL_VALUE = 50;
    private int childHeight;
    private final int animationDuration = 500;

    private NestedScrollingChildHelper childHelper;

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

    @Override
    public boolean onStartNestedScroll(CoordinatorLayout coordinatorLayout, View child, View directTargetChild, View target, int nestedScrollAxes) {
        if (target.getId() == R.id.rel_body) {
            if (childHeight == 0) {
                childHeight = child.getHeight();
            }
            if (childHelper == null) {
                childHelper = new NestedScrollingChildHelper(child);
            }
            return true;
        } else {
            return false;
        }
    }

    @Override
    public void onNestedPreScroll(CoordinatorLayout coordinatorLayout, View child, View target, int dx, int dy, int[] consumed) {
        super.onNestedPreScroll(coordinatorLayout, child, target, dx, dy, consumed);
        if (isAnimating) {
            return;
        }
        if (dy > SCROOL_VALUE && !isHeadHide) {
            hide(child, target);
        } else if (dy < -SCROOL_VALUE && isHeadHide) {
            show(child, target);
        }
    }


    public void hide(final View child, final View target) {
        isHeadHide = true;
        ValueAnimator valueAnimator = new ValueAnimator();
        valueAnimator.setIntValues(0, childHeight);
        valueAnimator.setDuration(animationDuration);
        valueAnimator.addUpdateListener(new ValueAnimator.AnimatorUpdateListener() {
            @Override
            public void onAnimationUpdate(ValueAnimator animation) {
                if (child.getBottom() > 0) {
                    int value = (int) animation.getAnimatedValue();
                    isAnimating = value != childHeight;
                    child.layout(child.getLeft(), -value, child.getRight(), -value + childHeight);
                    target.layout(target.getLeft(), -value + childHeight, target.getRight(), target.getBottom());
                }
            }
        });
        valueAnimator.start();
    }

    public void show(final View child, final View target) {
        isHeadHide = false;
        ValueAnimator valueAnimator = new ValueAnimator();
        valueAnimator.setIntValues(0, childHeight);
        valueAnimator.setDuration(animationDuration);
        valueAnimator.addUpdateListener(new ValueAnimator.AnimatorUpdateListener() {
            @Override
            public void onAnimationUpdate(ValueAnimator animation) {
                if (child.getBottom() < childHeight) {
                    int value = (int) animation.getAnimatedValue();
                    isAnimating = value != childHeight;
                    child.layout(child.getLeft(), value - childHeight, child.getRight(), value);
                    target.layout(target.getLeft(), value, target.getRight(), target.getBottom());
                }
            }
        });
        valueAnimator.start();
    }

    @Override
    public void setNestedScrollingEnabled(boolean enabled) {
        childHelper.setNestedScrollingEnabled(enabled);
    }

    @Override
    public boolean isNestedScrollingEnabled() {
        return childHelper.isNestedScrollingEnabled();
    }

    @Override
    public boolean startNestedScroll(int axes) {
        return childHelper.startNestedScroll(axes);
    }

    @Override
    public void stopNestedScroll() {
        childHelper.stopNestedScroll();
    }

    @Override
    public boolean hasNestedScrollingParent() {
        return childHelper.hasNestedScrollingParent();
    }

    @Override
    public boolean dispatchNestedScroll(int dxConsumed, int dyConsumed, int dxUnconsumed, int dyUnconsumed, int[] offsetInWindow) {
        return childHelper.dispatchNestedScroll(dxConsumed, dyConsumed, dxUnconsumed, dyUnconsumed, offsetInWindow);
    }

    @Override
    public boolean dispatchNestedPreScroll(int dx, int dy, int[] consumed, int[] offsetInWindow) {
        return childHelper.dispatchNestedPreScroll(dx, dy, consumed, offsetInWindow);
    }

    @Override
    public boolean dispatchNestedFling(float velocityX, float velocityY, boolean consumed) {
        return childHelper.dispatchNestedFling(velocityX, velocityY, consumed);
    }

    @Override
    public boolean dispatchNestedPreFling(float velocityX, float velocityY) {
        return childHelper.dispatchNestedPreFling(velocityX, velocityY);
    }
}

我将head实现了NestedScrollingChild接口，然后就没有做其他事情了。（这也说明了，想让控件通知CoordinatorLayout自己的状态其实只要实现了NestedScrollingChild接口就够了，假如你不需要关心滑动手势，就像小方块只关心head的位移一样，那你startNestedScroll之类的这样方法都不用要了）

那我们看一下小方块的Behavior

package com.mintmedical.mybehaviordemo;

import android.content.Context;
import android.support.design.widget.CoordinatorLayout;
import android.util.AttributeSet;
import android.view.View;

/**
 * Created by SidHu on 2016/8/18.
 */
public class MoveWithHeadBehavior extends CoordinatorLayout.Behavior{

    private int lastBottom = -1;

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

    @Override
    public boolean layoutDependsOn(CoordinatorLayout parent, View child, View dependency) {
        return dependency.getId() == R.id.rel_head;
    }

    @Override
    public boolean onDependentViewChanged(CoordinatorLayout parent, View child, View dependency) {
        if (lastBottom == -1) {
            lastBottom = dependency.getBottom();
        }
        if (dependency.getBottom() != lastBottom) {
            int d = dependency.getBottom()-lastBottom;
            lastBottom = dependency.getBottom();
            child.offsetTopAndBottom(d);
        }
        return super.onDependentViewChanged(parent, child, dependency);
    }
}

代码也是非~非~非~非常简单，布局依赖最主要的关系这两个方法，一个是判断是不是自己关心的target View（跟滑动的时候简直一毛一样），一个是被关心的target View变化以后的回调，代码我就不解释啦，也是很简单（大家有什么问题可以在评论里面问我啊）。

好了，关于Behavior的使用我就先介绍到这了
![图片上传中...]