Android-->Behavior上手入门

开始布局时,方法回调顺序:

1:StickBehavior([context, attrs])-> 
2:onAttachedToLayoutParams([params])->
3:layoutDependsOn([parent,child,dependency])->//当dependency是你需要监听的View时,需要返回true, 否则dependency View位置改变, 或者大小改变不会有onDependentViewChanged回调.
4:onMeasureChild([parent,child,parentWidthMeasureSpec,widthUsed,parentHeightMeasureSpec,heightUsed])->
5:layoutDependsOn([parent,child,dependency])->
6:onMeasureChild([parent,child,parentWidthMeasureSpec,widthUsed,parentHeightMeasureSpec,heightUsed])->
7:layoutDependsOn([parent,child,dependency])->
8:onMeasureChild([parent,child,parentWidthMeasureSpec,widthUsed,parentHeightMeasureSpec,heightUsed])->
9:layoutDependsOn([parent,child,dependency])->
10:onMeasureChild([parent,child,parentWidthMeasureSpec,widthUsed,parentHeightMeasureSpec,heightUsed])->
11:onLayoutChild([parent,child,layoutDirection])->
12:onDependentViewChanged([parent, child, dependency])-> //当layoutDependsOn返回true时, 才会有这个回调

开始滚动子View时, 方法回调顺序

1:onStartNestedScroll([coordinatorLayout, child, directTargetChild, target, nestedScrollAxes])-> //此方法必须返回true, 否则之后的滚动事件将没有回调
2:onNestedScrollAccepted([coordinatorLayout, child, directTargetChild, target, nestedScrollAxes])->
3:onNestedPreScroll([coordinatorLayout, child, target, dx, dy, consumed])-> 
4:onNestedScroll([coordinatorLayout, child, target, dxConsumed, dyConsumed, dxUnconsumed, dyUnconsumed])-> 
//当快速滑动的时候, 才会触发fling回调
//4.1:onNestedPreFling([coordinatorLayout, child, target, velocityX, velocityY])-> 
//4.2:onNestedFling([coordinatorLayout, child, target, velocityX, velocityY, consumed])-> 
5:onStopNestedScroll([coordinatorLayout, child, target])->

源码地址:
https://github.com/angcyo/uiview/blob/master/RLibrary/uiview/src/main/java/com/angcyo/uiview/design/StickBehavior.java

public class StickBehavior<V extends View> extends CoordinatorLayout.Behavior<V> {
    View mTargetView;

    /**
     * 悬停区域的高度 px
     */
    int stickHeight = 0;

    /**
     * 为了保存已经偏移的距离
     */
    int lastTop = 0;

    public StickBehavior() {
    }

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

    /**
     * 当CoordinatorLayout在layout的时候, 会回调此方法, 告诉你,
     * 是否需要得到dependency View的位置大小改变的监听,如果你需要, 那么必须返回true
     */
    @Override
    public boolean layoutDependsOn(CoordinatorLayout parent, V child, View dependency) {
        if (mTargetView == null) {
            lastTop = 0;
        }
        if (dependency instanceof StickLayout) {
            //StickLayout只是用来判断是否是目标的标识, 没有任何不同支持,
            //你也可以通过getId判断id是否相等, 来处理
            mTargetView = dependency;
            stickHeight = (int) (40 * child.getContext().getResources().getDisplayMetrics().density);
            return true;
        }
        return super.layoutDependsOn(parent, child, dependency);
    }

    /**
     * 只有当layoutDependsOn返回true时, 才会回调.
     * 当dependency对应的View, 发生了改变, 就会回调此方法.
     * 你可以在此更新child的位置
     */
    @Override
    public boolean onDependentViewChanged(CoordinatorLayout parent, V child, View dependency) {
        lastTop = dependency.getTop();
        child.setTop(dependency.getBottom());
        return true;
    }


    /**
     * 测量child的大小, 和自定义view的套路一样
     */
    @Override
    public boolean onMeasureChild(CoordinatorLayout parent, V child, int parentWidthMeasureSpec, int widthUsed, int parentHeightMeasureSpec, int heightUsed) {
        child.measure(View.MeasureSpec.makeMeasureSpec(parent.getMeasuredWidth(), View.MeasureSpec.EXACTLY),
                View.MeasureSpec.makeMeasureSpec(parent.getMeasuredHeight() - stickHeight, View.MeasureSpec.EXACTLY));
        return true;
    }

    /**
     * 布局child的位置, 和自定义view的套路一样
     */
    @Override
    public boolean onLayoutChild(CoordinatorLayout parent, V child, int layoutDirection) {
        if (mTargetView != null) {
            ViewCompat.offsetTopAndBottom(mTargetView, lastTop);
            int top = mTargetView.getBottom();// - Math.abs(lastTop);
            child.layout(0, top, child.getMeasuredWidth(), top + child.getMeasuredHeight());
            return true;
        }
        return super.onLayoutChild(parent, child, layoutDirection);
    }

    /**
     * 必须返回true, 否则你收不到子View滚动的事件
     */
    @Override
    public boolean onStartNestedScroll(CoordinatorLayout coordinatorLayout, V child, View directTargetChild, View target, int nestedScrollAxes) {
        return true;
    }

    /**
     * 当子View开始滚动之前, 你可以通过此方法消耗掉滚动事件, 并偏移child的位置
     */
    @Override
    public void onNestedPreScroll(CoordinatorLayout coordinatorLayout, V child, View target, int dx, int dy, int[] consumed) {
        if (dy == 0 || (dy < 0 && ViewCompat.canScrollVertically(target, -1))) {
            return;
        }

        int offsetMax = mTargetView.getMeasuredHeight() - stickHeight;

        int top = mTargetView.getTop();
        int offset = 0;
        if (dy > 0) {
            //上滑
            offset = Math.min(dy, offsetMax + top);
        } else if (dy < 0) {
            //下滑
            offset = Math.max(dy, top);
        }
        ViewCompat.offsetTopAndBottom(mTargetView, -offset);
        consumed[1] = offset;
    }

    /**
     * 用来处理快速滑动
     */
    @Override
    public boolean onNestedPreFling(CoordinatorLayout coordinatorLayout, V child, View target, float velocityX, float velocityY) {
        L.e("call: onNestedPreFling([coordinatorLayout, child, target, velocityX, velocityY])-> ");

        if (velocityY < 0 && ViewCompat.canScrollVertically(target, -1)) {
            return super.onNestedPreFling(coordinatorLayout, child, target, velocityX, velocityY);
        }

        int offsetMax = mTargetView.getMeasuredHeight() - stickHeight;

        if (velocityY > offsetMax) {
            mTargetView.setTop(-offsetMax);
            //mTargetView.setBottom(mTargetView.getMeasuredHeight() - offsetMax);
            animToBottom(mTargetView.getMeasuredHeight() - offsetMax);
        } else if (velocityY < -offsetMax) {
            mTargetView.setTop(0);
            //mTargetView.setBottom(mTargetView.getMeasuredHeight());
            animToBottom(mTargetView.getMeasuredHeight());
        }

        return super.onNestedPreFling(coordinatorLayout, child, target, velocityX, velocityY);
    }

    void animToBottom(int bottom) {
        ValueAnimator animator = ObjectAnimator.ofInt(mTargetView.getBottom(), bottom);
        animator.addUpdateListener(new ValueAnimator.AnimatorUpdateListener() {
            @Override
            public void onAnimationUpdate(ValueAnimator animation) {
                mTargetView.setBottom((Integer) animation.getAnimatedValue());
            }
        });
        animator.setInterpolator(new LinearInterpolator());
        animator.setDuration(100);
        animator.start();
    }
}

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