自定义ViewGroup添加布局动画

声明几个属性值：

<declare-styleable name="GridImageViewGroup">
     <attr name="childVerticalSpace" format="dimension"/>
     <attr name="childHorizontalSpace" format="dimension"/>
     <attr name="columnNum" format="integer"/>
</declare-styleable>

GridImageViewGroup.java 代码：

public class GridImageViewGroup extends ViewGroup {
    private int childVerticalSpace = 0;
    private int childHorizontalSpace = 0;
    private int columnNum = 3;
    private int childWidth = 0;
    private int childHeight = 0;


    public GridImageViewGroup(Context context, AttributeSet attrs) {
        super(context, attrs);
        TypedArray attributes = context.obtainStyledAttributes(attrs, R.styleable.GridImageViewGroup);
        if (attributes != null) {
            childVerticalSpace = attributes.getDimensionPixelSize(R.styleable.GridImageViewGroup_childVerticalSpace, 0);
            childHorizontalSpace = attributes.getDimensionPixelSize(R.styleable.GridImageViewGroup_childHorizontalSpace, 0);
            columnNum = attributes.getInt(R.styleable.GridImageViewGroup_columnNum, 3);
            attributes.recycle();
        }
    }

    @Override
    protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
        super.onMeasure(widthMeasureSpec, heightMeasureSpec);
        int rw = MeasureSpec.getSize(widthMeasureSpec);
        int rh = MeasureSpec.getSize(heightMeasureSpec);
        int childCount = getChildCount();
        if (childCount > 0) {
            childWidth = (rw - (columnNum - 1) * childHorizontalSpace) / columnNum;

            childHeight = childWidth;

            int vw = rw;
            if (childCount < columnNum) {
                vw = childCount * (childHeight + childVerticalSpace);
            }
            int rowCount = childCount / columnNum + (childCount % columnNum != 0 ? 1 : 0);

            int vh = rowCount * childHeight + (rowCount > 0 ? rowCount - 1 : 0) * childVerticalSpace;

            setMeasuredDimension(vw, vh);
        }
    }

    @Override
    protected void onLayout(boolean changed, int l, int t, int r, int b) {
        int left = 0;
        int top = 0;
        int count = getChildCount();
        for (int i = 0; i < count; i++) {
            View child = getChildAt(i);
            left = (i % columnNum) * (childWidth + childHorizontalSpace);
            top = (i / columnNum) * (childHeight + childVerticalSpace);
            child.layout(left, top, left + childWidth, top + childHeight);
        }
    }

在xml中引用：

<com.whoislcj.animation.GridImageViewGroup
            android:id="@+id/image_layout"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:layout_margin="10dp"
            android:animateLayoutChanges="true"
            lee:childHorizontalSpace="10dp"
            lee:childVerticalSpace="10dp"
            lee:columnNum="3"/>

在Activity中调用：

private void initViews() {
        mImageViewGroup = (GridImageViewGroup) findViewById(R.id.image_layout);
        ImageView imageView = new ImageView(this);
        imageView.setImageResource(R.mipmap.add_image);
        imageView.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                addImageView();
            }
        });
        mImageViewGroup.addView(imageView);
    }

    public void addImageView() {
        final ImageView imageView = new ImageView(MainActivity4.this);
        imageView.setImageResource(R.mipmap.lottery);
        imageView.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                mImageViewGroup.removeView(imageView);
            }
        });
        mImageViewGroup.addView(imageView, 0);
    }

实现效果如下：

布局动画产生的背景：

     凡事总要问个明白，为何要引入布局动画呢？其实通过上面的实现效果可以看出，在添加和删除图片时都显得很突兀，不知道该用什么语言形容了，总之就是感觉不舒服。其实我平时在开发中调用View.setVisibility()方法时也会有这种感受，这也是布局动画产生的一个背景吧。

布局动画：

   布局动画是指ViewGroup在布局时产生的动画效果 。实现布局动画有如下几种方式

第一种方式：在xml中，对ViewGrope设置android:animateLayoutChanges="true"属性：

<com.whoislcj.animation.GridImageViewGroup
            android:id="@+id/image_layout"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:layout_margin="10dp"
            android:animateLayoutChanges="true"
            lee:childHorizontalSpace="10dp"
            lee:childVerticalSpace="10dp"
            lee:columnNum="3"/>

就这么简单的一句话实现的效果就可以实现了，看看效果如何

这种方式虽然简单但是实现的布局动画比较单一，下面看第二种方式。

第二种方式：LayoutTransition实现

LayoutTransition mLayoutTransition = new LayoutTransition();

        //设置每个动画持续的时间
        mLayoutTransition.setStagger(LayoutTransition.CHANGE_APPEARING, 50);
        mLayoutTransition.setStagger(LayoutTransition.CHANGE_DISAPPEARING, 50);
        mLayoutTransition.setStagger(LayoutTransition.APPEARING, 50);
        mLayoutTransition.setStagger(LayoutTransition.DISAPPEARING, 50);

        PropertyValuesHolder appearingScaleX = PropertyValuesHolder.ofFloat("scaleX", 0.5f, 1.0f);
        PropertyValuesHolder appearingScaleY = PropertyValuesHolder.ofFloat("scaleY", 0.5f, 1.0f);
        PropertyValuesHolder appearingAlpha = PropertyValuesHolder.ofFloat("alpha", 0f, 1f);
        ObjectAnimator mAnimatorAppearing = ObjectAnimator.ofPropertyValuesHolder(this, appearingAlpha, appearingScaleX, appearingScaleY);
        //为LayoutTransition设置动画及动画类型
        mLayoutTransition.setAnimator(LayoutTransition.APPEARING, mAnimatorAppearing);


        PropertyValuesHolder disappearingAlpha = PropertyValuesHolder.ofFloat("alpha", 1f, 0f);
        PropertyValuesHolder disappearingRotationY = PropertyValuesHolder.ofFloat("rotationY", 0.0f, 90.0f);
        ObjectAnimator mAnimatorDisappearing = ObjectAnimator.ofPropertyValuesHolder(this, disappearingAlpha, disappearingRotationY);
        //为LayoutTransition设置动画及动画类型
        mLayoutTransition.setAnimator(LayoutTransition.DISAPPEARING, mAnimatorDisappearing);


        ObjectAnimator mAnimatorChangeDisappearing = ObjectAnimator.ofFloat(null, "alpha", 1f, 0f);
        //为LayoutTransition设置动画及动画类型
        mLayoutTransition.setAnimator(LayoutTransition.CHANGE_DISAPPEARING, mAnimatorChangeDisappearing);

        ObjectAnimator mAnimatorChangeAppearing = ObjectAnimator.ofFloat(null, "alpha", 1f, 0f);
        //为LayoutTransition设置动画及动画类型
        mLayoutTransition.setAnimator(LayoutTransition.CHANGE_APPEARING, mAnimatorChangeAppearing);

        //为mImageViewGroup设置mLayoutTransition对象
        mImageViewGroup.setLayoutTransition(mLayoutTransition);

上面通过自定义LayoutTransition 修改系统提高的默认动画效果，如果不需要自定义的动画效果的话，不调用mLayoutTransition.setAnimator(LayoutTransition.DISAPPEARING, mAnimatorDisappearing);就行了。

LayoutTransition 提供了以下几种过渡类型：

• APPEARING —— 元素在容器中显现时需要动画显示。
• CHANGE_APPEARING —— 由于容器中要显现一个新的元素，其它元素的变化需要动画显示。
• DISAPPEARING —— 元素在容器中消失时需要动画显示。
• CHANGE_DISAPPEARING —— 由于容器中某个元素要消失，其它元素的变化需要动画显示。

看下修改过的动画效果：

 

第三种方式：通过设置LayoutAnimation来实现布局动画

 AlphaAnimation alphaAnimation = new AlphaAnimation(0f, 1f);
        alphaAnimation.setDuration(200);
        LayoutAnimationController animationController = new LayoutAnimationController(alphaAnimation, 0.5f);
        animationController.setOrder(LayoutAnimationController.ORDER_NORMAL);
        mImageViewGroup.setLayoutAnimation(animationController);

 显示顺序有以下几种：

•  ORDER_NORMAL;//顺序显示
•  ORDER_REVERSE;//反显示
•  ORDER_RANDOM//随机显示

也可以通过xml实现

<?xml version="1.0" encoding="utf-8"?>
<layoutAnimation
    xmlns:android="http://schemas.android.com/apk/res/android"
    android:delay="0.5"
    android:animationOrder="normal"
    android:animation="@anim/alpha"
    />

ViewGroup xml添加android:layoutAnimation属性

<com.whoislcj.animation.GridImageViewGroup
            android:id="@+id/image_layout"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:layout_margin="10dp"
            android:layoutAnimation="@anim/layoutanimation"
            lee:childHorizontalSpace="10dp"
            lee:childVerticalSpace="10dp"
            lee:columnNum="3"/>

由于这种方式采用的是补间动画，个人不再推荐使用这种方式，原因很简单实现的动画效果相对单一。

总结：

   本篇学习了布局动画，自此Android的动画学习也将告一段落了，接下来准备总结一下学习动画的过程中遇见的编程知识，比如链式编程，TreadLocal等。