序言

做电商的都知道，作为商品的一种售卖方式，拼团是是提供商品售卖的一种及时有效的方式，而在拼团市场中，拼多多无疑是做的最好的一家。于是，研究拼多多的售卖方式之后，我们的产品也开始了这方面的开发。本文将要给大家介绍的就是通过自定义的方式实现堆叠头像，这种效果在直播app中非常常见。下面是部分效果：

通过分析，上面是一个使用ViewPager实现的一个可以左右无线循环的Galllery，相关实现可以访问我之前的介绍：PageTransformer使用简介下面是一个列表的方式，可以通过下拉来加载更多的Cell数据，也比较简单。对于组合头像的实现也是比较简单的，其实就是一个简单的流式布局，在本篇实现上，本文也参考了张鸿洋的FlowLayout，对于流式布局来说，只要按照某种线性规则依次排列即可。

我相信很多朋友之前一定遇到过这种需求:富文本自动换行，如下所示：

要实现这种富文本换行，最重要的就是对onMeasure方法，通常的做法是，测量出子View的宽度，当大于屏幕的宽度的时候就换行（当然，需要考虑文字本来就很长，一行显示不下的情况）。相关代码如下：

@Override
    protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
        super.onMeasure(widthMeasureSpec, heightMeasureSpec);

        int widthSpecMode = MeasureSpec.getMode(widthMeasureSpec);
        int widthSpecSize = MeasureSpec.getSize(widthMeasureSpec);
        int heightSpecMode = MeasureSpec.getMode(heightMeasureSpec);
        int heightSpecSize = MeasureSpec.getSize(heightMeasureSpec);
       

        //AT_MOST
        int width = 0;
        int height = 0;
        int rawWidth = 0;//当前行总宽度
        int rawHeight = 0;// 当前行高

        int count = getChildCount();
        for (int i = 0; i < count; i++) {
            View child = getChildAt(i);
            if(child.getVisibility() == GONE){
                if(i == count - 1){
                    //最后一个child
                    height += rawHeight;
                    width = Math.max(width, rawWidth);
                }
                continue;
            }

            measureChild(child, widthMeasureSpec, heightMeasureSpec);
            MarginLayoutParams lp = (MarginLayoutParams) child.getLayoutParams();

            int childWidth = child.getMeasuredWidth()  + lp.leftMargin + lp.rightMargin;
            int childHeight = child.getMeasuredHeight() + lp.topMargin + lp.bottomMargin;
            Log.e("=====", "childWidth 1: " + childWidth);
            if(rawWidth + childWidth > widthSpecSize - getPaddingLeft() - getPaddingRight()){
                //换行
                width = Math.max(width, rawWidth);
                rawWidth = childWidth;
                height += rawHeight;
                rawHeight = childHeight;
            } else {
                rawWidth += childWidth;
                rawHeight = Math.max(rawHeight, childHeight);
            }

            if(i == count - 1){
                width = Math.max(rawWidth, width);
                height += rawHeight;
            }
        }

        setMeasuredDimension(
                widthSpecMode == MeasureSpec.EXACTLY ? widthSpecSize : width + getPaddingLeft() + getPaddingRight(),
                heightSpecMode == MeasureSpec.EXACTLY ? heightSpecSize : height + getPaddingTop() + getPaddingBottom()
        );
    }

实现

说了这么多，那么具体怎么实现的呢？由于时间关系，这里我就直接贴代码了。首先自定义ViewGrop，实现后一个头像会覆盖一部分到前一个头像上，为了方便使用者控制堆叠头像的重叠大小，我们通过自定义属性来解决。

PileView.java

public class PileView extends ViewGroup {

    protected float vertivalSpace;//垂直间隙
    protected float pileWidth=0;//重叠宽度

    public PileView(Context context) {
        this(context, null, 0);
    }

    public PileView(Context context, AttributeSet attrs) {
        this(context, attrs, 0);
    }

    public PileView(Context context, AttributeSet attrs, int defStyleAttr) {
        super(context, attrs, defStyleAttr);
        initAttr(context, attrs);
    }

    private void initAttr(Context context, AttributeSet attrs) {
        TypedArray ta = context.obtainStyledAttributes(attrs, R.styleable.PileLayout);
        vertivalSpace = ta.getDimension(R.styleable.PileLayout_PileLayout_vertivalSpace, dp2px(4));
        pileWidth = ta.getDimension(R.styleable.PileLayout_PileLayout_pileWidth, dp2px(10));
        ta.recycle();
    }


    @Override
    protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
        super.onMeasure(widthMeasureSpec, heightMeasureSpec);

        int widthSpecMode = MeasureSpec.getMode(widthMeasureSpec);
        int widthSpecSize = MeasureSpec.getSize(widthMeasureSpec);
        int heightSpecMode = MeasureSpec.getMode(heightMeasureSpec);
        int heightSpecSize = MeasureSpec.getSize(heightMeasureSpec);

        //AT_MOST
        int width = 0;
        int height = 0;
        int rawWidth = 0;//当前行总宽度
        int rawHeight = 0;// 当前行高

        int rowIndex = 0;//当前行位置
        int count = getChildCount();
        for (int i = 0; i < count; i++) {
            View child = getChildAt(i);
            if(child.getVisibility() == GONE){
                if(i == count - 1){
                    //最后一个child
                    height += rawHeight;
                    width = Math.max(width, rawWidth);
                }
                continue;
            }

            //调用measureChildWithMargins 而不是measureChild
            measureChildWithMargins(child, widthMeasureSpec, 0, heightMeasureSpec, 0);
            MarginLayoutParams lp = (MarginLayoutParams) child.getLayoutParams();

            int childWidth = child.getMeasuredWidth()  + lp.leftMargin + lp.rightMargin;
            int childHeight = child.getMeasuredHeight() + lp.topMargin + lp.bottomMargin;
            if(rawWidth + childWidth  - (rowIndex > 0 ? pileWidth : 0)> widthSpecSize - getPaddingLeft() - getPaddingRight()){
                //换行
                width = Math.max(width, rawWidth);
                rawWidth = childWidth;
                height += rawHeight + vertivalSpace;
                rawHeight = childHeight;
                rowIndex = 0;
            } else {
                rawWidth += childWidth;
                if(rowIndex > 0){
                    rawWidth -= pileWidth;
                }
                rawHeight = Math.max(rawHeight, childHeight);
            }

            if(i == count - 1){
                width = Math.max(rawWidth, width);
                height += rawHeight;
            }

            rowIndex++;
        }

        setMeasuredDimension(
                widthSpecMode == MeasureSpec.EXACTLY ? widthSpecSize : width + getPaddingLeft() + getPaddingRight(),
                heightSpecMode == MeasureSpec.EXACTLY ? heightSpecSize : height + getPaddingTop() + getPaddingBottom()
        );
    }

    @Override
    protected void onLayout(boolean changed, int l, int t, int r, int b) {
        int viewWidth = r - l;
        int leftOffset = getPaddingLeft();
        int topOffset = getPaddingTop();
        int rowMaxHeight = 0;
        int rowIndex = 0;//当前行位置
        View childView;
        for( int w = 0, count = getChildCount(); w < count; w++ ){
            childView = getChildAt(w);
            if(childView.getVisibility() == GONE) continue;

            MarginLayoutParams lp = (MarginLayoutParams) childView.getLayoutParams();
            // 如果加上当前子View的宽度后超过了ViewGroup的宽度，就换行
            int occupyWidth = lp.leftMargin + childView.getMeasuredWidth() + lp.rightMargin;
            if(leftOffset + occupyWidth + getPaddingRight() > viewWidth){
                leftOffset = getPaddingLeft();  // 回到最左边
                topOffset += rowMaxHeight + vertivalSpace;  // 换行
                rowMaxHeight = 0;

                rowIndex = 0;
            }

            int left = leftOffset + lp.leftMargin;
            int top = topOffset + lp.topMargin;
            int right = leftOffset+ lp.leftMargin + childView.getMeasuredWidth();
            int bottom =  topOffset + lp.topMargin + childView.getMeasuredHeight();
            childView.layout(left, top, right, bottom);

            // 横向偏移
            leftOffset += occupyWidth;
            // 试图更新本行最高View的高度
            int occupyHeight = lp.topMargin + childView.getMeasuredHeight() + lp.bottomMargin;
            if(rowIndex != count - 1){
                leftOffset -= pileWidth;
            }
            rowMaxHeight = Math.max(rowMaxHeight, occupyHeight);
            rowIndex++;
        }
    }

    @Override
    public LayoutParams generateLayoutParams(AttributeSet attrs) {
        return new MarginLayoutParams(getContext(), attrs);
    }

    @Override
    protected LayoutParams generateDefaultLayoutParams() {
        return new MarginLayoutParams(LayoutParams.WRAP_CONTENT, LayoutParams.WRAP_CONTENT);
    }

    @Override
    protected LayoutParams generateLayoutParams(LayoutParams p) {
        return new MarginLayoutParams(p);
    }

    public float dp2px(float dpValue) {
        return TypedValue.applyDimension(TypedValue.COMPLEX_UNIT_DIP, dpValue, getResources().getDisplayMetrics());
    }
}

自定义的属性如下：

<declare-styleable name="PileLayout">
        <attr name="PileLayout_vertivalSpace" format="dimension"/>
        <attr name="PileLayout_pileWidth" format="dimension"/>
    </declare-styleable>

为了方便用户使用，我们在PileView的基础上再封装一下，封装完成后，只需要用户提供数据源即可实现头像堆叠。例如，下面的代码给控件设置数据源即可：

List<String> urls=new ArrayList<>();
        urls.clear();
        urls.add("http://ohe65w0xx.bkt.clouddn.com/u=2263418180,3668836868&fm=206&gp=0.jpg");
        urls.add("http://ohe65w0xx.bkt.clouddn.com/u=3637404049,2821183587&fm=214&gp=0.jpg");
       urls.add("http://ohe65w0xx.bkt.clouddn.com/avert.png");
//设置数据源
itemAvertView.setAvertImages(urls);

要完成上面的封装，主要会涉及如下的代码： PileAvertView.java

public class PileAvertView extends LinearLayout {

    @BindView(R.id.pile_view)
    PileView pileView;

    private Context context = null;
    public static final int VISIBLE_COUNT = 3;//默认显示个数

    public PileAvertView(Context context) {
        this(context, null);
        this.context = context;
    }

    public PileAvertView(Context context, AttributeSet attrs) {
        super(context, attrs);
        this.context = context;
        initView();
    }

    private void initView() {
        View view = LayoutInflater.from(context).inflate(R.layout.layout_group_pile_avert, this);
        ButterKnife.bind(view);
    }

    public void setAvertImages(List<String> imageList) {
        setAvertImages(imageList,VISIBLE_COUNT);
    }

    //如果imageList>visiableCount,显示List最上面的几个
    public void setAvertImages(List<String> imageList, int visibleCount) {
        List<String> visibleList = null;
        if (imageList.size() > visibleCount) {
            visibleList = imageList.subList(imageList.size() - 1 - visibleCount, imageList.size() - 1);
        }
        pileView.removeAllViews();
        for (int i = 0; i < imageList.size(); i++) {
            CircleImageView image= (CircleImageView) LayoutInflater.from(context).inflate(R.layout.item_group_round_avert, pileView, false);
            CommonImageUtil.loadImage(imageList.get(i), image);
            pileView.addView(image);
        }
    }

}

相关的布局： layout_group_pile_avert.xml

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:gravity="center_horizontal">

    <com.lanshan.shihuicommunity.grouppurchase.view.PileView
        android:id="@+id/pile_view"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        app:PileLayout_pileWidth="10dp"/>
</LinearLayout>

item_group_round_avert.xml

<?xml version="1.0" encoding="utf-8"?>
<com.makeramen.rounded.CircleImageView xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    android:id="@+id/circle_iamge"
    android:layout_width="30dp"
    android:layout_height="30dp"
    android:orientation="vertical"
    app:round_borderColor="#ffffff"
    app:round_borderWidth="1dp" />

Android仿拼多多拼团堆叠头像

序言

实现