时光荏苒，岁月如梭，不知不觉已有一年之久没写过文章，都生疏了（其实是不会写）

8cd85996d9ac394179ee3bed.jpg

刚好最近有一个连线题的需求，经过连夜奋战终于给肝出来了，感觉写的也还行，就想着分享出来，于是就有了这篇文章，如果有问题还希望大家能指出来~废话不多说，先放一张效果图：

效果图.png

实现思路

首先确定是自定义ViewGroup，两列view的边缘中点作为线的起始点，view的宽高最好统一，方便计算坐标。另外具体业务的数据和UI界面各有不同，所以不能约束太死，要做到解耦，还得用泛型。
github地址：https://github.com/zaaach/LineMatchingView，可以直接去看完整代码。

敲代码

①定义一条线，因为只在内部使用，就用内部类即可，记录起始坐标、颜色、连接左右view的索引

private static class Line {
    public float startX;
    public float startY;
    public float endX;
    public float endY;
    public int color;
    public int start;
    public int end;
}

②对数据和view进行封装

private class LinkableWrapper {
    public Line line;
    public float pointX;
    public float pointY;
    public boolean lined;
    public View view;
    public T item;
}

③对外提供接口，用于UI和数据的绑定。这里算是借鉴了RecyclerView的adpater，为了让两列view展示的更灵活一些，增加了itemType

public interface LinkableAdapter<T> {
    View getView(T item, ViewGroup parent, int itemType, int position);
    int getItemType(T item, int position);
    void onBindView(T item, View view, int position);
    void onItemStateChanged(T item, View view, int state, int position);
    boolean isCorrect(T left, T right, int l, int r);
}

主菜来了，自定义ViewGroup

public class LineMatchingView<T> extends ViewGroup {
    //item state
    public static final int NORMAL  = 100;
    public static final int CHECKED = 101;
    public static final int LINED   = 102;
    public static final int CORRECT = 103;
    public static final int ERROR   = 104;
    
    private List<LinkableWrapper> leftItems;
    private List<LinkableWrapper> rightItems;
    private final List<Line> oldLines = new ArrayList<>();//需要移除的线
    private final List<Line> newLines = new ArrayList<>();//需要画的线
    private LinkableAdapter<T> linkableAdapter;
}

然后就是onMeasure()和onLayout()两步走，在测量之前，先设置数据

public LineMatchingView<T> init(@NonNull LinkableAdapter<T> adapter){
    this.linkableAdapter = adapter;
    return this;
}

public void setItems(@NonNull List<T> left, @NonNull List<T> right){
    if (linkableAdapter == null) {
        throw new IllegalStateException("LinkableAdapter must not be null, please see method setLinkableAdapter()");
    }
    leftItems = new ArrayList<>();
    rightItems = new ArrayList<>();
    addItems(left, true);
    addItems(right, false);
    resultSize = Math.min(leftItems.size(), rightItems.size());
}

private void addItems(List<T> list, boolean isLeft){
    for (int i = 0; i < list.size(); i++) {
        T item = list.get(i);
        //生成view并添加到控件
        int type = linkableAdapter.getItemType(item, i);
        View view = linkableAdapter.getView(item, this, type, i);
        addView(view);
        int index = i;
        view.setOnClickListener(new OnClickListener() {
            @Override
            public void onClick(View v) {
                if (finished) return;
                if (isLeft) {
                    //先恢复上个点击的item状态
                    if (currLeftChecked >= 0) {
                        notifyItemStateChanged(currLeftChecked, leftItems.get(currLeftChecked).lined ? LINED : NORMAL, true);
                    }
                    if (currLeftChecked == index) {
                        currLeftChecked = -1;
                    } else {
                        currLeftChecked = index;
                        notifyItemStateChanged(index, CHECKED, true);
                        drawLineBetween(currLeftChecked, currRightChecked);
                    }
                }else {
                    if (currRightChecked >= 0) {
                        notifyItemStateChanged(currRightChecked, rightItems.get(currRightChecked).lined ? LINED : NORMAL, false);
                    }
                    if (currRightChecked == index){
                        currRightChecked = -1;
                    }else {
                        currRightChecked = index;
                        notifyItemStateChanged(index, CHECKED, false);
                        drawLineBetween(currLeftChecked, currRightChecked);
                    }
                }
            }
        });
        LinkableWrapper wrapper = new LinkableWrapper();
        wrapper.item = item;
        wrapper.view = view;
        if (isLeft){
            leftItems.add(wrapper);
        }else {
            rightItems.add(wrapper);
        }
    }
}

开始测量，分别测量左右两列view，计算出两列的最大宽度之和以及最大高度

@Override
protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
    int width = MeasureSpec.getSize(widthMeasureSpec);
    int height = MeasureSpec.getSize(heightMeasureSpec);

    int[] measuredLeftSize = measureColumn(leftItems, widthMeasureSpec, heightMeasureSpec);
    int measuredLeftWidth = measuredLeftSize[0];
    int measuredLeftHeight = measuredLeftSize[1];
    leftMaxWidth = measuredLeftSize[0];

    int[] measuredRightSize = measureColumn(rightItems, widthMeasureSpec, heightMeasureSpec);
    int measuredRightWidth = measuredRightSize[0];
    int measuredRightHeight = measuredRightSize[1];

    int wMode = MeasureSpec.getMode(widthMeasureSpec);
    int hMode = MeasureSpec.getMode(heightMeasureSpec);
    setMeasuredDimension(
            wMode == MeasureSpec.EXACTLY ? width : measuredLeftWidth + measuredRightWidth + getPaddingLeft() + getPaddingRight() + horizontalPadding,
            hMode == MeasureSpec.EXACTLY ? height : Math.max(measuredLeftHeight, measuredRightHeight) + getPaddingTop() + getPaddingBottom());
}

private int[] measureColumn(List<LinkableWrapper> list, int widthMeasureSpec, int heightMeasureSpec){
    int measuredWidth = 0;
    int measuredHeight = 0;
    for (int i = 0; i < list.size(); i++) {
        LinkableWrapper wrapper = list.get(i);
        View child = wrapper.view;
        LayoutParams lp = child.getLayoutParams();
        if (lp != null){
            if (itemWidth > 0){
                lp.width = itemWidth;
            }
            if (itemHeight > 0){
                lp.height = itemHeight;
            }
        }
        measureChild(child, widthMeasureSpec, heightMeasureSpec);
        measuredWidth = Math.max(measuredWidth, child.getMeasuredWidth());
        measuredHeight += child.getMeasuredHeight() + (i > 0 ? verticalPadding : 0);
    }
    return new int[]{measuredWidth, measuredHeight};
}

测量完毕之后开始布局，同时通过接口进行view的数据绑定

private void doLayout(List<LinkableWrapper> list, int left, int top, boolean isLeft){
    if (list == null) return;
    for (int i = 0; i < list.size(); i++) {
        LinkableWrapper wrapper = list.get(i);
        View view = wrapper.view;
        int w = view.getMeasuredWidth();
        int h = view.getMeasuredHeight();
        view.layout(left, top, left + w, top + h);
        if (linkableAdapter != null){
            linkableAdapter.onBindView(wrapper.item, view, i);
        }
        wrapper.pointX = isLeft ? left + w : left;
        wrapper.pointY = top + h / 2f;
        top += h + verticalPadding;
    }
}

最后就是关键的画线部分，需要重写dispatchDraw()方法。在画线之前，如果两边view连过线，需要先擦掉然后再画新的线，分别用两个列表oldLines和newLines记录这些线，擦掉就是把paint的color设置透明。具体操作：先把旧的line添加到oldLines中，再从newLines中移除，这里如果两条线的起始点坐标一样就视为同一条线。

private void drawLineBetween(int leftIndex, int rightIndex){
    if (leftIndex < 0 || rightIndex < 0) return;
    //移除旧的连线
    LinkableWrapper leftItem = leftItems.get(leftIndex);
    if (leftItem.lined){
        Line oldLine = leftItem.line;
        if (oldLine != null){
            oldLines.add(oldLine);
            setLined(oldLine.end, false, false);
            notifyItemStateChanged(oldLine.end, NORMAL, false);
        }
    }
    LinkableWrapper rightItem = rightItems.get(rightIndex);
    if (rightItem.lined){
        Line oldLine = rightItem.line;
        if (oldLine != null){
            oldLines.add(oldLine);
            setLined(oldLine.start, false, true);
            notifyItemStateChanged(oldLine.start, NORMAL, true);
        }
    }
    if (leftItem.lined || rightItem.lined) {
        for (Iterator<Line> iterator = newLines.iterator(); iterator.hasNext(); ) {
            Line line = iterator.next();
            if (line.equals(leftItem.line) || line.equals(rightItem.line)) {
                iterator.remove();
            }
        }
    }
    //生成新的连线
    Line newLine = new Line(leftItem.pointX, leftItem.pointY, rightItem.pointX, rightItem.pointY);
    newLine.start = leftIndex;
    newLine.end = rightIndex;
    newLine.color = lineNormalColor;
    newLines.add(newLine);
    leftItem.lined = true;
    rightItem.lined = true;
    notifyItemStateChanged(leftIndex, LINED, true);
    notifyItemStateChanged(rightIndex, LINED, false);
    //重置
    currLeftChecked = -1;
    currRightChecked = -1;
    if (resultSize == newLines.size()){
        finished = true;
        checkResult();
    }
    invalidate();
    leftItem.line = newLine;
    rightItem.line = newLine;
}

@Override
protected void dispatchDraw(Canvas canvas) {
    super.dispatchDraw(canvas);
    linePaint.setColor(Color.TRANSPARENT);
    for (Line line : oldLines) {
        canvas.drawLine(line.startX, line.startY, line.endX, line.endY, linePaint);
    }
    oldLines.clear();
    for (Line line : newLines) {
        linePaint.setColor(line.color);
        canvas.drawLine(line.startX, line.startY, line.endX, line.endY, linePaint);
    }
}

连线完成之后比对答案，是否正确也是通过接口让使用者去判断，这里只需要根据对错更新线的颜色和view的状态即可

private void checkResult() {
    for (Line line : newLines) {
        int l = line.start;
        int r = line.end;
        if (linkableAdapter != null){
            if (linkableAdapter.isCorrect(leftItems.get(l).item, rightItems.get(r).item, l, r)){
                line.color = lineCorrectColor;
                notifyItemStateChanged(l, CORRECT, true);
                notifyItemStateChanged(r, CORRECT, false);
            }else {
                line.color = lineErrorColor;
                notifyItemStateChanged(l, ERROR, true);
                notifyItemStateChanged(r, ERROR, false);
            }
        }
    }
}

OK、至此连线题的功能就全部实现了，使用时只需要调用init()和setItems()两个方法，很方便有没有~

再看下最终实现效果

line_matching_view.gif