FlowLayout实现

package com.loaderman.customviewdemo;

import android.content.Context;
import android.util.AttributeSet;
import android.view.View;
import android.view.ViewGroup;

public class FlowLayout extends ViewGroup {
    public FlowLayout(Context context) {
        super(context);
    }

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

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

    /**
     * 父容器生成 子view 的布局LayoutParams;
     * 一句话道出LayoutParams的本质：LayoutParams是Layout提供给其中的Children使用的。
     * 如果要自定义ViewGroup支持子控件的layout_margin参数，则自定义的ViewGroup类必须重载generateLayoutParams()函数，
     * 并且在该函数中返回一个ViewGroup.MarginLayoutParams派生类对象，这样才能使用margin参数。
     */
    @Override
    protected LayoutParams generateLayoutParams(
            LayoutParams p)
    {
        return new MarginLayoutParams(p);
    }

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

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

    @Override
    protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
        super.onMeasure(widthMeasureSpec, heightMeasureSpec);
        int measureWidth = MeasureSpec.getSize(widthMeasureSpec);
        int measureHeight = MeasureSpec.getSize(heightMeasureSpec);
        int measureWidthMode = MeasureSpec.getMode(widthMeasureSpec);
        int measureHeightMode = MeasureSpec.getMode(heightMeasureSpec);

        int lineWidth = 0;
        int lineHeight = 0;
        int height = 0;
        int width = 0;
        int count = getChildCount();
        for (int i=0;i<count;i++){
            View child = getChildAt(i);
            measureChild(child,widthMeasureSpec,heightMeasureSpec);
            //如果忘记重写generateLayoutParams，则hild.getLayoutParams()将不是MarginLayoutParams的实例
            //在强制转换时就会出错，此时我们把左右间距设置为0，但由于在计算布局宽高时没有加上间距值，就是计算出的宽高要比实际小，所以是onLayout时就会出错
            MarginLayoutParams lp = null;
            if (child.getLayoutParams() instanceof MarginLayoutParams) {
                lp = (MarginLayoutParams) child
                        .getLayoutParams();
            }else{
                lp = new MarginLayoutParams(0,0);
            }
            int childWidth = child.getMeasuredWidth() + lp.leftMargin +lp.rightMargin;
            int childHeight = child.getMeasuredHeight() + lp.topMargin + lp.bottomMargin;

            if (lineWidth + childWidth > measureWidth){
                //需要换行
                width = Math.max(lineWidth,width);
                height += lineHeight;
                //因为由于盛不下当前控件，而将此控件调到下一行，所以将此控件的高度和宽度初始化给lineHeight、lineWidth
                lineHeight = childHeight;
                lineWidth = childWidth;
            }else{
                // 否则累加值lineWidth,lineHeight取最大高度
                lineHeight = Math.max(lineHeight,childHeight);
                lineWidth += childWidth;
            }

            //最后一行是不会超出width范围的，所以要单独处理
            if (i == count -1){
                height += lineHeight;
                width = Math.max(width,lineWidth);
            }

        }
        //当属性是MeasureSpec.EXACTLY时，那么它的高度就是确定的，
        // 只有当是wrap_content时，根据内部控件的大小来确定它的大小时，大小是不确定的，属性是AT_MOST,此时，就需要我们自己计算它的应当的大小，并设置进去
        setMeasuredDimension((measureWidthMode == MeasureSpec.EXACTLY) ? measureWidth
                : width, (measureHeightMode == MeasureSpec.EXACTLY) ? measureHeight
                : height);
    }

    @Override
    protected void onLayout(boolean changed, int l, int t, int r, int b) {
        int count = getChildCount();
        int lineWidth = 0;
        int lineHeight = 0;
        int top=0,left=0;
        for (int i=0; i<count;i++){
            View child = getChildAt(i);
            MarginLayoutParams lp = (MarginLayoutParams) child
                    .getLayoutParams();
            int childWidth = child.getMeasuredWidth()+lp.leftMargin+lp.rightMargin;
            int childHeight = child.getMeasuredHeight()+lp.topMargin+lp.bottomMargin;

            if (childWidth + lineWidth >getMeasuredWidth()){
                //如果换行,当前控件将跑到下一行，从最左边开始，所以left就是0，而top则需要加上上一行的行高，才是这个控件的top点;
                top += lineHeight;
                left = 0;
                //同样，重新初始化lineHeight和lineWidth
                lineHeight = childHeight;
                lineWidth = childWidth;
            }else{
                lineHeight = Math.max(lineHeight,childHeight);
                lineWidth += childWidth;
            }
            //计算childView的left,top,right,bottom
            int lc = left + lp.leftMargin;
            int tc = top + lp.topMargin;
            int rc =lc + child.getMeasuredWidth();
            int bc = tc + child.getMeasuredHeight();
            child.layout(lc, tc, rc, bc);//布局控件
            //将left置为下一子控件的起始点
            left+=childWidth;
        }

    }

}

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:background="#ff00ff"
    tools:context=".MainActivity">

    <com.loaderman.customviewdemo.FlowLayout
        android:layout_width="wrap_content"
        android:layout_height="wrap_content">
        <TextView
            style="@style/text_flag_01"
            android:background="@drawable/flag_03"
            android:text="Welcome"
            android:textColor="@android:color/white" />

        <TextView
            style="@style/text_flag_01"
            android:background="@drawable/flag_03"
            android:text="IT工程师"
            android:textColor="@android:color/white" />

        <TextView
            style="@style/text_flag_01"
            android:background="@drawable/flag_03"
            android:text="我真是可以的"
            android:textColor="@android:color/white" />

        <TextView
            style="@style/text_flag_01"
            android:background="@drawable/flag_03"
            android:text="你觉得呢"
            android:textColor="@android:color/white" />

        <TextView
            style="@style/text_flag_01"
            android:background="@drawable/flag_03"
            android:text="不要只知道挣钱"
            android:textColor="@android:color/white" />

        <TextView
            style="@style/text_flag_01"
            android:background="@drawable/flag_03"
            android:text="努力ing"
            android:textColor="@android:color/white" />

        <TextView
            style="@style/text_flag_01"
            android:background="@drawable/flag_03"
            android:text="I thick i can"
            android:textColor="@android:color/white" />
    </com.loaderman.customviewdemo.FlowLayout>
</LinearLayout>

效果: