FlowLayout

package com.xiangxue.nestedscroll.flowlayoutimport android.content.Contextimport android.content.res.Resourcesimport android.util.AttributeSetimport android.util.TypedValueimport android.view.Viewimport android.view.ViewGroupimport kotlin.math.max// 流式布局class FlowLayout(context: Context?, attrs: AttributeSet?) : ViewGroup(context, attrs) {    val TAG = "FLowLayout"    var mHorizontalSpacing = dp2px(16F) //每个item横向间距    var mVerticalSpacing = dp2px(8F) //每个item横向间距    // 记录所有的行， 一行一行的存储，用于layout    val allLines = arrayListOf<List<View>>()    // 记录每一行的行高，用于layout    val lineHeights = arrayListOf<Float>()    private fun clearMeasureParams() {        allLines.clear()        lineHeights.clear()    }    override fun onMeasure(widthMeasureSpec: Int, heightMeasureSpec: Int) {        //super.onMeasure(widthMeasureSpec, heightMeasureSpec)        //测量所有子View的宽高        clearMeasureParams() //内存抖动        //先度量孩子        // ViewGroup 解析的父亲给我的宽度        val selfWidth = MeasureSpec.getSize(widthMeasureSpec)        // ViewGroup 解析的父亲给我的高度        val selfHeight = MeasureSpec.getSize(heightMeasureSpec)        //保存一行中的所有的View        var lineViews = arrayListOf<View>() // 换行要重新赋值        // 记录这行已经使用了多宽的size        var lineWidthUsed = 0f        // 一行的行高        var lineHeight = 0f        var parentNeededWidth = 0f //measure过程中，子View要求的ViewGroup的宽        var parentNeededHeight = 0f //measure过程中，子View要求的ViewGroup的高        for (i in 0 until childCount) {            val childView = getChildAt(i)            val childLP = childView.layoutParams            if (childView.visibility != View.GONE) {                // 将layoutparams转变为measureSpec                val childWidthMeasureSpec = getChildMeasureSpec(widthMeasureSpec, paddingLeft + paddingRight, childLP.width)                val childHeightMeasureSpec = getChildMeasureSpec(heightMeasureSpec, paddingLeft + paddingRight, childLP.height)                childView.measure(childWidthMeasureSpec, childHeightMeasureSpec)                //获取子View的度量宽高                val childMeasuredWidth = childView.measuredWidth                val childMeasureHeight = childView.measuredHeight                //如果需要换行                if (childMeasuredWidth + lineWidthUsed + mHorizontalSpacing > selfWidth) {                    // 一旦换行，我们就可以判断当前行需要的宽和高了，所以此时要记录下来                    allLines.add(lineViews)                    lineHeights.add(lineHeight)                    parentNeededHeight += lineHeight + mVerticalSpacing                    parentNeededWidth = max(parentNeededHeight, lineWidthUsed + mHorizontalSpacing)                    lineViews = arrayListOf()                    lineWidthUsed = 0f // 一行已经用过的宽度                    lineHeight = 0f //一行的高度                }                // view是分行layout的，所以要记录每一行有哪些view， 这样可以方便layout布局                lineViews.add(childView)                //每行都会有自己的宽高                lineWidthUsed += childMeasuredWidth + mHorizontalSpacing                lineHeight = Math.max(lineHeight, childMeasureHeight.toFloat())                //处理最后一行数据                if (i == childCount - 1) {                    allLines.add(lineViews)                    lineHeights.add(lineHeight)                    parentNeededHeight += lineHeight + mVerticalSpacing                    parentNeededWidth = Math.max(parentNeededWidth, lineWidthUsed + mHorizontalSpacing)                }            }        }        // 再度量自己，保存        // 根据子View的度量结果，来重新度量自己的ViewGroup        // 作为一个ViewGroup， 它自己也是一个View， 它的大小也需要根据它的父亲给它提供的宽高来度量        val widthMode = MeasureSpec.getMode(widthMeasureSpec)        val heightMode = MeasureSpec.getMode(heightMeasureSpec)        //val realWidth = if (widthMode == MeasureSpec.EXACTLY) selfWidth else parentNeededWidth.toInt()        //val realHeight = if (heightMode == MeasureSpec.EXACTLY) selfHeight else parentNeededHeight.toInt()        setMeasuredDimension(selfWidth, selfHeight)    }    override fun onLayout(changed: Boolean, l: Int, t: Int, r: Int, b: Int) {        val lineCount = allLines.size        var curL = paddingLeft        var curT = paddingTop        for (i in 0 until lineCount) {            val lineViews = allLines.get(i)            val lineHeight = lineHeights.get(i)            for (view in lineViews) {                val right = curL + view.measuredWidth                val bottom = curT + view.measuredHeight                view.layout(curL, curT, right, bottom)                curL = right + mHorizontalSpacing.toInt()            }            curT += lineHeight.toInt() + mVerticalSpacing.toInt()            curL = paddingLeft        }    }    private fun dp2px(dp: Float): Float {        return TypedValue.applyDimension(TypedValue.COMPLEX_UNIT_DIP, dp, Resources.getSystem().displayMetrics)    }}
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