流式布局初探

hackernew

发布于 2021-2-25 09:56

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背景

最近项目中用到了流式布局，最初就决定自己写一个，发现一时竟然没有思路。虽然自定义控件的博客看了不少，也写过简单的自定义控件，但是真正自己独立写出一个流式布局，还是有些考验的。查找了几篇博客，思路大同小异，理清思路，自己开干写了一下。中间改了几个问题，觉得可以正常使用后，这才有了这篇博客。

我想说，会写流式布局了，表示你对ViewGroup的测量（onMeasure）和布局（onLayout）有了一个较为深入的理解。流式布局主要涉及ViewGroup对子View的测量和摆放（布局）。流式布局初探-鸿蒙开发者社区

效果图

参考布局

参考布局，尺寸和颜色根据自己需求修改：

<com.istarshine.views.MFlowLayout
    android:id="@+id/flow_search_history"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:layout_marginLeft="@dimen/common_margin"
    android:layout_marginTop="2dp"
    android:layout_marginRight="18dp">


    <TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginLeft="6dp"
        android:layout_marginTop="6dp"
        android:background="@drawable/shape_solid_ff"
        android:paddingLeft="@dimen/common_margin"
        android:paddingTop="4dp"
        android:paddingRight="@dimen/common_margin"
        android:paddingBottom="4dp"
        android:text="鞋子"
        android:textColor="@color/common_text_22"
        android:textSize="@dimen/text_size_14" />

    <TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginLeft="6dp"
        android:layout_marginTop="6dp"
        android:background="@drawable/shape_solid_ff"
        android:paddingLeft="@dimen/common_margin"
        android:paddingTop="4dp"
        android:paddingRight="@dimen/common_margin"
        android:paddingBottom="4dp"
        android:text="吹风机"
        android:textColor="@color/common_text_22"
        android:textSize="@dimen/text_size_14" />

    <TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginLeft="6dp"
        android:layout_marginTop="6dp"
        android:background="@drawable/shape_solid_ff"
        android:paddingLeft="@dimen/common_margin"
        android:paddingTop="4dp"
        android:paddingRight="@dimen/common_margin"
        android:paddingBottom="4dp"
        android:text="袜子 男 纯棉"
        android:textColor="@color/common_text_22"
        android:textSize="@dimen/text_size_14" />

    <TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginLeft="6dp"
        android:layout_marginTop="6dp"
        android:background="@drawable/shape_solid_ff"
        android:paddingLeft="@dimen/common_margin"
        android:paddingTop="4dp"
        android:paddingRight="@dimen/common_margin"
        android:paddingBottom="4dp"
        android:text="豆浆机 九阳"
        android:textColor="@color/common_text_22"
        android:textSize="@dimen/text_size_14" />


    <TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginLeft="6dp"
        android:layout_marginTop="6dp"
        android:background="@drawable/shape_solid_ff"
        android:paddingLeft="@dimen/common_margin"
        android:paddingTop="4dp"
        android:paddingRight="@dimen/common_margin"
        android:paddingBottom="4dp"
        android:text="三只松鼠"
        android:textColor="@color/common_text_22"
        android:textSize="@dimen/text_size_14" />

    <TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginLeft="6dp"
        android:layout_marginTop="6dp"
        android:background="@drawable/shape_solid_ff"
        android:paddingLeft="@dimen/common_margin"
        android:paddingTop="4dp"
        android:paddingRight="@dimen/common_margin"
        android:paddingBottom="4dp"
        android:text="三只松鼠 三只松鼠  三只松鼠  三只松鼠  三只松鼠  三只松鼠  三只松鼠"
        android:textColor="@color/common_text_22"
        android:textSize="@dimen/text_size_14" />

    <TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginLeft="6dp"
        android:layout_marginTop="6dp"
        android:background="@drawable/shape_solid_ff"
        android:paddingLeft="@dimen/common_margin"
        android:paddingTop="4dp"
        android:paddingRight="@dimen/common_margin"
        android:paddingBottom="4dp"
        android:text="刮皮刀 水果刀"
        android:textColor="@color/common_text_22"
        android:textSize="@dimen/text_size_14" />


</com.istarshine.views.MFlowLayout>

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MFlowLayout 代码

在 onMeasure() 中测量子View，按流式布局算出MFlowLayout自己（ViewGroup）的宽高；在 onLayout()中按流式布局准确摆放子View。见如下代码：

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

/**
 * 流式布局
 */
public class MFlowLayout extends ViewGroup {

    public MFlowLayout(Context context) {
        super(context);
    }

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

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

    @Override
    protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
//        super.onMeasure(widthMeasureSpec, heightMeasureSpec);
        //测量所有的子元素（调用子元素的measure()），
        // 只有测量过的元素调用child.getMeasuredHeight/Width()才能获取到值，否则为0
//        measureChildren(widthMeasureSpec, heightMeasureSpec);

        int widthSize = MeasureSpec.getSize(widthMeasureSpec);
        int widthMode = MeasureSpec.getMode(widthMeasureSpec);
        int heightSize = MeasureSpec.getSize(heightMeasureSpec);
        int heightMode = MeasureSpec.getMode(heightMeasureSpec);

        int spaceWidth = widthSize - getPaddingLeft() - getPaddingRight();

        int resultWidth = 0;
        int resultHeight = 0;
        int lineWidth = 0;
        int lineHeight = 0;
        for (int i = 0; i < getChildCount(); i++) {
            View child = getChildAt(i);
            if (child.getVisibility() == View.GONE) {
                continue;
            }
            //测量每个子元素的宽高
            int widthUsed = getPaddingLeft() + getPaddingRight();
            int heightUsed = getPaddingTop() + getPaddingBottom();
            measureChildWithMargins(child, widthMeasureSpec, widthUsed, heightMeasureSpec, heightUsed);
//            measureChild(child, widthMeasureSpec, heightMeasureSpec);
            //测量后的宽高
            int childWidth = child.getMeasuredWidth();
            int childHeight = child.getMeasuredHeight();

            //因为子View可能设置margin，这里要加上margin的距离
            MarginLayoutParams childMlp = (MarginLayoutParams) child.getLayoutParams();
            int childWidthWithMargin = childWidth + childMlp.leftMargin + childMlp.rightMargin;
            int childHeightWithMargin = childHeight + childMlp.topMargin + childMlp.bottomMargin;

            //一行放不下了，就换行
            if (lineWidth + childWidthWithMargin > spaceWidth) {
                //换行，计算宽高
                resultWidth = Math.max(resultWidth, lineWidth);
                resultHeight += lineHeight;
                //换行结束，重新给lineWidth和lineHeight赋值
                lineWidth = childWidthWithMargin;
                lineHeight = childHeightWithMargin;
            } else {
                //不换行，宽度直接相加
                lineWidth += childWidthWithMargin;
                //高度取二者最大值
                lineHeight = Math.max(lineHeight, childHeightWithMargin);

            }

            //最后一个肯定是最后一行
            if (i == getChildCount() - 1) {
                resultWidth = Math.max(resultWidth, lineWidth);
                resultHeight += lineHeight;
            }

        }

        //因为上面resultWidth参与了宽度比较，所以计算padding必须放在这里
        resultWidth += getPaddingLeft() + getPaddingRight();
        resultHeight += getPaddingTop() + getPaddingBottom();

        //设置FlowLayout的宽高
        setMeasuredDimension(widthMode == MeasureSpec.EXACTLY ? widthSize : resultWidth,
                heightMode == MeasureSpec.EXACTLY ? heightSize : resultHeight);


    }

    @Override
    protected void onLayout(boolean changed, int l, int t, int r, int b) {
        int spaceWidth = getWidth() - getPaddingLeft() - getPaddingRight();
        int paddingTop = getPaddingTop();
        int paddingLeft = getPaddingLeft();
        int childLeft = 0;
        int childTop = 0;

        int lineHeight = 0;
        for (int i = 0; i < getChildCount(); i++) {
            View child = getChildAt(i);

            if (child.getVisibility() == View.GONE) {
                continue;
            }

            int childWidth = child.getMeasuredWidth();
            int childHeight = child.getMeasuredHeight();
            MarginLayoutParams childMlp = (MarginLayoutParams) child.getLayoutParams();
            int childWidthWithMargin = childWidth + childMlp.leftMargin + childMlp.rightMargin;
            int childHeightWithMargin = childHeight + childMlp.topMargin + childMlp.bottomMargin;

            if (childLeft + childWidthWithMargin > spaceWidth) {
                childTop += lineHeight;

                //换行处理
                childLeft = 0;
                lineHeight = childHeightWithMargin;
            } else {
                lineHeight = Math.max(lineHeight, childHeightWithMargin);

            }
            int left = childLeft + paddingLeft + childMlp.leftMargin;
            int top = childTop + paddingTop + childMlp.topMargin;
            int right = left + childWidth;
            int bottom = top + childHeight;
            child.layout(left, top, right, bottom);

            childLeft += childWidthWithMargin;

        }

    }


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

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

    @Override
    public void setLayoutParams(LayoutParams params) {
        super.setLayoutParams(params);
    }

    @Override
    protected boolean checkLayoutParams(LayoutParams p) {
        return p instanceof MarginLayoutParams;
    }
}

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如果想要MFlowLayout可以设置padding，子View可以设置margin，就需要使用measureChildWithMargins(child, widthMeasureSpec, widthUsed,

heightMeasureSpec, heightUsed)，这样就会在测量的时候把MFlowLayout设置的padding（wideUsed，heightUsed）和子View设置的margin计算在内。而子View可以设置margin，则需要MarginLayoutParams，具体见上面代码。

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Android 自定义

已于2021-2-25 09:56:12修改

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流式布局初探

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