安卓自定义 ViewGroup 需要注意的地方
至少需要提供 width, 和height两个属性
同样地，如果要使用自定义的属性，那么就需要创建自己的名字空间，在Android Studio中，第三方的控件都使用如下代码来引入名字空间。
xmlns:custom="http://schemas.android.com/apk/res-auto"
流动布局手写精简版
- 增加了'center'居中等三种排列方式
- 额外支持padding属性
- layout_newline属性支持自定义换行(类似'\n'的换行效果)
参考
- 改写鸿洋_ http://blog.csdn.net/lmj623565791/article/details/38352503/
- 参考 FlexboxLayout 是针对 Android 平台的，实现类似 Flexbox 布局方案的一个开源项目，开源地址：https://github.com/google/flexbox-layout
下一步升级
- 逆序排列子 view
- 倒序排列子 view
- 使每行 view 均分剩余空间
- 可尝试增加目前流行的 tag 效果
FlowLayout.java
package cn.lik.view;
import java.util.ArrayList;
import java.util.List;
import cn.lik.R;
import android.content.Context;
import android.content.res.TypedArray;
import android.util.AttributeSet;
import android.util.Log;
import android.view.View;
import android.view.ViewGroup;
/**
* 流式布局
*
* @author l1k
*/
public class FlowLayout extends ViewGroup {
private static final String TAG = FlowLayout.class.getSimpleName();
private static final boolean DEBUG = false;
/**
* 存储所有的View，按行记录
*/
private ArrayList<List<View>> mAllViews = new ArrayList<List<View>>();
/**
* 记录每一行的最大高度
*/
private ArrayList<Integer> mLineHeight = new ArrayList<Integer>();
/**
* The current value of the {@link AlignItems}, the default value is
* {@link AlignItems#CENTER}.
*
* @see AlignItems
*/
private int mAlignItems;
public FlowLayout(Context context) {
this(context, null);
}
public FlowLayout(Context context, AttributeSet attrs) {
this(context, attrs, 0);
}
public FlowLayout(Context context, AttributeSet attrs, int defStyleAttr) {
super(context, attrs, defStyleAttr);
TypedArray a = context.obtainStyledAttributes(attrs, R.styleable.FlexLayout, defStyleAttr, 0);
mAlignItems = a.getInt(R.styleable.FlexLayout_alignItems, AlignItems.CENTER);
a.recycle();
}
@AlignItems
public int getAlignItems() {
return mAlignItems;
}
public void setAlignItems(@AlignItems int alignItems) {
if (mAlignItems != alignItems) {
mAlignItems = alignItems;
requestLayout();
}
}
@Override
protected ViewGroup.LayoutParams generateLayoutParams(ViewGroup.LayoutParams p) {
return new LayoutParams(p);
}
@Override
public ViewGroup.LayoutParams generateLayoutParams(AttributeSet attrs) {
return new LayoutParams(getContext(), attrs);
}
@Override
protected ViewGroup.LayoutParams generateDefaultLayoutParams() {
return new LayoutParams(LayoutParams.WRAP_CONTENT, LayoutParams.WRAP_CONTENT);
}
/**
* 负责设置子控件的测量模式和大小 根据所有子控件设置自己的宽和高
*/
@Override
protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
super.onMeasure(widthMeasureSpec, heightMeasureSpec);
// 获得它的父容器为它设置的测量模式和大小
int sizeWidth = MeasureSpec.getSize(widthMeasureSpec);
int sizeHeight = MeasureSpec.getSize(heightMeasureSpec);
int modeWidth = MeasureSpec.getMode(widthMeasureSpec);
int modeHeight = MeasureSpec.getMode(heightMeasureSpec);
if (DEBUG) {
Log.i(TAG, "onMeasure: sizeWidth = " + sizeWidth + ", sizeHeight = " + sizeHeight);
}
// 如果是warp_content情况下，记录宽和高
int width = 0;
int height = 0;
/**
* 记录每一行的宽度，width不断取最大宽度
*/
int lineWidth = 0;
/**
* 每一行的高度，累加至height
*/
int lineHeight = 0;
int cCount = getChildCount();
final int paddingHorizontal = getPaddingLeft() + getPaddingRight();
// 遍历每个子元素
for (int i = 0; i < cCount; i++) {
final View child = getChildAt(i);
// 测量每一个child的宽和高
measureChild(child, widthMeasureSpec, heightMeasureSpec);
// 得到child的lp
final LayoutParams lp = (LayoutParams) child.getLayoutParams();
// 当前子空间实际占据的宽度
int childWidth = child.getMeasuredWidth() + lp.leftMargin + lp.rightMargin;
// 当前子空间实际占据的高度
int childHeight = child.getMeasuredHeight() + lp.topMargin + lp.bottomMargin;
/**
* 如果加入当前child，则超出最大宽度，则的到目前最大宽度给width，累加height 然后开启新行
*/
if ((i!=0) && (lp.newline || (lineWidth + childWidth > sizeWidth - paddingHorizontal))) {
width = Math.max(Math.max(lineWidth, childWidth), width);// 取最大
lineWidth = childWidth; // 开启新行，记录宽度
// 叠加当前高度，
height += lineHeight;
// 开启记录下一行的高度
lineHeight = childHeight;// 开启新行, 记录高度
} else { // 否则累加值lineWidth,lineHeight取最大高度
lineWidth += childWidth;
lineHeight = Math.max(lineHeight, childHeight);
}
// 如果是最后一个，则将当前记录的最大宽度和当前lineWidth做比较
if (i == cCount - 1) {
width = Math.max(width, lineWidth);
height += lineHeight;
}
}
super.setMeasuredDimension((modeWidth == MeasureSpec.EXACTLY) ? sizeWidth
: width + getPaddingLeft() + getPaddingRight(),
(modeHeight == MeasureSpec.EXACTLY) ? sizeHeight
: height + getPaddingTop() + getPaddingBottom());
}
@Override
protected void onLayout(boolean changed, int l, int t, int r, int b) {
mAllViews.clear();
mLineHeight.clear();
int width = getWidth();
int lineWidth = 0;
int lineHeight = 0;
int left = getPaddingLeft();
int top = getPaddingTop();
final int paddingHorizontal = left + getPaddingRight();
// 存储每一行所有的childView
List<View> lineViews = new ArrayList<View>();
int cCount = getChildCount();
// 遍历所有的孩子
for (int i = 0; i < cCount; i++) {
final View child = getChildAt(i);
LayoutParams lp = (LayoutParams) child.getLayoutParams();
int childWidth = child.getMeasuredWidth() + lp.leftMargin + lp.rightMargin;
// 当前子空间实际占据的高度
int childHeight = child.getMeasuredHeight() + lp.topMargin + lp.bottomMargin;
// 如果已经需要换行
if ((i!=0) && (lp.newline || (childWidth + lineWidth > width - paddingHorizontal))) {
// 记录这一行所有的View以及最大高度
mLineHeight.add(lineHeight);
// 将当前行的childView保存，然后开启新的ArrayList保存下一行的childView
mAllViews.add(lineViews);
lineWidth = 0;// 重置宽
lineHeight = 0;//重置高
lineViews = new ArrayList<View>();
}
/**
* 如果不需要换行，则累加
*/
lineWidth += childWidth;
lineHeight = Math.max(lineHeight, childHeight);
lineViews.add(child);
}
// 记录最后一行
mLineHeight.add(lineHeight);
mAllViews.add(lineViews);
// 得到总行数
int lineNums = mAllViews.size();
for (int i = 0; i < lineNums; i++) {
// 每一行的所有的views
lineViews = mAllViews.get(i);
// 当前行的最大高度
lineHeight = mLineHeight.get(i);
if (DEBUG) {
Log.e(TAG, "第" + i + "行 ：" + lineViews.size() + " , " + lineViews);
Log.e(TAG, "第" + i + "行， ：" + lineHeight);
}
// 遍历当前行所有的View
for (int j = 0; j < lineViews.size(); j++) {
View child = lineViews.get(j);
if (child.getVisibility() == View.GONE) {
continue;
}
MarginLayoutParams lp = (MarginLayoutParams) child.getLayoutParams();
// 计算childView的left,top,right,bottom
int lc = 0;
int tc = 0;
int rc = 0;
int bc = 0;
switch (mAlignItems) {
case AlignItems.FLEX_START:
lc = left + lp.leftMargin;
tc = top + lp.topMargin;
rc = lc + child.getMeasuredWidth();
bc = tc + child.getMeasuredHeight();
break;
case AlignItems.FLEX_END:
lc = left + lp.leftMargin;
tc = top + lineHeight - child.getMeasuredHeight() - lp.bottomMargin;
rc = lc + child.getMeasuredWidth();
bc = tc + child.getMeasuredHeight();
break;
case AlignItems.CENTER:
lc = left + lp.leftMargin;
tc = top + lp.topMargin
+ (lineHeight - lp.topMargin - child.getMeasuredHeight() - lp.bottomMargin) / 2;
rc = lc + child.getMeasuredWidth();
bc = tc + child.getMeasuredHeight();
break;
default:
throw new IllegalStateException("Invalid alignItems is set: " + mAlignItems);
}
child.layout(lc, tc, rc, bc);
left += child.getMeasuredWidth() + lp.rightMargin + lp.leftMargin;
}
left = getPaddingLeft();
top += lineHeight;
}
}
public static class LayoutParams extends ViewGroup.MarginLayoutParams {
/**
* need newline or not
*/
public boolean newline = false;
public LayoutParams(Context c, AttributeSet attrs) {
super(c, attrs);
final TypedArray a = c.obtainStyledAttributes(attrs, R.styleable.FlexLayout_Layout);
newline = a.getBoolean(R.styleable.FlexLayout_Layout_layout_newline, false);
a.recycle();
}
public LayoutParams(ViewGroup.LayoutParams lp) {
super(lp);
}
public LayoutParams(ViewGroup.MarginLayoutParams lp) {
super(lp);
}
/**
* Copy constructor. Clones the width, height, margin values, newline
*
* @param lp The layout params to copy from.
*/
public LayoutParams(LayoutParams lp) {
super(lp);
this.newline = lp.newline;
}
/**
* Copy constructor. Clones the width, height
*
* @param lp The layout params to copy from.
*/
public LayoutParams(int width, int height) {
super(width, height);
}
/**
* Copy constructor. Clones the width, height, newline
*
* @param lp The layout params to copy from.
*/
public LayoutParams(int width, int height, boolean newline) {
super(width, height);
this.newline = newline;
}
}
}
AlignItems.java
/*
* Copyright 2016 Google Inc. All rights reserved.
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package cn.lik.view.flexbox;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
/** This attribute controls the alignment along the cross axis. */
@Retention(RetentionPolicy.SOURCE)
public @interface AlignItems {
/** Flex item's edge is placed on the cross start line. */
int FLEX_START = 0;
/** Flex item's edge is placed on the cross end line. */
int FLEX_END = 1;
/** Flex item's edge is centered along the cross axis. */
int CENTER = 2;
}
res/values/attrs.xml
<?xml version="1.0" encoding="utf-8"?>
<resources>
<declare-styleable name="FlexLayout">
<attr name="alignItems">
<enum name="flex_start" value="0" />
<enum name="flex_end" value="1" />
<enum name="center" value="2" />
</attr>
</declare-styleable>
<declare-styleable name="FlexLayout_Layout">
<attr name="layout_newline" format="boolean" />
</declare-styleable>
</resources>
