Android 屏幕适配（一）百分比布局库(percent-support-lib) 解析与扩展
转载请标明出处：
http://blog.csdn.net/lmj623565791/article/details/46695347；
本文出自:【张鸿洋的博客】
一、概述
周末游戏打得过猛，于是周天熬夜码代码，周一早上浑浑噩噩的发现android-percent-support-lib-sample这个项目，Google终于开始支持百分比的方式布局了，瞬间脉动回来，啊咧咧。对于这种历史性的时刻，不出篇博客难以表达我内心的激动。
还记得不久前，发了篇博客：Android 屏幕适配方案，这篇博客以Web页面设计引出一种适配方案，最终的目的就是可以通过百分比控制控件的大小。当然了，存在一些问题，比如：
- 对于没有考虑到屏幕尺寸，可能会出现意外的情况；
- apk的大小会增加；
当然了android-percent-support这个库，基本可以解决上述问题，是不是有点小激动，稍等，我们先描述下这个support-lib。
这个库提供了：
-
两种布局供大家使用：
PercentRelativeLayout、PercentFrameLayout，通过名字就可以看出，这是继承自FrameLayout和RelativeLayout两个容器类； -
支持的属性有：
layout_widthPercent、layout_heightPercent、 layout_marginPercent、layout_marginLeftPercent、 layout_marginTopPercent、layout_marginRightPercent、 layout_marginBottomPercent、layout_marginStartPercent、layout_marginEndPercent。
可以看到支持宽高，以及margin。
也就是说，大家只要在开发过程中使用PercentRelativeLayout、PercentFrameLayout替换FrameLayout、RelativeLayout即可。
是不是很简单，不过貌似没有LinearLayout，有人会说LinearLayout有weight属性呀。但是，weight属性只能支持一个方向呀~~哈，没事，刚好给我们一个机会去自定义一个PercentLinearLayout。
好了，本文分为3个部分：
-
PercentRelativeLayout、PercentFrameLayout的使用 - 对上述控件源码分析
- 自定义
PercentLinearLayout
二、使用
关于使用，其实及其简单，并且github上也有例子，android-percent-support-lib-sample。我们就简单过一下：
首先记得在build.gradle添加：
compile 'com.android.support:percent:22.2.0'（一）PercentFrameLayout
<?xml version="1.0" encoding="utf-8"?>
<android.support.percent.PercentFrameLayout
xmlns:android="http://schemas.android.com/apk/res/android" xmlns:app="http://schemas.android.com/apk/res-auto" android:layout_width="match_parent" android:layout_height="match_parent"> <TextView android:layout_width="0dp" android:layout_height="0dp" android:layout_gravity="left|top" android:background="#44ff0000" android:text="width:30%,height:20%" app:layout_heightPercent="20%" android:gravity="center" app:layout_widthPercent="30%"/> <TextView android:layout_width="0dp" android:layout_height="0dp" android:layout_gravity="right|top" android:gravity="center" android:background="#4400ff00" android:text="width:70%,height:20%" app:layout_heightPercent="20%" app:layout_widthPercent="70%"/> <TextView android:layout_width="0dp" android:layout_height="0dp" android:layout_gravity="bottom" android:background="#770000ff" android:text="width:100%,height:10%" android:gravity="center" app:layout_heightPercent="10%" app:layout_widthPercent="100%"/> </android.support.percent.PercentFrameLayout> 3个TextView，很简单，直接看效果图：
(二) PercentRelativeLayout
<?xml version="1.0" encoding="utf-8"?>
<android.support.percent.PercentRelativeLayout
xmlns:android="http://schemas.android.com/apk/res/android" xmlns:app="http://schemas.android.com/apk/res-auto" android:layout_width="match_parent" android:layout_height="match_parent" android:clickable="true"> <TextView android:id="@+id/row_one_item_one" android:layout_width="0dp" android:layout_height="0dp" android:layout_alignParentTop="true" android:background="#7700ff00" android:text="w:70%,h:20%" android:gravity="center" app:layout_heightPercent="20%" app:layout_widthPercent="70%"/> <TextView android:id="@+id/row_one_item_two" android:layout_width="0dp" android:layout_height="0dp" android:layout_toRightOf="@+id/row_one_item_one" android:background="#396190" android:text="w:30%,h:20%" app:layout_heightPercent="20%" android:gravity="center" app:layout_widthPercent="30%"/> <ImageView android:id="@+id/row_two_item_one" android:layout_width="match_parent" android:layout_height="0dp" android:src="@drawable/tangyan" android:scaleType="centerCrop" android:layout_below="@+id/row_one_item_one" android:background="#d89695" app:layout_heightPercent="70%"/> <TextView android:layout_width="0dp" android:layout_height="0dp" android:layout_below="@id/row_two_item_one" android:background="#770000ff" android:gravity="center" android:text="width:100%,height:10%" app:layout_heightPercent="10%" app:layout_widthPercent="100%"/> </android.support.percent.PercentRelativeLayout> ok，依然是直接看效果图:
使用没什么好说的，就是直观的看一下。
三、源码分析
其实细想一下，Google只是对我们原本熟悉的RelativeLayout和FrameLayout进行的功能的扩展，使其支持了percent相关的属性。
那么，我们考虑下，如果是我们添加这种扩展，我们会怎么做：
- 通过LayoutParams获取child设置的percent相关属性的值
- onMeasure的时候，将child的width,height的值，通过获取的自定义属性的值进行计算（eg:容器的宽 * fraction ），计算后传入给child.measure(w,h);
ok，有了上面的猜想，我们直接看PercentFrameLayout的源码。
public class PercentFrameLayout extends FrameLayout { private final PercentLayoutHelper mHelper = new PercentLayoutHelper(this); //省略了，两个构造方法 public PercentFrameLayout(Context context, AttributeSet attrs) { super(context, attrs); } @Override public LayoutParams generateLayoutParams(AttributeSet attrs) { return new LayoutParams(getContext(), attrs); } @Override protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) { mHelper.adjustChildren(widthMeasureSpec, heightMeasureSpec); super.onMeasure(widthMeasureSpec, heightMeasureSpec); if (mHelper.handleMeasuredStateTooSmall()) { super.onMeasure(widthMeasureSpec, heightMeasureSpec); } } @Override protected void onLayout(boolean changed, int left, int top, int right, int bottom) { super.onLayout(changed, left, top, right, bottom); mHelper.restoreOriginalParams(); } public static class LayoutParams extends FrameLayout.LayoutParams implements PercentLayoutHelper.PercentLayoutParams { private PercentLayoutHelper.PercentLayoutInfo mPercentLayoutInfo; public LayoutParams(Context c, AttributeSet attrs) { super(c, attrs); mPercentLayoutInfo = PercentLayoutHelper.getPercentLayoutInfo(c, attrs); } //省略了一些代码... @Override public PercentLayoutHelper.PercentLayoutInfo getPercentLayoutInfo() { return mPercentLayoutInfo; } @Override protected void setBaseAttributes(TypedArray a, int widthAttr, int heightAttr) { PercentLayoutHelper.fetchWidthAndHeight(this, a, widthAttr, heightAttr); } } }代码是相当的短，可以看到PercentFrameLayout里面首先重写了generateLayoutParams方法，当然了，由于支持了一些新的layout_属性，那么肯定需要定义对应的LayoutParams。
（一）percent相关属性的获取
可以看到PercentFrameLayout.LayoutParams在原有的FrameLayout.LayoutParams基础上，实现了PercentLayoutHelper.PercentLayoutParams接口。
这个接口很简单，只有一个方法：
public interface PercentLayoutParams {
PercentLayoutInfo getPercentLayoutInfo();
}而，这个方法的实现呢，也只有一行：return mPercentLayoutInfo;，那么这个mPercentLayoutInfo在哪完成赋值呢？
看PercentFrameLayout.LayoutParams的构造方法：
public LayoutParams(Context c, AttributeSet attrs) {
super(c, attrs);
mPercentLayoutInfo = PercentLayoutHelper.getPercentLayoutInfo(c, attrs);
}可以看到，将attrs传入给getPercentLayoutInfo方法，那么不用说，这个方法的内部，肯定是获取自定义属性的值，然后将其封装到PercentLayoutInfo对象中，最后返回。
代码如下：
public static PercentLayoutInfo getPercentLayoutInfo(Context context,
AttributeSet attrs) {
PercentLayoutInfo info = null;
TypedArray array = context.obtainStyledAttributes(attrs, R.styleable.PercentLayout_Layout);
float value = array.getFraction(R.styleable.PercentLayout_Layout_layout_widthPercent, 1, 1, -1f); if (value != -1f) { if (Log.isLoggable(TAG, Log.VERBOSE)) { Log.v(TAG, "percent width: " + value); } info = info != null ? info : new PercentLayoutInfo(); info.widthPercent = value; } value = array.getFraction(R.styleable.PercentLayout_Layout_layout_heightPercent, 1, 1, -1f); if (value != -1f) { if (Log.isLoggable(TAG, Log.VERBOSE)) { Log.v(TAG, "percent height: " + value); } info = info != null ? info : new PercentLayoutInfo(); info.heightPercent = value; } value = array.getFraction(R.styleable.PercentLayout_Layout_layout_marginPercent, 1, 1, -1f); if (value != -1f) { if (Log.isLoggable(TAG, Log.VERBOSE)) { Log.v(TAG, "percent margin: " + value); } info = info != null ? info : new PercentLayoutInfo(); info.leftMarginPercent = value; info.topMarginPercent = value; info.rightMarginPercent = value; info.bottomMarginPercent = value; } value = array.getFraction(R.styleable.PercentLayout_Layout_layout_marginLeftPercent, 1, 1, -1f); if (value != -1f) { if (Log.isLoggable(TAG, Log.VERBOSE)) { Log.v(TAG, "percent left margin: " + value); } info = info != null ? info : new PercentLayoutInfo(); info.leftMarginPercent = value; } value = array.getFraction(R.styleable.PercentLayout_Layout_layout_marginTopPercent, 1, 1, -1f); if (value != -1f) { if (Log.isLoggable(TAG, Log.VERBOSE)) { Log.v(TAG, "percent top margin: " + value); } info = info != null ? info : new PercentLayoutInfo(); info.topMarginPercent = value; } value = array.getFraction(R.styleable.PercentLayout_Layout_layout_marginRightPercent, 1, 1, -1f); if (value != -1f) { if (Log.isLoggable(TAG, Log.VERBOSE)) { Log.v(TAG, "percent right margin: " + value); } info = info != null ? info : new PercentLayoutInfo(); info.rightMarginPercent = value; } value = array.getFraction(R.styleable.PercentLayout_Layout_layout_marginBottomPercent, 1, 1, -1f); if (value != -1f) { if (Log.isLoggable(TAG, Log.VERBOSE)) { Log.v(TAG, "percent bottom margin: " + value); } info = info != null ? info : new PercentLayoutInfo(); info.bottomMarginPercent = value; } value = array.getFraction(R.styleable.PercentLayout_Layout_layout_marginStartPercent, 1, 1, -1f); if (value != -1f) { if (Log.isLoggable(TAG, Log.VERBOSE)) { Log.v(TAG, "percent start margin: " + value); } info = info != null ? info : new PercentLayoutInfo(); info.startMarginPercent = value; } value = array.getFraction(R.styleable.PercentLayout_Layout_layout_marginEndPercent, 1, 1, -1f); if (value != -1f) { if (Log.isLoggable(TAG, Log.VERBOSE)) { Log.v(TAG, "percent end margin: " + value); } info = info != null ? info : new PercentLayoutInfo(); info.endMarginPercent = value; } array.recycle(); if (Log.isLoggable(TAG, Log.DEBUG)) { Log.d(TAG, "constructed: " + info); } return info; }是不是和我们平时的取值很类似，所有的值最终封装到PercentLayoutInfo对象中。
ok，到此我们的属性获取就介绍完成，有了这些属性，是不是onMeasure里面要进行使用呢？
(二) onMeasue中重新计算child的尺寸
@Override
protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) { mHelper.adjustChildren(widthMeasureSpec, heightMeasureSpec); super.onMeasure(widthMeasureSpec, heightMeasureSpec); if (mHelper.handleMeasuredStateTooSmall()) { super.onMeasure(widthMeasureSpec, heightMeasureSpec); } }可以看到onMeasure中的代码页很少，看来核心的代码都被封装在mHelper的方法中，我们直接看mHelper.adjustChildren方法。
/**
* Iterates over children and changes their width and height to one calculated from percentage
* values.
* @param widthMeasureSpec Width MeasureSpec of the parent ViewGroup.
* @param heightMeasureSpec Height MeasureSpec of the parent ViewGroup.
*/
public void adjustChildren(int widthMeasureSpec, int heightMeasureSpec) { //... int widthHint = View.MeasureSpec.getSize(widthMeasureSpec); int heightHint = View.MeasureSpec.getSize(heightMeasureSpec); for (int i = 0, N = mHost.getChildCount(); i < N; i++) { View view = mHost.getChildAt(i); ViewGroup.LayoutParams params = view.getLayoutParams(); if (params instanceof PercentLayoutParams) { PercentLayoutInfo info = ((PercentLayoutParams) params).getPercentLayoutInfo(); if (Log.isLoggable(TAG, Log.DEBUG)) { Log.d(TAG, "using " + info); } if (info != null) { if (params instanceof ViewGroup.MarginLayoutParams) { info.fillMarginLayoutParams((ViewGroup.MarginLayoutParams) params, widthHint, heightHint); } else { info.fillLayoutParams(params, widthHint, heightHint); } } } } } 通过注释也能看出，此方法中遍历所有的孩子，通过百分比的属性重新设置其宽度和高度。
首先在widthHint、heightHint保存容器的宽、高，然后遍历所有的孩子，判断其LayoutParams是否是PercentLayoutParams类型，如果是，通过params.getPercentLayoutInfo拿出info对象。
是否还记得，上面的分析中，PercentLayoutInfo保存了percent相关属性的值。
如果info不为null，则判断是否需要处理margin；我们直接看fillLayoutParams方法（处理margin也是类似的）。
/**
* Fills {@code ViewGroup.LayoutParams} dimensions based on percentage values.
*/
public void fillLayoutParams(ViewGroup.LayoutParams params, int widthHint, int heightHint) { // Preserve the original layout params, so we can restore them after the measure step. mPreservedParams.width = params.width; mPreservedParams.height = params.height; if (widthPercent >= 0) { params.width = (int) (widthHint * widthPercent); } if (heightPercent >= 0) { params.height = (int) (heightHint * heightPercent); } if (Log.isLoggable(TAG, Log.DEBUG)) { Log.d(TAG, "after fillLayoutParams: (" + params.width + ", " + params.height + ")"); } }首先保存原本的width和height，然后重置params的width和height为(int) (widthHint * widthPercent)和(int) (heightHint * heightPercent);。
到此，其实我们的百分比转换就结束了，理论上就已经实现了对于百分比的支持，不过Google还考虑了一些细节。
我们回到onMeasure方法：
@Override
protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) { mHelper.adjustChildren(widthMeasureSpec, heightMeasureSpec); super.onMeasure(widthMeasureSpec, heightMeasureSpec); if (mHelper.handleMeasuredStateTooSmall()) { super.onMeasure(widthMeasureSpec, heightMeasureSpec); } }下面还有个mHelper.handleMeasuredStateTooSmall的判断，也就是说，如果你设置的百分比，最终计算出来的MeasuredSize过小的话，会进行一些操作。
代码如下：
public boolean handleMeasuredStateTooSmall() {
boolean needsSecondMeasure = false; for (int i = 0, N = mHost.getChildCount(); i < N; i++) { View view = mHost.getChildAt(i); ViewGroup.LayoutParams params = view.getLayoutParams(); if (Log.isLoggable(TAG, Log.DEBUG)) { Log.d(TAG, "should handle measured state too small " + view + " " + params); } if (params instanceof PercentLayoutParams) { PercentLayoutInfo info = ((PercentLayoutParams) params).getPercentLayoutInfo(); if (info != null) { if (shouldHandleMeasuredWidthTooSmall(view, info)) { needsSecondMeasure = true; params.width = ViewGroup.LayoutParams.WRAP_CONTENT; } if (shouldHandleMeasuredHeightTooSmall(view, info)) { needsSecondMeasure = true; params.height = ViewGroup.LayoutParams.WRAP_CONTENT; } } } } if (Log.isLoggable(TAG, Log.DEBUG)) { Log.d(TAG, "should trigger second measure pass: " + needsSecondMeasure); } return needsSecondMeasure; }首先遍历所有的孩子，拿出孩子的layoutparams，如果是PercentLayoutParams实例，则取出info。如果info不为null，调用shouldHandleMeasuredWidthTooSmall判断：
private static boolean shouldHandleMeasuredWidthTooSmall(View view, PercentLayoutInfo info) {
int state = ViewCompat.getMeasuredWidthAndState(view) & ViewCompat.MEASURED_STATE_MASK; return state == ViewCompat.MEASURED_STATE_TOO_SMALL && info.widthPercent >= 0 && info.mPreservedParams.width == ViewGroup.LayoutParams.WRAP_CONTENT; }这里就是判断，如果你设置的measuredWidth或者measureHeight过小的话，并且你在布局文件中layout_w/h 设置的是WRAP_CONTENT的话，将params.width / height= ViewGroup.LayoutParams.WRAP_CONTENT，然后重新测量。
哈，onMeasure终于结束了~~~现在我觉得应该代码结束了吧，尺寸都设置好了，还需要干嘛么，but，你会发现onLayout也重写了，我们又不改变layout规则，在onLayout里面干什么毛线：
@Override
protected void onLayout(boolean changed, int left, int top, int right, int bottom) { super.onLayout(changed, left, top, right, bottom); mHelper.restoreOriginalParams(); }继续看mHelper.restoreOriginalParams
/**
* Iterates over children and restores their original dimensions that were changed for
* percentage values. Calling this method only makes sense if you previously called
* {@link PercentLayoutHelper#adjustChildren(int, int)}.
*/
public void restoreOriginalParams() {
for (int i = 0, N = mHost.getChildCount(); i < N; i++) { View view = mHost.getChildAt(i); ViewGroup.LayoutParams params = view.getLayoutParams(); if (Log.isLoggable(TAG, Log.DEBUG)) { Log.d(TAG, "should restore " + view + " " + params); } if (params instanceof PercentLayoutParams) { PercentLayoutInfo info = ((PercentLayoutParams) params).getPercentLayoutInfo(); if (Log.isLoggable(TAG, Log.DEBUG)) { Log.d(TAG, "using " + info); } if (info != null) { if (params instanceof ViewGroup.MarginLayoutParams) { info.restoreMarginLayoutParams((ViewGroup.MarginLayoutParams) params); } else { info.restoreLayoutParams(params); } } } } } 噗，原来是重新恢复原本的尺寸值，也就是说onMeasure里面的对值进行了改变，测量完成后。在这个地方，将值又恢复成如果布局文件中的值，上面写的都是0。恢复很简单：
public void restoreLayoutParams(ViewGroup.LayoutParams params) {
params.width = mPreservedParams.width;
params.height = mPreservedParams.height;
}你应该没有忘在哪存的把~忘了的话，麻烦Ctrl+F ‘mPreservedParams.width’ 。
也就是说，你去打印上面写法，布局文件中view的v.getLayoutParams().width，这个值应该是0。
这里感觉略微不爽~这个0没撒用处呀，还不如不重置~~
好了，到此就分析完了，其实主要就几个步骤：
- LayoutParams中属性的获取
- onMeasure中，改变params.width为百分比计算结果，测量
- 如果测量值过小且设置的w/h是wrap_content，重新测量
- onLayout中，重置params.w/h为布局文件中编写的值
可以看到，有了RelativeLayout、FrameLayout的扩展，竟然没有LinearLayout几个意思。好在，我们的核心代码都由PercentLayoutHelper封装了，自己扩展下LinearLayout也不复杂。
三、实现PercentLinearlayout
可能有人会说，有了weight呀，但是weight能做到宽、高同时百分比赋值嘛？
好了，代码很简单，如下：
（一）PercentLinearLayout
package com.juliengenoud.percentsamples;
import android.content.Context;
import android.content.res.TypedArray;
import android.support.percent.PercentLayoutHelper;
import android.util.AttributeSet; import android.view.ViewGroup; import android.widget.LinearLayout; /** * Created by zhy on 15/6/30. */ public class PercentLinearLayout extends LinearLayout { private PercentLayoutHelper mPercentLayoutHelper; public PercentLinearLayout(Context context, AttributeSet attrs) { super(context, attrs); mPercentLayoutHelper = new PercentLayoutHelper(this); } @Override protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) { mPercentLayoutHelper.adjustChildren(widthMeasureSpec, heightMeasureSpec); super.onMeasure(widthMeasureSpec, heightMeasureSpec); if (mPercentLayoutHelper.handleMeasuredStateTooSmall()) { super.onMeasure(widthMeasureSpec, heightMeasureSpec); } } @Override protected void onLayout(boolean changed, int l, int t, int r, int b) { super.onLayout(changed, l, t, r, b); mPercentLayoutHelper.restoreOriginalParams(); } @Override public LayoutParams generateLayoutParams(AttributeSet attrs) { return new LayoutParams(getContext(), attrs); } public static class LayoutParams extends LinearLayout.LayoutParams implements PercentLayoutHelper.PercentLayoutParams { private PercentLayoutHelper.PercentLayoutInfo mPercentLayoutInfo; public LayoutParams(Context c, AttributeSet attrs) { super(c, attrs); mPercentLayoutInfo = PercentLayoutHelper.getPercentLayoutInfo(c, attrs); } @Override public PercentLayoutHelper.PercentLayoutInfo getPercentLayoutInfo() { return mPercentLayoutInfo; } @Override protected void setBaseAttributes(TypedArray a, int widthAttr, int heightAttr) { PercentLayoutHelper.fetchWidthAndHeight(this, a, widthAttr, heightAttr); } public LayoutParams(int width, int height) { super(width, height); } public LayoutParams(ViewGroup.LayoutParams source) { super(source); } public LayoutParams(MarginLayoutParams source) { super(source); } } } 如果你详细看了上面的源码分析，这个代码是不是没撒解释的了~
（二）测试布局
<?xml version="1.0" encoding="utf-8"?>
<com.juliengenoud.percentsamples.PercentLinearLayout
xmlns:android="http://schemas.android.com/apk/res/android" xmlns:app="http://schemas.android.com/apk/res-auto" android:layout_width="match_parent" android:layout_height="match_parent" android:orientation="vertical"> <TextView android:layout_width="0dp" android:layout_height="0dp" android:background="#ff44aacc" android:text="width:60%,height:5%" android:textColor="#ffffff" app:layout_heightPercent="5%" app:layout_marginBottomPercent="5%" app:layout_widthPercent="60%"/> <TextView android:layout_width="0dp" android:layout_height="0dp" android:background="#ff4400cc" android:gravity="center" android:textColor="#ffffff" android:text="width:70%,height:10%" app:layout_heightPercent="10%" app:layout_marginBottomPercent="5%" app:layout_widthPercent="70%"/> <TextView android:layout_width="0dp" android:layout_height="0dp" android:background="#ff44aacc" android:gravity="center" android:text="width:80%,height:15%" android:textColor="#ffffff" app:layout_heightPercent="15%" app:layout_marginBottomPercent="5%" app:layout_widthPercent="80%"/> <TextView android:layout_width="0dp" android:layout_height="0dp" android:background="#ff4400cc" android:gravity="center" android:text="width:90%,height:5%" android:textColor="#ffffff" app:layout_heightPercent="20%" app:layout_marginBottomPercent="10%" app:layout_widthPercent="90%"/> <TextView android:layout_width="match_parent" android:layout_height="0dp" android:background="#ff44aacc" android:gravity="center" android:text="width:100%,height:25%" android:textColor="#ffffff" app:layout_heightPercent="25%" app:layout_marginBottomPercent="5%" /> </com.juliengenoud.percentsamples.PercentLinearLayout> 我们纵向排列的几个TextView，分别设置宽/高都为百分比，且之间的间隔为5%p。
(三)效果图
ok，到此，我们使用、源码分析、扩展PercentLinearLayout就结束了。
添加PercentLinearLayout后的地址：点击查看
扩展下载:android-percent-support-extend 包含android studio, eclipse项目，以及上述源码。
本文转自 一点点征服 博客园博客，原文链接：http://www.cnblogs.com/ldq2016/p/5293002.html，如需转载请自行联系原作者
