Android 百分比布局
1.引入：compile 'com.android.support:percent:24.0.0'
2.点开源码可以看到，主要有两个布局类PercentFrameLayout和PercentRelativeLayout，一个工具类PercentLayoutHelper。
3.点开布局类比如PercentRelativeLayout的源码，可以看到实现的很简单。
public class PercentRelativeLayout extends RelativeLayout { private final PercentLayoutHelper mHelper = new PercentLayoutHelper(this); /**省略若干行构造方法之类的代码**/ @Override protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) { //重点在这 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 RelativeLayout.LayoutParams implements PercentLayoutHelper.PercentLayoutParams { private PercentLayoutHelper.PercentLayoutInfo mPercentLayoutInfo; public LayoutParams(Context c, AttributeSet attrs) { super(c, attrs); mPercentLayoutInfo = PercentLayoutHelper.getPercentLayoutInfo(c, attrs); } /**省略若干行构造方法之类的代码**/ @Override public PercentLayoutHelper.PercentLayoutInfo getPercentLayoutInfo() { if (mPercentLayoutInfo == null) { mPercentLayoutInfo = new PercentLayoutHelper.PercentLayoutInfo(); } return mPercentLayoutInfo; } @Override protected void setBaseAttributes(TypedArray a, int widthAttr, int heightAttr) { PercentLayoutHelper.fetchWidthAndHeight(this, a, widthAttr, heightAttr); } } }
就是在onMeasure和onLayout里面调用了PercentLayoutHelper 的一些方法，另外在里面定义了自己的LayoutParams ，而这个LayoutParams 也相当简单。
这里关键的一行代码是在onMeasure方法里面，mHelper.adjustChildren(widthMeasureSpec, heightMeasureSpec);通过PercentLayoutHelper 的adjustChildren 遍历子view来设置 子view的宽高，宽高在PercentLayoutHelper 的内部类PercentLayoutInfo通过在布局文件中设置的值计算好了。
public void adjustChildren(int widthMeasureSpec, int heightMeasureSpec) { // Calculate available space, accounting for host's paddings int widthHint = View.MeasureSpec.getSize(widthMeasureSpec) - mHost.getPaddingLeft() - mHost.getPaddingRight(); int heightHint = View.MeasureSpec.getSize(heightMeasureSpec) - mHost.getPaddingTop() - mHost.getPaddingBottom(); for (int i = 0, N = mHost.getChildCount(); i < N; i++) { //遍历子view来设置 子view的宽高 View view = mHost.getChildAt(i); ViewGroup.LayoutParams params = view.getLayoutParams(); if (DEBUG) { Log.d(TAG, "should adjust " + view + " " + params); } if (params instanceof PercentLayoutParams) { PercentLayoutInfo info = ((PercentLayoutParams) params).getPercentLayoutInfo(); if (info != null) { if (params instanceof ViewGroup.MarginLayoutParams) { info.fillMarginLayoutParams(view, (ViewGroup.MarginLayoutParams) params, widthHint, heightHint); } else { info.fillLayoutParams(params, widthHint, heightHint); } } } } }
4.布局中的使用方法：以PercentRelativeLayout为例
<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:background="@color/background_color" > <TextView android:id="@+id/mian_tab_name" android:layout_width="wrap_content" android:layout_height="wrap_content" android:gravity="center" android:textColor="@color/back_green" android:textSize="15sp" android:text="name" /> <ImageView app:layout_widthPercent="50%" app:layout_heightPercent="50%" android:src="@drawable/ic_launcher_icon" android:scaleType="fitXY" android:layout_below="@+id/mian_tab_name" android:background="@color/black" /> </android.support.percent.PercentRelativeLayout>
引入xmlns:app的命名空间，然后app:layout_widthPercent="50%"就可以设置宽高的百分比了。相当简单 。
5.不过在使用的过程中，可能会有一些其他的需求，比如app:layout_widthPercent="50%",app:layout_heightPercent="50%"都是相对于屏幕的宽高的，假如要显示一张正方形的图片，以宽的50%为准呢？这个时候就可以这样写了：
<ImageView app:layout_widthPercent="50%" app:layout_aspectRatio="100%" android:src="@drawable/ic_launcher_icon" android:scaleType="fitXY" android:layout_below="@+id/mian_tab_name" android:background="@color/CS_black" />
使用layout_aspectRatio属性，设置app:layout_aspectRatio="100%"，layout_aspectRatio就是宽高比。这个时候就不要设置app:layout_heightPercent属性了。在PercentLayoutHelper 里面， 源代码如下：
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; // We assume that width/height set to 0 means that value was unset. This might not // necessarily be true, as the user might explicitly set it to 0. However, we use this // information only for the aspect ratio. If the user set the aspect ratio attribute, // it means they accept or soon discover that it will be disregarded. final boolean widthNotSet = (mPreservedParams.mIsWidthComputedFromAspectRatio || mPreservedParams.width == 0) && (widthPercent < 0); final boolean heightNotSet = (mPreservedParams.mIsHeightComputedFromAspectRatio || mPreservedParams.height == 0) && (heightPercent < 0); if (widthPercent >= 0) { params.width = (int) (widthHint * widthPercent); } if (heightPercent >= 0) { params.height = (int) (heightHint * heightPercent); } //这一段代码是关键，如果aspectRatio >=0，aspectRatio是宽高比 if (aspectRatio >= 0) { if (widthNotSet) { //如果宽没有设置，就以高为准 params.width = (int) (params.height * aspectRatio); // Keep track that we've filled the width based on the height and aspect ratio. mPreservedParams.mIsWidthComputedFromAspectRatio = true; } if (heightNotSet) { //如果高没有设置，就以宽为准 params.height = (int) (params.width / aspectRatio); // Keep track that we've filled the height based on the width and aspect ratio. mPreservedParams.mIsHeightComputedFromAspectRatio = true; } } if (DEBUG) { Log.d(TAG, "after fillLayoutParams: (" + params.width + ", " + params.height + ")"); } }
6.另外，假如我们要定义自己的PercentLinearLayout，基本可以直接改一下名字，继承自LinearLayout就好了：public class PercentLinearLayout extends LinearLayout ,在仿照PercentRelativeLayout里面的LayoutParams定义一个自己的LayoutParams就好了。
不过官方为什么没有直接提供一个PercentLinearLayout 类，而只提供了两个PercentFrameLayout和PercentRelativeLayout呢？或许是由于LinearLayout 本身就有权重属性，自带百分比效果了。
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