Android 百分比布局(percent-support-lib)的使用及源码详解

百分比布局提供的了两种布局PercentFrameLayout和PercentRelativeLayout，很明显前者继承于FrameLayout，后者继承于RelativeLayout，所以父类的各种属性还是可以使用。百分比布局给我们提供了以下特有的属性：

app:layout_heightPercent
app:layout_widthPercent
app:layout_marginPercent
app:layout_marginTopPercent
app:layout_marginBottomPercent
app:layout_marginLeftPercent
app:layout_marginRightPercent
app:layout_marginStartPercent
app:layout_marginEndPercent

app:layout_aspectRatio

也就是说我们宽高和各种margin都可以用百分比表示

当使用百分比布局时，就没用必要再去指定宽高（layout_width和layout_height），只需要设置layout_widthPercent和layout_heightPercent就可以了。

如果通过百分比获取的宽高太小或者想要更大的话，可以把layout_width和layout_height指定为wrap_content。

layout_aspectRatio代表横纵比，比如想要把宽高比例设置为2:10，以下代码示例

<TextView

android:id="@+id/tv2"

android:layout_width="0dp"

android:layout_height="0dp"

android:layout_toRightOf="@id/tv1"

android:background="#D5AD34"

android:gravity="center"

android:text="aspectRatio:2:10,height:100%"

android:textColor="@android:color/white"

app:layout_aspectRatio="20%"

app:layout_heightPercent="100%" />

app:layout_aspectRatio设置为20%，这个值是宽高的比值，这里就只是指定了app:layout_heightPercent，宽度就很根据这个比值计算出来。

百分比布局的导入

compile 'com.android.support:percent:23.4.0'

PercentFrameLayout使用



<?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"

xmlns:tools="http://schemas.android.com/tools"

android:layout_width="match_parent"

android:layout_height="match_parent"

android:orientation="vertical"

tools:context="com.lzy.test.MainActivity">

<TextView

android:layout_width="0dp"

android:layout_height="0dp"

android:layout_gravity="left|top"

android:background="#53DBB9"

android:gravity="center"

android:text="width:30%,height:50%"

app:layout_heightPercent="50%"

app:layout_widthPercent="30%" />

<TextView

android:layout_width="0dp"

android:layout_height="0dp"

android:layout_gravity="right|top"

android:background="#4400ff00"

android:gravity="center"

android:text="width:70%,height:20%"

app:layout_heightPercent="20%"

app:layout_widthPercent="70%" />

<TextView

android:layout_width="0dp"

android:layout_height="0dp"

android:background="#327217"

android:gravity="center"

android:text="width:70%,height:20%\nmarginTop:20%,marginLeft:30%"

app:layout_heightPercent="30%"

app:layout_marginLeftPercent="30%"

app:layout_marginTopPercent="20%"

app:layout_widthPercent="70%" />

<TextView

android:layout_width="0dp"

android:layout_height="0dp"

android:background="#DF65A2"

android:gravity="center"

android:text="width:100%,height:40%\nmarginTop:50%"

app:layout_heightPercent="40%"

app:layout_marginTopPercent="50%"

app:layout_widthPercent="100%" />

<TextView

android:layout_width="0dp"

android:layout_height="0dp"

android:layout_gravity="bottom"

android:background="#770000ff"

android:gravity="center"

android:text="width:100%,height:10%"

app:layout_heightPercent="10%"

app:layout_widthPercent="100%" />

</android.support.percent.PercentFrameLayout>

PercentRelativeLayout



<?xml version="1.0" encoding="utf-8"?>

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"

xmlns:app="http://schemas.android.com/apk/res-auto"

xmlns:tools="http://schemas.android.com/tools"

android:layout_width="match_parent"

android:layout_height="match_parent"

android:orientation="vertical"

tools:context="com.lzy.test.Main2Activity">

<View

android:layout_width="match_parent"

android:layout_height="80dp"

android:background="#1A807C" />

<android.support.percent.PercentRelativeLayout

android:layout_width="match_parent"

android:layout_height="match_parent">

<TextView

android:id="@+id/tv1"

android:background="#B5256D"

android:gravity="center"

android:text="width:60%,height:50%"

android:textColor="@android:color/white"

app:layout_heightPercent="50%"

app:layout_widthPercent="60%" />

<TextView

android:id="@+id/tv2"

android:layout_width="0dp"

android:layout_height="0dp"

android:layout_toRightOf="@id/tv1"

android:background="#D5AD34"

android:gravity="center"

android:text="aspectRatio:2:10,height:100%"

android:textColor="@android:color/white"

app:layout_aspectRatio="20%"

app:layout_heightPercent="100%" />

<android.support.percent.PercentRelativeLayout

android:layout_width="0dp"

android:layout_height="0dp"

android:layout_below="@id/tv1"

app:layout_heightPercent="50%"

app:layout_widthPercent="60%">

<TextView

android:layout_width="0dp"

android:layout_height="0dp"

android:background="#4E3ED7"

android:gravity="center"

android:text="width:40%,height:100%"

android:textColor="@android:color/white"

app:layout_heightPercent="100%"

app:layout_widthPercent="40%" />

<TextView

android:layout_width="0dp"

android:layout_height="0dp"

android:layout_alignParentRight="true"

android:background="#93E684"

android:gravity="center"

android:text="width:60%,height:100%"

android:textColor="@android:color/white"

app:layout_heightPercent="100%"

app:layout_widthPercent="60%" />

</android.support.percent.PercentRelativeLayout>

</android.support.percent.PercentRelativeLayout>

</LinearLayout>

源码分析

看看PercentFrameLayout的主要源码，其中省略了部分代码

public class PercentFrameLayout extends FrameLayout {
private final PercentLayoutHelper mHelper = new PercentLayoutHelper(this);

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

@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);
}

public LayoutParams(LayoutParams source) {
this((FrameLayout.LayoutParams) source);
mPercentLayoutInfo = source.mPercentLayoutInfo;
}

@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);
}
}
}

为了获得PercentFrameLayout的子view里面的自定义属性，所以我们重写了generateLayoutParams方法，把它的返回值修改为我们自己定义的LayoutParams，就相当于把原来的LayoutParams包装了一层，在此过程中就可以截取到属性值，找出子view里面的自定义属性，这些自定义属性就是设置的宽高百分比。

这个自定义的LayoutParams是继承于FrameLayout.LayoutParams，同时实现了PercentLayoutHelper.PercentLayoutParams接口

public interface PercentLayoutParams {

PercentLayoutInfo getPercentLayoutInfo();

}

这个接口就一个返回PercentLayoutInfo的方法，PercentLayoutInfo类就是存储了各种百分比的信息。

public LayoutParams(Context c, AttributeSet attrs) {

super(c, attrs);

mPercentLayoutInfo = PercentLayoutHelper.getPercentLayoutInfo(c, attrs);

}

这里显然就是获取attrs里面的各种百分比信息，然后存储在PercentLayoutInfo里面，没什么好说的，点进去看就是各种获取自定义属性的方法，和我们平常的差不多。

下面看看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);

}

}

首先是mHelper.adjustChildren(widthMeasureSpec, heightMeasureSpec)，点进去看看

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 (info != null) {
if (params instanceof ViewGroup.MarginLayoutParams) {
info.fillMarginLayoutParams(view, (ViewGroup.MarginLayoutParams) params,
widthHint, heightHint);
} else {
info.fillLayoutParams(params, widthHint, heightHint);
}
}
}
}
}

首先这里计算出PercentFrameLayout的宽高，通过百分比计算子view宽高当然需要这个PercentFrameLayout的宽高咯，接着遍历里面的所以子view，判断是否是PercentLayoutParams，如果是就可以调用getPercentLayoutInfo方法来获取到PercentLayoutInfo，最后拿着里面的百分比信息去计算出实际的大小，这里有两种方法来计算，一个是有margin和没有margin的，其实都差不多

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);
}

if (aspectRatio >= 0) {
if (widthNotSet) {
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) {
params.height = (int) (params.width / aspectRatio);
// Keep track that we've filled the height based on the width and aspect ratio.
mPreservedParams.mIsHeightComputedFromAspectRatio = true;
}
}
}

首先是通过mPreservedParams记录了子view原始的宽高，然后判断是否设置了宽高，这个在后面aspectRatio用，接着就是根据百分比计算出宽高了，最后根据设置的横纵比aspectRatio来计算宽高。这样就根据百分比来重新设置了宽高，大功告成了！

好了，这里面就完成了，回到onMeasure方法，这里

if (mHelper.handleMeasuredStateTooSmall()) {
super.onMeasure(widthMeasureSpec, heightMeasureSpec);
}

很显然，就是判断测量的宽高是不是太小，如果太小的话，就会使用wrap_content来重新测量，这里就不具体看了。

@Override
protected void onLayout(boolean changed, int left, int top, int right, int bottom) {
super.onLayout(changed, left, top, right, bottom);
mHelper.restoreOriginalParams();
}

这里调用了一个 mHelper.restoreOriginalParams()方法，作用是恢复原始的参数值，在上面的fillLayoutParams方法中不是把原始的值存储到mPreservedParams中了吗，目的就是在这里用于恢复的，因为在利用百分比计算宽高时已经改变了它原始的值。至于为什么要恢复这个原始的值，具体我也不太清楚，毕竟也是菜鸟一个~~分析就到此完毕了。

其实PercentRelativeLayout源码和PercentFrameLayout基本都差不多，只是其中自定义的LayoutParams是继承于RelativeLayout的LayoutParams，所以你想要实现LinearLayout的百分比布局，也只需要把自定义的LayoutParams继承于LinearLayout的LayoutParams就OK了

百分比布局的扩展地址：https://github.com/hongyangAndroid/android-percent-support-extend