1.引入：compile ‘com.android.support:percent:24.0.0‘

2.點(diǎn)開源碼可以看到，主要有兩個(gè)布局類PercentFrameLayout和PercentRelativeLayout，一個(gè)工具類PercentLayoutHelper。

3.點(diǎn)開布局類比如PercentRelativeLayout的源碼，可以看到實(shí)現(xiàn)的很簡(jiǎn)單。

public class PercentRelativeLayout extends RelativeLayout {

private final PercentLayoutHelper mHelper = new PercentLayoutHelper(this);

/**省略若干行構(gòu)造方法之類的代碼**/

@Override

protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {

//重點(diǎn)在這

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);

}

/**省略若干行構(gòu)造方法之類的代碼**/

@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里面調(diào)用了PercentLayoutHelper 的一些方法，另外在里面定義了自己的LayoutParams ，而這個(gè)LayoutParams 也相當(dāng)簡(jiǎn)單。

這里關(guān)鍵的一行代碼是在onMeasure方法里面，mHelper.adjustChildren(widthMeasureSpec, heightMeasureSpec);通過(guò)PercentLayoutHelper 的adjustChildren 遍歷子view來(lái)設(shè)置 子view的寬高，寬高在PercentLayoutHelper 的內(nèi)部類PercentLayoutInfo通過(guò)在布局文件中設(shè)置的值計(jì)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++) {

//遍歷子view來(lái)設(shè)置 子view的寬高

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為例

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

android:layout_width="match_parent"

android:layout_height="match_parent"

android:background="@color/background_color"

>

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"

/>

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"

/>

引入xmlns:app的命名空間，然后app:layout_widthPercent="50%"就可以設(shè)置寬高的百分比了。相當(dāng)簡(jiǎn)單 。

5.不過(guò)在使用的過(guò)程中，可能會(huì)有一些其他的需求，比如app:layout_widthPercent="50%",app:layout_heightPercent="50%"都是相對(duì)于屏幕的寬高的，假如要顯示一張正方形的圖片，以寬的50%為準(zhǔn)呢?這個(gè)時(shí)候就可以這樣寫了：

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屬性，設(shè)置app:layout_aspectRatio="100%"，layout_aspectRatio就是寬高比。這個(gè)時(shí)候就不要設(shè)置app:layout_heightPercent屬性了。在PercentLayoutHelper 里面， 源代碼如下：

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);

}

//這一段代碼是關(guān)鍵，如果aspectRatio >=0，aspectRatio是寬高比

if (aspectRatio >= 0) {

if (widthNotSet) {

//如果寬沒(méi)有設(shè)置，就以高為準(zhǔn)

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) {

//如果高沒(méi)有設(shè)置，就以寬為準(zhǔn)

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，假如我們要定義自己的PercentLinearLayout，基本可以直接改一下名字，繼承自LinearLayout就好了：public class PercentLinearLayout extends LinearLayout ,在仿照PercentRelativeLayout里面的LayoutParams定義一個(gè)自己的LayoutParams就好了。

不過(guò)官方為什么沒(méi)有直接提供一個(gè)PercentLinearLayout 類，而只提供了兩個(gè)PercentFrameLayout和PercentRelativeLayout呢?