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安卓百分比布局解析

作者:时间:2018-08-08来源:网络收藏

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

本文引用地址:http://www.eepw.com.cn/article/201808/385776.htm

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

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:

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?



关键词: 安卓

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