百分比布局适配
文章目录一、简述二、google推荐的百分比布局的使用方式三、实现3.1 创建属性文件3.2 解析3.3 计算并设置百分比布局四、使用五、完整代码六、注意
一、简述
作者：墨玉浮白
百分比布局适配，就是以父容器的尺寸作为基准，在view的加载过程中，根据当前父容器实际尺寸换算出目标尺寸，再作用在view上。
百分比布局，实际是对容器的一种扩展，即对宽高百分比的设置。
二、google推荐的百分比布局的使用方式首先要引入：implementation ‘com.android.support:percent:28.0.0’
然后将布局引用为：android.support.percent.PercentRelativeLayout
给控件设置：app:layout_widthPercent=“50%”
百分比布局，实际是对容器的一种扩展，即对宽高百分比的设置。
attrs.xml中来定义必备的属性
3.2 解析
解析在哪做？以RelativeLayout为例，重要属性都封装在静态类LayoutParams中。这个静态类中就定义了一些自定义属性，也是RelativeLayout特有的属性（相对布局中的独有属性，不能作用于线性布局中）：
public LayoutParams(Context c, AttributeSet attrs) {
super(c, attrs);
TypedArray a = c.obtainStyledAttributes(attrs,
com.android.internal.R.styleable.RelativeLayout_Layout);
final int targetSdkVersion = c.getApplicationInfo().targetSdkVersion;
mIsRtlCompatibilityMode = (targetSdkVersion < JELLY_BEAN_MR1 ||
!c.getApplicationInfo().hasRtlSupport());
final int[] rules = mRules;
//noinspection MismatchedReadAndWriteOfArray
final int[] initialRules = mInitialRules;
final int N = a.getIndexCount();
for (int i = 0; i < N; i++) {
int attr = a.getIndex(i);
switch (attr) {
case com.android.internal.R.styleable.RelativeLayout_Layout_layout_alignWithParentIfMissing:
alignWithParent = a.getBoolean(attr, false);
break;
case com.android.internal.R.styleable.RelativeLayout_Layout_layout_toLeftOf:
rules[LEFT_OF] = a.getResourceId(attr, 0);
break;
case com.android.internal.R.styleable.RelativeLayout_Layout_layout_toRightOf:
rules[RIGHT_OF] = a.getResourceId(attr, 0);
break;
case com.android.internal.R.styleable.RelativeLayout_Layout_layout_above:
rules[ABOVE] = a.getResourceId(attr, 0);
break;
case com.android.internal.R.styleable.RelativeLayout_Layout_layout_below:
rules[BELOW] = a.getResourceId(attr, 0);
break;
case com.android.internal.R.styleable.RelativeLayout_Layout_layout_alignBaseline:
rules[ALIGN_BASELINE] = a.getResourceId(attr, 0);
break;
case com.android.internal.R.styleable.RelativeLayout_Layout_layout_alignLeft:
rules[ALIGN_LEFT] = a.getResourceId(attr, 0);
break;
case com.android.internal.R.styleable.RelativeLayout_Layout_layout_alignTop:
rules[ALIGN_TOP] = a.getResourceId(attr, 0);
break;
case com.android.internal.R.styleable.RelativeLayout_Layout_layout_alignRight:
rules[ALIGN_RIGHT] = a.getResourceId(attr, 0);
break;
case com.android.internal.R.styleable.RelativeLayout_Layout_layout_alignBottom:
rules[ALIGN_BOTTOM] = a.getResourceId(attr, 0);
break;
case com.android.internal.R.styleable.RelativeLayout_Layout_layout_alignParentLeft:
rules[ALIGN_PARENT_LEFT] = a.getBoolean(attr, false) ? TRUE : 0;
break;
case com.android.internal.R.styleable.RelativeLayout_Layout_layout_alignParentTop:
rules[ALIGN_PARENT_TOP] = a.getBoolean(attr, false) ? TRUE : 0;
break;
case com.android.internal.R.styleable.RelativeLayout_Layout_layout_alignParentRight:
rules[ALIGN_PARENT_RIGHT] = a.getBoolean(attr, false) ? TRUE : 0;
break;
case com.android.internal.R.styleable.RelativeLayout_Layout_layout_alignParentBottom:
rules[ALIGN_PARENT_BOTTOM] = a.getBoolean(attr, false) ? TRUE : 0;
break;
case com.android.internal.R.styleable.RelativeLayout_Layout_layout_centerInParent:
rules[CENTER_IN_PARENT] = a.getBoolean(attr, false) ? TRUE : 0;
break;
case com.android.internal.R.styleable.RelativeLayout_Layout_layout_centerHorizontal:
rules[CENTER_HORIZONTAL] = a.getBoolean(attr, false) ? TRUE : 0;
break;
case com.android.internal.R.styleable.RelativeLayout_Layout_layout_centerVertical:
rules[CENTER_VERTICAL] = a.getBoolean(attr, false) ? TRUE : 0;
break;
case com.android.internal.R.styleable.RelativeLayout_Layout_layout_toStartOf:
rules[START_OF] = a.getResourceId(attr, 0);
break;
case com.android.internal.R.styleable.RelativeLayout_Layout_layout_toEndOf:
rules[END_OF] = a.getResourceId(attr, 0);
break;
case com.android.internal.R.styleable.RelativeLayout_Layout_layout_alignStart:
rules[ALIGN_START] = a.getResourceId(attr, 0);
break;
case com.android.internal.R.styleable.RelativeLayout_Layout_layout_alignEnd:
rules[ALIGN_END] = a.getResourceId(attr, 0);
break;
case com.android.internal.R.styleable.RelativeLayout_Layout_layout_alignParentStart:
rules[ALIGN_PARENT_START] = a.getBoolean(attr, false) ? TRUE : 0;
break;
case com.android.internal.R.styleable.RelativeLayout_Layout_layout_alignParentEnd:
rules[ALIGN_PARENT_END] = a.getBoolean(attr, false) ? TRUE : 0;
break;
}
}
mRulesChanged = true;
System.arraycopy(rules, LEFT_OF, initialRules, LEFT_OF, VERB_COUNT);
a.recycle();
}
通过TypedArray来进行属性的解析，然后switch case中一堆特有属性的获取、解析。解析完成后，就可以在onMeasure方法中用到这些自定义属性了。
这里涉及到了View的加载过程-setContentView方法，简单说就是：我们一个控件的布局属性的创建，是通过父容器来完成的。
创建静态内部类LayoutParams并继承RelativeLayout的LayoutParams来保证相对布局的属性都能用
public static class LayoutParams extends RelativeLayout.LayoutParams{
//在arrts.xml中定义的属性
private float widthPercent;
private float heightPercent;
private float marginLeftPercent;
private float marginRightPercent;
private float marginTopPercent;
private float marginBottomPercent;
public LayoutParams(Context c, AttributeSet attrs) {
super(c, attrs);
//解析自定义属性
TypedArray a = c.obtainStyledAttributes(attrs,R.styleable.PercentLayout);
widthPercent = a.getFloat(R.styleable.PercentLayout_widthPercent, 0);
heightPercent = a.getFloat(R.styleable.PercentLayout_heightPercent, 0);
marginLeftPercent = a.getFloat(R.styleable.PercentLayout_marginLeftPercent, 0);
marginRightPercent = a.getFloat(R.styleable.PercentLayout_marginRightPercent, 0);
marginTopPercent = a.getFloat(R.styleable.PercentLayout_marginTopPercent, 0);
marginBottomPercent = a.getFloat(R.styleable.PercentLayout_marginBottomPercent, 0);
a.recycle();
}
}
总结一下就是先在attrs.xml中定义的属性，然后再解析自定义属性（宽、高、四周间距）
3.3 计算并设置百分比布局先通过MeasureSpec.getSize()方法获取父容器尺寸：
//获取父容器的尺寸
int widthSize = MeasureSpec.getSize(widthMeasureSpec);
int heightSize = MeasureSpec.getSize(heightMeasureSpec);
根据view加载的源码分析，还得重写父容器generateLayoutParams方法，return内部的LayoutParams：
public LayoutParams generateLayoutParams(AttributeSet attrs){
return new LayoutParams(getContext(), attrs);
}
在onMeasure中判断，这个params是否属于当前类的LayoutParams
@Override
protected boolean checkLayoutParams(ViewGroup.LayoutParams p) {
return p instanceof LayoutParams;
}
然后就可以进行百分比布局的设置了，从params中取出百分比的值后赋值。如果各个属性已经设置好了百分比的值，就能进行换算了
float widthPercent = lp.widthPercent;
params.width = (int) (widthSize * widthPercent);
四、使用
在xml的控件中，直接使用这些属性，并给定浮点型的值
五、完整代码attrs.xml
PercentLayout.xml
public class PercentLayout extends RelativeLayout {
public PercentLayout(Context context) {
super(context);
}
public PercentLayout(Context context, AttributeSet attrs) {
super(context, attrs);
}
public PercentLayout(Context context, AttributeSet attrs, int defStyleAttr) {
super(context, attrs, defStyleAttr);
}
@Override
protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
//获取父容器的尺寸
int widthSize = MeasureSpec.getSize(widthMeasureSpec);
int heightSize = MeasureSpec.getSize(heightMeasureSpec);
int count = getChildCount();
//遍历子控件
for (int i = 0; i 0){
params.width = (int) (widthSize * widthPercent);
}
if (heightPercent > 0){
params.height = (int) (heightSize * heightPercent);
}
if (marginLeftPercent > 0){
((LayoutParams) params).leftMargin = (int) (widthSize * marginLeftPercent);
}
if (marginRightPercent > 0){
((LayoutParams) params).rightMargin = (int) (widthSize * marginRightPercent);
}
if (marginTopPercent > 0){
((LayoutParams) params).topMargin = (int) (heightSize * marginTopPercent);
}
if (marginBottomPercent > 0){
((LayoutParams) params).bottomMargin = (int) (heightSize * marginBottomPercent);
}
}
}
super.onMeasure(widthMeasureSpec, heightMeasureSpec);
}
@Override
protected boolean checkLayoutParams(ViewGroup.LayoutParams p) {
return p instanceof LayoutParams;
}
public LayoutParams generateLayoutParams(AttributeSet attrs){
return new LayoutParams(getContext(), attrs);
}
public static class LayoutParams extends RelativeLayout.LayoutParams{
//在arrts.xml中定义的属性
private float widthPercent;
private float heightPercent;
private float marginLeftPercent;
private float marginRightPercent;
private float marginTopPercent;
private float marginBottomPercent;
public LayoutParams(Context c, AttributeSet attrs) {
super(c, attrs);
//解析自定义属性
TypedArray a = c.obtainStyledAttributes(attrs,R.styleable.PercentLayout);
widthPercent = a.getFloat(R.styleable.PercentLayout_widthPercent, 0);
heightPercent = a.getFloat(R.styleable.PercentLayout_heightPercent, 0);
marginLeftPercent = a.getFloat(R.styleable.PercentLayout_marginLeftPercent, 0);
marginRightPercent = a.getFloat(R.styleable.PercentLayout_marginRightPercent, 0);
marginTopPercent = a.getFloat(R.styleable.PercentLayout_marginTopPercent, 0);
marginBottomPercent = a.getFloat(R.styleable.PercentLayout_marginBottomPercent, 0);
a.recycle();
}
}
}
六、注意
这些属性的设定，对原有属性没有任何影响，我们只是扩展了它的使用。
作者：墨玉浮白
