屏幕适配-百分比布局
原理：以父容器尺寸作为参考，在View的加载过程，根据当前父容器实际尺寸换算出目标尺寸，在作用在View上。
百分比布局实际是对容器的一中扩展，扩展的是宽高等比例的设置。
1、自定义属性
attrs.xml
<?xml version="1.0" encoding="utf-8"?>
<resources>
<declare-styleable name="PercentLayout">
<attr name="widthPercent" format="float" />
<attr name="heightPercent" format="float" />
<attr name="marginLeftPercent" format="float" />
<attr name="marginRightPercent" format="float" />
<attr name="marginTopPercent" format="float" />
<attr name="marginBottomPercent" format="float" />
</declare-styleable>
</resources>
2、对属性进行解析
以RelativeLayout为例，看一下它是如何对属性进行解析的？
RelativeLayout的工作原理：在它里面定义了一个LayoutParams静态内部类，在这里面定义了我们的自定义属性，这些属性都是我们这个容器的特有的属性。
解析是在 public LayoutParams(Context c, AttributeSet attrs)构造方法中：
现在我们看一下，这些属性是如何添加到我们的View中的。
我们都知道PhoneWindow是Window的唯一实现类，我们从PhoneWindow的setContentView开始
public View inflate(XmlPullParser parser, @Nullable ViewGroup root, boolean attachToRoot) {
synchronized (mConstructorArgs) {
Trace.traceBegin(Trace.TRACE_TAG_VIEW, "inflate");
final Context inflaterContext = mContext;
final AttributeSet attrs = Xml.asAttributeSet(parser);
Context lastContext = (Context) mConstructorArgs[0];
mConstructorArgs[0] = inflaterContext;
View result = root;
........
if (TAG_MERGE.equals(name)) {
if (root == null || !attachToRoot) {
throw new InflateException("<merge /> can be used only with a valid "
+ "ViewGroup root and attachToRoot=true");
}
rInflate(parser, root, inflaterContext, attrs, false);
} else {
// Temp is the root view that was found in the xml 表示我们布局文件的根布局
final View temp = createViewFromTag(root, name, inflaterContext, attrs);
ViewGroup.LayoutParams params = null;
if (root != null) {
if (DEBUG) {
System.out.println("Creating params from root: " +
root);
}
// Create layout params that match root, if supplied
params = root.generateLayoutParams(attrs);
if (!attachToRoot) {
// Set the layout params for temp if we are not
// attaching. (If we are, we use addView, below)
temp.setLayoutParams(params);
}
}
...........
}
我们看到重要的核心代码 params = root.generateLayoutParams(attrs);和
temp.setLayoutParams(params);
如下就是我们自定义的百分不布局:
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();
for (int i = 0; i < count; i++) {
View child = getChildAt(i);//重新设置子View的布局属性，在进行View的测量
ViewGroup.LayoutParams params = child.getLayoutParams();
//如果说是百分比布局属性
if (checkLayoutParams(params)){
LayoutParams lp = (LayoutParams)params;
//自定百分比属性
float widthPercent = lp.widthPercent;
float heightPercent = lp.heightPercent;
float marginLeftPercent = lp.marginLeftPercent;
float marginRightPercent= lp.marginRightPercent;
float marginTopPercent= lp.marginTopPercent;
float marginBottomPercent = lp.marginBottomPercent;
//根据当前父容器实际尺寸换算出目标尺寸
if (widthPercent > 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{
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();
}
}
}
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