自定义ViewGroup(二)
2019-08-29 本文已影响0人
cao苗子
根据我们上一次 文章 修改我们的布局
<?xml version="1.0" encoding="utf-8"?>
<com.miaozi.myviewgroup.MyViewGroup
xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:background="@color/colorPrimary"
tools:context=".MainActivity">
<Button
android:text="第一"
android:layout_width="match_parent"
android:layout_height="100dp" />
<Button
android:text="第一"
android:layout_width="200dp"
android:layout_height="100dp" />
<Button
android:text="第一"
android:layout_width="100dp"
android:layout_height="100dp" />
<TextView
android:text="我的妈妈呀"
android:layout_width="wrap_content"
android:layout_height="wrap_content" />
</com.miaozi.myviewgroup.MyViewGroup>
修改的只有：
android:layout_width="wrap_content"
android:layout_height="wrap_content"
效果还是没有变化，这是为什么呢？
下面我们就来分析：
（1）view的三种设计模式
1.MeasureSpec.AT_MOST：大小不可超过某数值，如：wrap_content
2.MeasureSpec.EXACTLY：确切的大小，如：100dp或者march_parent
3.MeasureSpec.UNSPECIFIED：不对View大小做限制，如：ListView，ScrollView
（2）我们看MeasureSpec的源码
public static class MeasureSpec {
private static final int MODE_SHIFT = 30;
private static final int MODE_MASK = 0x3 << MODE_SHIFT;
/** @hide */
@IntDef({UNSPECIFIED, EXACTLY, AT_MOST})
@Retention(RetentionPolicy.SOURCE)
public @interface MeasureSpecMode {}
/**
* Measure specification mode: The parent has not imposed any constraint
* on the child. It can be whatever size it wants.
*/
public static final int UNSPECIFIED = 0 << MODE_SHIFT;
/**
* Measure specification mode: The parent has determined an exact size
* for the child. The child is going to be given those bounds regardless
* of how big it wants to be.
*/
public static final int EXACTLY = 1 << MODE_SHIFT;
/**
* Measure specification mode: The child can be as large as it wants up
* to the specified size.
*/
public static final int AT_MOST = 2 << MODE_SHIFT;
/**
* Creates a measure specification based on the supplied size and mode.
*
* The mode must always be one of the following:
* <ul>
* <li>{@link android.view.View.MeasureSpec#UNSPECIFIED}</li>
* <li>{@link android.view.View.MeasureSpec#EXACTLY}</li>
* <li>{@link android.view.View.MeasureSpec#AT_MOST}</li>
* </ul>
*
* <p><strong>Note:</strong> On API level 17 and lower, makeMeasureSpec's
* implementation was such that the order of arguments did not matter
* and overflow in either value could impact the resulting MeasureSpec.
* {@link android.widget.RelativeLayout} was affected by this bug.
* Apps targeting API levels greater than 17 will get the fixed, more strict
* behavior.</p>
*
* @param size the size of the measure specification
* @param mode the mode of the measure specification
* @return the measure specification based on size and mode
*/
public static int makeMeasureSpec(@IntRange(from = 0, to = (1 << MeasureSpec.MODE_SHIFT) - 1) int size,
@MeasureSpecMode int mode) {
if (sUseBrokenMakeMeasureSpec) {
return size + mode;
} else {
return (size & ~MODE_MASK) | (mode & MODE_MASK);
}
}
/**
* Like {@link #makeMeasureSpec(int, int)}, but any spec with a mode of UNSPECIFIED
* will automatically get a size of 0. Older apps expect this.
*
* @hide internal use only for compatibility with system widgets and older apps
*/
public static int makeSafeMeasureSpec(int size, int mode) {
if (sUseZeroUnspecifiedMeasureSpec && mode == UNSPECIFIED) {
return 0;
}
return makeMeasureSpec(size, mode);
}
/**
* Extracts the mode from the supplied measure specification.
*
* @param measureSpec the measure specification to extract the mode from
* @return {@link android.view.View.MeasureSpec#UNSPECIFIED},
* {@link android.view.View.MeasureSpec#AT_MOST} or
* {@link android.view.View.MeasureSpec#EXACTLY}
*/
@MeasureSpecMode
public static int getMode(int measureSpec) {
//noinspection ResourceType
return (measureSpec & MODE_MASK);
}
/**
* Extracts the size from the supplied measure specification.
*
* @param measureSpec the measure specification to extract the size from
* @return the size in pixels defined in the supplied measure specification
*/
public static int getSize(int measureSpec) {
return (measureSpec & ~MODE_MASK);
}
static int adjust(int measureSpec, int delta) {
final int mode = getMode(measureSpec);
int size = getSize(measureSpec);
if (mode == UNSPECIFIED) {
// No need to adjust size for UNSPECIFIED mode.
return makeMeasureSpec(size, UNSPECIFIED);
}
size += delta;
if (size < 0) {
Log.e(VIEW_LOG_TAG, "MeasureSpec.adjust: new size would be negative! (" + size +
") spec: " + toString(measureSpec) + " delta: " + delta);
size = 0;
}
return makeMeasureSpec(size, mode);
}
/**
* Returns a String representation of the specified measure
* specification.
*
* @param measureSpec the measure specification to convert to a String
* @return a String with the following format: "MeasureSpec: MODE SIZE"
*/
public static String toString(int measureSpec) {
int mode = getMode(measureSpec);
int size = getSize(measureSpec);
StringBuilder sb = new StringBuilder("MeasureSpec: ");
if (mode == UNSPECIFIED)
sb.append("UNSPECIFIED ");
else if (mode == EXACTLY)
sb.append("EXACTLY ");
else if (mode == AT_MOST)
sb.append("AT_MOST ");
else
sb.append(mode).append(" ");
sb.append(size);
return sb.toString();
}
}
可见MeasureSpec由两个部分组成，一个mode一个size，总共32位，最高两位代码mode，剩下30位代表size。
主要的方法有三个：
第一个：设置mode和size
public static int makeSafeMeasureSpec(int size, int mode) {
if (sUseZeroUnspecifiedMeasureSpec && mode == UNSPECIFIED) {
return 0;
}
return makeMeasureSpec(size, mode);
}
第二个：获取模式
public static int getSize(int measureSpec) {
return (measureSpec & ~MODE_MASK);
}
第三个：获取size
public static int getMode(int measureSpec) {
//noinspection ResourceType
return (measureSpec & MODE_MASK);
}
带着上面的分析我们重新写onMeasure()方法中的代码：
/**
* 测量宽高
* @param widthMeasureSpec
* @param heightMeasureSpec
*/
@Override
protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
//获取宽度的模式
int widthMode = MeasureSpec.getMode(widthMeasureSpec);
//获取高度模式
int heightMode = MeasureSpec.getMode(heightMeasureSpec);
//获取width的大小
int widthSize = MeasureSpec.getSize(widthMeasureSpec);
//获取height的大小
int heightSize = MeasureSpec.getSize(heightMeasureSpec);
//最大宽度
int maxWidth = 0;
//最大高度
int maxHeight = 0;
int childCount = getChildCount();
for (int i = 0; i < childCount; i++) {
View childView = getChildAt(i);
//测量子view的宽高
measureChild(childView,widthMeasureSpec,heightMeasureSpec);
MarginLayoutParams lp = (MarginLayoutParams) childView.getLayoutParams();
if(maxWidth < lp.width){
maxWidth = lp.width;
}
maxHeight += lp.height;
}
//测量自己的宽高
if(childCount == 0){
super.onMeasure(widthMeasureSpec,heightMeasureSpec);
}else if(widthMode == MeasureSpec.AT_MOST && heightMode == MeasureSpec.AT_MOST){
//宽高都是wrap_content
setMeasuredDimension(maxWidth,maxHeight);
}else if(widthMode == MeasureSpec.AT_MOST){
//只有宽是wrap_content
setMeasuredDimension(maxWidth,heightSize);
}else if(heightMode == MeasureSpec.AT_MOST){
//只有高是wrap_content
setMeasuredDimension(widthSize,maxHeight);
}else {
setMeasuredDimension(widthSize,heightSize);
}
}
无论你怎么设置都是正确的了。
注意要复写：
@Override
public ViewGroup.LayoutParams generateLayoutParams(AttributeSet attrs) {
return new MarginLayoutParams(getContext(),attrs);
}
否则会报错的
