Android 自定義View總結 —— onMeasure()
阿新 • • 發佈：2019-02-06
說明：本部落格為原創，轉載請註明出處 CSDN-ANDROID筆記棧
由於作者水平有限，錯誤在所難免，請見諒，可以留言，本人會及時改正
索引
onMeasure
該方法為 protected級，只有View的子類 才能過載該方法
// 主要用於測量檢視及其內容的大小,該方法被View類的measure(int,int)方法呼叫
// 過載該方法需要注意幾點：
// 1.必須呼叫setMeasuredDimension(int width, int height)來儲存測量結果，否則會拋IllegalStateException異常
// 2.引數widthSpec,heightSpec並不是大小值，而是由MeasureSpec類生成的“mode&size”複合值 // measure方法才是測量的入口,onMeasure中確定測量值
public final void measure(int widthMeasureSpec, int heightMeasureSpec) {
...
onMeasure(int,int);
...
}onMeasure(int widthMeasureSpec, int heightMeasureSpec)原始碼如下：
protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
// 呼叫setMeasureDemension()確定測量結果
// getSuggestedMiniumWidth()根據minWidth還有background drawable返回一個最小值
setMeasuredDimension(getDefaultSize(getSuggestedMinimumWidth(),widthMeasureSpec),
getDefaultSize(getSuggestedMinimumHeight(),heightMeasureSpec));
} View getDefaultSize(int size, int measureSpec)原始碼如下：
public static int getDefaultSize(int size, int measureSpec) {
int result = size;
// 通過MeasureSpec類，拆分measureSpec值，獲得mode和size值
// 後面會對這兩個值做解釋
int specMode = MeasureSpec.getMode(measureSpec);
int specSize = MeasureSpec.getSize(measureSpec);
switch (specMode) {
//無限制模式
case MeasureSpec.UNSPECIFIED:
result = size;
break;
//至多模式
case MeasureSpec.AT_MOST:
//精確模式
case MeasureSpec.EXACTLY:
result = specSize;
break;
}
return result;
}ViewGroup
ViewGroup 在onMeasure過程中稍有不同，因為你只有知道了所有的子View的大小，才能知道你自己需要多大。
Linearlayout 中遍歷所有子View，如果是橫向佈局則把所有子View的width相加，如果是縱向佈局則把所有子View的height相加（當然還需要考慮Padding，累加的值是不是超過了ParentView允許的值等等）。
// 大致如下
// 具體程式碼可以參考LinearLayout、FrameLayout原始碼
public void onMeasure(int widthMeasureSpec,int heightMeasureSpec){
int childCount=getChildCount();
// 遍歷所有子View
for(int i=0;i<childCount;i++){
View child=getChildAt(i);
child.measure(childWidthMeasureSpec,childHeightMeasureSpec);
}
}ViewGroup中定義了幾個protected方法用於測量子View
//ViewGroup自己完成所有子View的測量
protected void measureChildren(int widthMeasureSpec, int heightMeasureSpec) {
final int size = mChildrenCount;
final View[] children = mChildren;
for (int i = 0; i < size; ++i) {
final View child = children[i];
//過濾GONE狀態的View
if ((child.mViewFlags & VISIBILITY_MASK) != GONE) {
measureChild(child, widthMeasureSpec, heightMeasureSpec);
}
}
}protected void measureChild(View child, int parentWidthMeasureSpec,int parentHeightMeasureSpec) {
final LayoutParams lp = child.getLayoutParams();
final int childWidthMeasureSpec = getChildMeasureSpec(parentWidthMeasureSpec,
mPaddingLeft + mPaddingRight, lp.width);
final int childHeightMeasureSpec = getChildMeasureSpec(parentHeightMeasureSpec,
mPaddingTop + mPaddingBottom, lp.height);
child.measure(childWidthMeasureSpec, childHeightMeasureSpec);
}protected void measureChildWithMargins(View child,
int parentWidthMeasureSpec, int widthUsed,
int parentHeightMeasureSpec, int heightUsed) {
final MarginLayoutParams lp = (MarginLayoutParams) child.getLayoutParams();
final int childWidthMeasureSpec = getChildMeasureSpec(parentWidthMeasureSpec,
mPaddingLeft + mPaddingRight + lp.leftMargin + lp.rightMargin
+ widthUsed, lp.width);
final int childHeightMeasureSpec = getChildMeasureSpec(parentHeightMeasureSpec,
mPaddingTop + mPaddingBottom + lp.topMargin + lp.bottomMargin
+ heightUsed, lp.height);
child.measure(childWidthMeasureSpec, childHeightMeasureSpec);
}// 生成child measureSpec
public static int getChildMeasureSpec(int spec, int padding, int childDimension) {
int specMode = MeasureSpec.getMode(spec);
int specSize = MeasureSpec.getSize(spec);
int size = Math.max(0, specSize - padding);
int resultSize = 0;
int resultMode = 0;
switch (specMode) {
// Parent has imposed an exact size on us
case MeasureSpec.EXACTLY:
if (childDimension >= 0) {
resultSize = childDimension;
resultMode = MeasureSpec.EXACTLY;
} else if (childDimension == LayoutParams.MATCH_PARENT) {
// Child wants to be our size. So be it.
resultSize = size;
resultMode = MeasureSpec.EXACTLY;
} else if (childDimension == LayoutParams.WRAP_CONTENT) {
// Child wants to determine its own size. It can't be
// bigger than us.
resultSize = size;
resultMode = MeasureSpec.AT_MOST;
}
break;
// Parent has imposed a maximum size on us
case MeasureSpec.AT_MOST:
if (childDimension >= 0) {
// Child wants a specific size... so be it
resultSize = childDimension;
resultMode = MeasureSpec.EXACTLY;
} else if (childDimension == LayoutParams.MATCH_PARENT) {
// Child wants to be our size, but our size is not fixed.
// Constrain child to not be bigger than us.
resultSize = size;
resultMode = MeasureSpec.AT_MOST;
} else if (childDimension == LayoutParams.WRAP_CONTENT) {
// Child wants to determine its own size. It can't be
// bigger than us.
resultSize = size;
resultMode = MeasureSpec.AT_MOST;
}
break;
// Parent asked to see how big we want to be
case MeasureSpec.UNSPECIFIED:
if (childDimension >= 0) {
// Child wants a specific size... let him have it
resultSize = childDimension;
resultMode = MeasureSpec.EXACTLY;
} else if (childDimension == LayoutParams.MATCH_PARENT) {
// Child wants to be our size... find out how big it should
// be
resultSize = View.sUseZeroUnspecifiedMeasureSpec ? 0 : size;
resultMode = MeasureSpec.UNSPECIFIED;
} else if (childDimension == LayoutParams.WRAP_CONTENT) {
// Child wants to determine its own size.... find out how
// big it should be
resultSize = View.sUseZeroUnspecifiedMeasureSpec ? 0 : size;
resultMode = MeasureSpec.UNSPECIFIED;
}
break;
}
//noinspection ResourceType
return MeasureSpec.makeMeasureSpec(resultSize, resultMode);
}MeasureSpec類
MeasureSpec類中定義了三種模式分別是：UNSPECIFIED（無限制模式）、
EXACTLY（精確模式）、AT_MOST（至多模式）
private static final int MODE_SHIFT = 30; //30位
private static final int MODE_MASK = 0x3 << MODE_SHIFT; //二進位制11(低30位為0),左移了30位
public static final int UNSPECIFIED = 0 << MODE_SHIFT; //二進位制00(低30位為0)
public static final int EXACTLY = 1 << MODE_SHIFT; //二進位制01(低30位為0)
public static final int AT_MOST = 2 << MODE_SHIFT; //二進位制11(低30位為0)UNSPECIFIED模式
ParentView不約束子View，子View想多大就多大
EXACTLY模式
ParentView已經指定一個精確的大小給子View，子View大小已被確定
<TextView android:layout_width="48dp"
android:layout_height="48dp"/>AT_MOST模式
ParentView指定一個最大值，子View的大小不能超過這個值
// match_parent 會根據ParentView的模式不同而不同
<TextView android:layout_width="wrap_content"
android:layout_height="wrap_content"/>獲取Mode和Size
MeasureSpec類定義了幾個公共靜態方法來獲取Mode和size值
//java int型別是32位的，MODE_MASK是110...0（共32位），做&操作能取高2位值也就是mode(UNSPECIFIED,EXACTLY,AT_MOST)值
public static int getMode(int measureSpec) {
return (measureSpec & MODE_MASK);
}//java int型別是32位的，~MODE_MASK是001...1（共32位），做&操作能取低位30位值也就是size值
public static int getSize(int measureSpec) {
return (measureSpec & ~MODE_MASK);
}measureSpec可以通過下面的方法生成
// 低30位size值和高2位mode值
public static int makeMeasureSpec(int size,int mode) {
if (sUseBrokenMakeMeasureSpec) {
return size + mode;
} else {
return (size & ~MODE_MASK) | (mode & MODE_MASK);
}
}Demo
GitHub地址: GitHub
環境: Windows7+JAVA8
IDE: AndroidStdio2.2.2
compileSdkVersion:24
測試裝置:Nexus5(6.0.1)
執行結果截圖
自定義View 過載onMeasure方法並輸出日誌
@Override
protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec)
{
int widthMode = MeasureSpec.getMode(widthMeasureSpec);
int widthSize = MeasureSpec.getSize(widthMeasureSpec);
int heightMode = MeasureSpec.getMode(heightMeasureSpec);
int heightSize = MeasureSpec.getSize(heightMeasureSpec);
DLDebug.debug(TAG, "onMeasure: ---->");
DLDebug.debug(TAG, "[width] " + "mode:" + ViewHelper.parseMeasureMode(widthMode) + " , size:" + widthSize);
DLDebug.debug(TAG, "[height] " + "mode:" + ViewHelper.parseMeasureMode(heightMode) + " , size:" + heightSize);
super.onMeasure(widthMeasureSpec, heightMeasureSpec);
DLDebug.debug(TAG, "[result] " + getMeasuredWidth() + "," + getMeasuredHeight());
DLDebug.debug(TAG, "<----");
}//XML原始碼
<?xml version="1.0" encoding="utf-8"?>
<com.neulion.android.dl.customviewdemo.widget.DLFrameLayout
xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:id="@+id/activity_main"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:background="#ffffff"
tools:context="com.neulion.android.dl.customviewdemo.MainActivity">
<com.neulion.android.dl.customviewdemo.widget.DLCustomViewGroup
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:background="#ffeb3b">
<com.neulion.android.dl.customviewdemo.widget.DLCustomView
android:layout_width="48dp"
android:layout_height="48dp"
android:background="#ff0000" />
<com.neulion.android.dl.customviewdemo.widget.DLCustomView
android:layout_width="48dp"
android:layout_height="48dp"
android:background="#00ff00" />
<com.neulion.android.dl.customviewdemo.widget.DLCustomView
android:layout_width="48dp"
android:layout_height="48dp"
android:background="#0000ff" />
<com.neulion.android.dl.customviewdemo.widget.DLCustomView
android:layout_width="48dp"
android:layout_height="48dp"
android:background="#000000" />
</com.neulion.android.dl.customviewdemo.widget.DLCustomViewGroup>
<com.neulion.android.dl.customviewdemo.widget.DLCustomView
android:id="@+id/dl_custom_view_exactly"
android:layout_width="48dp"
android:layout_height="48dp"
android:layout_gravity="left|center_vertical"
android:background="@color/colorAccent" />
<TextView
android:id="@+id/device_info"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_gravity="right|top|end"
android:minHeight="48dp"
android:maxWidth="240dp"
android:textSize="14dp"
android:textColor="#000000"
tools:ignore="SpUsage" />
</com.neulion.android.dl.customviewdemo.widget.DLFrameLayout>
結果如下：
// onMeasure方法可能會被多次呼叫!
12-08 14:48:03.489 I/DL_DLFrameLayout: onMeasure: ---->
12-08 14:48:03.489 I/DL_DLFrameLayout: [width] mode:EXACTLY , size:1080(1080是當前ParentView及Activity根View允許其子View的最大值,DLFrameLayout寬高設定的是match_parent/wrap_content返回這個結果)
12-08 14:48:03.489 I/DL_DLFrameLayout: [height] mode:EXACTLY , size:1392（這個值可以看出是螢幕的高-statusBar高度-actionBar高度-navigationBar高度的結果）
12-08 14:48:03.489 I/DL_DLCustomViewGroup: onMeasure: ---->
12-08 14:48:03.489 I/DL_DLCustomViewGroup: [width] mode:EXACTLY size:1080
12-08 14:48:03.489 I/DL_DLCustomViewGroup: [height] mode:AT_MOST size:1392
12-08 14:48:03.489 D/DL_DLCustomView: onMeasure: ---->
12-08 14:48:03.489 D/DL_DLCustomView: [width] mode:EXACTLY , size:144 // DLCustomView中寬高設定的是48dp，返回這個結果
12-08 14:48:03.489 D/DL_DLCustomView: [height] mode:EXACTLY , size:144
12-08 14:48:03.490 D/DL_DLCustomView: [result] 144,144
12-08 14:48:03.490 D/DL_DLCustomView: <----
12-08 14:48:03.490 D/DL_DLCustomView: onMeasure: ---->
12-08 14:48:03.490 D/DL_DLCustomView: [width] mode:EXACTLY , size:144
12-08 14:48:03.490 D/DL_DLCustomView: [height] mode:EXACTLY , size:144
12-08 14:48:03.490 D/DL_DLCustomView: [result] 144,144
12-08 14:48:03.490 D/DL_DLCustomView: <----
12-08 14:48:03.490 D/DL_DLCustomView: onMeasure: ---->
12-08 14:48:03.490 D/DL_DLCustomView: [width] mode:EXACTLY , size:144
12-08 14:48:03.490 D/DL_DLCustomView: [height] mode:EXACTLY , size:144
12-08 14:48:03.490 D/DL_DLCustomView: [result] 144,144
12-08 14:48:03.490 D/DL_DLCustomView: <----
12-08 14:48:03.490 D/DL_DLCustomView: onMeasure: ---->
12-08 14:48:03.490 D/DL_DLCustomView: [width] mode:EXACTLY , size:144
12-08 14:48:03.490 D/DL_DLCustomView: [height] mode:EXACTLY , size:144
12-08 14:48:03.490 D/DL_DLCustomView: [result] 144,144
12-08 14:48:03.490 D/DL_DLCustomView: <----
12-08 14:48:03.490 I/DL_DLCustomViewGroup: [result] 1080,576
12-08 14:48:03.490 I/DL_DLCustomViewGroup: <----
12-08 14:48:03.490 D/DL_DLCustomView: onMeasure: ---->
12-08 14:48:03.490 D/DL_DLCustomView: [width] mode:EXACTLY , size:144
12-08 14:48:03.490 D/DL_DLCustomView: [height] mode:EXACTLY , size:144
12-08 14:48:03.490 D/DL_DLCustomView: [result] 144,144
12-08 14:48:03.490 D/DL_DLCustomView: <----
12-08 14:48:03.508 I/DL_DLFrameLayout: [result] 1080,1392
12-08 14:48:03.508 I/DL_DLFrameLayout: <----
12-08 14:48:03.557 I/DL_DLFrameLayout: onMeasure: ---->
12-08 14:48:03.557 I/DL_DLFrameLayout: [width] mode:EXACTLY , size:1080
12-08 14:48:03.557 I/DL_DLFrameLayout: [height] mode:EXACTLY , size:1536
12-08 14:48:03.557 I/DL_DLCustomViewGroup: onMeasure: ---->
12-08 14:48:03.557 I/DL_DLCustomViewGroup: [width] mode:EXACTLY size:1080
12-08 14:48:03.557 I/DL_DLCustomViewGroup: [height] mode:AT_MOST size:1536
12-08 14:48:03.557 D/DL_DLCustomView: onMeasure: ---->
12-08 14:48:03.557 D/DL_DLCustomView: [width] mode:EXACTLY , size:144
12-08 14:48:03.557 D/DL_DLCustomView: [height] mode:EXACTLY , size:144
12-08 14:48:03.557 D/DL_DLCustomView: [result] 144,144
12-08 14:48:03.557 D/DL_DLCustomView: <----
12-08 14:48:03.557 D/DL_DLCustomView: onMeasure: ---->
12-08 14:48:03.557 D/DL_DLCustomView: [width] mode:EXACTLY , size:144
12-08 14:48:03.557 D/DL_DLCustomView: [height] mode:EXACTLY , size:144
12-08 14:48:03.557 D/DL_DLCustomView: [result] 144,144
12-08 14:48:03.557 D/DL_DLCustomView: <----
12-08 14:48:03.557 D/DL_DLCustomView: onMeasure: ---->
12-08 14:48:03.557 D/DL_DLCustomView: [width] mode:EXACTLY , size:144
12-08 14:48:03.557 D/DL_DLCustomView: [height] mode:EXACTLY , size:144
12-08 14:48:03.557 D/DL_DLCustomView: [result] 144,144
12-08 14:48:03.557 D/DL_DLCustomView: <----
12-08 14:48:03.557 D/DL_DLCustomView: onMeasure: ---->
12-08 14:48:03.557 D/DL_DLCustomView: [width] mode:EXACTLY , size:144
12-08 14:48:03.558 D/DL_DLCustomView: [height] mode:EXACTLY , size:144
12-08 14:48:03.558 D/DL_DLCustomView: [result] 144,144
12-08 14:48:03.558 D/DL_DLCustomView: <----
12-08 14:48:03.558 I/DL_DLCustomViewGroup: [result] 1080,576
12-08 14:48:03.558 I/DL_DLCustomViewGroup: <----
12-08 14:48:03.558 D/DL_DLCustomView: onMeasure: ---->
12-08 14:48:03.558 D/DL_DLCustomView: [width] mode:EXACTLY , size:144
12-08 14:48:03.558 D/DL_DLCustomView: [height] mode:EXACTLY , size:144
12-08 14:48:03.558 D/DL_DLCustomView: [result] 144,144
12-08 14:48:03.558 D/DL_DLCustomView: <----
12-08 14:48:03.558 I/DL_DLFrameLayout: [result] 1080,1536
12-08 14:48:03.558 I/DL_DLFrameLayout: <----
12-08 14:48:03.558 I/DL_DLFrameLayout: onSizeChanged: 1080x1536 , old 0x0
12-08 14:48:03.559 I/DL_DLFrameLayout: onLayout: true [0,0,1080,1536]
12-08 14:48:03.559 I/DL_DLCustomViewGroup: onSizeChanged: 1080x576 , old 0x0
12-08 14:48:03.559 I/DL_DLCustomViewGroup: onLayout: true [0,0,1080,576]
12-08 14:48:03.559 D/DL_DLCustomView: onSizeChanged: 144x144 , old 0x0
12-08 14:48:03.559 D/DL_DLCustomView: onLayout: true [0,0,144,144]
12-08 14:48:03.559 D/DL_DLCustomView: onSizeChanged: 144x144 , old 0x0
12-08 14:48:03.559 D/DL_DLCustomView: onLayout: true [144,144,288,288]
12-08 14:48:03.559 D/DL_DLCustomView: onSizeChanged: 144x144 , old 0x0
12-08 14:48:03.559 D/DL_DLCustomView: onLayout: true [288,288,432,432]
12-08 14:48:03.559 D/DL_DLCustomView: onSizeChanged: 144x144 , old 0x0
12-08 14:48:03.559 D/DL_DLCustomView: onLayout: true [432,432,576,576]
12-08 14:48:03.559 D/DL_DLCustomView: onSizeChanged: 144x144 , old 0x0
12-08 14:48:03.559 D/DL_DLCustomView: onLayout: true [0,696,144,840]
12-08 14:48:03.572 I/DL_DLFrameLayout: onMeasure: ---->
12-08 14:48:03.572 I/DL_DLFrameLayout: [width] mode:EXACTLY , size:1080
12-08 14:48:03.572 I/DL_DLFrameLayout: [height] mode:EXACTLY , size:1536
12-08 14:48:03.572 I/DL_DLCustomViewGroup: onMeasure: ---->
12-08 14:48:03.572 I/DL_DLCustomViewGroup: [width] mode:EXACTLY size:1080
12-08 14:48:03.572 I/DL_DLCustomViewGroup: [height] mode:AT_MOST size:1536
12-08 14:48:03.572 D/DL_DLCustomView: onMeasure: ---->
12-08 14:48:03.572 D/DL_DLCustomView: [width] mode:EXACTLY , size:144
12-08 14:48:03.572 D/DL_DLCustomView: [height] mode:EXACTLY , size:144
12-08 14:48:03.572 D/DL_DLCustomView: [result] 144,144
12-08 14:48:03.572 D/DL_DLCustomView: <----
12-08 14:48:03.572 D/DL_DLCustomView: onMeasure: ---->
12-08 14:48:03.572 D/DL_DLCustomView: [width] mode:EXACTLY , size:144
12-08 14:48:03.572 D/DL_DLCustomView: [height] mode:EXACTLY , size:144
12-08 14:48:03.572 D/DL_DLCustomView: [result] 144,144
12-08 14:48:03.572 D/DL_DLCustomView: <----
12-08 14:48:03.572 D/DL_DLCustomView: onMeasure: ---->
12-08 14:48:03.572 D/DL_DLCustomView: [width] mode:EXACTLY , size:144
12-08 14:48:03.572 D/DL_DLCustomView: [height] mode:EXACTLY , size:144
12-08 14:48:03.572 D/DL_DLCustomView: [result] 144,144
12-08 14:48:03.572 D/DL_DLCustomView: <----
12-08 14:48:03.573 D/DL_DLCustomView: onMeasure: ---->
12-08 14:48:03.573 D/DL_DLCustomView: [width] mode:EXACTLY , size:144
12-08 14:48:03.573 D/DL_DLCustomView: [height] mode:EXACTLY , size:144
12-08 14:48:03.573 D/DL_DLCustomView: [result] 144,144
12-08 14:48:03.573 D/DL_DLCustomView: <----
12-08 14:48:03.573 I/DL_DLCustomViewGroup: [result] 1080,576
12-08 14:48:03.573 I/DL_DLCustomViewGroup: <----
12-08 14:48:03.573 D/DL_DLCustomView: onMeasure: ---->
12-08 14:48:03.573 D/DL_DLCustomView: [width] mode:EXACTLY , size:144
12-08 14:48:03.573 D/DL_DLCustomView: [height] mode:EXACTLY , size:144
12-08 14:48:03.573 D/DL_DLCustomView: [result] 144,144
12-08 14:48:03.573 D/DL_DLCustomView: <----
12-08 14:48:03.574 I/DL_DLFrameLayout: [result] 1080,1536
12-08 14:48:03.574 I/DL_DLFrameLayout: <----
12-08 14:48:03.574 I/DL_DLFrameLayout: onLayout: false [0,0,1080,1536]
12-08 14:48:03.574 I/DL_DLCustomViewGroup: onLayout: false [0,0,1080,576]
12-08 14:48:03.574 D/DL_DLCustomView: onLayout: false [0,0,144,144]
12-08 14:48:03.574 D/DL_DLCustomView: onLayout: false [144,144,288,288]
12-08 14:48:03.574 D/DL_DLCustomView: onLayout: false [288,288,432,432]
12-08 14:48:03.574 D/DL_DLCustomView: onLayout: false [432,432,576,576]
12-08 14:48:03.574 D/DL_DLCustomView: onLayout: false [0,696,144,840]
12-08 14:48:03.575 I/DL_DLFrameLayout: onDraw
12-08 14:48:03.575 I/DL_DLCustomViewGroup: onDraw
12-08 14:48:03.575 D/DL_DLCustomView: onDraw
12-08 14:48:03.575 D/DL_DLCustomView: onDraw
12-08 14:48:03.576 D/DL_DLCustomView: onDraw
12-08 14:48:03.576 D/DL_DLCustomView: onDraw
12-08 14:48:03.576 D/DL_DLCustomView: onDraw