Android View的绘制机制前世今生---前世
就像上个文章说的，触摸事件的传递机制是从外层到内层的过程。
我们想来看看这个页面里面的层级关系：
以下我们就用what-how-why三部曲的方式来分析View的绘制过程。
由于篇幅很大，所以分几篇来解析这个过程。
这篇主要是自定义view/viewgroup，以及从Activity到DecorView的加载过程。
1.what：怎么自定义一个View
1.1自定义View
自定义View的话，常见过程如下：
/**
* @author DemanMath
* @date 2020-02-16
*
*/
class CustomView : View {
constructor(context: Context):super(context)
constructor(context: Context,attributeSet: AttributeSet):super(context,attributeSet)
constructor(context: Context,attributeSet: AttributeSet,def:Int):super(context,attributeSet,def)
override fun onDraw(canvas: Canvas?) {
super.onDraw(canvas)
AppLog.i()
}
override fun onLayout(changed: Boolean, left: Int, top: Int, right: Int, bottom: Int) {
super.onLayout(changed, left, top, right, bottom)
AppLog.i()
}
override fun onMeasure(widthMeasureSpec: Int, heightMeasureSpec: Int) {
super.onMeasure(widthMeasureSpec, heightMeasureSpec)
AppLog.i()
}
}
三个构造方法+三个可以复写的方法。
我们先看下这3个方法的顺序：
2020-02-16 13:50:28.212 23141-23141/com.joyfulmath.androidarchitecture I/Arch_App.CustomView: onMeasure: [at (CustomView.kt:32)]
2020-02-16 13:50:28.222 23141-23141/com.joyfulmath.androidarchitecture I/Arch_App.CustomView: onMeasure: [at (CustomView.kt:32)]
2020-02-16 13:50:28.253 23141-23141/com.joyfulmath.androidarchitecture I/Arch_App.CustomView: onMeasure: [at (CustomView.kt:32)]
2020-02-16 13:50:28.255 23141-23141/com.joyfulmath.androidarchitecture I/Arch_App.CustomView: onMeasure: [at (CustomView.kt:32)]
2020-02-16 13:50:28.259 23141-23141/com.joyfulmath.androidarchitecture I/Arch_App.CustomView: onLayout: [at (CustomView.kt:27)]
2020-02-16 13:50:28.403 23141-23141/com.joyfulmath.androidarchitecture I/Arch_App.CustomView: onDraw: [at (CustomView.kt:22)]
1.2自定义ViewGroup
上代码
package com.joyfulmath.androidarchitecture.view
import android.content.Context
import android.util.AttributeSet
import android.view.ViewGroup
import com.joyfulmath.androidarchitecture.base.AppLog
import kotlin.math.PI
import kotlin.math.cos
import kotlin.math.min
import kotlin.math.sin
/**
* @author DemanMath
* @date 2020-02-16
*
*/
class FerrisWheel:ViewGroup {
var count = 12
var a = 2*PI/count
var startA = PI/2
constructor(context: Context):super(context){
initViews()
}
constructor(context: Context,attributeSet: AttributeSet):super(context,attributeSet){
initViews()
}
constructor(context: Context,attributeSet: AttributeSet,def:Int):super(context,attributeSet,def){
initViews()
}
private fun initViews() {
for(i in 0 until count){
this.addView(CustomView(context))
}
}
override fun onLayout(changed: Boolean, l: Int, t: Int, r: Int, b: Int) {
var mViewWidth = measuredWidth
var mViewHeight = measuredHeight
AppLog.i("$mViewWidth,$mViewHeight")
var cx = mViewWidth/2
var cy = mViewHeight/2
var r = min(measuredWidth,measuredHeight)*0.5f -20
AppLog.i("r:$r,cx:$cx")
for(i in 0 until count){
var view = getChildAt(i)
var width = view.measuredWidth
var height = view.measuredHeight
var cx1 = r* sin(startA+a*i)
var cy1 = -r* cos(startA+a*i)
AppLog.i("width:$width,height:$height")
AppLog.i("cx1:$cx1,cy1:$cy1")
view.layout(cx+(cx1-width/2).toInt(),
cy+(cy1-height/2).toInt(),
cx+(cx1+width/2).toInt(),
cy+(cy1+height/2).toInt())
}
}
override fun onMeasure(widthMeasureSpec: Int, heightMeasureSpec: Int) {
measureChildren(widthMeasureSpec,heightMeasureSpec)
super.onMeasure(widthMeasureSpec, heightMeasureSpec)
}
}
效果如下：
这里override了layout方法。可见View的绘制跟他的父View只有一个关系，ViewGroup指定了子View的位置。
关于View/ViewGroup绘制的机制，在下一节讨论。
2.How：View的绘制机制是什么
从上一节看出：整个绘制流程三个过程，measure，layout，draw这三个过程。
下面我们从源码的角度来分析下是不是这个过程。
final void handleResumeActivity(IBinder token,
boolean clearHide, boolean isForward, boolean reallyResume, int seq, String reason) {
.......
// TODO Push resumeArgs into the activity for consideration
r = performResumeActivity(token, clearHide, reason);
if (r != null) {
final Activity a = r.activity;
if (localLOGV) Slog.v(
TAG, "Resume " + r + " started activity: " +
a.mStartedActivity + ", hideForNow: " + r.hideForNow
+ ", finished: " + a.mFinished);
final int forwardBit = isForward ?
WindowManager.LayoutParams.SOFT_INPUT_IS_FORWARD_NAVIGATION : 0;
// If the window hasn't yet been added to the window manager,
// and this guy didn't finish itself or start another activity,
// then go ahead and add the window.
boolean willBeVisible = !a.mStartedActivity;
if (!willBeVisible) {
try {
willBeVisible = ActivityManager.getService().willActivityBeVisible(
a.getActivityToken());
} catch (RemoteException e) {
throw e.rethrowFromSystemServer();
}
}
if (r.window == null && !a.mFinished && willBeVisible) {
r.window = r.activity.getWindow();
View decor = r.window.getDecorView();
decor.setVisibility(View.INVISIBLE);
ViewManager wm = a.getWindowManager();
WindowManager.LayoutParams l = r.window.getAttributes();
a.mDecor = decor;
l.type = WindowManager.LayoutParams.TYPE_BASE_APPLICATION;
l.softInputMode |= forwardBit;
if (r.mPreserveWindow) {
a.mWindowAdded = true;
r.mPreserveWindow = false;
// Normally the ViewRoot sets up callbacks with the Activity
// in addView->ViewRootImpl#setView. If we are instead reusing
// the decor view we have to notify the view root that the
// callbacks may have changed.
ViewRootImpl impl = decor.getViewRootImpl();
if (impl != null) {
impl.notifyChildRebuilt();
}
}
if (a.mVisibleFromClient) {
if (!a.mWindowAdded) {
a.mWindowAdded = true;
wm.addView(decor, l);
} else {
// The activity will get a callback for this {@link LayoutParams} change
// earlier. However, at that time the decor will not be set (this is set
// in this method), so no action will be taken. This call ensures the
// callback occurs with the decor set.
a.onWindowAttributesChanged(l);
}
}
// If the window has already been added, but during resume
// we started another activity, then don't yet make the
// window visible.
} else if (!willBeVisible) {
if (localLOGV) Slog.v(
TAG, "Launch " + r + " mStartedActivity set");
r.hideForNow = true;
}
// Get rid of anything left hanging around.
cleanUpPendingRemoveWindows(r, false /* force */);
// The window is now visible if it has been added, we are not
// simply finishing, and we are not starting another activity.
if (!r.activity.mFinished && willBeVisible
&& r.activity.mDecor != null && !r.hideForNow) {
if (r.newConfig != null) {
performConfigurationChangedForActivity(r, r.newConfig);
if (DEBUG_CONFIGURATION) Slog.v(TAG, "Resuming activity "
+ r.activityInfo.name + " with newConfig " + r.activity.mCurrentConfig);
r.newConfig = null;
}
if (localLOGV) Slog.v(TAG, "Resuming " + r + " with isForward="
+ isForward);
WindowManager.LayoutParams l = r.window.getAttributes();
if ((l.softInputMode
& WindowManager.LayoutParams.SOFT_INPUT_IS_FORWARD_NAVIGATION)
!= forwardBit) {
l.softInputMode = (l.softInputMode
& (~WindowManager.LayoutParams.SOFT_INPUT_IS_FORWARD_NAVIGATION))
| forwardBit;
if (r.activity.mVisibleFromClient) {
ViewManager wm = a.getWindowManager();
View decor = r.window.getDecorView();
wm.updateViewLayout(decor, l);
}
}
r.activity.mVisibleFromServer = true;
mNumVisibleActivities++;
if (r.activity.mVisibleFromClient) {
r.activity.makeVisible();
}
}
if (!r.onlyLocalRequest) {
r.nextIdle = mNewActivities;
mNewActivities = r;
if (localLOGV) Slog.v(
TAG, "Scheduling idle handler for " + r);
Looper.myQueue().addIdleHandler(new Idler());
}
r.onlyLocalRequest = false;
// Tell the activity manager we have resumed.
if (reallyResume) {
try {
ActivityManager.getService().activityResumed(token);
} catch (RemoteException ex) {
throw ex.rethrowFromSystemServer();
}
}
} else {
// If an exception was thrown when trying to resume, then
// just end this activity.
try {
ActivityManager.getService()
.finishActivity(token, Activity.RESULT_CANCELED, null,
Activity.DONT_FINISH_TASK_WITH_ACTIVITY);
} catch (RemoteException ex) {
throw ex.rethrowFromSystemServer();
}
}
}
2.1 关键是页面绘制流程
整个的过程就是一开始讲的层级关系。
第一点：performResumeActivity 比wm.addView(decor, l)先执行。所以Activity是先获取焦点，才绘制view。
performResumeActivity->r.activity.performResume()->mInstrumentation.callActivityOnResume(this)->activity.onResume()
在performResume最后可以看到onPostResume
final void performResume() {
performRestart();
...
// mResumed is set by the instrumentation
mInstrumentation.callActivityOnResume(this);
...
onPostResume();
...
}
protected void onPostResume() {
final Window win = getWindow();
if (win != null) win.makeActive();
if (mActionBar != null) mActionBar.setShowHideAnimationEnabled(true);
mCalled = true;
}
window出现了，这个就是phonewindow。
下面我们去看docorview的过程。
//2020.02.18 phonewindow在这里获取
if (r.window == null && !a.mFinished && willBeVisible) {
r.window = r.activity.getWindow();
//2020.02.18 docorview在这里获取
View decor = r.window.getDecorView();
decor.setVisibility(View.INVISIBLE);
ViewManager wm = a.getWindowManager();
WindowManager.LayoutParams l = r.window.getAttributes();
a.mDecor = decor;
...
if (a.mVisibleFromClient) {
if (!a.mWindowAdded) {
a.mWindowAdded = true;
wm.addView(decor, l);
} else {
// The activity will get a callback for this {@link LayoutParams} change
// earlier. However, at that time the decor will not be set (this is set
// in this method), so no action will be taken. This call ensures the
// callback occurs with the decor set.
a.onWindowAttributesChanged(l);
}
}
我们来看下wm.addView(decor, l);这个的过程。wm的实现就是WindowManagerImpl
@Override
public void addView(@NonNull View view, @NonNull ViewGroup.LayoutParams params) {
applyDefaultToken(params);
mGlobal.addView(view, params, mContext.getDisplay(), mParentWindow);
}
mGlobal是WindowManagerGlobal， addview的核心代码如下
root = new ViewRootImpl(view.getContext(), display);
view.setLayoutParams(wparams);
mViews.add(view);
mRoots.add(root);
mParams.add(wparams);
root.setView(view, wparams, panelParentView);
关于从ViewGroup开始的绘制流程，请看下篇。
更多内容：demanmath
公共号：
Android View的绘制机制前世今生---前世的更多相关文章
- Android View的绘制机制流程深入详解（四）
本系列文章主要着重深入介绍Android View的绘制机制及流程,第四篇主要介绍Android自定义View及ViewGroup的实现方法和流程. 主要介绍了自绘控件.自定义组合控件.自定义继承控件 ...
- Android View的绘制机制流程深入详解（三）
本系列文章主要着重深入介绍Android View的绘制机制及流程,第三篇主要介绍并分析视图状态以及重绘流程,首先剖析了 视图的几种状态,然后在深入分析视图的重绘机制流程. 真题园网:http://w ...
- Android View的绘制机制流程深入详解（二）
本系列文章主要着重深入介绍Android View的绘制机制及流程,第二篇主要介绍并分析Android视图的绘制的原理和流程.主要从 onMeasure().onLayout()和onDraw()这三 ...
- Android View的绘制机制流程深入详解（一）
本系列文章主要着重深入介绍Android View的绘制机制及流程,第一篇主要介绍并分析LayoutInflater的原理, 从而理解setContentView的加载原理.对于LayoutInfla ...
- Android 中View的绘制机制源代码分析 三
到眼下为止,measure过程已经解说完了,今天開始我们就来学习layout过程.只是在学习layout过程之前.大家有没有发现我换了编辑器,哈哈.最终下定决心从Html编辑器切换为markdown编 ...
- Android 中View的绘制机制源代码分析 一
尊重原创: http://blog.csdn.net/yuanzeyao/article/details/46765113 差点儿相同半年没有写博客了,一是由于工作比較忙,二是认为没有什么内容值得写, ...
- Android 中View的绘制机制源代码分析 二
尊重原创:http://blog.csdn.net/yuanzeyao/article/details/46842891 本篇文章接着上篇文章的内容来继续讨论View的绘制机制,上篇文章中我们主要解说 ...
- Android View 如何绘制
上文说道了Android如何测量,但是一个漂亮的控件我只知道您长到哪儿,这当然不行.只需要简单重写OnDraw方法,并在Canvas(画布)对象上调用那根五颜六色的画笔就能够画出这控件"性感 ...
- Android View 的绘制流程之 Layout 和 Draw 过程详解 (二)
View 的绘制系列文章: Android View 的绘制流程之 Measure 过程详解 (一) Android View 绘制流程之 DecorView 与 ViewRootImpl 在上一篇 ...
随机推荐
- 005.kubernets之pods的资源限制和健康检查
一 POD的容器资源限制 1.1 限制内容 有两个参数 QoS Class: BestEffort,表示尽可能的满足使用,级别较低,但当资源不够时,会杀掉这个容器 resources: {}这里指定为 ...
- spring get方法 中文(UTF-8)乱码
问题: 前端用Get方法进行如下请求: 在浏览器中输入:http://localhost:8080/dmaList/ExportBySQL?sql=&names=分区级别&size=1 ...
- JSON小记
json: { "1" : "2", "1" : "3" } 在json中如果有重复的key,会取最后一个key的值,如 ...
- mongodb学习（三）——函数使用的小技巧
$group 下 $sum 函数 Returns a sum of numerical values. Ignores non-numeric values 只能对数字求和,非数字没有作用 查询一段时 ...
- JS中使用FormData上传图片
<!DOCTYPE html> <html> <head> <meta name="viewport" content="wid ...
- 机器学习-特征工程-Feature generation 和 Feature selection
概述:上节咱们说了特征工程是机器学习的一个核心内容.然后咱们已经学习了特征工程中的基础内容,分别是missing value handling和categorical data encoding的一些 ...
- Ansible Playbooks常用模块
File模块 在目标主机创建文件或目录,并赋予其系统权限 - name: create a file file:'path=/oot/foo.txt state=touch mode=0755 own ...
- python 判断文件的字符编码
import chardet f = open(file='test1.txt', mode='rb') data = f.read() print(chardet.detect(data))
- 基于bootstrap和knockoutjs使用 mvc 查询
这是我摘抄的码 http://pan.baidu.com/s/1nvKWdsd
- 使用doxygen
Getting started with Doxygen 可执行文件doxygen是解析源文件并生成文档的主程序. 另外, 也可以使用可执行文件doxywizard, 是用于编辑配置文件, 以及在图形 ...