Android艺术探索第四 view的自定义
一.初见View
View的层级关系(Veiw到底分成几层,自定义view是从那一层开始绘制的)
R:Veiw树的结构如下 ,自定义View是从DecorView开始的;DecorView是View树的最顶层View,
View树的遍历过程
父布局对View绘制模式的影响 (P182表)
4.为什么父view为wrap_parent时,继承的view布局为warp_parent行不通达不到预期效果?
5.如果在activity启动时获取某个view的尺寸,怎么获取?
onWindowsFocusChanges方法时获取
6.getwidth()和getMeasurewidth()有什么区别?Touch事件分析 包含2个一个是 dispatchTouchEvent 和OnTouchEvent();
如何处理滑动冲突
二. MeasureSpec
1.由来:在View的测量过程中系统会将View的LayoutParams根据父容器所施加的规格转换成对应的MeasureSpec,然后偶再根据这个MeasureSpec来测量Veiw的宽高;
2.MeasureSpec是一个32位的int值,可以通过getMode和getSize来获取SpecMode和SpecSize;
3.SpecSize的有3种类型:
|无限制类型unspecified |精确类型exactly |至多型at_most |
| 无限制 |对应match_parent和精确数值 |对应于wrap_content |
2.1MeasureSpec和Layoutparams对应关系
4.顶层DecorView的MeasureSpec的产生,在ViewRootImpl中
private static int getRootMeasureSpec(int windowSize, int rootDimension) {
int measureSpec;
switch (rootDimension) {
case ViewGroup.LayoutParams.MATCH_PARENT:
// Window can't resize. Force root view to be windowSize.
measureSpec = MeasureSpec.makeMeasureSpec(windowSize, MeasureSpec.EXACTLY);
break;
case ViewGroup.LayoutParams.WRAP_CONTENT:
// Window can resize. Set max size for root view.
measureSpec = MeasureSpec.makeMeasureSpec(windowSize, MeasureSpec.AT_MOST);
break;
default:
// Window wants to be an exact size. Force root view to be that size.
measureSpec = MeasureSpec.makeMeasureSpec(rootDimension, MeasureSpec.EXACTLY);
break;
}
return measureSpec;
}
由上可以得出 :
Layoutparmas.match_parent | wrap_parent | 精确(50dp) |
---|---|---|
精确模式,大小就是窗口大小 | 最大模式 at_most | 精确模式,大小就是制定大小 |
5.普通View的产生,由于View的measure是由ViewGrop传递而来
/**
* Does the hard part of measureChildren: figuring out the MeasureSpec to
* pass to a particular child. This method figures out the right MeasureSpec
* for one dimension (height or width) of one child view.
*
* The goal is to combine information from our MeasureSpec with the
* LayoutParams of the child to get the best possible results. For example,
* if the this view knows its size (because its MeasureSpec has a mode of
* EXACTLY), and the child has indicated in its LayoutParams that it wants
* to be the same size as the parent, the parent should ask the child to
* layout given an exact size.
*
* @param spec The requirements for this view
* @param padding The padding of this view for the current dimension and
* margins, if applicable
* @param childDimension How big the child wants to be in the current
* dimension
* @return a MeasureSpec integer for the child
*/
public static int getChildMeasureSpec(int spec, int padding, int childDimension) {
int specMode = MeasureSpec.getMode(spec); // 一般来说这是父View传进来的
int specSize = MeasureSpec.getSize(spec); // 同上
int size = Math.max(0, specSize - padding); //去掉padding得到内容的大小
int resultSize = 0;
int resultMode = 0;
switch (specMode) {
// Parent has imposed an exact size on us
// childDimension是layout文件里设置的大小:可以是MATCH_PARENT, WRAP_CONTENT或者具体大小, 代码中分别对三种做不同的处理
case MeasureSpec.EXACTLY:
if (childDimension >= 0) {
//如果childDimension是具体大小,那么就按照这个大小来, Mode为Exactly,这样子View就知道要按照填写的大小来draw
resultSize = childDimension;
resultMode = MeasureSpec.EXACTLY;
} else if (childDimension == LayoutParams.MATCH_PARENT) {
// Child wants to be our size. So be it.
// 子View填的是Match_parent, 那么父View就给子view自己的size(去掉padding), 然后告诉子view这是Exactly的大小
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.
// 子View 填的是wrap_Content,那么父View就告诉子View自己的size(去掉padding), 然后告诉子View, 你最多有这么多, 你自己决定大小
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.
// 如果子View是Match_parent,但是父View是告诉子View, 你最多有size这么多, 那么就告诉子View,你最多有父View的size
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.
// 基本和上一个情况一样
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 = 0;
resultMode = MeasureSpec.UNSPECIFIED;
} else if (childDimension == LayoutParams.WRAP_CONTENT) {
// Child wants to determine its own size.... find out how
// big it should be
resultSize = 0;
resultMode = MeasureSpec.UNSPECIFIED;
}
break;
}
return MeasureSpec.makeMeasureSpec(resultSize, resultMode);
}
从上面的方法不难理解,他的代码主要是阐述根据父容器的MeasureSpec同时结合View本身的Layoutparams来确定子元素的MeasureSpec,列表如下
三. View的工作流程
View的工作流程主要是指Measure layout draw三个流程,即测量布局和绘制
3.1 View的测量
1.测量代码主要如下
protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
setMeasuredDimension(getDefaultSize(getSuggestedMinimumWidth(), widthMeasureSpec),
getDefaultSize(getSuggestedMinimumHeight(), heightMeasureSpec));
}
这段代码主要是确定View的测量后的值
/**
* Utility to return a default size. Uses the supplied size if the
* MeasureSpec imposed no constraints. Will get larger if allowed
* by the MeasureSpec.
*
* @param size Default size for this view
* @param measureSpec Constraints imposed by the parent
* @return The size this view should be.
*/
public static int getDefaultSize(int size, int measureSpec) {
int result = size;
int specMode = MeasureSpec.getMode(measureSpec);
int specSize = MeasureSpec.getSize(measureSpec);
switch (specMode) {
case MeasureSpec.UNSPECIFIED:
result = size;
break;
case MeasureSpec.AT_MOST:
case MeasureSpec.EXACTLY:
result = specSize;
break;
}
return result;
}
由上面的代码可知在at_most和exactly的模式下,返回的view的specsize就是测量后的大小,(测量后的大小!=view的最终大小,最终大小是在layout时确定的),而unspecified,这种情况下,由上面代码可知
result=size,即宽高分别为传入值,那么这个传入值的方法是什么呢,往下看
/**
* Returns the suggested minimum height that the view should use. This
* returns the maximum of the view's minimum height
* and the background's minimum height
* ({@link android.graphics.drawable.Drawable#getMinimumHeight()}).
* <p>
* When being used in {@link #onMeasure(int, int)}, the caller should still
* ensure the returned height is within the requirements of the parent.
*
* @return The suggested minimum height of the view.
*/
protected int getSuggestedMinimumHeight() {
return (mBackground == null) ? mMinHeight : max(mMinHeight, mBackground.getMinimumHeight());
}
/**
* Returns the suggested minimum width that the view should use. This
* returns the maximum of the view's minimum width
* and the background's minimum width
* ({@link android.graphics.drawable.Drawable#getMinimumWidth()}).
* <p>
* When being used in {@link #onMeasure(int, int)}, the caller should still
* ensure the returned width is within the requirements of the parent.
*
* @return The suggested minimum width of the view.
*/
protected int getSuggestedMinimumWidth() {
return (mBackground == null) ? mMinWidth : max(mMinWidth, mBackground.getMinimumWidth());
}
从上面代码可以看出 如果view没有设置背景,view宽度对应xml里面的Android:minwidth属性所对应的值,如果没有指定即为0;如果有设置背景则取二者的较大值,
综合上面2段代码来看,也就很好的解释了开头的问题4,直接继承属性为wrap_parent的view的自定义控件需要重写onMeasure并设置其自身大小,因为如果父view为wrap,那么他的Specmode就是at_most,其子view如果是wrap属性,那么子veiw大小就是父控件的大小,和子view使用match_parent无异;
2 ViewGroup的测量
其实一开始我以为ViewGroup和View的测量代码是一样的都是调用onMeasure去完成,后来发现虽然逻辑上它的确是遍历所有子元素Measure方法然后子元素递归执行这个过程,但是实际上有点区别..由于
Viewgroup是一个抽象类,里面没有Onmeasure方法,他把测量工作交给了各个子类去实现,原因也是因为不同的布局是有不同的计算方式
/**
* Ask all of the children of this view to measure themselves, taking into
* account both the MeasureSpec requirements for this view and its padding.
* We skip children that are in the GONE state The heavy lifting is done in
* getChildMeasureSpec.
*
* @param widthMeasureSpec The width requirements for this view
* @param heightMeasureSpec The height requirements for this view
*/
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];
if ((child.mViewFlags & VISIBILITY_MASK) != GONE) {
measureChild(child, widthMeasureSpec, heightMeasureSpec);
}
}
}
/**
* Ask one of the children of this view to measure itself, taking into
* account both the MeasureSpec requirements for this view and its padding.
* The heavy lifting is done in getChildMeasureSpec.
*
* @param child The child to measure
* @param parentWidthMeasureSpec The width requirements for this view
* @param parentHeightMeasureSpec The height requirements for this view
*/
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);
}
3.2view的布局过程
1.先普及下坐标概念
View获取自身宽高
getHeight():获取View自身高度
getWidth():获取View自身宽度
View自身坐标
通过如下方法可以获得View到其父控件(ViewGroup)的距离:
getTop():获取View自身顶边到其父布局顶边的距离
getLeft():获取View自身左边到其父布局左边的距离
getRight():获取View自身右边到其父布局左边的距离
getBottom():获取View自身底边到其父布局顶边的距离
MotionEvent提供的方法
我们看上图那个深蓝色的点,假设就是我们触摸的点,我们知道无论是View还是ViewGroup,最终的点击事件都会由onTouchEvent(MotionEvent event)方法来处理,MotionEvent也提供了各种获取焦点坐标的方法:
getX():获取点击事件距离控件左边的距离,即视图坐标
getY():获取点击事件距离控件顶边的距离,即视图坐标
getRawX():获取点击事件距离整个屏幕左边距离,即绝对坐标
getRawY():获取点击事件距离整个屏幕顶边的的距离,即绝对坐标
2.layout的作用是ViewGroup用来确定子元素的位置,当ViewGroup位置被确定后,他会遍历所有的子元素并调用其layout方法,layout确定veiw本身的位子,onLayout确定所有子元素的位子
public void layout(int l, int t, int r, int b) {
if ((mPrivateFlags3 & PFLAG3_MEASURE_NEEDED_BEFORE_LAYOUT) != 0) {
onMeasure(mOldWidthMeasureSpec, mOldHeightMeasureSpec);
mPrivateFlags3 &= ~PFLAG3_MEASURE_NEEDED_BEFORE_LAYOUT;
}
int oldL = mLeft;
int oldT = mTop;
int oldB = mBottom;
int oldR = mRight;
boolean changed = isLayoutModeOptical(mParent) ?
setOpticalFrame(l, t, r, b) : setFrame(l, t, r, b);
if (changed || (mPrivateFlags & PFLAG_LAYOUT_REQUIRED) == PFLAG_LAYOUT_REQUIRED) {
onLayout(changed, l, t, r, b);
if (shouldDrawRoundScrollbar()) {
if(mRoundScrollbarRenderer == null) {
mRoundScrollbarRenderer = new RoundScrollbarRenderer(this);
}
} else {
mRoundScrollbarRenderer = null;
}
mPrivateFlags &= ~PFLAG_LAYOUT_REQUIRED;
ListenerInfo li = mListenerInfo;
if (li != null && li.mOnLayoutChangeListeners != null) {
ArrayList<OnLayoutChangeListener> listenersCopy =
(ArrayList<OnLayoutChangeListener>)li.mOnLayoutChangeListeners.clone();
int numListeners = listenersCopy.size();
for (int i = 0; i < numListeners; ++i) {
listenersCopy.get(i).onLayoutChange(this, l, t, r, b, oldL, oldT, oldR, oldB);
}
}
}
mPrivateFlags &= ~PFLAG_FORCE_LAYOUT;
mPrivateFlags3 |= PFLAG3_IS_LAID_OUT;
}
在第12行通过setFrame设定View的四个顶点位置然后在调用onlayout方法去确定子Veiw的在Veiw中的位子;
3.getwidth()和getMeasurewidth()有什么区别?
前者是最终的宽高,后者是测量的宽高,后者形成早于前者,如果一般默认情况下二者的确是相等的,但是如果我们自定义时人为更改,就会比测量的多出100
@Override
public void layout(@Px int l, @Px int t, @Px int r, @Px int b) {
super.layout(l, t, r+100, b+100);
}
3.3View的绘制过程
draw过程的作用是将view绘制在屏幕上面
1.draw的步骤遵循以下几步
- 绘制背景 background.draw(canvas)
- 绘制自己 ondraw
- 绘制Children dispatchdraw
- 绘制装饰 ondrawScrollbars
源码里面其实写的也很清楚
/**
* Manually render this view (and all of its children) to the given Canvas.
* The view must have already done a full layout before this function is
* called. When implementing a view, implement
* {@link #onDraw(android.graphics.Canvas)} instead of overriding this method.
* If you do need to override this method, call the superclass version.
*
* @param canvas The Canvas to which the View is rendered.
*/
@CallSuper
public void draw(Canvas canvas) {
final int privateFlags = mPrivateFlags;
final boolean dirtyOpaque = (privateFlags & PFLAG_DIRTY_MASK) == PFLAG_DIRTY_OPAQUE &&
(mAttachInfo == null || !mAttachInfo.mIgnoreDirtyState);
mPrivateFlags = (privateFlags & ~PFLAG_DIRTY_MASK) | PFLAG_DRAWN;
/*
* Draw traversal performs several drawing steps which must be executed
* in the appropriate order:
*
* 1. Draw the background
* 2. If necessary, save the canvas' layers to prepare for fading
* 3. Draw view's content
* 4. Draw children
* 5. If necessary, draw the fading edges and restore layers
* 6. Draw decorations (scrollbars for instance)
*/
// Step 1, draw the background, if needed
int saveCount;
if (!dirtyOpaque) {
drawBackground(canvas);
}
// skip step 2 & 5 if possible (common case)
final int viewFlags = mViewFlags;
boolean horizontalEdges = (viewFlags & FADING_EDGE_HORIZONTAL) != 0;
boolean verticalEdges = (viewFlags & FADING_EDGE_VERTICAL) != 0;
if (!verticalEdges && !horizontalEdges) {
// Step 3, draw the content
if (!dirtyOpaque) onDraw(canvas);
// Step 4, draw the children
dispatchDraw(canvas);
// Overlay is part of the content and draws beneath Foreground
if (mOverlay != null && !mOverlay.isEmpty()) {
mOverlay.getOverlayView().dispatchDraw(canvas);
}
// Step 6, draw decorations (foreground, scrollbars)
onDrawForeground(canvas);
// we're done...
return;
}
四.自定义Veiw的分类
1.继承View重新Ondraw()方法
2.继承viewGroup派生特殊的layout
3.继承特定的某个view
4.继承特定的viewGroup(LinearLayout)
Android艺术探索第四 view的自定义的更多相关文章
- Android自动化测试探索(四)uiautomator2简介和使用
uiautomator2简介 项目Git地址: https://github.com/openatx/uiautomator2 安装 #1. 安装 uiautomator2 使用pip进行安装, 注意 ...
- 《android开发艺术探索》读书笔记(四)--View工作原理
接上篇<android开发艺术探索>读书笔记(三) No1: View的三大流程:测量流程.布局流程.绘制流程 No2: ViewRoot对应于ViewRootImpl类,它是连接Wind ...
- Android艺术开发探索第四章——View的工作原理(下)
Android艺术开发探索第四章--View的工作原理(下) 我们上篇BB了这么多,这篇就多多少少要来点实战了,上篇主席叫我多点自己的理解,那我就多点真诚,少点套路了,老司机,开车吧! 我们这一篇就扯 ...
- Android艺术开发探索第三章————View的事件体系(下)
Android艺术开发探索第三章----View的事件体系(下) 在这里就能学习到很多,主要还是对View的事件分发做一个体系的了解 一.View的事件分发 上篇大致的说了一下View的基础知识和滑动 ...
- Android艺术开发探索第三章——View的事件体系(上)
Android艺术开发探索第三章----View的事件体系(上) 我们继续来看这本书,因为有点长,所以又分了上下,你在本片中将学习到 View基础知识 什么是View View的位置参数 Motion ...
- Android开发艺术探索笔记——View(二)
Android开发艺术探索笔记--View(二) View的事件分发机制 学习资料: 1.Understanding Android Input Touch Events System Framewo ...
- Android开发艺术探索笔记—— View(一)
Android开发艺术探索笔记 --View(一) View的基础知识 什么是View View是Android中所有控件的基类.是一种界面层控件的抽象. View的位置参数 参数名 获取方式 含义 ...
- 《Android开发艺术探索》读书笔记 (3) 第3章 View的事件体系
本节和<Android群英传>中的第五章Scroll分析有关系,建议先阅读该章的总结 第3章 View的事件体系 3.1 View基本知识 (1)view的层次结构:ViewGroup也是 ...
- 《android开发艺术探索》读书笔记(十四)--JNI和NDK编程
接上篇<android开发艺术探索>读书笔记(十三)--综合技术 No1: Java JNI--Java Native Interface(java本地接口),它是为了方便java调用C. ...
随机推荐
- (转)linux中项目部署和日志查看
1 查找进程 ps -ef | grep java 查看所有关于java的进程 root 17540 1 0 2009 ? 01:42:27 /usr/java/ ...
- (转)递归算法的时间复杂度终结篇与Master method
开篇前言:为什么写这篇文章?笔者目前在学习各种各样的算法,在这个过程中,频繁地碰到到递归思想和分治思想,惊讶于这两种的思想的伟大与奇妙的同时,经常要面对的一个问题就是,对于一个给定的递归算法或者用分治 ...
- arcgis for javascript 自定义infowindow
arcgis 自己的infowindow 太难看了,放在系统中与系统中的风格格格不入,在参考了网上的一些资料后,整理编写了适合自己系统的infowindow,与大家分享. 1.自定义展示效果 2.In ...
- redis 一般性使用概述
最近一段时间与redis接触比较频繁.发现有些东西还是工作中经常会用到的,自己也花了点时间巩固下.本篇文章主要是以总结性的方式梳理,因为redis的主题很大,任何一个技术点展开都是几篇文章的量.也可以 ...
- 初学Python(七)——控制语句
初学Python(七)——控制语句 初学Python,主要整理一些学习到的知识点,这次是控制语句. if : #-*- coding:utf-8 -*- age=raw_input('input yo ...
- 谈谈渲染,玩玩nginx——前后端分离,转发请求到Tomcat的尝试
一.谈谈"渲染" 相信好多人都挺听过"渲染"这个词,但不清楚它是什么意思?前端开发以为这是后端的活儿,后端开发以为是前端的事儿,推着推着就不了了之.其实渲染很简 ...
- html+css3实现长方体效果
网上大都是正方体的效果,由于做一个东西需要,写了一个HTML+css3实现的长方体,有需要的也可以看看. 2017-07-25 21:30:23 h ...
- mac系统读写NTFS格式的移动硬盘
Mac OS X默认情况下,对于NTFS的移动硬盘只能读不能写,可通过将移动硬盘格式化为exFAT 或者安装NTFS相关的工具,达到可读写的目的,但对于系统的安全性方面,以上方式得不到保证:在Mac ...
- Git的commit your changes or stash them before you can merge
今天用git pull来更新代码,遇到了下面的问题: error: Your local changes to the following files would be overwritten by ...
- JMeter之Throughput Controller详解(实验)
Throughput Contoller,直译是吞吐量控制器,它是用来控制该控制器下面元件的执行次数,与控制吞吐量的功能无关.(注:用Constant Throughput Timer可以控制吞吐量. ...