【移动应用开发技术】Android中如何自定义View

【移动应用开发技术】Android中如何自定义View

前言/upload/information/20210522/379/528689.jpg思维导图/upload/information/20210522/379/528690.jpg工作流程@Override

protected

void

onMeasure(int

widthMeasureSpec,

int

heightMeasureSpec)

{

super.onMeasure(widthMeasureSpec,

heightMeasureSpec);

//用于获取设定的模式

int

widthMode

=

MeasureSpec.getMode(widthMeasureSpec);

int

heightMode

=

MeasureSpec.getMode(heightMeasureSpec);

//

用于获取设定的长度

int

widthSize

=

MeasureSpec.getSize(widthMeasureSpec);

int

heightSize

=

MeasureSpec.getSize(heightMeasureSpec);

//

类似这样的判断，后面不过多复述

//

用于判断是不是wrap_content

//

如果不进行处理，效果会是match_parent

if(widthMode

==

MeasureSpec.AT_MOST

&&

heightMode

==

MeasureSpec.AT_MOST){

setMeasuredDimension(20,

20);

}

}/upload/information/20210522/379/528691.jpg/upload/information/20210522/379/528692.jpgdrawprivate

Paint

paint

=

new

Paint(Paint.ANTI_ALIAS_FLAG);

@Override

protected

void

onDraw(Canvas

canvas)

{

super.onDraw(canvas);

int

width

=

getWidth();

int

height

=

getHeight();

//

在画布上进行类似这样的操作

canvas.drawLine(0,

height/2,

width,height/2,

paint);

}入门自定义View<?xml

version="1.0"

encoding="utf-8"?>

<resources>

<declare-styleable

name="DefaultView">

<attr

name="color"

format="color"/>

</declare-styleable>

</resources>/**

*

author:

ClericYi

*

time:

2020-01-30

*/

public

class

DefaultView

extends

View

{

private

Paint

paint

=

new

Paint(Paint.ANTI_ALIAS_FLAG);

private

int

mColor

=

Color.RED;

public

DefaultView(Context

context,

@Nullable

AttributeSet

attrs)

{

super(context,

attrs);

initAttrs(context,

attrs);

initDraw();

}

private

void

initAttrs(Context

context,

@Nullable

AttributeSet

attrs)

{

TypedArray

array

=

context.obtainStyledAttributes(attrs,

R.styleable.DefaultView);

//

从styleable中获取的名字是系统会生成的，一般是

类名_name

的形式

mColor

=

array.getColor(R.styleable.DefaultView_color,

Color.GREEN);

//

获取完资源后即使回收

array.recycle();

}

private

void

initDraw()

{

paint.setColor(mColor);

paint.setStrokeWidth(3f);

}

@Override

protected

void

onDraw(Canvas

canvas)

{

super.onDraw(canvas);

int

width

=

getWidth();

int

height

=

getHeight();

canvas.drawLine(0,

height/2,

width,height/2,

paint);

}

@Override

protected

void

onMeasure(int

widthMeasureSpec,

int

heightMeasureSpec)

{

super.onMeasure(widthMeasureSpec,

heightMeasureSpec);

int

widthMode

=

MeasureSpec.getMode(widthMeasureSpec);

int

heightMode

=

MeasureSpec.getMode(heightMeasureSpec);

int

widthSize

=

MeasureSpec.getSize(widthMeasureSpec);

int

heightSize

=

MeasureSpec.getSize(heightMeasureSpec);

if(widthMode

==

MeasureSpec.AT_MOST){

setMeasuredDimension(20,

20);

}

}

}基础的性能优化/upload/information/20210522/379/528693.png/upload/information/20210522/379/528694.jpg那如何做到性能优化呢?方案1：减少嵌套层数。/upload/information/20210522/379/528695.png方案2：去除默认的背景/upload/