Android 自定义View 加 lifecycle 简单使用详解_Android

前言

本文是自定义view中最简单的使用方法，分别进行 ‘onmeasure’、‘ondraw’、‘自定义样式’、‘lifecycle’的简单使用，了解自定义view的使用。

通过lifecycle来控制动画的状态

一、onmeasure做了什么？

在onmeasure中获取view 的宽和高是 ‘0’

测量view的宽 / 高

在某些情况下，需要多次测量（measure）才能确定view最终的宽/高；
该情况下，measure过程后得到的宽 / 高可能不准确；
此处建议：在layout过程中onlayout()去获取最终的宽 / 高

必须要了解 measurespec 作用

测量规格(measurespec)是由测量模式(mode)和测量大小(size)组成，共32位(int类型)，其中：

测量模式(mode)：占测量规格(measurespec)的高2位；
测量大小(size)：占测量规格(measurespec)的低30位。

measurespec类用一个变量封装了测量模式(mode)和测量大小(size)：通过使用二进制，将测量模式（mode)和测量大小(size）打包成一个int值，并提供了打包和解包的方法，这样的做法是为了减少对象内存分配和提高存取效率。具体使用如下所示：

 override fun onmeasure(widthmeasurespec: int, heightmeasurespec: int) {
        super.onmeasure(widthmeasurespec, heightmeasurespec)
        val widthmodel = measurespec.getmode(widthmeasurespec)
        val widthsize = measurespec.getsize(widthmeasurespec)
        val heightmodel = measurespec.getmode(heightmeasurespec)
        val heightsize = measurespec.getsize(heightmeasurespec)
//        @todo 在 onmeasure 中获取view的 宽高 获取到是 0
        log.e(tag, "onmeasure: ${widthsize}-${width}__${heightsize}__${height}")
        val defwidth = 400
        val defheight = 400
//        @todo measurespec.at_most:wrap_content ; measurespec.exactly:match_parent ;
        if (widthmodel == measurespec.at_most && heightmodel == measurespec.at_most) {
            setmeasureddimension(defwidth, defheight)
        } else if (widthmodel == measurespec.at_most) {
            setmeasureddimension(defwidth, heightsize)
        } else if (heightmodel == measurespec.at_most) {
            setmeasureddimension(widthsize, defheight)
        }
    }

1、onlayout 做了什么

计算位置，里面包含子view 的情况下才会用到这个函数

一般继承自viewgroup或者重新写layout布局

2、ondraw 做了什么

绘制view自身，设置padding 时要在ondraw中计算

1. 绘制view背景
2. 绘制view内容
3. 绘制子view
4. 绘制装饰（渐变框，滑动条等等）

  override fun ondraw(canvas: canvas?) {
        super.ondraw(canvas)
        canvas?.let {
            val pl = paddingleft
            val pr = paddingright
            val pt = paddingtop
            val pb = paddingbottom
            var mheight = height - pt - pb
            var mwidth = width - pl - pr
            val cy = pt.plus(pb).div(2) + mheight.div(2).tofloat()
            val cx = pl.plus(pr).div(2) + mwidth.div(2).tofloat()
            val cc = math.min(mheight, mwidth).div(2).tofloat()
            it.drawcircle(
                cx,
                cy,
                cc,
                mpaint
            )
        }
    }

3、lifecycle控制动画的状态

自定义view 继承 defaultlifecycleobserver 类 然后实现  生命周期=中的方法
    override fun onstart(owner: lifecycleowner) {
        super.onstart(owner)
        animsetcolor.start()
    }
    override fun ondestroy(owner: lifecycleowner) {
        super.ondestroy(owner)
        animsetcolor.cancel()
    }
    override fun onpause(owner: lifecycleowner) {
        super.onpause(owner)
        animsetcolor.pause()
    }
    override fun onresume(owner: lifecycleowner) {
        super.onresume(owner)
        animsetcolor.resume()
    }
在act中 进行生命周期监听的绑定
  lifecycle.addobserver(customview)

4、代码示例

自定义view代码

 
/**
 * @todo 自定义view
 *
 *
 */
class myview(context: context?, attrs: attributeset?) :
    view(context, attrs), defaultlifecycleobserver {
    private val mpaint by lazy { paint() }
    private val tag = "myview"
    private var i = 0
    //  @todo 动画实现改变颜色  然后 通过  lifecycle 控制动画的状态：开始、暂停、恢复、取消
    private val animsetcolor by lazy {
        valueanimator.ofint(0, 100).apply {
            addlistener(object : animatorlistener {
                override fun onanimationstart(animation: animator) {
                }
                override fun onanimationend(animation: animator) {
                }
                override fun onanimationcancel(animation: animator) {
                }
                override fun onanimationrepeat(animation: animator) {
                    i++
                    if (i % 2 == 0) {
                        mpaint.color = android.graphics.color.blue
                    }
                    mpaint.color = when (i % 5) {
                        0 -> android.graphics.color.blue
                        1 -> android.graphics.color.yellow
                        2 -> android.graphics.color.cyan
                        3 -> android.graphics.color.magenta
                        4 -> android.graphics.color.ltgray
                        else -> android.graphics.color.transparent
                    }
//                    @todo 每次设置颜色后 调用postinvalidate 重新绘制view
                    postinvalidate()
                }
            })
//            动画无线循环执行
            repeatcount = valueanimator.infinite
//            间隔一秒执行一次
            duration = 1000
        }
    }
    init {
        mpaint.color = color.blue.hashcode()
        mpaint.style = paint.style.fill
        mpaint.strokewidth = 20f
        context?.obtainstyledattributes(attrs, r.styleable.myview)?.apply {
            mpaint.color = getcolor(r.styleable.myview_circlr_color, android.graphics.color.green)
            recycle()
        }
    }
    override fun onmeasure(widthmeasurespec: int, heightmeasurespec: int) {
        super.onmeasure(widthmeasurespec, heightmeasurespec)
        val widthmodel = measurespec.getmode(widthmeasurespec)
        val widthsize = measurespec.getsize(widthmeasurespec)
        val heightmodel = measurespec.getmode(heightmeasurespec)
        val heightsize = measurespec.getsize(heightmeasurespec)
//        @todo 在 onmeasure 中获取view的 宽高 获取到是 0
        log.e(tag, "onmeasure: ${widthsize}-${width}__${heightsize}__${height}")
        val defwidth = 400
        val defheight = 400
//        @todo measurespec.at_most:wrap_content ; measurespec.exactly:match_parent ;
        if (widthmodel == measurespec.at_most && heightmodel == measurespec.at_most) {
            setmeasureddimension(defwidth, defheight)
        } else if (widthmodel == measurespec.at_most) {
            setmeasureddimension(defwidth, heightsize)
        } else if (heightmodel == measurespec.at_most) {
            setmeasureddimension(widthsize, defheight)
        }
    }
//挂在到act上时
//    override fun onattachedtowindow() {
//        super.onattachedtowindow()
//        log.e(tag, "onattachedtowindow: ")
//        anim.start()
//    }
//在act 销毁时
//    override fun ondetachedfromwindow() {
//        super.ondetachedfromwindow()
//        log.e(tag, "ondetachedfromwindow: ")
//        anim.cancel()
//
//    }
    override fun onstart(owner: lifecycleowner) {
        super.onstart(owner)
        animsetcolor.start()
    }
    override fun ondestroy(owner: lifecycleowner) {
        super.ondestroy(owner)
        animsetcolor.cancel()
    }
    override fun onpause(owner: lifecycleowner) {
        super.onpause(owner)
        animsetcolor.pause()
    }
    override fun onresume(owner: lifecycleowner) {
        super.onresume(owner)
        animsetcolor.resume()
    }
    override fun onlayout(changed: boolean, left: int, top: int, right: int, bottom: int) {
        super.onlayout(changed, left, top, right, bottom)
        log.e(tag, "onlayout: ")
    }
    /**
     * 作用：根据给定的 canvas 自动渲染view包括其所有子 view）。
     * 绘制过程：
     *   1. 绘制view背景
     *   2. 绘制view内容
     *   3. 绘制子view
     *   4. 绘制装饰（渐变框，滑动条等等）
     * 注：
     *    a. 在调用该方法之前必须要完成 layout 过程
     *    b. 所有的视图最终都是调用 view 的 draw()绘制视图（ viewgroup 没有复写此方法）
     *    c. 在自定义view时，不应该复写该方法，而是复写 ondraw(canvas) 方法进行绘制
     *    d. 若自定义的视图确实要复写该方法，那么需先调用 super.draw(canvas)完成系统的绘制，然后再进行自定义的绘制
     */
    override fun ondraw(canvas: canvas?) {
        super.ondraw(canvas)
        canvas?.let {
            val pl = paddingleft
            val pr = paddingright
            val pt = paddingtop
            val pb = paddingbottom
            var mheight = height - pt - pb
            var mwidth = width - pl - pr
            val cy = pt.plus(pb).div(2) + mheight.div(2).tofloat()
            val cx = pl.plus(pr).div(2) + mwidth.div(2).tofloat()
            val cc = math.min(mheight, mwidth).div(2).tofloat()
            it.drawcircle(
                cx,
                cy,
                cc,
                mpaint
            )
        }
    }
}

自定义view的xml样式文件

<?xml version="1.0" encoding="utf-8"?>
<resources>
 <declare-styleable name="myview">
     <attr name="circlr_color" format="color"/>
 </declare-styleable>
</resources>

layout布局文件

<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.constraintlayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:background="#11008811"
    tools:context=".customviewactivity">
    <com.andriod.police.view.myview
        android:id="@+id/customview"
        android:layout_width="wrap_content"
        android:layout_height="130dp"
        android:background="#11f08811"
        app:circlr_color="@color/cardview_light_background"
        android:padding="20dp"
        app:layout_constraintstart_tostartof="parent"
        app:layout_constrainttop_totopof="parent" />
</androidx.constraintlayout.widget.constraintlayout>

act

class customviewactivity : appcompatactivity() {
    private val customview: myview by lazy { findviewbyid(r.id.customview) }
    override fun oncreate(savedinstancestate: bundle?) {
        super.oncreate(savedinstancestate)
        setcontentview(r.layout.activity_custom_view)
//        @todo 通过  lifecycle 控制动画的状态：开始、暂停、恢复、取消
        lifecycle.addobserver(customview)
    }
}