Android 自定義View 加 lifecycle 簡單使用

前言

?本文是自定義view中最簡單的使用方法，分別進行 ‘onMeasure’、‘onDraw’、‘自定義樣式’、‘lifecycle’的簡單使用，了解自定義view的使用。

通過lifecycle來控制動畫的狀態

一、onMeasure做了什么？

在onMeasure中獲取view 的寬和高是 ‘0’

?測量`View`的寬 / 高

在某些情況下，需要多次測量（measure）才能確定View最終的寬/高；
該情況下，measure過程后得到的寬 / 高可能不準確；
此處建議：在layout過程中onLayout()去獲取最終的寬 / 高

?必須要了解 MeasureSpec 作用

測量規格(MeasureSpec)是由測量模式(mode)和測量大小(size)組成，共32位(int類型)，其中：

測量模式(mode)：占測量規格(MeasureSpec)的高2位；
測量大小(size)：占測量規格(MeasureSpec)的低30位。

MeasureSpec類用一個變量封裝了測量模式(mode)和測量大小(size)：通過使用二進制，將測量模式（mode)和測量大小(size）打包成一個int值，并提供了打包和解包的方法，這樣的做法是為了減少對象內存分配和提高存取效率。具體使用如下所示：

 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 中獲取view的 寬高 獲取到是 0Log.e(TAG, "onMeasure: ${widthSize}-${width}__${heightSize}__${height}")val defWidth = 400val 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)}}

2、onLayout 做了什么

計算位置，里面包含子view 的情況下才會用到這個函數

一般繼承自viewGroup或者重新寫layout布局

3、onDraw 做了什么

繪制View自身，設置padding 時要在onDraw中計算

1. 繪制view背景
2. 繪制view內容
3. 繪制子View
4. 繪制裝飾（漸變框，滑動條等等）

  override fun onDraw(canvas: Canvas?) {super.onDraw(canvas)canvas?.let {val pL = paddingLeftval pR = paddingRightval pT = paddingTopval pB = paddingBottomvar mHeight = height - pT - pBvar mWidth = width - pL - pRval 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)}}

4、lifecycle控制動畫的狀態

自定義view 繼承 DefaultLifecycleObserver 類 然后實現  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 進行生命周期監聽的綁定lifecycle.addObserver(customView)

5、代碼示例

自定義View代碼


/*** @TODO 自定義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 動畫實現改變顏色  然后 通過  lifecycle 控制動畫的狀態：開始、暫停、恢復、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.BLUE1 -> android.graphics.Color.YELLOW2 -> android.graphics.Color.CYAN3 -> android.graphics.Color.MAGENTA4 -> android.graphics.Color.LTGRAYelse -> android.graphics.Color.TRANSPARENT}
//                    @TODO 每次設置顏色后 調用postInvalidate 重新繪制ViewpostInvalidate()}})
//            動畫無線循環執行repeatCount = ValueAnimator.INFINITE
//            間隔一秒執行一次duration = 1000}}init {mPaint.color = Color.Blue.hashCode()mPaint.style = Paint.Style.FILLmPaint.strokeWidth = 20fcontext?.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 中獲取view的 寬高 獲取到是 0Log.e(TAG, "onMeasure: ${widthSize}-${width}__${heightSize}__${height}")val defWidth = 400val 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)}}
//掛在到Act上時
//    override fun onAttachedToWindow() {
//        super.onAttachedToWindow()
//        Log.e(TAG, "onAttachedToWindow: ")
//        anim.start()
//    }//在Act 銷毀時
//    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：根據給定的 Canvas 自動渲染View包括其所有子 View）。* 繪制過程：*   1. 繪制view背景*   2. 繪制view內容*   3. 繪制子View*   4. 繪制裝飾（漸變框，滑動條等等）* 注：*    a. 在調用該方法之前必須要完成 layout 過程*    b. 所有的視圖最終都是調用 View 的 draw()繪制視圖（ ViewGroup 沒有復寫此方法）*    c. 在自定義View時，不應該復寫該方法，而是復寫 onDraw(Canvas) 方法進行繪制*    d. 若自定義的視圖確實要復寫該方法，那么需先調用 super.draw(canvas)完成系統的繪制，然后再進行自定義的繪制*/override fun onDraw(canvas: Canvas?) {super.onDraw(canvas)canvas?.let {val pL = paddingLeftval pR = paddingRightval pT = paddingTopval pB = paddingBottomvar mHeight = height - pT - pBvar mWidth = width - pL - pRval 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)}}
}

自定義View的xml樣式文件

<?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.MyViewandroid: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 通過  lifecycle 控制動畫的狀態：開始、暫停、恢復、取消lifecycle.addObserver(customView)}
}