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本篇文章来自谭嘉俊的投稿，分享了Kotlin的自定义View实战，相信会对大家有所帮助！同时也感谢作者贡献的精彩文章。
谭嘉俊的博客地址：
https://juejin.im/user/593f7b33fe88c2006a37eb9b
这是一个带弧形的进度条，其实这个控件很久之前已经实现了，但是我想用Kotlin去重写优化一遍，并且对此铺开来讲解。
项目的Github地址：
https://github.com/TanJiaJunBeyond/CircularArcProgressView
效果图
属性
使用
导入你的项目中
dependencies {
implementation ‘com.tanjiajun.widget:CircularArcProgressView:1.0.2’
}
implementation ‘com.tanjiajun.widget:CircularArcProgressView:1.0.2’
}
布局文件
<com.tanjiajun.widget.CircularArcProgressView
android:id=“@+id/capv_first”
android:layout_width=“0dp”
android:layout_height=“30dp”
android:layout_marginStart=“16dp”
android:layout_marginTop=“16dp”
android:layout_marginEnd=“16dp”
app:capv_background_color=“@color/circular_arc_progress_view_first_background_color”
app:capv_is_show_progress_text=“true”
app:capv_percent=“0.8”
app:capv_progress_color=“@color/circular_arc_progress_view_first_progress_color”
app:layout_constraintEnd_toEndOf=“parent”
app:layout_constraintStart_toStartOf=“parent”
app:layout_constraintTop_toTopOf=“parent” />
android:id=“@+id/capv_first”
android:layout_width=“0dp”
android:layout_height=“30dp”
android:layout_marginStart=“16dp”
android:layout_marginTop=“16dp”
android:layout_marginEnd=“16dp”
app:capv_background_color=“@color/circular_arc_progress_view_first_background_color”
app:capv_is_show_progress_text=“true”
app:capv_percent=“0.8”
app:capv_progress_color=“@color/circular_arc_progress_view_first_progress_color”
app:layout_constraintEnd_toEndOf=“parent”
app:layout_constraintStart_toStartOf=“parent”
app:layout_constraintTop_toTopOf=“parent” />
Kotlin
findViewById<CircularArcProgressView>(R.id.capv_first).startAnimator(duration = 2000)
Java
((CircularArcProgressView) findViewById(R.id.capv_first)).startAnimator(2000);
/ 源码分析 /
定义自定义属性，据此写出对应的获取自定义属性的代码，并且暴露一些需要用户设置的方法，代码如下：
/**
* Set percent to show the progress.
*/
var percent: Float = 0f
set(value) {
var percent = value
if (percent < 0f) {
percent = 0f
} else if (percent > 1f) {
percent = 1f
}
if (percent != field) {
field = percent
invalidate()
}
}
init {
attrs?.let { set ->
context.obtainStyledAttributes(set, R.styleable.CircularArcProgressView).apply {
bgColor =
getColor(R.styleable.CircularArcProgressView_capv_background_color, Color.BLACK)
progressColor =
getColor(R.styleable.CircularArcProgressView_capv_progress_color, Color.RED)
progressTextColor =
getColor(
R.styleable.CircularArcProgressView_capv_progress_text_color,
Color.WHITE
)
getFloat(R.styleable.CircularArcProgressView_capv_percent, 0f).let {
percent = it
}
isShowProgressText =
getBoolean(
R.styleable.CircularArcProgressView_capv_is_show_progress_text,
false
)
recycle()
}
}
}
* Set percent to show the progress.
*/
var percent: Float = 0f
set(value) {
var percent = value
if (percent < 0f) {
percent = 0f
} else if (percent > 1f) {
percent = 1f
}
if (percent != field) {
field = percent
invalidate()
}
}
init {
attrs?.let { set ->
context.obtainStyledAttributes(set, R.styleable.CircularArcProgressView).apply {
bgColor =
getColor(R.styleable.CircularArcProgressView_capv_background_color, Color.BLACK)
progressColor =
getColor(R.styleable.CircularArcProgressView_capv_progress_color, Color.RED)
progressTextColor =
getColor(
R.styleable.CircularArcProgressView_capv_progress_text_color,
Color.WHITE
)
getFloat(R.styleable.CircularArcProgressView_capv_percent, 0f).let {
percent = it
}
isShowProgressText =
getBoolean(
R.styleable.CircularArcProgressView_capv_is_show_progress_text,
false
)
recycle()
}
}
}
根据用户设置的宽高去绘制一个半径为高度一半的圆角矩形，注意要对padding属性进行处理，这部分就是背景，代码如下：
val halfHeight = height / 2f
val saveCount = canvas.saveLayer(0f, 0f, width.toFloat(), height.toFloat(), null)
// Draw background.
backgroundRectF.left = paddingStart.toFloat()
backgroundRectF.top = paddingTop.toFloat()
backgroundRectF.right = width – paddingEnd.toFloat()
backgroundRectF.bottom = height – paddingBottom.toFloat()
canvas.drawRoundRect(backgroundRectF, halfHeight, halfHeight, backgroundPaint)
val saveCount = canvas.saveLayer(0f, 0f, width.toFloat(), height.toFloat(), null)
// Draw background.
backgroundRectF.left = paddingStart.toFloat()
backgroundRectF.top = paddingTop.toFloat()
backgroundRectF.right = width – paddingEnd.toFloat()
backgroundRectF.bottom = height – paddingBottom.toFloat()
canvas.drawRoundRect(backgroundRectF, halfHeight, halfHeight, backgroundPaint)
在背景圆角矩形的左边绘制另外一个半径为高度一半的圆角矩形，宽高和背景圆角矩形一样，但是左右坐标会随着percent的增加而增加，绘制完毕后的表现就是往右移动，然后利用PorterDuffXfermode处理重叠部分，这部分就是进度，代码如下：
private val progressTextPaint by lazy {
TextPaint().apply {
isAntiAlias = true
isDither = true
style = Paint.Style.FILL
color = progressTextColor
}
}
TextPaint().apply {
isAntiAlias = true
isDither = true
style = Paint.Style.FILL
color = progressTextColor
}
}
// Draw progress.
progressRectF.left = -backgroundRectF.width() + percent * width
progressRectF.top = backgroundRectF.top
progressRectF.right = progressRectF.left + backgroundRectF.width()
progressRectF.bottom = backgroundRectF.bottom
canvas.drawRoundRect(progressRectF, halfHeight, halfHeight, progressPaint)
canvas.restoreToCount(saveCount)
progressRectF.left = -backgroundRectF.width() + percent * width
progressRectF.top = backgroundRectF.top
progressRectF.right = progressRectF.left + backgroundRectF.width()
progressRectF.bottom = backgroundRectF.bottom
canvas.drawRoundRect(progressRectF, halfHeight, halfHeight, progressPaint)
canvas.restoreToCount(saveCount)
根据用户需要绘制一个百分比文本，左右坐标也是随着percent增加而增加，绘制完毕后的表现也是向右移动，不过是位于进度条弧形的左边，注意要准确测量文字的宽高，代码如下：
if (isShowProgressText && percent >= 0.1f) {
progressTextPaint.run {
textSize = halfHeight
fontMetrics.let {
val progressText = (percent * 100).toInt().toString() + “%”
canvas.drawText(
progressText,
percent * width – progressTextPaint.measureText(progressText) – height / 5f,
halfHeight – it.descent + (it.descent – it.ascent) / 2f,
progressTextPaint
)
}
}
}
progressTextPaint.run {
textSize = halfHeight
fontMetrics.let {
val progressText = (percent * 100).toInt().toString() + “%”
canvas.drawText(
progressText,
percent * width – progressTextPaint.measureText(progressText) – height / 5f,
halfHeight – it.descent + (it.descent – it.ascent) / 2f,
progressTextPaint
)
}
}
}
暴露一个设置动画的方法。
/**
* Start animator.
*
* @param timeInterpolator the interpolator to be used by this animation. The default value is
* android.view.animation.AccelerateInterpolator.
*
* @param duration the length of the animation.
*/
@JvmOverloads
fun startAnimator(
timeInterpolator: TimeInterpolator? = AccelerateInterpolator(),
duration: Long
) =
with(ObjectAnimator.ofFloat(this, “percent”, 0f, percent)) {
interpolator = timeInterpolator
this.duration = duration
start()
}
* Start animator.
*
* @param timeInterpolator the interpolator to be used by this animation. The default value is
* android.view.animation.AccelerateInterpolator.
*
* @param duration the length of the animation.
*/
@JvmOverloads
fun startAnimator(
timeInterpolator: TimeInterpolator? = AccelerateInterpolator(),
duration: Long
) =
with(ObjectAnimator.ofFloat(this, “percent”, 0f, percent)) {
interpolator = timeInterpolator
this.duration = duration
start()
}
/ PorterDuff.Mode /
来源
为什么叫PorterDuff呢？其实是两个人名来的，一个叫Thomas Porter，另一个叫Tom Duff，他们在1984年7月发表了Compositing Digital Images，描述了12个合成运算符。
它们控制着要渲染的图像和渲染目标的内容组成的颜色，然后这个类还提供了除了那12种的其他几种混合模式，但是这些不是由这两人定义的，只是为了方便才在此类中，所以总共有18种。
源码
我们可以看下PorterDuff这个类，里面有个枚举Mode，代码如下：
public enum Mode {
CLEAR (0),
SRC (1),
DST (2),
SRC_OVER (3),
DST_OVER (4),
SRC_IN (5),
DST_IN (6),
SRC_OUT (7),
DST_OUT (8),
SRC_ATOP (9),
DST_ATOP (10),
XOR (11),
DARKEN (16),
LIGHTEN (17),
MULTIPLY (13),
SCREEN (14),
ADD (12),
OVERLAY (15);
Mode(int nativeInt) {
this.nativeInt = nativeInt;
}
/**
* @hide
*/
@UnsupportedAppUsage
public final int nativeInt;
}
CLEAR (0),
SRC (1),
DST (2),
SRC_OVER (3),
DST_OVER (4),
SRC_IN (5),
DST_IN (6),
SRC_OUT (7),
DST_OUT (8),
SRC_ATOP (9),
DST_ATOP (10),
XOR (11),
DARKEN (16),
LIGHTEN (17),
MULTIPLY (13),
SCREEN (14),
ADD (12),
OVERLAY (15);
Mode(int nativeInt) {
this.nativeInt = nativeInt;
}
/**
* @hide
*/
@UnsupportedAppUsage
public final int nativeInt;
}
PorterDuff总共有18种模式，以下展示了这些模式对应的名字、图片和描述，可以点开图片查看，图片如下：
/ 延迟属性Lazy /
这个控件的代码也用上了延迟属性Lazy，代码如下：
private val progressTextPaint by lazy {
TextPaint().apply {
isAntiAlias = true
isDither = true
style = Paint.Style.FILL
color = progressTextColor
}
}
TextPaint().apply {
isAntiAlias = true
isDither = true
style = Paint.Style.FILL
color = progressTextColor
}
}
我们可以看到，lazy函数是接受一个Lambda表达式，如果函数最后一个参数是Lambda表达式的话，可以提到小括号外边，并且小括号也可以省略；
调用延迟属性有这样的特征，第一次拿到属性的值（调用get方法）会执行已传递给函数的Lambda表达式并且记录结果，后续调用get()只是返回记录的结果。
我们可以看下源码，提供了三个函数。
lazy(initializer: () -> T)
public actual fun <T> lazy(initializer: () -> T): Lazy<T> = SynchronizedLazyImpl(initializer)
这个函数接受一个Lambda表达式，并且返回Lazy，并且调用SynchronizedLazyImpl函数，而且我们可以得知多个线程去调用这个lazy函数是安全的，代码如下：
private class SynchronizedLazyImpl<out T>(initializer: () -> T, lock: Any? = null) : Lazy<T>, Serializable {
private var initializer: (() -> T)? = initializer
@Volatile private var _value: Any? = UNINITIALIZED_VALUE
// final field is required to enable safe publication of constructed instance
private val lock = lock ?: this
override val value: T
get() {
val _v1 = _value
if (_v1 !== UNINITIALIZED_VALUE) {
@Suppress(“UNCHECKED_CAST”)
return _v1 as T
}
return synchronized(lock) {
val _v2 = _value
if (_v2 !== UNINITIALIZED_VALUE) {
@Suppress(“UNCHECKED_CAST”) (_v2 as T)
} else {
val typedValue = initializer!!()
_value = typedValue
initializer = null
typedValue
}
}
}
override fun isInitialized(): Boolean = _value !== UNINITIALIZED_VALUE
override fun toString(): String = if (isInitialized()) value.toString() else “Lazy value not initialized yet.”
private fun writeReplace(): Any = InitializedLazyImpl(value)
}
private var initializer: (() -> T)? = initializer
@Volatile private var _value: Any? = UNINITIALIZED_VALUE
// final field is required to enable safe publication of constructed instance
private val lock = lock ?: this
override val value: T
get() {
val _v1 = _value
if (_v1 !== UNINITIALIZED_VALUE) {
@Suppress(“UNCHECKED_CAST”)
return _v1 as T
}
return synchronized(lock) {
val _v2 = _value
if (_v2 !== UNINITIALIZED_VALUE) {
@Suppress(“UNCHECKED_CAST”) (_v2 as T)
} else {
val typedValue = initializer!!()
_value = typedValue
initializer = null
typedValue
}
}
}
override fun isInitialized(): Boolean = _value !== UNINITIALIZED_VALUE
override fun toString(): String = if (isInitialized()) value.toString() else “Lazy value not initialized yet.”
private fun writeReplace(): Any = InitializedLazyImpl(value)
}
我们可以看到用的是**双重检查锁（Double Checked Locking）**来保证线程安全。
lazy(mode: LazyThreadSafetyMode, initializer: () -> T)
public actual fun <T> lazy(mode: LazyThreadSafetyMode, initializer: () -> T): Lazy<T> =
when (mode) {
LazyThreadSafetyMode.SYNCHRONIZED -> SynchronizedLazyImpl(initializer)
LazyThreadSafetyMode.PUBLICATION -> SafePublicationLazyImpl(initializer)
LazyThreadSafetyMode.NONE -> UnsafeLazyImpl(initializer)
}
when (mode) {
LazyThreadSafetyMode.SYNCHRONIZED -> SynchronizedLazyImpl(initializer)
LazyThreadSafetyMode.PUBLICATION -> SafePublicationLazyImpl(initializer)
LazyThreadSafetyMode.NONE -> UnsafeLazyImpl(initializer)
}
这个函数接受两个参数，一个是LazyThreadSafetyMode，另外一个是Lambda表达式，并且返回Lazy，LazyThreadSafetyMode是个枚举类，代码如下：
public enum class LazyThreadSafetyMode {
SYNCHRONIZED,
PUBLICATION,
NONE,
}
SYNCHRONIZED,
PUBLICATION,
NONE,
}
使用SYNCHRONIZED可以保证只有一个线程初始化实例，实现细节在上面也说过了；使用PUBLICATION允许多个线程并发初始化值，但是只有第一个返回值用作实例的值；使用NONE不会有任何线程安全的保证以及的相关的开销，所以你如果你确认初始化总是发生在同一个线程的话可以用此模式，减少一些性能上的开销。
lazy(lock: Any?, initializer: () -> T)
public actual fun <T> lazy(lock: Any?, initializer: () -> T): Lazy<T> = SynchronizedLazyImpl(initializer, lock)
这个函数接受两个参数，一个是你使用指定的对象（lock）进行同步，另外一个是Lambda表达式，返回的是Lazy，调用的是SynchronizedLazyImpl函数，上面也说过了，这里不再赘述。
/ @JvmOverloads /
如果写一个有默认参数值的Kotlin函数，在Java中只会有个一个所有参数都存在的方法可以调用，如果希望向Java调用者暴露多个重载，可以使用**@JvmOverloads**注解。
拿这个控件的代码举例，代码如下：
class CircularArcProgressView @JvmOverloads constructor(
context: Context,
attrs: AttributeSet? = null,
defStyleAttr: Int = 0
) : View(context, attrs, defStyleAttr) {
// 省略实现代码
}
context: Context,
attrs: AttributeSet? = null,
defStyleAttr: Int = 0
) : View(context, attrs, defStyleAttr) {
// 省略实现代码
}
反编译成Java代码，代码如下：
public final class CircularArcProgressView extends View {
@JvmOverloads
public CircularArcProgressView(@NotNull Context context, @Nullable AttributeSet attrs, int defStyleAttr) {
// 省略实现代码
}
@JvmOverloads
public CircularArcProgressView(@NotNull Context context, @Nullable AttributeSet attrs) {
// 省略实现代码
}
@JvmOverloads
public CircularArcProgressView(@NotNull Context context) {
// 省略实现代码
}
}
@JvmOverloads
public CircularArcProgressView(@NotNull Context context, @Nullable AttributeSet attrs, int defStyleAttr) {
// 省略实现代码
}
@JvmOverloads
public CircularArcProgressView(@NotNull Context context, @Nullable AttributeSet attrs) {
// 省略实现代码
}
@JvmOverloads
public CircularArcProgressView(@NotNull Context context) {
// 省略实现代码
}
}
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本文链接: https://leetcode.jp/kotlin的自定义view，实现带弧形的进度条/