Android Weekly Notes #477

2021-09-13 本文已影响0人圣骑士wind

Android Weekly Issue #477

Jetpack Compose: styling Text

Text composable方法:

textDecoration属性

None
Underline
LineThrough

我们可以用combine和plus结合多个效果.

如果只有两个:

Text(
    text = "Jetpack Compose: Text",
    textDecoration = TextDecoration.Underline
           .plus(TextDecoration.LineThrough)
)

如果有多个:

Text(
    text = "Jetpack Compose: Text",
    textDecoration = TextDecoration.combine(
        listOf(
            TextDecoration.Underline,
            TextDecoration.LineThrough
        )
    )
)

overflow属性

Clip: 截断.
Ellipsis: 末尾带点点点.
Visibile: 可能会超出范围显示.

style属性

颜色, 字体, 方向, 阴影等.

Text(
    text = "Jetpack Compose",
    style = TextStyle(
        color = Color.Green,
        fontSize = 24.sp,
        fontFamily = FontFamily.Monospace,
        letterSpacing = 4.sp,
        textAlign = TextAlign.Center,
        shadow = Shadow(
            color = Color.Black,
            offset = Offset(8f, 8f),
            blurRadius = 4f
        ),
        textGeometricTransform = TextGeometricTransform(
            scaleX = 2.5f,
            skewX = 1f
        )
    ),
    modifier = Modifier.width(300.dp)
)

使用AnnotatedString可以给文字带上多种样式.

eBook sample with Jetpack Window Manager

Microsoft Surface Duo可折叠屏上的Two Page layout.

sample: https://github.com/microsoft/surface-duo-window-manager-samples/tree/main/EBookReader

How does suspension work in Kotlin coroutines?

协程的挂起是如何工作的, 一些简单的例子.

Coroutines (Part I) – Grasping the Fundamentals

协程基础.

Android Sleep API Tutorial: Getting Started

Sleep API: https://developers.google.com/location-context/sleep

系统会收集周围光线和设备运动等信息来假设用户是否在睡觉.

这篇文章可以教你弄个睡眠追踪app.

NavigationRailView MaterialDesign 1.4.0 Stable

竖屏下用BottomNavigationView.
横屏下用NavigationRailView.

Atomic Updates on MutableStateFlow

如果并发地改stateFlow, 有可能会出现问题.

比如下面这两段代码分别要改不同的字段:

// Assume the state flow value has the following existing properties:
// title: "Default title"
// doneButtonEnabled: false

// Label: Launch A
viewModelScope.launch(Dispatchers.IO) {
    val currentValueA = _viewState.value
    val newValueA = currentValueA.copy(doneButtonEnabled = true)
    _viewState.value = newValueA
}

// Label: Launch B
viewModelScope.launch(Dispatchers.Default) {
    val currentValueB = _viewState.value
    val newValueB = currentValueB.copy(title = "New Title")
    _viewState.value = newValueB
}

很可能第二个修改会覆盖第一个修改的字段.

一种解决方案是用mutex:

val mutex = Mutex()
// Assume the state flow value has the following existing properties:
// title: "Default title"
// doneButtonEnabled: false

// Label: Launch A
viewModelScope.launch(Dispatchers.IO) {
    mutex.withLock { 
        _viewState.value = _viewState.value.copy(doneButtonEnabled = true)
    }
}

// Label: Launch B
viewModelScope.launch(Dispatchers.Default) {
    mutex.withLock { 
        _viewState.value = _viewState.value.copy(title = "New title")
    }
}

还有一种解决方案就是用Kotlin 1.5的新api:

// Assume the state flow value has the following existing properties:
// title: "Default title"
// doneButtonEnabled: false

// Label: Launch A
viewModelScope.launch(Dispatchers.IO) {
  _viewState.update { it.copy(doneButtonEnabled = true) }
}

// Label: Launch B
viewModelScope.launch(Dispatchers.Default) {
  _viewState.update { it.copy(title = "New title") }
}