Flutter 与 Compose 组件辣么像,难道是同一个google团队整的;也未深究,只是猜测。
需要使用新版本Android studio,忽略步骤…
@Preview 修饰的方法,只用来供开发者预览使用,删除不影响运行
@Composable 修饰的方法 只能被@Composable修饰的方法调用
预览效果
MyApplicationTheme 对应的时 ui.theme 中的Theme.kt中的 MyApplicationTheme ; ctrl+左键点过去
下面看代码
@Composable
fun MyApplicationTheme(
darkTheme: Boolean = isSystemInDarkTheme(),
// Dynamic color is available on Android 12+
dynamicColor: Boolean = true,
content: @Composable () -> Unit
) {
咋看这这么像flutter 万物皆组件嘞;咱也不懂,咱也不敢吭;
那么我们把它写死成ture;
预览结果 变黑啦
暂未发现有啥变化
代码里判断了支持动态颜色,调用了
/**
* Creates a light dynamic color scheme.
*
* Use this function to create a color scheme based off the system wallpaper. If the developer
* changes the wallpaper this color scheme will change accordingly. This dynamic scheme is a
* light theme variant.
*
* @param context The context required to get system resource data.
*/
@RequiresApi(Build.VERSION_CODES.S)
fun dynamicLightColorScheme(context: Context): ColorScheme {
val tonalPalette = dynamicTonalPalette(context)
return lightColorScheme(
primary = tonalPalette.primary40,
onPrimary = tonalPalette.primary100,
primaryContainer = tonalPalette.primary90,
onPrimaryContainer = tonalPalette.primary10,
inversePrimary = tonalPalette.primary80,
secondary = tonalPalette.secondary40,
onSecondary = tonalPalette.secondary100,
secondaryContainer = tonalPalette.secondary90,
onSecondaryContainer = tonalPalette.secondary10,
tertiary = tonalPalette.tertiary40,
onTertiary = tonalPalette.tertiary100,
tertiaryContainer = tonalPalette.tertiary90,
onTertiaryContainer = tonalPalette.tertiary10,
background = tonalPalette.neutral99,
onBackground = tonalPalette.neutral10,
surface = tonalPalette.neutral99,
onSurface = tonalPalette.neutral10,
surfaceVariant = tonalPalette.neutralVariant90,
onSurfaceVariant = tonalPalette.neutralVariant30,
inverseSurface = tonalPalette.neutral20,
inverseOnSurface = tonalPalette.neutral95,
outline = tonalPalette.neutralVariant50,
)
}
content 应该就是Surface,kotlin 最后一个参数如果是lambda表达式,那么lambda表达式可以放在外边
@Preview(showBackground = true)
@Composable
fun GreetingPreview() {
MyApplicationTheme(
content = {
Surface(
modifier = Modifier.fillMaxSize(),
color = MaterialTheme.colorScheme.background
) {
Greeting("Android")
}
}
)
}
即
@Preview(showBackground = true)
@Composable
fun GreetingPreview() {
MyApplicationTheme(){
Surface(
modifier = Modifier.fillMaxSize(),
color = MaterialTheme.colorScheme.background
) {
Greeting("Android")
}
}
}
val colorScheme = when {
dynamicColor && Build.VERSION.SDK_INT >= Build.VERSION_CODES.S -> { //这就是动态颜色
val context = LocalContext.current
if (darkTheme) dynamicDarkColorScheme(context) else dynamicLightColorScheme(context)
}
darkTheme -> DarkColorScheme
else -> LightColorScheme
}
val view = LocalView.current
if (!view.isInEditMode) { //这个就是判断 是否在编辑模式 然后设置了状态栏的颜色
SideEffect {
val window = (view.context as Activity).window
window.statusBarColor = colorScheme.primary.toArgb()
WindowCompat.getInsetsController(window, view).isAppearanceLightStatusBars = darkTheme //这一样也是设置状态栏的颜色 大概意思就是看翻译
}
}
MaterialTheme(
colorScheme = colorScheme, //设置主题颜色 ui.theme.Color
typography = Typography, // ui.theme.Type
content = content
)
view.isInEditMode 注释的翻译
WindowCompat.getInsetsController(window, view).isAppearanceLightStatusBars = darkTheme
组件一般都包含Modifier的参数
@Composable
fun Greeting(name: String, modifier: Modifier = Modifier) {
Text(
text = "Hello $name!",
modifier = Modifier.padding()
)
}
方法参数有个 modifier: Modifier = Modifier ctrl+左键 点
发现是Modifier.kt 的对象
// The companion object implements `Modifier` so that it may be used as the start of a
// modifier extension factory expression.
companion object : Modifier {
override fun foldIn(initial: R, operation: (R, Element) -> R): R = initial
override fun foldOut(initial: R, operation: (Element, R) -> R): R = initial
override fun any(predicate: (Element) -> Boolean): Boolean = false
override fun all(predicate: (Element) -> Boolean): Boolean = true
override infix fun then(other: Modifier): Modifier = other
override fun toString() = "Modifier"
}
使用Modifier都是使用 此伴生对象;是所有链式调用的起点
打个断点看看
例如我们写了如下代码
Text(
text = "Hello $name!",
modifier = Modifier.padding(20.dp)
)
调用的是Padding.kt的 其实使用的是 PaddingModifier
@Stable
fun Modifier.padding(all: Dp) =
this.then(
PaddingModifier(
start = all,
top = all,
end = all,
bottom = all,
rtlAware = true,
inspectorInfo = debugInspectorInfo {
name = "padding"
value = all
}
)
)
PaddingModifier 其实实现LayoutModifier
private class PaddingModifier(
val start: Dp = 0.dp,
val top: Dp = 0.dp,
val end: Dp = 0.dp,
val bottom: Dp = 0.dp,
val rtlAware: Boolean,
inspectorInfo: InspectorInfo.() -> Unit
) : LayoutModifier, InspectorValueInfo(inspectorInfo) {
LayoutModifier
@JvmDefaultWithCompatibility
interface LayoutModifier : Modifier.Element {
Modifier.Element
@JvmDefaultWithCompatibility
interface Element : Modifier {
override fun foldIn(initial: R, operation: (R, Element) -> R): R =
operation(initial, this)
override fun foldOut(initial: R, operation: (Element, R) -> R): R =
operation(this, initial)
override fun any(predicate: (Element) -> Boolean): Boolean = predicate(this)
override fun all(predicate: (Element) -> Boolean): Boolean = predicate(this)
}
Modifier 是个接口 实现如下
Modifier 可用来设置形状,大小,位置,边距,透明度,点击 等
例如 Text的modifier可以设置如下
modifier = Modifier.padding()
Padding.kt Modifer的扩展方法
@Composable
fun Greeting(name: String, modifier: Modifier = Modifier) {
Text(
text = "Hello $name!",
modifier = modifier
)
}
Image(
painter = painterResource(id = R.drawable.img_lufei), //资源
contentDescription = "", //描述
modifier = Modifier.size(80.dp).clip(CircleShape), //大小 形状
contentScale = ContentScale.Crop //渲染方式
)
Text(text = "Hello $name!")
Spacer(modifier = Modifier.padding(20.dp))
Text(text = "Hello llo lo $name!")
Column(
modifier = Modifier.padding(10.dp)
) {
Text(text = "Hello $name!")
Spacer(modifier = Modifier.padding(20.dp))
Text(text = "Hello llo lo $name!")
}
Row(
modifier = Modifier.wrapContentHeight(align = Alignment.CenterVertically)
) {
Image(
painter = painterResource(id = R.drawable.img_lufei),
contentDescription = "",
modifier = Modifier.size(80.dp).clip(CircleShape),
contentScale = ContentScale.Crop
)
Column(
modifier = Modifier.padding(10.dp)
) {
Text(text = "Hello $name!")
Spacer(modifier = Modifier.padding(20.dp))
Text(text = "Hello llo lo $name!")
}
}