Android Compose 一：基础控件

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。

创建项目

需要使用新版本Android studio，忽略步骤...

项目目录

MainActivity说明

1 系统默认页面

@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

2 MyApplicationTheme 说明

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；

同样MyApplicationTheme 是被@Composable注解修饰

darkTheme: Boolean = isSystemInDarkTheme(), //判断是否是暗黑主题

那么我们把它写死成ture；

预览结果变黑啦

dynamicColor: Boolean = false, //动态颜色

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,
    )
}

百度翻译

content: @Composable () -> Unit 页面布局内容@Composable修饰的组件

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")
        }
    }
}

MyApplicationTheme 方法的实现代码分析

 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

通过以上的分析，我们或许可以实现多主题的功能用来更改app的主题颜色字体显示大小（比如老年模式）等功能 //TODO 后续尝试

基础组件

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 <R> foldIn(initial: R, operation: (R, Element) -> R): R = initial
        override fun <R> 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 <R> foldIn(initial: R, operation: (R, Element) -> R): R =
           operation(initial, this)

       override fun <R> 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

Text 文本

@Composable
fun Greeting(name: String, modifier: Modifier = Modifier) {
    Text(
        text = "Hello $name!",
        modifier = modifier
    )
}

Image 图片

 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
        )

Spacer 空白

 Text(text = "Hello $name!")
            Spacer(modifier = Modifier.padding(20.dp))
            Text(text = "Hello llo lo $name!")

Column 横布局

 Column(
            modifier = Modifier.padding(10.dp)
        ) {
            Text(text = "Hello $name!")
            Spacer(modifier = Modifier.padding(20.dp))
            Text(text = "Hello llo lo $name!")
        }

Row 竖布局

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!")
        }
    }

效果

其他布局用到时详解

接下来的问题

布局的对齐方式在父布局中的位置父布局控制子布局的位置