Android Jetpack Compose 高级开发核心技术

Android Compose 高级技术总结

1. 性能优化

1.1 状态管理优化

• 状态提升原则：将状态提升到共享的最近共同父组件
• derivedStateOf：当需要基于多个状态计算派生状态时使用

val scrollState = rememberScrollState()
val showButton by remember {derivedStateOf { scrollState.value > 0 }
}

1.2 重组优化

• remember：缓存计算结果避免不必要的重组
• key 参数：帮助 Compose 识别列表项的唯一性

items(items = list, key = { it.id }) { item ->ItemView(item)
}

1.3 延迟加载

• LazyColumn/LazyRow：仅渲染可见项
• LazyLayout：自定义懒加载布局

2. 自定义布局

2.1 Layout 修饰符

fun Modifier.customLayout() = layout { measurable, constraints ->val placeable = measurable.measure(constraints)layout(placeable.width, placeable.height) {placeable.placeRelative(x, y)}
}

2.2 自定义布局

@Composable
fun CustomLayout(modifier: Modifier = Modifier,content: @Composable () -> Unit
) {Layout(content = content,modifier = modifier) { measurables, constraints ->// 测量和定位逻辑}
}

3. 动画高级用法

3.1 自定义动画

val transition = updateTransition(targetState = isSelected)
val borderColor by transition.animateColor { state ->if (state) Color.Green else Color.White
}

3.2 AnimatedVisibility 扩展

AnimatedVisibility(visible = visible,enter = slideInHorizontally() + fadeIn(),exit = slideOutHorizontally() + fadeOut()
) {// 内容
}

3.3 手势动画

val offset = remember { Animatable(Offset(0f, 0f), Offset.VectorConverter) }
LaunchedEffect(offset) {offset.animateTo(targetValue, spring())
}

4. 高级状态管理

4.1 状态容器

class MyViewModel : ViewModel() {private val _state = mutableStateOf(MyState())val state: State<MyState> = _statefun update() {_state.value = _state.value.copy(...)}
}

4.2 状态恢复

@Composable
fun RememberSaveableExample() {var state by rememberSaveable { mutableStateOf(initialValue) }
}

5. 主题与样式

5.1 动态主题

@Composable
fun MyTheme(darkTheme: Boolean = isSystemInDarkTheme(),content: @Composable () -> Unit
) {val colors = if (darkTheme) DarkColors else LightColorsMaterialTheme(colors = colors, content = content)
}

5.2 自定义形状和颜色

val MyShapes = Shapes(small = CutCornerShape(4.dp),medium = CutCornerShape(8.dp),large = CutCornerShape(0.dp)
)

6. 与 View 系统互操作

6.1 AndroidView 嵌入传统 View

AndroidView(factory = { context ->CustomView(context).apply {// 初始化}},update = { view ->// 更新逻辑}
)

6.2 ComposeView 嵌入 Compose 内容

val composeView = ComposeView(context).apply {setContent {MyComposableContent()}
}

7. 测试

7.1 UI 测试

composeTestRule.setContent {MyAppTheme {MyScreen()}
}composeTestRule.onNodeWithText("Button").performClick()

7.2 状态测试

@Test
fun testState() {val viewModel = MyViewModel()assertEquals(expectedState, viewModel.state.value)
}

8. 高级图形绘制

8.1 Canvas 绘制

Canvas(modifier = Modifier.fillMaxSize()) {drawCircle(color = Color.Red, radius = 50f)
}

8.2 自定义绘制

@Composable
fun CustomDraw(modifier: Modifier = Modifier) {DrawModifier(modifier)
}private class DrawModifier(val modifier: Modifier) : Modifier.Element {// 实现绘制逻辑
}

9. 高级交互

9.1 多点触控

var scale by remember { mutableStateOf(1f) }
Modifier.pointerInput(Unit) {detectTransformGestures { _, pan, zoom, _ ->scale *= zoom}
}

9.2 嵌套滚动

val nestedScrollConnection = remember {object : NestedScrollConnection {override fun onPreScroll(available: Offset, source: NestedScrollSource): Offset {// 处理滚动return Offset.Zero}}
}

10. 组合模式与架构

10.1 组合式设计模式

• Slot API：通过 @Composable lambda 参数提供灵活性

@Composable
fun Card(modifier: Modifier = Modifier,content: @Composable () -> Unit
) {Surface(modifier) {content()}
}

10.2 分层架构

• UI 层：纯 Compose 组件
• 状态管理层：ViewModel/State Holder
• 业务逻辑层：Repository/Use Cases

这些高级技术可以帮助开发者构建更高效、更灵活的 Compose 应用，同时保持良好的架构和可维护性。