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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。