Modifier — Compose 中的修饰符链与性能

@Composable
fun ModifierDemo() {
    // 顺序正确的修饰符链
    Box(
        modifier = Modifier
            .size(150.dp)
            .padding(8.dp)
            .border(2.dp, Color.Gray)
            .background(Color(0xFFE3F2FD))
            .clickable { /* handle click */ }
            .semantics {
                contentDescription = "Demo card with click action"
                role = Role.Button
            }
    ) {
        Text("触摸我")
    }
}

// 通过 composed 带状态的自定义修饰符
fun Modifier.cardStyle(
    elevation: Dp = 4.dp,
    isSelected: Boolean = false
): Modifier = this.composed {
    val backgroundColor = if (isSelected)
        MaterialTheme.colorScheme.primaryContainer
    else
        MaterialTheme.colorScheme.surface

    this
        .fillMaxWidth()
        .padding(12.dp)
        .background(backgroundColor, RoundedCornerShape(8.dp))
        .shadow(elevation, RoundedCornerShape(8.dp))
}

// 使用示例
@Composable
fun CardList() {
    Column {
        Box(Modifier.cardStyle()) { Text("项目 1") }
        Box(Modifier.cardStyle(isSelected = true)) { Text("已选择") }
    }
}

// 静态版本（不含 composed）— 更快
fun Modifier.simpleCardStyle(): Modifier =
    this.fillMaxWidth().padding(8.dp).clip(RoundedCornerShape(4.dp))

// ✅ 好：Composable 外部常量
private val cardModifier = Modifier
    .fillMaxWidth()
    .padding(16.dp)
    .clip(RoundedCornerShape(8.dp))

@Composable
fun CardContent() {
    Box(cardModifier.background(Color.White)) { ... }
}

// ❌ 差：每次重组时重新创建
@Composable
fun BadCard() {
    Box(Modifier.fillMaxWidth().padding(16.dp)) { ... }
}

// ✅ 好：对动态 Modifier 使用 remember
@Composable
fun DynamicCard(color: Color) {
    val modifier = remember(color) {
        Modifier.fillMaxWidth().background(color)
    }
    Box(modifier) { ... }
}