Kotlin and Jetpack Compose Parameter Design Complete Guide (Latest Recommendation)

As developers of Kotlin and Jetpack Compose, reasonable parameter design can significantly improve the readability and ease of use of code. This article will systematically organize various parameter rules to help you write a more elegant API.

1. Basic parameter rules

1. Method parameters

// Basic definitionfun Method name(Required parameters: type, Optional parameters: type = default value): 返回type {
    // Method body}
// Actual examplefun fetchData(
    url: String,              // Required parameters    timeout: Int = 5000,      // Optional parameters    callback: (Result) -&gt; Unit // Function parameters) { /*...*/ }

Call method:

// Required parameters must be passedfetchData("")  // Missing callback compilation error// Named parameter call (recommended)fetchData(
    url = "",
    callback = { result -&gt; /*...*/ }
)
// Skip optional parametersfetchData("", callback = { /*...*/ })

2. Class constructor parameters

class User(
    val id: String,          // Read-only attributes    var name: String,        // Variable properties    age: Int = 18,           // Private attributes (no val/var)    val status: String = "active"
) {
    // age can only be accessed inside the class}

2. Advanced parameter characteristics

1. Variable parameters (vararg)

fun printAll(vararg messages: String) {
     { println(it) }
}
// CallprintAll("Hello")            // Single parameterprintAll("A", "B", "C")      // Multiple parametersprintAll(*arrayOf("D", "E")) // Array expansion

2. Deconstruct the declared parameters

data class Point(val x: Int, val y: Int)
fun draw((x, y): Point) {  // Parameter destruction    println("Drawing at ($x, $y)")
}

3. Compose component parameter specifications

1. Basic component templates

@Composable
fun MyComponent(
    // 1. Modifier (must be first)    modifier: Modifier = Modifier,
    // 2. Required status parameters    value: Int,
    // 3. Optional status parameters    secondaryValue: Int = 0,
    // 4. Callback function    onValueChange: (Int) -&gt; Unit,
    // 5. Content slot    content: @Composable () -&gt; Unit = {}
) {
    Box(modifier) {
        // Component implementation    }
}

2. Parameter design best practices

Parameter Type	specification	Example	Necessary
Modifier	First place, default`Modifier`	`modifier: Modifier = Modifier`	no
Status value	Clearly read-only/writeable	`value: T`, `onValueChange: (T) -> Unit`	yes
Callback function	by`on`Prefix naming	`onClick: () -> Unit`	Depending on the situation
Content slot	Last position	`content: @Composable () -> Unit`	Yes (can be passed on to empty)
Configuration parameters	Using data class encapsulation	`style: ButtonStyle =`	no

3. Example of status parameters

@Composable
fun Counter(
    count: Int,                   // Read-only state    onIncrement: () -&gt; Unit,       // Incremental callback    modifier: Modifier = Modifier, // Modifier    maxCount: Int = Int.MAX_VALUE  // Optional configuration) {
    Button(
        onClick = { if (count &lt; maxCount) onIncrement() },
        modifier = modifier,
        enabled = count &lt; maxCount
    ) {
        Text("Count: $count")
    }
}

4. Parameter scenarios can be omitted

1. All parameters with default values

// Definitionfun search(
    query: String,
    caseSensitive: Boolean = false,
    limit: Int = 10
) { /*...*/ }
// Callsearch("kotlin")  // Only the required parameters are passed

2. Compose unique omission

// Definition@Composable
fun IconLabel(
    icon: @Composable () -&gt; Unit,
    label: String = "",      // Optional text    modifier: Modifier = Modifier
) { /*...*/ }
// CallIconLabel(icon = { Icon() })  // Omitted label and modifier

3. Trailing Lambda omit

// Definitionfun runAfterDelay(
    delay: Long,
    block: () -&gt; Unit = {}
) { /*...*/ }
// CallrunAfterDelay(1000)  // Omitted block parameter

V. Parameter design principles

Necessary parameters are preferred: Key parameters are placed in front
Reasonable default value: Provide default values for common options
Naming consistency: Maintain a consistent naming with the standard library
Parameter grouping: Related parameters are placed adjacently
Avoid too many parameters: More than 5 considerations for using configuration classes

// Bad designfun badDesign(
    param1: Int,
    param2: String,
    param3: Boolean,
    param4: Float,
    param5: Long,
    param6: Double
) { /*...*/ }
// Optimized designdata class Config(
    val setting1: Int,
    val setting2: String,
    val setting3: Boolean = false,
    /*...*/
)
fun goodDesign(config: Config) { /*...*/ }

By following these parameter design specifications, your Kotlin and Compose code will be clearer, easier to use, and easier to maintain. Remember, a good API design should make common usage scenarios simple and support the possibility of complex scenarios.

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