Kotlin 开发 - orEmpty 函数、ifEmpty 函数、ifBlank 函数、takeIf 函数

orEmpty 函数

1、基本介绍

• orEmpty 函数是一个用于处理可空对象的扩展函数，当对象为 null 时，它会返回一个对应类型的空实例

@kotlin.internal.InlineOnly
public inline fun String?.orEmpty(): String = this ?: ""

@kotlin.internal.InlineOnly
public inline fun <T> List<T>?.orEmpty(): List<T> = this ?: emptyList()

@kotlin.internal.InlineOnly
public inline fun <T> Set<T>?.orEmpty(): Set<T> = this ?: emptySet()

@kotlin.internal.InlineOnly
public inline fun <K, V> Map<K, V>?.orEmpty(): Map<K, V> = this ?: emptyMap()

public actual inline fun <reified T> Array<out T>?.orEmpty(): Array<out T> = this ?: emptyArray<T>()

2、基本使用

val s: String? = null

println(s.orEmpty())
println(s.orEmpty().length)

# 输出结果

0

val list: List<Int>? = null

println(list.orEmpty())
println(list.orEmpty().size)

# 输出结果

[]
0

val set: Set<String>? = null

println(set.orEmpty())
println(set.orEmpty().size)

# 输出结果

[]
0

val map: Map<Int, String>? = null

println(map.orEmpty())
println(map.orEmpty().size)

# 输出结果

{}
0

val arr: Array<Int>? = null

println(arr.orEmpty().contentToString())
println(arr.orEmpty().size)

# 输出结果

[]
0

ifEmpty 函数、ifBlank 函数、takeIf 函数

val handleContent = if (etHandleContent.text.toString().isEmpty()) {
null
} else {
etHandleContent.text.toString()
}

val handleContent = if (etHandleContent.text.toString().isBlank()) {
null
} else {
etHandleContent.text.toString()
}

String handleContent = etHandleContent.getText().toString().isEmpty() ? null : etHandleContent.getText().toString();

String handleContent = etHandleContent.getText().toString().isBlank() ? null : etHandleContent.getText().toString();

val handleContent = etHandleContent.text.toString().ifEmpty { null }

val handleContent = etHandleContent.text.toString().ifBlank { null }

val handleContent = etHandleContent.text.toString().takeIf { it.isNotEmpty() }

val handleContent = etHandleContent.text.toString().takeIf { it.isNotBlank() }