Android kotlin exception handling

Throws Exception

Kotlin Exceptions and Java The same as , try…catch…finally Code block handling exception , The only difference is ：Kotlin All the exceptions are Unchecked exceptions.

checked exceptions Is an exception that must be defined and handled on a method , such as Java Of IoException.

Kotlin Throw an exception using Throws Annotation to achieve , as follows ：

@Throws(IOException::class)
fun createDirectory(file: File) {
    if (file.exists())
        throw IOException("Directory already exists")
    file.createNewFile()
}

When we're in java When used in code , as follows ：

Will remind us to report errors , But if kotlin When used in the document , There will be no hint .

Custom exception

/**
 * @author : zhaoyanjun
 * @time : 2021/7/5
 * @desc :  Custom exception 
 */
class CommonException(code: Int, message: String) : Exception(message)

Use ：

@Throws(CommonException::class)
fun createDirectory(file: File) {
    if (file.exists())
        throw CommonException(0, "file is exists")
    file.createNewFile()
}

runCatching

class MainActivity : AppCompatActivity() {

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)

        kotlin.runCatching {
            sum(2, 4)
        }.onSuccess {
            Log.d("yy--", " Normal results $it")
        }.onFailure {
            it.printStackTrace()
            Log.d("yy--", " The result is abnormal ${it.message}")
        }

    }

    fun sum(num1: Int, num2: Int): Int {
        1 / 0
        return num1 + num2
    }
}

getOrDefault

val result = kotlin.runCatching {
            sum(2, 4)
        }.onSuccess {
            Log.d("yy--", " Normal results $it")
        }.onFailure {
            it.printStackTrace()
            Log.d("yy--", " The result is abnormal ${it.message}")
        }.getOrDefault(100)

// If it works properly , Just go back to 6, Return if the operation is abnormal 100
Log.d("yy--", " result $result")

isSuccess、isFailure

val result = kotlin.runCatching {
            sum(2, 4)
        }.onSuccess {
            Log.d("yy--", " Normal results $it")
        }.onFailure {
            it.printStackTrace()
            Log.d("yy--", " The result is abnormal ${it.message}")
        }.isFailure

exceptionOrNull

    public fun exceptionOrNull(): Throwable? =
        when (value) {
            is Failure -> value.exception
            else -> null
        }

If there is an exception, it returns an exception , Otherwise return to Null

getOrNull

    @InlineOnly
    public inline fun getOrNull(): T? =
        when {
            isFailure -> null
            else -> value as T
        }

If it fails , Just go back to null , Otherwise return to