Kotlin：使用flow实现倒计时功能

一、效果图

二、ExtendContext.kt 文件代码

注意：创建ExtendContext.kt选择file
使用kotlin扩展方法的特性创建countDown扩展方法，避免多个地方使用倒计时重复创建countDown方法

package com.example.baselib.extension

import androidx.fragment.app.FragmentActivity
import androidx.lifecycle.lifecycleScope
import kotlinx.coroutines.CoroutineScope
import kotlinx.coroutines.delay
import kotlinx.coroutines.flow.catch
import kotlinx.coroutines.flow.flow
import kotlinx.coroutines.flow.onCompletion
import kotlinx.coroutines.flow.onStart
import kotlinx.coroutines.launch

fun FragmentActivity.countDown(
    timeMillis: Long = 1000,//默认时间间隔 1 秒
    time: Int = 3,//默认时间为 3 秒
    start: (scop: CoroutineScope) -> Unit,
    end: () -> Unit,
    next: (time: Int) -> Unit,
    error: (msg: String?) -> Unit
) {
    lifecycleScope.launch {
        flow {
            (time downTo 1).forEach {
                delay(timeMillis)
                emit(it)
            }
        }.onStart {
            start(this@launch)
        }.onCompletion {
            end()
        }.catch {
            error(it.message ?: "countDown 出现未知错误")
        }.collect {
            next(it)
        }
    }
}

三、MainActivity.kt代码

package com.example.testkotlin

import androidx.appcompat.app.AppCompatActivity
import android.os.Bundle
import android.util.Log
import com.example.baselib.extension.countDown
import kotlinx.coroutines.CoroutineScope
import kotlinx.coroutines.cancel

class MainActivity : AppCompatActivity() {
    private var mCountDown: CoroutineScope? = null

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

    }

    private fun loadData() {
        this.countDown(time = 5, start = {
            mCountDown = it
        }, end = {
            Log.i("==", "倒计时结束了")

        }, next = {
            Log.i("==", "剩余 $it 秒")

        }, error = {

        })
    }

    override fun onDestroy() {
        mCountDown?.let {
            it.cancel()
        }
        super.onDestroy()
    }
}

四、build.gradle.kts代码

plugins {
    id("com.android.application")
    id("org.jetbrains.kotlin.android")
}

android {
    namespace = "com.example.testkotlin"
    compileSdk = 34

    defaultConfig {
        applicationId = "com.example.testkotlin"
        minSdk = 23
        targetSdk = 34
        versionCode = 1
        versionName = "1.0"

        testInstrumentationRunner = "androidx.test.runner.AndroidJUnitRunner"
    }

    buildTypes {
        release {
            isMinifyEnabled = false
            proguardFiles(
                getDefaultProguardFile("proguard-android-optimize.txt"),
                "proguard-rules.pro"
            )
        }
    }
    compileOptions {
        sourceCompatibility = JavaVersion.VERSION_1_8
        targetCompatibility = JavaVersion.VERSION_1_8
    }
    kotlinOptions {
        jvmTarget = "1.8"
    }
}

dependencies {

    implementation("androidx.core:core-ktx:1.9.0")
    implementation("androidx.appcompat:appcompat:1.6.1")
    implementation("com.google.android.material:material:1.11.0")
    implementation("androidx.constraintlayout:constraintlayout:2.1.4")
    testImplementation("junit:junit:4.13.2")
    androidTestImplementation("androidx.test.ext:junit:1.1.5")
    androidTestImplementation("androidx.test.espresso:espresso-core:3.5.1")
}