Kotlin使用flow实现倒计时功能(示例详解)

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)
        }
    }
}

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()
    }
}

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")
}

var TotalTime : Long = 2*60*60*1000 //总时长 2小时
    var countDownTimer=object : CountDownTimer(TotalTime,1000){//1000ms运行一次onTick里面的方法
        override fun onFinish() {
            Log.d(TAG,"==倒计时结束")
        }
        override fun onTick(millisUntilFinished: Long) {
            var hour=millisUntilFinished/1000/60/60
            var minute=millisUntilFinished/1000/60%60
            var second=millisUntilFinished/1000%60
            Log.d(TAG,"==倒计时"+hour+"小时"+minute+"分"+second+"秒")
        }
    }.start()

import android.util.Log
import androidx.appcompat.app.AppCompatActivity
import androidx.lifecycle.lifecycleScope
import kotlinx.coroutines.CoroutineScope
import kotlinx.coroutines.delay
import kotlinx.coroutines.flow.catch
import kotlinx.coroutines.flow.*
import kotlinx.coroutines.flow.onCompletion
import kotlinx.coroutines.flow.onStart
import kotlinx.coroutines.launch
/**
 * 扩展方法
 * 倒计时的实现
 */
fun AppCompatActivity.countDown(
    time: Int = 30,
    start: (scop: CoroutineScope) -> Unit,
    next: (time: String) -> Unit,
    end: () -> Unit
) {
    lifecycleScope.launch {
        // 在这个范围内启动的协程会在Lifecycle被销毁的时候自动取消
        flow {
            (time downTo 0).forEach {
                delay(1000)
                emit(it)
            }
        }.onStart {
            // 倒计时开始 ，在这里可以让Button 禁止点击状态
            start(this@launch)
        }.onCompletion {
            // 倒计时结束 ，在这里可以让Button 恢复点击状态
            end()
        }.catch {
            //错误
            Log.e("", it.message ?: "Unkown Error")
        }.collect {
            // 在这里 更新值来显示到UI
            next(it.toString())
        }
    }
}