Flutter与Kotlin实现前后台及终止状态自动发送SMS问题排查

我通过Telephony实现了短信的接收与发送功能，前台状态下运行正常，但后台状态下发送短信会出错，不过后台能正常接收短信。

现有权限配置 #

<uses-permission android:name="android.permission.SEND_SMS"/>
<uses-permission android:name="android.permission.RECEIVE_SMS"/>

发送短信的Method Channel实现 #

import android.telephony.SmsManager

val CHANNEL = "example.sms"

override fun configureFlutterEngine(@NonNull flutterEngine: FlutterEngine) {
    super.configureFlutterEngine(flutterEngine)
    MethodChannel(flutterEngine.dartExecutor.binaryMessenger, CHANNEL).setMethodCallHandler {
        call, result ->
        if(call.method == "sendsms") {
            val phone = call.argument<String>("phone")
            val msg = call.argument<String>("msg")
            if (phone != null && msg != null) {
                sendSms(phone, msg)
            }
        } else {
            result.notImplemented()
        }
    }
}

private fun sendSms(phoneNumber: String, message: String) {
    try {
        val smsManager = SmsManager.getDefault()
        smsManager.sendTextMessage(phoneNumber, null, message, null, null)
    } catch (e: Exception) {
        e.printStackTrace()
    }
}

问题原因及解决办法 #

1. 适配Android 12+权限要求 #

从Android 12（API 31）开始，后台发送短信需要额外申请REQUEST_SEND_SMS权限，仅SEND_SMS无法满足后台操作需求。需在AndroidManifest.xml中添加：

<uses-permission android:name="android.permission.REQUEST_SEND_SMS" />

同时要在代码中动态申请该权限，因为它属于危险权限范畴。

2. 规避后台任务限制 #

Android的后台调度限制会阻止非前台应用直接执行短信发送操作，建议使用WorkManager来处理后台短信发送任务，确保操作能被系统正常调度：

• 添加WorkManager依赖到build.gradle：

implementation "androidx.work:work-runtime:2.8.1"

• 创建短信发送Worker类：

class SmsSendWorker(context: Context, params: WorkerParameters) : Worker(context, params) {
    override fun doWork(): Result {
        val phone = inputData.getString("phone")
        val msg = inputData.getString("msg")
        return try {
            val smsManager = SmsManager.getDefault()
            smsManager.sendTextMessage(phone, null, msg, null, null)
            Result.success()
        } catch (e: Exception) {
            e.printStackTrace()
            Result.failure()
        }
    }
}

• 修改Method Channel中的调用逻辑，替换直接发送为调度Worker：

private fun scheduleSmsSend(phoneNumber: String, message: String) {
    val data = Data.Builder()
        .putString("phone", phoneNumber)
        .putString("msg", message)
        .build()
    
    val constraints = Constraints.Builder()
        .setRequiredNetworkType(NetworkType.CONNECTED) // 可选，根据需求配置网络要求
        .build()
    
    val smsWorkRequest = OneTimeWorkRequestBuilder<SmsSendWorker>()
        .setInputData(data)
        .setConstraints(constraints)
        .build()
    
    WorkManager.getInstance(applicationContext).enqueue(smsWorkRequest)
}

之后在Method Channel回调里调用scheduleSmsSend(phone, msg)代替原sendSms方法。

3. 优化异常反馈机制 #

原代码仅在本地打印异常，无法将错误信息传递给Flutter端，建议修改Method Channel的回调逻辑，把异常信息返回：

if (phone != null && msg != null) {
    try {
        scheduleSmsSend(phone, msg)
        result.success("短信发送任务已调度")
    } catch (e: Exception) {
        result.error("SEND_FAILED", e.message, null)
    }
} else {
    result.error("INVALID_PARAMS", "手机号或短信内容为空", null)
}

内容的提问来源于stack exchange，提问作者Prem Singh