.NET Maui在Android端日志写入文件时规避路径访问拒绝问题

问题场景 #

在.NET Maui开发中，已实现Android设备NLog文件日志功能，但在Android 13 API33真机运行时触发System.AggregateException，提示路径/storage/self/primary/Documents/xxx/Logs/xxx.log访问被拒绝，Android 15 API35模拟器可正常运行。

解决方案 #

1. 替换硬编码路径为MAUI标准存储路径 #

不要直接写死公共存储路径，改用MAUI提供的FileSystem类获取符合Android版本规范的路径，优先选择应用专属存储路径（无需额外权限，更安全）：

• 获取应用私有文档目录：FileSystem.AppDataDirectory
• 获取公共文档目录：FileSystem.Current.GetDirectoryPath(SpecialFolder.MyDocuments)

可以通过代码动态配置NLog路径，确保目录存在：

var logDir = Path.Combine(FileSystem.Current.GetDirectoryPath(SpecialFolder.MyDocuments), "HubSurveyor", "Logs");
Directory.CreateDirectory(logDir); // 提前创建目录避免权限或不存在问题

var fileTarget = new NLog.Targets.FileTarget("f")
{
    FileName = Path.Combine(logDir, "HubSurveyor.log"),
    ArchiveFileName = Path.Combine(logDir, "archive", "HubSurveyor-{#}.log"),
    Layout = "${longdate} ${threadid} ${uppercase:${level}} ${callsite} ${message} ${exception:format=Message,StackTrace,Data:maxInnerExceptionLevel=10}",
    ArchiveEvery = NLog.Targets.FileArchivePeriod.Day,
    ArchiveNumbering = NLog.Targets.ArchiveNumberingMode.Date,
    ArchiveDateFormat = "yyyyMMdd",
    MaxArchiveFiles = 21
};

var config = new NLog.Config.LoggingConfiguration();
config.AddRule(NLog.LogLevel.Trace, NLog.LogLevel.Fatal, fileTarget);
config.AddRule(NLog.LogLevel.Trace, NLog.LogLevel.Fatal, new NLog.Targets.DebuggerTarget("debugger")
{
    Layout = "${longdate} ${threadid} ${uppercase:${level}} ${callsite} ${message} ${exception:format=Message,StackTrace,Data:maxInnerExceptionLevel=10}"
});
NLog.LogManager.Configuration = config;

2. 适配Android 13公共存储权限（如需保留原路径） #

如果必须使用公共Documents目录，需处理Android 13的权限限制：

• 在Platforms/Android/AndroidManifest.xml中添加权限声明：

  <!-- Android 13+ 访问公共存储需要 -->
  <uses-permission android:name="android.permission.MANAGE_EXTERNAL_STORAGE" />
  <!-- 兼容Android 12及以下版本 -->
  <uses-permission android:name="android.permission.READ_EXTERNAL_STORAGE" android:maxSdkVersion="32" />
  <uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE" android:maxSdkVersion="32" />
  

• 在应用启动时主动请求权限：

  var permissionStatus = await Permissions.RequestAsync<Permissions.StorageWrite>();
  if (permissionStatus != PermissionStatus.Granted)
  {
      // 提示用户开启权限，或降级使用应用专属存储
  }
  

注意：MANAGE_EXTERNAL_STORAGE权限需要用户手动在应用设置中开启，Google Play对使用该权限的应用审核严格，非必要不建议使用。

3. 利用NLog内部日志排查细节 #

你的配置已开启NLog内部日志，可查看/storage/self/primary/Documents/HubSurveyor/Logs/nlog-internal.log中的详细错误信息，确认是否存在目录未创建、权限以外的配置问题。

原NLog配置 #

<?xml version="1.0" encoding="utf-8" ?>
<nlog xmlns="http://www.nlog-project.org/schemas/NLog.xsd"
      xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
      xsi:schemaLocation="http://www.nlog-project.org/schemas/NLog.xsd C:\Users\Ian\.nuget\packages\nlog.schema\5.3.4\contentFiles\any\any\NLog.xsd"
      autoReload="true"
      throwExceptions="true"
      throwConfigExceptions="true"
      internalLogLevel="Error"
      internalLogFile="/storage/self/primary/Documents/HubSurveyor/Logs/nlog-internal.log">

    <targets>
        <!--
            Output to emulator and phone
        -->
        <target 
            xsi:type="File" 
            name="f" 
            fileName="/storage/self/primary/Documents/HubSurveyor/Logs/HubSurveyor.log" 
            layout="${longdate} ${threadid} ${uppercase:${level}} ${callsite} ${message} ${exception:format=Message,StackTrace,Data:maxInnerExceptionLevel=10}" 
            archiveEvery="Day"
            archiveFileName="/storage/self/primary/Documents/HubSurveyor/Logs/archive/HubSurveyor-{#}.log"
            archiveNumbering="Date"
            archiveDateFormat="yyyyMMdd"
            maxArchiveFiles="21"
        />
        <target xsi:type="Debugger" name="debugger" layout="${longdate} ${threadid} ${uppercase:${level}} ${callsite} ${message} ${exception:format=Message,StackTrace,Data:maxInnerExceptionLevel=10}"  />
    </targets>

    <rules>
        <logger name="*" minlevel="Trace" writeTo="f" />
        <logger name="*" minlevel="${when:when='${environment:MAUI_ENVIRONMENT}' == 'Development':inner=Trace:else=Off}" writeTo="debugger" />
    </rules>
</nlog>

内容的提问来源于stack exchange，提问作者Ian