About file generation when the application is started for the first time

Question

When the app is started for the first time, folders and files are created, but the app crashes due to an error.
I have file permissions, what should I do?

[AndroidManifest.xml] Permission is set and
At the first startup, the permission confirmation screen is displayed.
After that, [Start.cs] is executed.

//AndroidManifest.xml-------------
<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android" android:versionName="1.0.0" package="jp.XXXXXX.XXXX" android:installLocation="preferExternal" android:versionCode="000000">
    <uses-sdk android:minSdkVersion="21" android:targetSdkVersion="29" />
    <application android:label="XXXXXXXX" android:networkSecurityConfig="@xml/network_security_config" android:hardwareAccelerated="false" android:requestLegacyExternalStorage="true" android:largeHeap="true" android:supportsRtl="true" android:usesCleartextTraffic="true" android:icon="@drawable/splash_logo">
        <meta-data android:name="com.google.android.geo.API_KEY" android:value="AIzaSyB34hG3jxWQBog6MMjkaUEK43ZKrtXtWOM" />
        <meta-data android:name="com.google.android.gms.version" android:value="@integer/google_play_services_version" />
        <uses-library android:name="org.apache.http.legacy" android:required="false" />
        <provider android:name="android.support.v4.content.FileProvider" android:authorities="${applicationId}.fileprovider" android:exported="false" android:grantUriPermissions="true">
            <meta-data android:name="android.support.FILE_PROVIDER_PATHS" android:resource="@xml/file_paths"></meta-data>
        </provider>
    </application>
    <uses-permission android:name="android.permission.CAMERA" />
    <uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE" />
    <uses-permission android:name="android.permission.READ_EXTERNAL_STORAGE" />
    <uses-permission android:name="android.permission.ACCESS_NETWORK_STATE" />
    <uses-permission android:name="android.permission.READ_PHONE_STATE" />
    <uses-permission android:name="android.permission.VIBRATE" />
    <uses-permission android:name="android.permission.INTERNET" />
    <uses-permission android:name="android.permission.ACCESS_WIFI_STATE" />
</manifest>
//-------------

//Start.cs--------------------------
public Start()
{

    try
    {

        private string FolderPath = "XXXXXXXX";

        InitializeComponent();

        if (Directory.Exists(FolderPath) == false)
        {
            Directory.CreateDirectory(FolderPath);
        }

     }
     catch
     {

     }
}
//--------------------------

Answer 1

Hello,​

Welcome to our Microsoft Q&A platform!

Do you get System.UnauthorizedAccessException?

If so, you did not grant the runtime write external permission. So you cannot create a directory without permission(your permission confirmation screen pop up, but you did not grand the permssion at this time).

So, please open your MainActivity.cs, find the OnRequestPermissionsResult method. using following code to check the write permission if granded. If granted, we can execute the start.

   public override void OnRequestPermissionsResult(int requestCode, string[] permissions, [GeneratedEnum] Android.Content.PM.Permission[] grantResults)  
           {   
               Xamarin.Essentials.Platform.OnRequestPermissionsResult(requestCode, permissions, grantResults);   
     
               int WRITE_EXTERNAL_STORAGE=0;   
               if (requestCode == WRITE_EXTERNAL_STORAGE)   
               {   
     
                   for (int i = 0; i < permissions.Length; i++)   
                   {   
                       if (permissions[i] == "android.permission.WRITE_EXTERNAL_STORAGE" && grantResults[i] == Permission.Granted)   
                       {   
                           Start();   
                       }   
                       else   
                       {   
                           Log.Info("TAG", "WRITE_EXTERNAL_STORAGE  permission was NOT granted.");   
                       }   
                   }   
                      
     
                     
               }   
               else   
               {   
                   base.OnRequestPermissionsResult(requestCode, permissions, grantResults);   
               }   
                  
           }  
 

Best Regards,

Leon Lu

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