NullReferenceException - File.WriteAllText Xamarin/Android-CodePudding

I'm new to Xamarin, so I searched for a way to easily save file on Android/iOS. Found that File.ReadAllText/File.WriteAllText should work... When I call File.WriteAllText() a NullReferenceException is thrown.

Here is the code. Originally it was just one line. But I split it up to do some testing.

public static void SAVE()
{
            if (!File.Exists("RecentHosts.json")) File.Create("RecentHosts.json");
            string text = JsonConvert.SerializeObject(new JsonHosts() { hosts = RecentHosts.Values.ToList() });
            File.WriteAllText("RecentHosts.json", text);
}

That's all I get from the Exception:

System.NullReferenceException: 'Object reference not set to an instance of an object.'

{System.NullReferenceException: Object reference not set to an instance of an object. at Android.Runtime.JNINativeWrapper._unhandled_exception (System.Exception e) [0x0000e] in /Users/runner/work/1/s/xamarin-android/src/Mono.Android/Android.Runtime/JNINativeWrapper.g.cs:12 at Android.Runtime.JNINativeWrapper.Wrap_JniMarshal_PPL_V (_JniMarshal_PPL_V callback, System.IntPtr jnienv, System.IntPtr klazz, System.IntPtr p0) [0x0001d] in /Users/runner/work/1/s/xamarin-android/src/Mono.Android/Android.Runtime/JNINativeWrapper.g.cs:111 at (wrapper native-to-managed) Android.Runtime.JNINativeWrapper.Wrap_JniMarshal_PPL_V(intptr,intptr,intptr)}

Has anyone any idea what's happening here? Of course, I can provide the whole code from this class, but I don't think that's doing really anything to solve this.

CodePudding user response：

Try changing this:

if (File.Exists("RecentHosts.json")) File.Create("RecentHosts.json");

To this:

if (!File.Exists("RecentHosts.json")) File.Create("RecentHosts.json");

You're creating the file when it already exists, when what you want to is create it if it doesn't.

CodePudding user response：

The error occurs because the path you write in is invalid, we have to set a complete folder path .

Try the following code

//file path
var filePath = Path.Combine(System.Environment.GetFolderPath(System.Environment.SpecialFolder.Personal), "RecentHosts.txt");
if (!File.Exists(filePath))
{
    File.Create(filePath);
}

string text = JsonConvert.SerializeObject(new JsonHosts() { hosts = RecentHosts.Values.ToList() });
//write in file
File.WriteAllText(filePath, text);