Xamarin.Forms DependencyService始终返回null

Question

Hej,

im trying to load some data from the native iOS project using the Dependency Service.

Its a simple task im trying to desirialize some Data that i had saved before, but regardless what i do it always returns null.

If i check the values with the debugger in iOS project theyre never null. Very strange maybe im missing something ...

My Interface Implementation:

[assembly: Xamarin.Forms.Dependency(typeof(SaveRead))]
namespace LindeXF.iOS {
 public class SaveRead : ISaveRead {

        public async Task<ApplicationModel> LoadApplicationModel(string userName) {
            try {

                var userPath = CreatePathJson(userName);

                if (File.Exists(userPath)) {
                    await Task.Run(() => {
                        using (var file = File.OpenText(userPath)) {
                            var serializer = new JsonSerializer();
                            var m = (ApplicationModel) serializer.Deserialize(file, typeof(ApplicationModel));

                        }
                    });
                }
            }
            catch (Exception ex) {
                throw new Exception(ex, "LoadApplicationModel()");
            }

            return new ApplicationModel {Username = userName};
        }
    }

in the Portable Project

DependencyService = Xamarin.Forms.DependencyService.Get<ISaveRead>();
var s = await ApplicationModel.DependencyService.LoadApplication(userName);  

thanks for your Time.

Answer 1

One doubt you are calling method LoadApplication from dependency service.

var s = await ApplicationModel.DependencyService.LoadApplication(userName);

and method declaration is LoadApplicationModel .

public async Task<ApplicationModel> LoadApplicationModel(string userName) {
}

maybe that's the problem? Try using below code for call:

var data = await DependencyService.Get<ISaveRead>()
        .LoadApplicationModel(userName);

Answer 2

First you deserialize the file contents and store the ApplicationModel object in m .

using (var file = File.OpenText(userPath)) {
    var serializer = new JsonSerializer();
    var m = (ApplicationModel) serializer.Deserialize(file, typeof(ApplicationModel));
}

That looks all good but instead of returning m , you create a new ApplicationModel object and return that.

return new ApplicationModel {Username = userName};

I think you should return m like this (for example):

using (var file = File.OpenText(userPath)) {
    var serializer = new JsonSerializer();
    var m = (ApplicationModel) serializer.Deserialize(file, typeof(ApplicationModel));
    m.Username = userName;
    return m;
}