Updating sharepoint online list item with xamarin.android app

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Mobile

Android

SharePoint2013

, +

Hello codeproject peps

After following this article https://blog.xamarin.com/add-collaboration-to-your-mobile-apps-with-sharepoint/[^]

i was able to authenticate to sharepoint online, add a list and some list items. Now i would like to update list items but cannot seem to get it right, i continuously get a 400 bad request response. Here is my method:

protected async Task<Boolean> UpdateListItem(string token)
{

    var client = new HttpClient();
    client.DefaultRequestHeaders.Authorization = new System.Net.Http.Headers.AuthenticationHeaderValue("Bearer", token);
    client.DefaultRequestHeaders.Add("X-HTTP-Method", "MERGE");
    client.DefaultRequestHeaders.Add("IF-MATCH", "*");
    var mediaType = new MediaTypeWithQualityHeaderValue("application/json");
    mediaType.Parameters.Add(new NameValueHeaderValue("odata", "verbose"));
    client.DefaultRequestHeaders.Accept.Add(mediaType);


    var itemToUpdateTitle = "Item updated on: " + DateTime.Now.ToString("dd/MM HH:mm");
    var body = "{\"__metadata\":{\"type\":\"SP.Data.TasksByAndroidListItem\"},\"Title\":\"" + itemToUpdateTitle + "}";
    var contents = new StringContent(body);
    contents.Headers.ContentType = MediaTypeHeaderValue.Parse("application/json;odata=verbose");
    try
    {
        var postResult = await client.PostAsync("https://mysite.sharepoint.com/_api/web/lists/GetByTitle('TasksByAndroid')/items(1)", contents);
        var result = postResult.EnsureSuccessStatusCode();
        if (result.IsSuccessStatusCode)
            Toast.MakeText(this, "List item updated successfully!", ToastLength.Long).Show();
        return true;
    }
    catch (Exception ex)
    {
        Log.Info("---UPDATE ITEM EXCEPTION---", ex.Message);
        var msg = "Unable to update list item. " + ex.Message;
        Toast.MakeText(this, msg, ToastLength.Long).Show();
        return false;
    }
}

I would really appreciate it if someone could tell me what im doing wrong.