Error : Validation failed for one or more entities. See 'EntityValidationErrors' property for more details

Validation failed for one or more entities. 

See 'EntityValidationErrors' property for more details

To resolve this issue, you can find where is the issue using below code...

 catch (DbEntityValidationException e)

            {

                foreach (var eve in e.EntityValidationErrors)

                {

                    Console.WriteLine("Entity of type \"{0}\" in state \"{1}\" has the following validation errors:",

                        eve.Entry.Entity.GetType().Name, eve.Entry.State);

                    foreach (var ve in eve.ValidationErrors)

                    {

                        Console.WriteLine("- Property: \"{0}\", Error: \"{1}\"",

                            ve.PropertyName, ve.ErrorMessage);

                    }

                }

                throw;

            }

Xamarin : How to call API POST method

Xamarin : API call

How to consume API method in xamarin application ? 

I tried on google but couldn't find proper example. I got help of my friend who have knowledge of xamarin and some help from google, and created successful demo, which I am sharing with you.

Steps:

1. First check that API is working or not
2. Install "newtonsoft json" from NuGet package manager

Design 

<Grid>

    <Grid.RowDefinitions>

      <RowDefinition Height="50"></RowDefinition>

      <RowDefinition Height="50"></RowDefinition>

      <RowDefinition Height="*"></RowDefinition>

    </Grid.RowDefinitions>

    <Grid.ColumnDefinitions>

      <ColumnDefinition Width="*"></ColumnDefinition>      

    </Grid.ColumnDefinitions>

    <Button Text="Get Data"

            Clicked="OnGetDataButtonClicked"

            Grid.Row="0"

            Grid.Column="0"></Button>

    <Label x:Name="lblMsg"

           Grid.Row="1"

           Grid.Column="0"></Label>

    <ListView x:Name="MainList"  ItemTapped="OnTapped" Grid.Row="2" Grid.Column="0"> 

      <ListView.ItemTemplate>

        <DataTemplate>

          <ViewCell>

            <StackLayout Orientation="Horizontal">

              <Label Text="{Binding EmailId}"></Label> 

            </StackLayout>

          </ViewCell>

        </DataTemplate>

      </ListView.ItemTemplate>

    </ListView>

    

  </Grid>

Code

async void OnGetDataButtonClicked(object sender, EventArgs e)

        {

            try

            {

                HttpClient client = new HttpClient();

                string requestPayload = @"{

""UserId"": ""123"",

""dataTableCommon"":{

""param"" :{""Start"": ""21"",

""Length"": ""10"",

""Draw"" :""1""}

}

}";

                var response = await client.PostAsync("http://Domainname/DemoAPI/API/User/GetUsersList", 

new StringContent(requestPayload, Encoding.UTF8, "application/json"));

                if (response.StatusCode == HttpStatusCode.OK)

                {

                    var json = await response.Content.ReadAsStringAsync();

   

                    //Here you need to create class for output results

    // To generate class, you can use http://json2csharp.com

                    var results = JsonConvert.DeserializeObject<RootObject>(json);

                    MainList.ItemsSource = results.data;                    

                }

            }

            catch (Exception ex)

            {

                lblMsg.Text = ex.Message;

            }            

        }

        void OnTapped(object sender, ItemTappedEventArgs e)

        {

            var selected = e.Item as Users;

            DisplayAlert("Name", selected.FirstName + " " + selected.LastName, "Okay");

        }

Generate Class

    // To generate class, you can use http://json2csharp.com

    

    public class Users

    {

        public string UserId { get; set; }    

        public string FirstName { get; set; }

        public string LastName { get; set; }

        public string EmailId { get; set; }

    }

    public class RootObject

    {        

        public List<Users> data { get; set; } 

    }

Output

I hope, you like the article !!! ENJOY !!!

Xamarin : Resource Contents - Stylesheet

Xamarin : Resource Contents - Stylesheet

Design Page

<ContentPage.Resources>

    <ResourceDictionary>

      <Style x:Key="ColorfullLabel" TargetType="Label">

        <Setter Property="TextColor" Value="Red"></Setter>

        <Setter Property="BackgroundColor" Value="Yellow"></Setter>

      </Style>

      <Style x:Key="lblMargin" TargetType="Label">

        <Setter Property="Margin" Value="20"></Setter>

        <Setter Property="FontSize" Value="20"></Setter>

      </Style>

      <Style x:Key="btnMargin" TargetType="Button">

        <Setter Property="Margin" Value="20"></Setter>

        <Setter Property="FontSize" Value="20"></Setter>

        <Setter Property="Rotation" Value="20"></Setter>

        <Setter Property="BorderWidth" Value="20"></Setter>

      </Style>

    </ResourceDictionary>

  </ContentPage.Resources>

  

  <StackLayout Orientation="Vertical">

    <Label Text="Different color"

           Style="{StaticResource ColorfullLabel}"></Label>

    <Label Text="Font Size"

           FontSize="20"></Label>

    <Label Text="Margin"

           Style="{StaticResource lblMargin}"></Label>

    <Label Text="Italic"

           FontAttributes="Italic"></Label>

    <Label Text="Left Justified"

           HorizontalTextAlignment="End"

           FontSize="Large"></Label>

    <Label Text="Hello, World!"

         VerticalOptions="Start"

         HorizontalTextAlignment="Center"

         Rotation="-15"

         IsVisible="true"

         FontSize="Large"

         FontAttributes="Bold"

         TextColor="Blue" />

    <Button Text="Verticle Button"

        Style="{StaticResource btnMargin}">

    </Button>

  </StackLayout>

Xamarin : Button Formatting & Click Event

Xamarin : Button Formatting & Click Event

Design

<StackLayout Orientation="Vertical">

    <Button Text="Different color"

           TextColor="Yellow"

           BackgroundColor="Blue"></Button>

    <Button Text="Font Size"

           FontSize="20">

    </Button>

    <Button Text="Margin"

           Margin="20"></Button>

    <Button Text="Center"

           HorizontalOptions="Center"

            VerticalOptions="Center">

    </Button>

    <Button Text="Verticle Button"

           Rotation="20"

            BorderWidth="20" Clicked="btnClick">

    </Button>

  </StackLayout>

Code:

       void btnClick(object sender, EventArgs e)

        {

            DisplayAlert("Button Click", "You clicked on button :)", "Okay");

        }

Xamarin : Label Formatting

Xamarin : Label Formatting

<?xml version="1.0" encoding="utf-8" ?>
<ContentPage xmlns="http://xamarin.com/schemas/2014/forms"
             xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
             x:Class="App1.NewPage"
             Title="Label Formatting">

  <StackLayout Orientation="Vertical">
 
    <Label Text="Different color"
           TextColor="Red"
           BackgroundColor="Yellow"></Label>
 
    <Label Text="Font Size"
           FontSize="20"></Label>
 
    <Label Text="Margin"
           Margin="20"></Label>
 
    <Label Text="Italic"
           FontAttributes="Italic"></Label>
 
    <Label Text="Left Justified"
           HorizontalTextAlignment="End"
           FontSize="Large"></Label>

     <Label Text="Hello, World!"
         VerticalOptions="Start"
         HorizontalTextAlignment="Center"
         Rotation="-15"
         IsVisible="true"
         FontSize="Large"
         FontAttributes="Bold"
         TextColor="Blue" />
 
  </StackLayout>

</ContentPage>

• Run the application

Xamarin : OnTapped navigation to new page

Xamarin : OnTapped navigation to new page

• Add listview  in page

<?xml version="1.0" encoding="utf-8" ?>
<ContentPage xmlns="http://xamarin.com/schemas/2014/forms"
 xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
 x:Class="App1.MainMaster"
 Title="My Application">
  <ListView x:Name="MainList" ItemTapped="OnTapped">
<ListView.ItemTemplate>
  <DataTemplate>
<ViewCell>
  <StackLayout Orientation="Horizontal">
<Label Text="{Binding Name}"></Label>
<Label Text="{Binding Description}"></Label>
<Label Text="{Binding OrderNumber}"></Label>
  </StackLayout>
</ViewCell>
  </DataTemplate>
</ListView.ItemTemplate>
  </ListView>
</ContentPage>

• Write a code to bind listview 

public partial class MainMaster : ContentPage
{
public MainMaster()
{
InitializeComponent();
MainList.ItemsSource = new List<ListViewTemplate>
{
new ListViewTemplate { Name="One", Description="One", OrderNumber=1 },
new ListViewTemplate { Name="Two", Description="Two", OrderNumber=2 },
new ListViewTemplate { Name="Three", Description="Three", OrderNumber=3 }, new ListViewTemplate { Name="Four", Description="Four", OrderNumber=4 },
new ListViewTemplate { Name="Five", Description="Five", OrderNumber=5 },
};
}
}

• Add new page, I set name "NewPage"

         async void OnTapped(object sender, ItemTappedEventArgs e)
        {
            var selected = e.Item as ListViewTemplate;

            switch (selected.OrderNumber)
            {
                case 1:
                    await Navigation.PushAsync(new NewPage());
                    break;
                case 2:
                    break;
                case 3:
                    break;
                case 4:
                    break;
                case 5:
                    break;
            }

            //Set not to selected item : optional
            ((ListView)sender).SelectedItem = null;
        }

• Set page in to run the application

public class App : Application
{
public App()
{
MainPage = new NavigationPage(new MainMaster());
}

}

• Run the application

Xamarin : OnTapped (on clicked) item in listview

Xamarin : OnTapped (on clicked) item in listview

• Add listview  in page

<?xml version="1.0" encoding="utf-8" ?>
<ContentPage xmlns="http://xamarin.com/schemas/2014/forms"
 xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
 x:Class="App1.MainMaster"
 Title="My Application">
  <ListView x:Name="MainList" ItemTapped="OnTapped">
<ListView.ItemTemplate>
  <DataTemplate>
<ViewCell>
  <StackLayout Orientation="Horizontal">
<Label Text="{Binding Name}"></Label>
<Label Text="{Binding Description}"></Label>
<Label Text="{Binding OrderNumber}"></Label>
  </StackLayout>
</ViewCell>
  </DataTemplate>
</ListView.ItemTemplate>
  </ListView>
</ContentPage>

• Write a code to bind listview 

public partial class MainMaster : ContentPage
{
public MainMaster()
{
InitializeComponent();
MainList.ItemsSource = new List<ListViewTemplate>
{
new ListViewTemplate { Name="One", Description="One", OrderNumber=1 },
new ListViewTemplate { Name="Two", Description="Two", OrderNumber=2 },
new ListViewTemplate { Name="Three", Description="Three", OrderNumber=3 }, new ListViewTemplate { Name="Four", Description="Four", OrderNumber=4 },
new ListViewTemplate { Name="Five", Description="Five", OrderNumber=5 },
};
}
}

        void OnTapped(object sender, ItemTappedEventArgs e)
        {
            var selected = e.Item as ListViewTemplate;
            DisplayAlert("Item Selecte", selected.Name, "Okay");
        }

• Set page in to run the application

public class App : Application
{
public App()
{
MainPage = new MainMaster();
}

}

• Run the application

Xamarin : Create simple List

• Create new page

• Create new class for listing properties

public class ListViewTemplate

{

public string Name { get; set; }

public string Description { get; set; }

public int OrderNumber { get; set; }

}

• Add listview  in page

<?xml version="1.0" encoding="utf-8" ?>
<ContentPage xmlns="http://xamarin.com/schemas/2014/forms"
xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
x:Class="App1.MainMaster"
Title="My Application">
 <ListView x:Name="MainList">
<ListView.ItemTemplate>
 <DataTemplate>
<ViewCell>
 <StackLayout Orientation="Horizontal">
<Label Text="{Binding Name}"></Label>
<Label Text="{Binding Description}"></Label>
<Label Text="{Binding OrderNumber}"></Label>
 </StackLayout>
</ViewCell>
 </DataTemplate>
</ListView.ItemTemplate>
 </ListView>
</ContentPage>

• Write a code to bind listview 

public partial class MainMaster : ContentPage
{
public MainMaster()
{
InitializeComponent();
MainList.ItemsSource = new List<ListViewTemplate>
{
new ListViewTemplate { Name="One", Description="One", OrderNumber=1 },
new ListViewTemplate { Name="Two", Description="Two", OrderNumber=2 },
new ListViewTemplate { Name="Three", Description="Three", OrderNumber=3 }, new ListViewTemplate { Name="Four", Description="Four", OrderNumber=4 },
new ListViewTemplate { Name="Five", Description="Five", OrderNumber=5 },
};
}
}

• Set page in to run the application

public class App : Application
{
public App()
{
MainPage = new MainMaster();
}

}

• Run the application