运行时，调用的目标已引发异常

Question

Im working on a simple Xamarin Form application after . I created a simple login content page and when i try to run the android emulator im getting this error ' Exception has been thrown by the target of an invocation. ' ,I have Mentioned my code below.Both LoginPage.xaml and LoginPage.xaml.cs

LoginPage.xaml

<?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="XLoginApplication.Views.LoginPage">
        <StackLayout x:Name="MasterLayout">


                <StackLayout x:Name="LogoStack" VerticalOptions="FillAndExpand">
                    <Image x:Name="LoginIcon" Source="icon.png" Margin="0.80.0.0"/>
                </StackLayout>

            <StackLayout x:Name="LoginEntriesStack" VerticalOptions="StartAndExpand">
                <StackLayout.Padding>
                    <OnIdiom x:TypeArguments ="Thickness">
                            <OnIdiom.Phone>40,0,40,0</OnIdiom.Phone>
                            <OnIdiom.Tablet>140,150,140,0</OnIdiom.Tablet>
                        </OnIdiom>
                </StackLayout.Padding>

                <ActivityIndicator x:Name="ActivitySpinner" Color="Red" IsRunning="True"></ActivityIndicator>

                <Label x:Name="Lbl_Username" Text="Username" />
                <Entry x:Name="Entry_Username" Placeholder="Username" />
                <Label x:Name="Lbl_Password"  Text="Password"/>
                <Entry x:Name ="Entry_Password" Placeholder="Password" />
                <Button x:Name ="Btn_Signin"  Text="Sign In"  Clicked="SignInProcedure"/>
            </StackLayout>

            </StackLayout>

    </ContentPage>

LoginPage.xaml.cs

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

using Xamarin.Forms;
using Xamarin.Forms.Xaml;
using XLoginApplication.Models;

namespace XLoginApplication.Views
{
    [XamlCompilation(XamlCompilationOptions.Compile)]
    public partial class LoginPage : ContentPage
    {
        public LoginPage ()
        {
            InitializeComponent ();
            Init();
        }

        void Init()
        {
            BackgroundColor = Constants.BackgroundColor;
            Lbl_Username.TextColor = Constants.MainTextColor;
            Lbl_Password.TextColor = Constants.MainTextColor;
            ActivitySpinner.IsVisible = false;
            LoginIcon.HeightRequest = Constants.LoginIconHeight;

            Entry_Username.Completed += (s, e) => Entry_Password.Focus();
            Entry_Password.Completed += (s, e) => SignInProcedure(s, e);

        }

        public void SignInProcedure(object sender ,EventArgs e)
        {
            User user = new User(Entry_Username.Text ,Entry_Password.Text);

            if (user.CheckInformation())
            {
                DisplayAlert("Login", "Login Success", "Oke");
            }
            else
            {
                DisplayAlert("Login", "Login Not Suceesfull User name or Password is empty", "Oke");
            }
        }
    }
}

Answer 1

I have tested your code, the problem is caused by the <Image> in your xaml.
The number in Margin should be separated by ',' not '.'
For example:

<Image x:Name="LoginIcon" Source="icon.png" Margin="0,80,0,0"/>

Answer 2

On the line where the exception is thrown, try to wrap that line in this:

Device.BeginInvokeOnMainThread (() => {
    // Your line(s) with the exception here
}

Answer 3

Its mainly xaml issue.

Some property name is given for the control,which is not there.

Implement Try Catch in Initialize Component method & find out.