Xamarin Forms Currency Mask for Entry fields

CurrencyConverter.cs

using System;
using System.Globalization;
using System.Text.RegularExpressions;
using Xamarin.Forms;

namespace MyProject.Util
{
    /// <summary>
    /// Converter for using in Entry fields for masked input of currency.
    /// <para>The binded property must be of type decimal, and must invoke the PropertyChangedEventArgs event whenever the value is changed, so that the desired mask behavior is kept.</para>
    /// </summary>
    public class CurrencyConverter : IValueConverter
    {
        public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
        {
            return Decimal.Parse(value.ToString()).ToString("C");
        }

        public object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture)
        {
            string valueFromString = Regex.Replace(value.ToString(), @"\D", "");

            if (valueFromString.Length <= 0)
                return 0m;

            long valueLong;
            if (!long.TryParse(valueFromString, out valueLong))
                return 0m;

            if (valueLong <= 0)
                return 0m;

            return valueLong / 100m;
        }
    }
}

SomeView.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"
             xmlns:util="clr-namespace:MyProject.Util;assembly=MyProject"
             x:Class="MyProject.View.SomeView"
             Title="Some View">
  <ContentPage.Resources>
    <ResourceDictionary>
      <util:CurrencyConverter x:Key="currencyConverter" />
    </ResourceDictionary>
  </ContentPage.Resources>
  <ContentPage.Content>
    <StackLayout Padding="20">
      <Entry x:Name="ValueConvert" Placeholder="Value" Text="{Binding SomeProperty, Converter={StaticResource currencyConverter}}" Keyboard="Numeric" />
      <!-- your fields go here -->
    </StackLayout>
  </ContentPage.Content>
</ContentPage>

SomeViewModel.cs

//Create a property in the ViewModel that wraps the decimal property/model you want to receive the currency value
public decimal SomeProperty
{
    get {
        return YourDecimalProperty; 
    }
    set
    {
        YourDecimalProperty = value;

        //invoke PropertyChangedEventArgs here
        //...
    }
}

You'd probably need to change the ConvertBack() method logic to preserve the negative sign entered from the input.
I'd change the Regex.Replace call to some conditional logic, see if there's a negative sign before any number, and then return the negative number.
It's been a while since I don't play with C# so I can't test it right now =/

I must be doing something wrong..
I always see in the entry text Gs. 0

I have a problem about formatting. I tryed all of sample project . When I want to delete amount , comma is not skipped. For Example , entry amount default : 0,00
I entry 12.345,34 . I pressed backspace key for once. Amount: 1.234,53 , Normally I would expect to set as 12.345,30.

Also When I started to write amount, 0,00 amount isn't deleted. For Example I want to write "3". Amount set as 30,00 .

I can't find where I'm doing wrong. Could you help me with that please ?

great work, thank you so much for this.

how allow negative numbers?

public class DecimcalCurrencyConverter : IValueConverter
{
    public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
    {
        return decimal.Parse(value.ToString()).ToString("$0.00;-$0.00");
    }

    public object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture)
    {
        var isNegative = Regex.IsMatch(value.ToString(), "^-", RegexOptions.CultureInvariant);
        string valueFromString = Regex.Replace(value.ToString(), @"\$|,", "");
        if (valueFromString.Length <= 0)
        {
            return 0m;
        }

        if (!decimal.TryParse(valueFromString, out var decimalVal ))
        {
            return 0m;
        }

        return isNegative ? decimalVal * -1 : decimalVal ;
    }
}

I have the same problem :
I have a problem about formatting. I tryed all of sample project . When I want to delete amount , comma is not skipped. For Example , entry amount default : 0,00
I entry 12.345,34 . I pressed backspace key for once. Amount: 1.234,53 , Normally I would expect to set as 12.345,30.

Also When I started to write amount, 0,00 amount isn't deleted. For Example I want to write "3". Amount set as 30,00 .

I can't find where I'm doing wrong. Could you help me with that please ?