BINDING CONVERTER THROWS EXCEPTION

Question

BINDING CONVERTER THROWS EXCEPTION

Giorgio Sfiligoi 616

HELP

I have a simple binding like that:

    <Entry Text="{Binding Amount"     OK

    <Entry Text="{Binding Amount, Converter={StaticResource amountConverter}}"  THROWS an exception.

Here is the complete page:

<?xml version="1.0" encoding="utf-8" ?>
<ContentPage xmlns="http://schemas.microsoft.com/dotnet/2021/maui"
             xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
             xmlns:cvt="clr-namespace:TestVari.Converters"
             x:Class="TestVari.Pages.TestMyKeyboardPage"
             Title="Test">
    <ContentPage.Resources>
        <cvt:AmountConverter x:Key="amountConverter" />
    </ContentPage.Resources>
    <VerticalStackLayout>
        <Label Text="dummy label" />
        <Entry Text="{Binding Amount, Converter={StaticResource amountConverter}}"
               WidthRequest="300" IsReadOnly="True"
               VerticalOptions="Start" HorizontalOptions="Start"
               TextColor="Blue" BackgroundColor="WhiteSmoke">
            <Entry.GestureRecognizers>
                <TapGestureRecognizer Tapped="OnFieldTapped" />
            </Entry.GestureRecognizers>
        </Entry>
        <Button Text="37" WidthRequest="60" HorizontalOptions="Start" Clicked="On37" />
    </VerticalStackLayout>
</ContentPage>

When I try to navigate to this page I have the following exception:

System.Reflection.TargetInvocationException

Message=Exception has been thrown by the target of an invocation.

Stack:

 	0xFFFFFFFFFFFFFFFF in Android.Runtime.RuntimeNativeMethods.monodroid_debugger_unhandled_exception	C#
 	0x1A in Android.Runtime.JNINativeWrapper._unhandled_exception at /Users/runner/work/1/s/xamarin-android/src/Mono.Android/Android.Runtime/JNINativeWrapper.g.cs:12,5	C#
 	0x1D in Android.Runtime.JNINativeWrapper.Wrap_JniMarshal_PP_V at /Users/runner/work/1/s/xamarin-android/src/Mono.Android/Android.Runtime/JNINativeWrapper.g.cs:23,26	C#
 	0x17 in System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw	C#
 	0x6 in System.Threading.Tasks.Task.<>c.<ThrowAsync>b__128_0	C#
 	0xC in Android.App.SyncContext. at /Users/runner/work/1/s/xamarin-android/src/Mono.Android/Android.App/SyncContext.cs:36,19	C#
 	0xE in Java.Lang.Thread.RunnableImplementor.Run at /Users/runner/work/1/s/xamarin-android/src/Mono.Android/Java.Lang/Thread.cs:37,6	C#
 	0x8 in Java.Lang.IRunnableInvoker.n_Run at /Users/runner/work/1/s/xamarin-android/src/Mono.Android/obj/Release/net8.0/android-34/mcw/Java.Lang.IRunnable.cs:84,4	C#
 	0x8 in Android.Runtime.JNINativeWrapper.Wrap_JniMarshal_PP_V at /Users/runner/work/1/s/xamarin-android/src/Mono.Android/Android.Runtime/JNINativeWrapper.g.cs:22,5	C#

What makes me very confused is that I have other pages with similar binding and the same 'amountConverter', and they work fine.

Can anybody give me a clue on how to address this issue?

Wenyan Zhang (Shanghai Wicresoft Co,.Ltd.) 36,451 Reputation points Microsoft External Staff

2024-10-17T01:15:00.1433333+00:00

Could you share the amountConverter method with me? Form the code snippets, it's not clear how the text converted.

What makes me very confused is that I have other pages with similar binding and the same 'amountConverter', and they work fine.

If it's possible, would you mind sharing the code snippets of that page so that I can test?

Giorgio Sfiligoi 616

Here is the AmountConverter:

using System.Diagnostics;
using System.Globalization;
namespace TestVari.Converters;
internal class AmountConverter : IValueConverter
{
    public object? Convert(object? value, Type targetType, object? parameter, CultureInfo culture)
    {
        if (value == null) return String.Empty;
        var nfi = new NumberFormatInfo();
        nfi.NumberDecimalDigits = 2;
        // the method converts only Int64 to string
        Debug.Assert(targetType == typeof(string));
        Debug.Assert(value.GetType() == typeof(Int64));
        double d = System.Convert.ToDouble(Math.Abs((Int64)value));
        // Use the ToString method to format the value.
        return (d / 100).ToString("N", nfi);
    }
    public object? ConvertBack(object? value, Type targetType, object? parameter, CultureInfo culture) =>
        throw new NotImplementedException();
}

It converts e.g 1234 to a string 12.34 i.e. the amount is stored in cents.

However, as I said, this converter works fine in other pages.

Giorgio Sfiligoi 616

The following 'ConvertersPage' works fine with both 'AmountConverter' and 'SignedConverter'

<?xml version="1.0" encoding="utf-8" ?>
<ContentPage xmlns="http://schemas.microsoft.com/dotnet/2021/maui"
             xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
             xmlns:cvt="clr-namespace:TestVari.Converters"
             xmlns:components="clr-namespace:TestVari.Components"
             x:Class="TestVari.Pages.ConvertersPage"
             Title="Converters Page">
    <ContentPage.Resources>
        <cvt:SignedAmountConverter x:Key="SignedConverter" />
        <cvt:AmountConverter x:Key="AmountConverter" />
        <cvt:AmountColorConverter x:Key="AmountColorConverter" />
        <cvt:DateConverter x:Key="DateConverter" />
        <cvt:DateColorConverter x:Key="DateColorConverter" />
    </ContentPage.Resources>
    <Grid Margin="10" RowDefinitions="Auto,Auto,Auto,*,Auto" ColumnDefinitions="*,75,105">
        <Label Grid.Row="0" Grid.Column="0" Text="Date:" x:Name="lblText"/>
        <Label Grid.Row="0" Grid.Column="1" BackgroundColor="Aquamarine" HorizontalOptions="Fill"
               Text="{Binding date, Converter={StaticResource DateConverter}}"
               TextColor="{Binding date, Converter={StaticResource DateColorConverter}}"/>
        <Label Grid.Row="1" Grid.Column="0" Text="Amount:"/>
        <Label Grid.Row="1" Grid.Column="2" BackgroundColor="Aquamarine" HorizontalOptions="Fill"
               Text="{Binding Amount, Converter={StaticResource AmountConverter}}"
               TextColor="{Binding Amount, Converter={StaticResource AmountColorConverter}}"/>
        <Entry Grid.Row="2" Grid.Column="0" Text="{Binding Amount, Mode=TwoWay}" />
        
        <!--<components:MyNumericKeyboard Grid.Row="4" Grid.ColumnSpan="3" HorizontalOptions="Center" />-->
    </Grid>
</ContentPage>

using System.ComponentModel;
namespace TestVari.Pages;
public partial class ConvertersPage : ContentPage , INotifyPropertyChanged
{
    public DateTime date { get; set; }
    private Int64 amount;
    public Int64 Amount
    {
        get { return amount; }
        set
        {
            if (this.amount != value)
            {
                this.amount = value;
                OnPropertyChanged("Amount");
            }
        }
    }
    public ConvertersPage()
    {
        InitializeComponent();
        date = DateTime.Today.AddDays(-1);
        amount = 99988877744;
        BindingContext = this;
    }
}

AmountConverter display the Abs of the value, but AmountColorConverter makes it red if it's negative; SignedConverter is pratically the same, but it displays also the sign.

Forget about the DateConverter.

Incidentally, 'MyNumericKeyboard' is a custom component; if I try to uncomment it, the page throws the same error as described in my initial query.

Giorgio Sfiligoi 616 Reputation points

2024-10-17T15:12:55.6766667+00:00

I found that Label accepts the Converter; Entry and Editor accept only binding but not converters and throw as I described in my initial query.

This seems very strange and not documented.
Wenyan Zhang (Shanghai Wicresoft Co,.Ltd.) 36,451 Reputation points Microsoft External Staff

2024-10-18T07:41:20.4633333+00:00

After testing, the converter doesn't work on Lable and Entry. I tried to enter 1234 for the label and I got the same exception. Does 1234 work on your side?
Giorgio Sfiligoi 616 Reputation points

2024-10-18T08:08:12.44+00:00

Yes, 1234 gives 12.34 in the Label.

Throws for Entry and Editor.
Wenyan Zhang (Shanghai Wicresoft Co,.Ltd.) 36,451 Reputation points Microsoft External Staff

2024-10-18T09:30:14.2166667+00:00

All labels on your page can display 12.34, right? I understand you are testing on Android platform, does it work on other platforms?
Giorgio Sfiligoi 616 Reputation points

2024-10-18T18:05:15.55+00:00
I added an Entry in the ConvertersPage that I sent before:

<Grid Margin="10" RowDefinitions="Auto,Auto,Auto,*,Auto" ColumnDefinitions="*,75,105"> ... <Label Grid.Row="1" Grid.Column="0" Text="Amount:"/> <Label Grid.Row="1" Grid.Column="2" BackgroundColor="Aquamarine" HorizontalOptions="Fill" Text="{Binding Amount, Converter={StaticResource AmountConverter}}" TextColor="{Binding Amount, Converter={StaticResource AmountColorConverter}}"/> <Entry Grid.Row="2" Grid.Column="0" Text="{Binding Amount, Mode=TwoWay}" /> </Grid>

(no change in the C# back code)

When you type some number in the Entry field, its conversion is displayed in the Label.

Typing 1234 gives 12.34.

I sent already the AmountConverter.

I played with Android and WindowsMachine and it works on both.

If you replace the Label with either Entry or Editor, in Android throws the cryptic exception that I described in my initial query; in WindowsMachine it also throws an exception: specifically the

throw new NotImplementedException();

in the ConvertBack of AmountConverter - and this is very strange too.
Wenyan Zhang (Shanghai Wicresoft Co,.Ltd.) 36,451 Reputation points Microsoft External Staff

2024-10-21T06:47:20.1333333+00:00

It looks like you have resolved the problem, right? I will convert your comment to an answer. If you have any other questions, please feel free to post in here.

1 answer

Your answer

Wenyan Zhang (Shanghai Wicresoft Co,.Ltd.) 36,451 Reputation points Microsoft External Staff

2024-10-17T01:15:00.1433333+00:00

Could you share the amountConverter method with me? Form the code snippets, it's not clear how the text converted.

What makes me very confused is that I have other pages with similar binding and the same 'amountConverter', and they work fine.

If it's possible, would you mind sharing the code snippets of that page so that I can test?
Giorgio Sfiligoi 616 Reputation points

2024-10-17T09:08:44.1466667+00:00

Here is the AmountConverter:

using System.Diagnostics; using System.Globalization; namespace TestVari.Converters; internal class AmountConverter : IValueConverter { public object? Convert(object? value, Type targetType, object? parameter, CultureInfo culture) { if (value == null) return String.Empty; var nfi = new NumberFormatInfo(); nfi.NumberDecimalDigits = 2; // the method converts only Int64 to string Debug.Assert(targetType == typeof(string)); Debug.Assert(value.GetType() == typeof(Int64)); double d = System.Convert.ToDouble(Math.Abs((Int64)value)); // Use the ToString method to format the value. return (d / 100).ToString("N", nfi); } public object? ConvertBack(object? value, Type targetType, object? parameter, CultureInfo culture) => throw new NotImplementedException(); }

It converts e.g 1234 to a string 12.34 i.e. the amount is stored in cents.

However, as I said, this converter works fine in other pages.
Giorgio Sfiligoi 616 Reputation points

2024-10-17T15:12:55.6766667+00:00

I found that Label accepts the Converter; Entry and Editor accept only binding but not converters and throw as I described in my initial query.

This seems very strange and not documented.
Wenyan Zhang (Shanghai Wicresoft Co,.Ltd.) 36,451 Reputation points Microsoft External Staff

2024-10-18T07:41:20.4633333+00:00

After testing, the converter doesn't work on Lable and Entry. I tried to enter 1234 for the label and I got the same exception. Does 1234 work on your side?
Giorgio Sfiligoi 616 Reputation points

2024-10-18T08:08:12.44+00:00

Yes, 1234 gives 12.34 in the Label.

Throws for Entry and Editor.
Wenyan Zhang (Shanghai Wicresoft Co,.Ltd.) 36,451 Reputation points Microsoft External Staff

2024-10-18T09:30:14.2166667+00:00

All labels on your page can display 12.34, right? I understand you are testing on Android platform, does it work on other platforms?
Giorgio Sfiligoi 616 Reputation points

2024-10-18T18:05:15.55+00:00

I added an Entry in the ConvertersPage that I sent before:

<Grid Margin="10" RowDefinitions="Auto,Auto,Auto,*,Auto" ColumnDefinitions="*,75,105"> ... <Label Grid.Row="1" Grid.Column="0" Text="Amount:"/> <Label Grid.Row="1" Grid.Column="2" BackgroundColor="Aquamarine" HorizontalOptions="Fill" Text="{Binding Amount, Converter={StaticResource AmountConverter}}" TextColor="{Binding Amount, Converter={StaticResource AmountColorConverter}}"/> <Entry Grid.Row="2" Grid.Column="0" Text="{Binding Amount, Mode=TwoWay}" /> </Grid>

(no change in the C# back code)

When you type some number in the Entry field, its conversion is displayed in the Label.

Typing 1234 gives 12.34.

I sent already the AmountConverter.

I played with Android and WindowsMachine and it works on both.

If you replace the Label with either Entry or Editor, in Android throws the cryptic exception that I described in my initial query; in WindowsMachine it also throws an exception: specifically the

throw new NotImplementedException();

in the ConvertBack of AmountConverter - and this is very strange too.
Wenyan Zhang (Shanghai Wicresoft Co,.Ltd.) 36,451 Reputation points Microsoft External Staff

2024-10-21T06:47:20.1333333+00:00

It looks like you have resolved the problem, right? I will convert your comment to an answer. If you have any other questions, please feel free to post in here.

Answer 1

I changed the ConvertBack of AmountConverter to: return 0;

Now it does not throw the exception when I changed Label to Entry in the ConvertersPage; however, to obtain the same experience as before, it is necessary to use Mode=OneWay:

        <Entry Grid.Row="1" Grid.Column="2" BackgroundColor="Aquamarine" HorizontalOptions="Fill"
               Text="{Binding Amount, Converter={StaticResource AmountConverter}, Mode=OneWay}"
               TextColor="{Binding Amount, Converter={StaticResource AmountColorConverter}}"/>

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BINDING CONVERTER THROWS EXCEPTION

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