xamarin.forms entry binding on blur - xamarin.forms

Question

It appears the default binding trigger for an entry text is the TextChanged event. I want to defer updating the source until the blur event. In WPF there was the UpdateSourceTrigger parameter that could be set to modify the binding trigger, but there isn’t any documentation I’ve found on this in Xamarin.Form.
How can that be achieved in Xaramin.Forms with binding in XAML. For obvious reasons, I don’t want to manually handle it in the code behind.

Answer 1

This question is old but still actual. Especially for fields with decimal point...
First option to use Xamarin Community Toolkit EventToCommandBehavior (or similar implementations, like Prism). Then possible to bind "Unfocused" event to some command:
<Entry.Behaviors>
<xct:EventToCommandBehavior
EventName="Unfocused"
Command="{Binding MyCustomCommand}" />
</Entry.Behaviors>
Other option to add custom Entry component that handle this event, this option fits me better with numeric input with decimal point (float, double, decimal). This a little modified solution from MSDN forum Entry binding Decimal:
public class NumericEntry : Entry
{
#region Bindables
public static readonly BindableProperty NumericValueProperty = BindableProperty.Create(
"NumericValue",
typeof(decimal?),
typeof(NumericEntry),
null,
BindingMode.TwoWay,
coerceValue: (_, value) => (decimal?)value,
propertyChanged: (bindable, _, __) => SetDisplayFormat((NumericEntry)bindable)
);
public static readonly BindableProperty NumericValueFormatProperty = BindableProperty.Create(
"NumericValueFormat",
typeof(string),
typeof(NumericEntry),
"N0",
BindingMode.TwoWay,
propertyChanged: (bindable, _, __) => SetDisplayFormat((NumericEntry)bindable)
);
#endregion Bindables
#region Constructor
public NumericEntry()
{
Keyboard = Keyboard.Numeric;
Focused += OnFocused;
Unfocused += OnUnfocused;
}
#endregion Constructor
#region Events
private void OnFocused(object sender, FocusEventArgs e)
{
SetEditFormat(this);
}
private void OnUnfocused(object sender, FocusEventArgs e)
{
var numberFormant = CultureInfo.CurrentCulture.NumberFormat;
var _text = Text.Replace(".", numberFormant.NumberDecimalSeparator);
if (decimal.TryParse(_text, NumberStyles.Number, CultureInfo.CurrentCulture, out var numericValue))
{
var round = Convert.ToInt32(NumericValueFormat.Substring(1));
NumericValue = Math.Round(numericValue, round);
}
else
{
NumericValue = null;
}
SetDisplayFormat(this);
}
#endregion Events
#region Properties
public decimal? NumericValue
{
get => (decimal?)GetValue(NumericValueProperty);
set => SetValue(NumericValueProperty, value);
}
public string NumericValueFormat
{
get => (string)GetValue(NumericValueFormatProperty) ?? "N0";
set
{
var _value = string.IsNullOrWhiteSpace(value) ? "N0" : value;
SetValue(NumericValueFormatProperty, _value);
}
}
#endregion Properties
#region Methods
private static void SetDisplayFormat(NumericEntry textBox)
{
if (textBox.NumericValue.HasValue)
{
textBox.Text = textBox.NumericValue.Value.ToString(textBox.NumericValueFormat, CultureInfo.DefaultThreadCurrentCulture);
}
else
{
textBox.Text = string.Empty;
}
}
private static void SetEditFormat(NumericEntry textBox)
{
if (textBox.NumericValue.HasValue)
{
var numberFormant = CultureInfo.CurrentCulture.NumberFormat;
textBox.Text = textBox.NumericValue.Value.ToString(textBox.NumericValueFormat, CultureInfo.CurrentCulture).Replace(numberFormant.NumberGroupSeparator, string.Empty);
}
else
{
textBox.Text = string.Empty;
}
}
#endregion Methods
}
And use it like this:
// import our component
xmlns:ex="clr-namespace:BoganPos.Extensions"
//...
<ex:NumericEntry NumericValue="{Binding DecimalValue}" NumericValueFormat="F2" Placeholder="Placeholder"/>