WPF Textbox accept INT but not NULLABLE INT?

Question

Model

public int? SizeLength { get; set; }

XAML

<TextBox Text="{Binding [someViewModel].SizeLength, Mode=TwoWay}"></TextBox>

Once user try to backspace or delete the value in this textbox, a message Value '' cannot be converted.

May I know what's wrong with it?

Answer 1

Use:

{Binding TargetNullValue=''}

Answer 2

Since the integrated converters from string to single/double/int of WPF are expecting a string to parse they won't default the null value to 0 because you won't always want that behavior, so as it is written in MSDN :

Gets or sets the value that is used in the target when the value of the source is null.

you use this to define your default value for null input:

{Binding TargetNullValue=''}

TargetNullValue msdn

Answer 3

You need to add a reference of mscorlib in your XAML, Nullable or ? in your prop and use TargetNullValue with value "" like Elios said.

xmlns:sys="clr-namespace:System;assembly=mscorlib"

public Nullable<int> Prop { get; set; }

{Binding prop, TargetNullValue=''}