我为WPF文本框写了一个名为"IsValid"的小附加属性，如下所示:
public enum InputTypes
{
Any,
Integer,
Double,
Float
}
/// <summary>
/// This attached property can be used to validate input for <see cref="TextBox"/>.
/// </summary>
public class IsValid : DependencyObject
{
public static readonly DependencyProperty InputProperty = DependencyProperty.Register(
"Input",
typeof(InputTypes),
typeof(IsValid),
new UIPropertyMetadata(InputTypes.Any, onInput));
public static InputTypes GetInput(DependencyObject d)
{
return (InputTypes)d.GetValue(InputProperty);
}
public static void SetInput(DependencyObject d, InputTypes value)
{
d.SetValue(InputProperty, value);
}
private static void onInput(DependencyObject d, DependencyPropertyChangedEventArgs e)
{
var textBox = (TextBox)d;
var value = (InputTypes)e.NewValue;
switch (value)
{
case InputTypes.Any:
textBox.PreviewTextInput -= validateInput;
textBox.PreviewKeyDown -= validateKeyDown;
break;
default:
textBox.PreviewTextInput += validateInput;
textBox.PreviewKeyDown += validateKeyDown;
break;
}
}
private static void validateInput(object sender, TextCompositionEventArgs e)
{
// enforce numeric input when configured ...
var textBox = (TextBox) sender;
var inputTypes = (InputTypes) textBox.GetValue(InputProperty);
foreach (var c in e.Text)
{
switch (inputTypes)
{
case InputTypes.Integer:
if (!char.IsDigit(c))
{
e.Handled = true;
return;
}
break;
case InputTypes.Double:
case InputTypes.Float:
if (!char.IsNumber(c))
{
e.Handled = true;
return;
}
break;
default:
throw new ArgumentOutOfRangeException();
}
}
}
private static void validateKeyDown(object sender, KeyEventArgs e)
{
// block [SPACE] when numeric input is expected ...
var textBox = (TextBox)sender;
var inputTypes = (InputTypes)textBox.GetValue(InputProperty);
if (inputTypes != InputTypes.Any && e.Key == Key.Space)
e.Handled = true;
}
}
结束，下面是我的用法:
<Window x:Class="Spike.Wpf.Controls.TestApp.MainWindow"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:values="clr-namespace:Spike.Wpf.Controls.Input;assembly=Spike.Wpf.Controls"
Title="MainWindow" Height="350" Width="525">
<Grid>
<TextBox values:IsValid.Input="Double" />
</Grid>
初始化(DependencyProperty)之后，IsValid中的任何方法都不会被调用。我错过了什么?
早些时候你可能得到一个错误告诉你IsValid需要从DependecyObject派生，所以你补充说，你应该问自己为什么会这样。答案就在这里:
public static readonly DependencyProperty InputProperty = DependencyProperty.Register(...
你尝试在IsValid类型上为对象注册一个普通属性，将其更改为RegisterAttached，它应该工作。(我还会删除继承并使IsValid成为静态类)
好的，所以问题的核心是微不足道的(参见公认的答案):我需要调用DependencyProperty.RegisterAttached(...)(而不是DependencyProperty.Register(...))。
只是想分享一下结果。我决定放弃使用简单的enum来指定输入类型，并决定使用标记扩展来代替。
附加属性实现现在看起来像这样:
public static class IsValid
{
public static readonly DependencyProperty InputProperty = DependencyProperty.RegisterAttached(
"Input",
typeof(IsValidInputExtension),
typeof(IsValid),
new UIPropertyMetadata(onInput));
public static IsValidInputExtension GetInput(DependencyObject d)
{
return (IsValidInputExtension)d.GetValue(InputProperty);
}
public static void SetInput(DependencyObject d, IsValidInputExtension value)
{
d.SetValue(InputProperty, value);
}
private static void onInput(DependencyObject d, DependencyPropertyChangedEventArgs e)
{
var textBox = (TextBox)d;
var value = (IsValidInputExtension)e.NewValue;
if (value == null)
{
textBox.PreviewTextInput -= validateInput;
textBox.PreviewKeyDown -= validateKeyDown;
return;
}
textBox.PreviewTextInput += validateInput;
textBox.PreviewKeyDown += validateKeyDown;
}
private static void validateInput(object sender, TextCompositionEventArgs e)
{
// dispatch validation to specified markup class ...
var textBox = (TextBox) sender;
var markup = (IsValidInputExtension)textBox.GetValue(InputProperty);
markup.ValidateInput(sender, e);
}
private static void validateKeyDown(object sender, KeyEventArgs e)
{
// dispatch validation to specified markup class ...
var textBox = (TextBox)sender;
var markup = (IsValidInputExtension)textBox.GetValue(InputProperty);
markup.ValidateKeyDown(sender, e);
}
}
下面是部分标记扩展类:
public abstract class IsValidInputExtension : MarkupExtension
{
internal abstract void ValidateInput(object sender, TextCompositionEventArgs e);
internal abstract void ValidateKeyDown(object sender, KeyEventArgs e);
}
public class NumericExtension : IsValidInputExtension
{
public double Minimum { get; set; }
public double Maximum { get; set; }
public uint Decimals { get; set; }
public override object ProvideValue(IServiceProvider serviceProvider)
{
return this;
}
internal override void ValidateInput(object sender, TextCompositionEventArgs e)
{
var textBox = (TextBox) sender;
if (isDecimalSeparator(e.Text) && Decimals == 0)
{
e.Handled = true;
return;
}
// todo: honor Minimum and Maximum ...
}
private static bool isDecimalSeparator(string s)
{
return CultureInfo.CurrentUICulture.NumberFormat.CurrencyDecimalSeparator == s;
}
internal override void ValidateKeyDown(object sender, KeyEventArgs e)
{
// block [SPACE] when numeric input is expected ...
e.Handled = e.Key == Key.Space;
}
}
public class StringExtension : IsValidInputExtension
{
public double MaximumLength { get; set; }
public override object ProvideValue(IServiceProvider serviceProvider)
{
return this;
}
internal override void ValidateInput(object sender, TextCompositionEventArgs e)
{
// (nop)
}
internal override void ValidateKeyDown(object sender, KeyEventArgs e)
{
// todo: honor MaximumLength here
}
}
最终结果，在XAML中，非常好，易于阅读…
<TextBox v:IsValid.Input="{v:Numeric Minimum=0, Maximum=99, Decimals=0}" />
/乔纳斯