【发布时间】：2010-12-07 01:42:12
【问题描述】：
如何将 maxlength 设置为组合框，它应用了一种样式。
谢谢
【问题讨论】：
-
MaxLength 是什么意思？
【发布时间】：2010-12-07 01:42:12
【问题描述】：
在使用 DependencyProperty 时，我们可以在不修改样式/模板的情况下设置组合框的最大长度。
public class EditableComboBox
{
public static int GetMaxLength(DependencyObject obj)
{
return (int)obj.GetValue(MaxLengthProperty);
}
public static void SetMaxLength(DependencyObject obj, int value)
{
obj.SetValue(MaxLengthProperty, value);
}
// Using a DependencyProperty as the backing store for MaxLength. This enables animation, styling, binding, etc...
public static readonly DependencyProperty MaxLengthProperty = DependencyProperty.RegisterAttached("MaxLength", typeof(int), typeof(EditableComboBox), new UIPropertyMetadata(OnMaxLenghtChanged));
private static void OnMaxLenghtChanged(DependencyObject obj, DependencyPropertyChangedEventArgs args)
{
var comboBox = obj as ComboBox;
if (comboBox == null) return;
comboBox.Loaded +=
(s, e) =>
{
var textBox = comboBox.FindChild(typeof(TextBox), "PART_EditableTextBox");
if (textBox == null) return;
textBox.SetValue(TextBox.MaxLengthProperty, args.NewValue);
};
}
}
使用示例：
<ComboBox ComboboxHelper:EditableComboBox.MaxLength="50" />
ComboboxHelper 在哪里：
xmlns:ComboboxHelper="clr-namespace:yourNameSpace;assembly=yourAssembly"
comboBox.FindChild(...) 方法已发布here。
【讨论】：
或者您可以使用组合框的 GotFocus 或 Loaded 事件来设置 maxlength。如果在运行时 maxlength 没有太大变化，您可以使用加载事件或使用 gotfocus 事件
<ComboBox Height="30" IsEditable="True" Loaded="ComboBox_Loaded"/>
在相应的事件中......
var obj = (ComboBox)sender;
if (obj != null)
{
var myTextBox = (TextBox)obj.Template.FindName("PART_EditableTextBox",obj);
if (myTextBox != null)
{
myTextBox.MaxLength = maxLength;
}
}
【讨论】：
你是对的。文本框有一个最大长度，但组合框没有。您必须使用文本框作为中介来滚动自己。这是一些代码：
public int MaxLength {get; set;}
protected override void OnGotFocus(System.Windows.RoutedEventArgs e)
{
base.OnGotFocus(e);
TextBox thisTextBox = (TextBox)base.GetTemplateChild("PART_EditableTextBox");
if (thisTextBox != null)
thisTextBox.MaxLength = MaxLength;
}
【讨论】：
我用的是PreviewKeyDown事件，很简单+你可以显示警告什么的。
将以下方法注册到您的 ComboBox.PreviewKeyDown += 事件中，
如果用户按空格键，则不会触发 KeyDown 事件。
private void ComboBox_PreviewKeyDown(object sender, KeyEventArgs e)
{
if (ComboBox.Text.Length > 19) // allow max 20 chars
{
if (e.Key != Key.Back) // allow removing chars
{
e.Handled = true; // block any additional key press if there is more than allowed max
System.Media.SystemSounds.Beep.Play(); // optional: beep to let user know he is out of space :)
}
}
}
【讨论】：
此 TextBox 即将为空。 给出的样式如下。
<ControlTemplate x:Key="ComboBoxToggleButton" TargetType="ToggleButton">
<Grid>
<Grid.ColumnDefinitions>
<ColumnDefinition Width="*" />
<ColumnDefinition Width="{Binding Path=(local:ToggleComboBox.Width),
RelativeSource={RelativeSource FindAncestor, AncestorType={x:Type ComboBox}}}" />
</Grid.ColumnDefinitions>
<Border x:Name="Border"
Grid.Column="1"
CornerRadius="2"
Background="#CCFFCC"
BorderBrush="#000080"
BorderThickness="4" />
<Border Grid.Column="0"
CornerRadius="8,8,8,8"
Margin="0"
Background="#CCFFCC"
BorderBrush="#000080"
BorderThickness="4,4,4,4" />
<Image x:Name="Arrow"
Grid.Column="1"
Source="Arrow.png" Margin="4,4,4,4"
HorizontalAlignment="Center"
VerticalAlignment="Center"/>
</Grid>
<ControlTemplate.Triggers>
<Trigger Property="ToggleButton.IsMouseOver" Value="true">
<Setter TargetName="Border" Property="Background" Value="{StaticResource DarkBrush}" />
</Trigger>
<Trigger Property="ToggleButton.IsChecked" Value="true">
<Setter TargetName="Border" Property="Background" Value="{StaticResource PressedBrush}" />
</Trigger>
<Trigger Property="IsEnabled" Value="False">
<Setter TargetName="Border" Property="Background" Value="{StaticResource DisabledBackgroundBrush}" />
<Setter TargetName="Border" Property="BorderBrush" Value="{StaticResource DisabledBorderBrush}" />
<Setter Property="Foreground" Value="{StaticResource DisabledForegroundBrush}"/>
<!--<Setter TargetName="Arrow" Property="Fill" Value="{StaticResource DisabledForegroundBrush}" />-->
</Trigger>
</ControlTemplate.Triggers>
</ControlTemplate>
<ControlTemplate x:Key="ComboBoxTextBox" TargetType="TextBox">
<Border x:Name="PART_ContentHost" Focusable="False" Background="{TemplateBinding Background}" />
</ControlTemplate>
<Style x:Key="ComboBoxStyle" TargetType="ComboBox">
<Setter Property="SnapsToDevicePixels" Value="true"/>
<Setter Property="OverridesDefaultStyle" Value="true"/>
<Setter Property="ScrollViewer.HorizontalScrollBarVisibility" Value="Auto"/>
<Setter Property="ScrollViewer.VerticalScrollBarVisibility" Value="Auto"/>
<Setter Property="ScrollViewer.CanContentScroll" Value="true"/>
<Setter Property="MinWidth" Value="120"/>
<Setter Property="MinHeight" Value="20"/>
<Setter Property="Template">
<Setter.Value>
<ControlTemplate TargetType="ComboBox">
<Grid>
<ToggleButton Name="ToggleButton"
Template="{StaticResource ComboBoxToggleButton}"
Grid.Column="2"
Focusable="false"
IsChecked="{Binding Path=IsDropDownOpen,
Mode=TwoWay,
RelativeSource={RelativeSource TemplatedParent}}"
ClickMode="Press"/>
<ContentPresenter Name="ContentSite"
IsHitTestVisible="False"
Content="{TemplateBinding SelectionBoxItem}"
ContentTemplate="{TemplateBinding SelectionBoxItemTemplate}"
ContentTemplateSelector="{TemplateBinding ItemTemplateSelector}"
Margin="9,2,28,2"
VerticalAlignment="Center"
HorizontalAlignment="Left" />
<TextBox x:Name="PART_EditableTextBox"
Style="{x:Null}"
Template="{StaticResource ComboBoxTextBox}"
HorizontalAlignment="Left"
VerticalAlignment="Center"
Margin="3,3,23,3"
Focusable="True"
Background="Transparent"
Visibility="Hidden"
IsReadOnly="{TemplateBinding IsReadOnly}"/>
<Popup Name="Popup"
Placement="Bottom"
IsOpen="{TemplateBinding IsDropDownOpen}"
AllowsTransparency="True"
Focusable="False"
PopupAnimation="Slide">
<Grid Name="DropDown"
SnapsToDevicePixels="True"
MinWidth="{TemplateBinding ActualWidth}"
MaxHeight="{TemplateBinding MaxDropDownHeight}">
<Border x:Name="DropDownBorder"
Background="#CCFFCC"
BorderBrush="#000080"
BorderThickness="2"/>
<ScrollViewer Margin="4,6,4,6" SnapsToDevicePixels="True">
<ScrollViewer.Resources>
<sys:Double x:Key="{x:Static SystemParameters.VerticalScrollBarWidthKey}">25</sys:Double>
</ScrollViewer.Resources>
<StackPanel IsItemsHost="True" />
</ScrollViewer>
</Grid>
</Popup>
</Grid>
<ControlTemplate.Triggers>
<Trigger Property="HasItems" Value="false">
<Setter TargetName="DropDownBorder" Property="MinHeight" Value="95"/>
</Trigger>
<Trigger Property="IsEnabled" Value="false">
<Setter Property="Foreground" Value="{StaticResource DisabledForegroundBrush}"/>
</Trigger>
<Trigger Property="IsGrouping" Value="true">
<Setter Property="ScrollViewer.CanContentScroll" Value="false"/>
</Trigger>
<Trigger SourceName="Popup" Property="Popup.AllowsTransparency" Value="true">
<Setter TargetName="DropDownBorder" Property="CornerRadius" Value="4"/>
<Setter TargetName="DropDownBorder" Property="Margin" Value="0,2,0,0"/>
</Trigger>
<Trigger Property="IsEditable" Value="true">
<Setter Property="IsTabStop" Value="false"/>
<Setter TargetName="PART_EditableTextBox" Property="Visibility" Value="Visible"/>
<Setter TargetName="ContentSite" Property="Visibility" Value="Hidden"/>
</Trigger>
</ControlTemplate.Triggers>
</ControlTemplate>
</Setter.Value>
</Setter>
<Setter Property="ItemContainerStyle" >
<Setter.Value>
<Style TargetType="{x:Type ComboBoxItem}">
<Setter Property="FontSize" Value="20" />
</Style>
</Setter.Value>
</Setter>
</Style>
【讨论】：
我通过 XAML 找到了简单的解决方案。在组合框资源中，我们可以设置文本框的样式，并通过 setter set maxlenth。
<ComboBox Name="comboBox" Width="100" IsEditable="True">
<ComboBox.Resources>
<Style TargetType="{x:Type TextBox}">
<Setter Property="MaxLength" Value="yourValue"></Setter>
</Style>
</ComboBox.Resources>
</ComboBox>
编辑：这适用于 Actipro ComboBox。对于通常的组合框来完成这项工作，看看here
【讨论】：