为什么在XAML TextBox中没有类似PlaceHolder的属性

Question

Windows Phone 8中的xaml中是否有可用于文本框的“占位符类型”属性

Answer 1

官方Windows Phone Toolkit中有PhoneTextBox，涵盖here。

示例代码：

<toolkit:PhoneTextBox Hint="Password"/>

要将工具包添加到项目中： 在包管理器控制台中键入以下内容：
PM> Install-Package WPtoolkit
并且

xmlns:toolkit="clr-namespace:Microsoft.Phone.Controls;assembly=Microsoft.Phone.Controls.Toolkit"

<phone:PhoneApplicationPage页面

中的xaml标记内的

Answer 2

TextBox没有占位符属性。我使用以下解决方案来处理用户名文本框：

XAML：

<Grid>
    <TextBlock Name="UsernamePlaceholder" Text="Username" />
    <TextBox Name="UsernameTextBox" Text="" GotFocus="TextBox_GotFocus" LostFocus="TextBox_LostFocus"/>
</Grid>

代码：

private void TextBox_GotFocus(object sender, RoutedEventArgs e) 
{    
    UsernamePlaceholder.Visibility = Visibility.Collapsed;
}

private void TextBox_LostFocus(object sender, RoutedEventArgs e)
{
    if (sender is TextBox)
    {
        var textbox = sender as TextBox;
        if (string.IsNullOrEmpty(textbox.Text))
        {
            UsernamePlaceholder.Visibility = Visibility.Visible;
        }
    }
}

这基本上用Grid元素替换TextBox，包含TextBox和TextBlock（用作占位符）。然后，当文本框被聚焦时，文本块被隐藏，当它失去焦点时，如果文本框为空，则显示文本块。

Answer 3

我的解决方案基于PKENO的答案

XAML（UserControl）：

<UserControl x:Class="FestivalProject.Controls.TextBoxPH"
             xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
             xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
             xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006" 
             xmlns:d="http://schemas.microsoft.com/expression/blend/2008"            
             mc:Ignorable="d">
    <TextBox x:Name="testTextBox" Margin="0" LostFocus="testTextBox_LostFocus" GotFocus="testTextBox_GotFocus"/>
</UserControl>

UserControl背后的代码：

public partial class TextBoxPH : UserControl
    {
        private String _Text;

        public String Text
        {
            get { return _Text; }
            set { 
                _Text = testTextBox.Text = value;               
            }
        }



        private String _PlaceHolder;
        public String PlaceHolder
        {
            get { return _PlaceHolder; }
            set { 
                _PlaceHolder =testTextBox.Text = value;      
            }
        }        

        public TextBoxPH()
        {           
            InitializeComponent();  
        }   

        private void testTextBox_LostFocus(object sender, RoutedEventArgs e)
        {
            if (string.IsNullOrEmpty(testTextBox.Text)) testTextBox.Text = PlaceHolder;              

        }

        private void testTextBox_GotFocus(object sender, RoutedEventArgs e)
        {
            if (testTextBox.Text.Equals(PlaceHolder, StringComparison.OrdinalIgnoreCase)) testTextBox.Text = string.Empty;

        }
    }

XAML（在窗口中）：

<txtPH:TextBoxPH  Margin="5"  Grid.ColumnSpan="2" PlaceHolder="PlaceholderText"/>

可能不是最有效的方式，但它有效。

Answer 4

请尝试以下代码：

<TextBox x:Name="InvoiceDate" Text="" Width="300"  TextAlignment="Left" Height="30" Grid.Row="0" Grid.Column="3" Grid.ColumnSpan="2" />
                    <TextBlock IsHitTestVisible="False" Text="Men att läsa" Width="300"  TextAlignment="Left" Height="30" Grid.Row="0" Grid.Column="3" Grid.ColumnSpan="2" Padding="5, 5, 5, 5"  Foreground="LightGray">
                        <TextBlock.Style>
                            <Style TargetType="{x:Type TextBlock}">
                                <Setter Property="Visibility" Value="Collapsed"/>
                                <Style.Triggers>
                                    <DataTrigger Binding="{Binding Text, ElementName=InvoiceDate}" Value="">
                                        <Setter Property="Visibility" Value="Visible"/>
                                    </DataTrigger>                                    
                                </Style.Triggers>
                            </Style>
                        </TextBlock.Style>
                    </TextBlock>