Silverlight 控件之 WatermarkedTextBox

atermarkedTextBox这个控件存在与Silverlight2.0，但在3.0的时候别去掉了，估计微软是想在TextBox中用一个类似watermarked的属性来实现这个控件功能，但现在为止还没有看到类似属性。如果真想实现这个控件可以使用以下方法：

 

方法一：自己编写继承控件

public class WatermarkedTextBox : TextBox
    {
        public static readonly DependencyProperty DefaultTextProperty = DependencyProperty.Register("DefaultText", typeof(string), typeof(WatermarkedTextBox), new PropertyMetadata(""));
        public event EventHandler WatermarkedTextChanged;

        public WatermarkedTextBox()
        {
            base.TextChanged += new TextChangedEventHandler(this.OnWotermarkedTextBoxTextChanged);
        }

        public override void OnApplyTemplate()
        {
            base.Text = this.DefaultText;
            base.OnApplyTemplate();
        }

        protected override void OnGotFocus(RoutedEventArgs e)
        {
            if (string.Equals(base.Text, this.DefaultText, StringComparison.OrdinalIgnoreCase))
            {
                base.Text = string.Empty;
            }
            base.OnGotFocus(e);
        }

        protected override void OnLostFocus(RoutedEventArgs e)
        {
            if (string.IsNullOrEmpty(base.Text))
            {
                base.Text = this.DefaultText;
            }
            base.OnLostFocus(e);
        }

        private void OnWotermarkedTextBoxTextChanged(object sender, TextChangedEventArgs e)
        {
            if (!string.Equals(base.Text, this.DefaultText, StringComparison.OrdinalIgnoreCase))
            {
                if(this.WatermarkedTextChanged != null)
                    this.WatermarkedTextChanged(this, e);
            }
        }

        public string DefaultText
        {
            get
            {
                return (string)base.GetValue(DefaultTextProperty);
            }
            set
            {
                base.SetValue(DefaultTextProperty, value);
            }
        }
    }

 

方法二：将DLL添加引用到project类库，然后导入xaml（DLL见附件）

首先将DLL放置到硬盘的任意位置，建议放到工程目录下，然后添加引用到你的项目中，如下图：

 


 
然后在你xaml页面中的UserControl控件中加入如下代码：

xmlns:my="clr-namespace:Microsoft.Windows.Controls;assembly=Microsoft.Windows.Controls.WatermarkedTextBox"

 

 最后你就可以在xaml中引用WatermarkedTextBox控件了，代码如下：

<my:WatermarkedTextBox Name="txtSearchTopic" Grid.Column="1" FontSize="14" Watermark="Topic..." GotFocus="TextBox_GotFocus"/>

 

在xaml中引用控件详情请参考：

添加Silverligh控件引用

（http://lujinan858.iteye.com/admin/blogs/729771）

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以下文章转自http://www.michaelsnow.com/2010/05/06/silverlight-tip-of-the-day-14-dynamically-loading-a-control-from-a-dll-on-a-server/

Dynamically Loading a Control from a DLL on a Server

In this tip I will be showing you how to load a Silverlight control from a DLL that is on a server somewhere. This technique is useful if you want the initial XAP download size of your application kept to a minimum. That is, the controls and resources you place in the DLL are items that you can download on demand when your application actually needs to load them.

To start, I will create a simple control that displays an image. This control will be packaged in a Silverlight class library DLL.

1. Open Visual Studio.

2. Create a new Silverlight application

3. Right click on the top node in your Solution Explorer. Choose  Add->New Project.

4. Select “Silverlight Class Library” and give it a name (mine is called TestCtrl). This project will create the DLL that will contain your control(s).

5. In your class library add a new a new Silverlight User Control (mine is called ImageTest).

6. Open up the XAML page (ImageTest.xaml) for this user control and add something like an Image control. If you are using a relative path to an image, make certain the image you reference is also included in your class library project.

 

<Image Source="scarlett.jpg"></Image>

At this point your class library DLL is good to go. Build the and place it on your server in a location you can reference. Note that after building the DLL you will find it in your projects Bin\Debug folder. Clicking the “Show all Files” in the toolbar for your Solution Explorer will make this bin folder visible.

 

7. Next, proceed to your Silverlight Application opening up MainPage.xaml.cs

8. Add a reference to System.Reflection;

9. Use the WebClient class to download the DLL from the server. From the purpose of this demo, I have placed my test DLL at http://www.flaired.com/TestCtrl.dll  

private Assembly _testCtrl; 

 

public MainPage() 

{ 

    InitializeComponent(); 

 

    WebClient downloader = new WebClient(); 

    string path = "http://www.flaired.com/TestCtrl.dll"; 

    downloader.OpenReadCompleted += new OpenReadCompletedEventHandler 

      (downloader_OpenReadCompleted);  

    downloader.OpenReadAsync(new Uri(path, UriKind.Absolute)); 

} 

 

void downloader_OpenReadCompleted(object sender, OpenReadCompletedEventArgs e) 

{ 

    AssemblyPart assemblyPart = new AssemblyPart(); 

    _testCtrl = assemblyPart.Load(e.Result); 

    UserControl control = (UserControl) 

    _testCtrl.CreateInstance("TestCtrl.ImageTest"); 

    LayoutRoot.Children.Add(control); 

}

 

10. Before you run this code, as a final step, make certain to have a ClientAccessPolicy.xml file located in the same location as your DLL. Silverlight will look for this file for permissions when making calls cross-domain. By default Silverlight only allows site-of -origin communication.

<?xml version="1.0" encoding="utf-8"?> 

<access-policy> 

  <cross-domain-access> 

    <policy> 

      <allow-from http-request-headers= "*"> 

        <domain uri="*"/> 

      </allow-from> 

      <grant-to> 

        <resource path="/" include-subpaths="true"/> 

      </grant-to> 

    </policy> 

  </cross-domain-access> 

</access-policy>