Question 402068 in Html Question posted in
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Html – How to add common properties across custom server controls that inherited different base classes

I need a Server Control (named FormLayout here) that renders child controls based on their attribute.

The goal is to be able to write something like the following:

<custom:FormLayout runat="server" ID="myForm">
   <custom:MyDropDownList runat="server" ID="field1" ColumnSpan="12"></custom:MyDropDownList>
   <custom:MyTextBox runat="server" ID="field2"></custom:MyTextBox>
</custom:FormLayout>

This is the current implementation for these server controls: (In reality there will be more types of child server control, not only these two.)

public interface ICommonFieldProperties{
  public int ColumnSpan {get;set;}
}
public class MyDropDownList:System.Web.UI.WebControls.DropDownList,
 ICommonFieldProperties {
  public int ColumnSpan {get;set;}
}

public class MyTextBox:System.Web.UI.WebControls.TextBox,
 ICommonFieldProperties {
  public int ColumnSpan {get;set;}
}

public class FormLayout:Panel{
protected override void RenderContents(HtmlTextWriter writer){
 foreach (Control i in Controls)
    // can't access the newly added common properties such as "ColumnSpan"
    i.RenderControl(writer);
}

I tried to add the common properties by inheriting a common interface, but then I need to cast these child controls to ICommonFieldProperties whenever I want to access properties defined in it and cast them back to Control whenever I want to use the methods inherited from Control. For exmaple:

protected override void RenderContents(HtmlTextWriter writer) {
  var orderedControls = Controls
    .OfType<ICommonFieldProperties>()
    .Where(c => c.ColumnSpan == 0);
  foreach (var field in orderedControls){
    // Group them into different wrappers based on some other common properties  in ICommon Field
    // ...
    // render
    ((Control)field).RenderControl(writer);
  }
}

Another big problem is that since this is on .Net 4.8, interfaces don’t support default methods so I will need to duplicate every implementation for methods/auto properties in ICommonFieldProperties in each child server control even if they are all the same. Is there an easier way to do this?

Tags:

2

Answers


  1. 0 
    public partial class MyUserControl: UserControl
{
  public MyUserControl()
  {
     InitializeComponent();
  }
user control
   public string FirstName`enter code here`
    {
        get { return FirstNameTextBox.Text; }
        set { FirstNameTextBox.Text = value; }
    }

    public string LastName
    {
        get { return LastNameTextBox.Text; }
        set { LastNameTextBox.Text = value; }
    }
}

public partial class MainWindow: Window
{
    public MainWindow()
    {
        InitializeComponent();

        MyUserControlInstance.FirstName = "John";
        MyUserControlInstance.LastName = "Doe";

        string firstName = MyUserControlInstance.FirstName;
        string lastName = MyUserControlInstance.LastName;
    }
}
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  2. 0

    Separate FormSlot elements from Control elements.

    <custom:FormLayout runat="server" ID="myForm">

   <custom:FormSlot ColumnSpan="12">
      <custom:MyDropDownList runat="server" ID="field1" >
      </custom:MyDropDownList>
   </custom:FormSlot>

   <custom:FormSlot>
      <custom:MyTextBox runat="server" ID="field2">
      </custom:MyTextBox>
   </custom:FormSlot>

</custom:FormLayout>

    Since the common properties you mentioned seem to be all layout-related.
    If so, it’s better to abstract the FormSlot from Control itself, which acts more like a container for setting arranging properties such as the ColumnSpan you mentioned above.

    public class FormSlot: PlaceHolder
{
  public int ColumnSpan {get;set;}
}
public class MyDropDownList:System.Web.UI.WebControls.DropDownList
{
}

public class MyTextBox:System.Web.UI.WebControls.TextBox
{
}

public class FormLayout:Panel
{
   protected override void RenderContents(HtmlTextWriter writer)
   {
      var slots = Controls
        .OfType<FormSlot>()
        .Where(c => c.ColumnSpan == 0);
      // This way you can access the common properties as FormSlot
   }
}
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