How to LoadControl a control that uses VaryByControl OutputCache, specifying values for properties

问题

I've got a user control that should use caching, with VaryByControl. The .ascx file looks like this :

<%@ Control Language="C#" AutoEventWireup="true" CodeBehind="TestControl.ascx.cs" Inherits="mynamespace.TestControl" %>
<%@ OutputCache Duration="10" Shared="true" VaryByControl="Test" %>
<p id="SomeText" runat="server">Nothing</p>

The TestControl class in the code-behind file has a int Test {...} property and an Page_Load() event handler that fills the SomeText paragraph with:

SomeText.InnerText = string.Format(@"Test={0} at {1}", Test, DateTime.Now)

I've got a .aspx file that looks like this:

<%@ Page Language="C#" AutoEventWireup="true" CodeBehind="TestPage.aspx.cs" Inherits="mynamespace.TestPage" %>
<%@ Register TagPrefix="xxx" TagName="TestControl" Src="Controls\TestControl.ascx" %>

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">

<html xmlns="http://www.w3.org/1999/xhtml">
<head runat="server">
    <title></title>
</head>
<body>
    <xxx:TestControl Test="6" runat="server" />
    <xxx:TestControl Test="7" runat="server" />
    <hr />
    <asp:PlaceHolder ID="Suport" runat="server" />
</body>
</html>

The two <xxx:TestControl> tags properly load instances of TestControl with Test set to the expected value, I can refresh the browser a few times and I can see the cache properly doing it's job.

Now I'd like to fill the <asp:PlaceHolder ID="Suport" /> with some instances of TestControl, using varying Test values, that should all benefit from proper caching. I'm trying to use the LoadControl method, but I can't find a way to specify a value for the Test property. I expect such a method to exist, after all asp.net code loading the .aspx page manages to find the proper cached control. All I get is an instance of PartialCachingControl without CachedControl initialized and at runtime the rendered TestControl shows Test has the default value of 0.

This is how my .aspx Page_Load() event handler looks like:

protected void Page_Load(object sender, EventArgs e)
{
    PartialCachingControl tc = (PartialCachingControl) LoadControl(@"Controls\TestControl.ascx");
    if (tc.CachedControl != null)
        ((TestControl)tc.CachedControl).Test = 67;            
    Suport.Controls.Add(tc);
}

Edit

I could work around the problem by caching the whole page, but it just seems odd that I can't find a way to do it this way. Especially since invoking the control through the ASPX file works as expected (proving there's a way).

Edit 2

Hmm, no answers so far. I started a bounty, hopefully it gets a bit more attention.

回答1:

I think you have misunderstood the VarByControl-property, it does not tell the cache to change upon a property on the control, but on the ID of controls on the page. Here is the text from MSDN:

The VaryByControl property is set to fully qualified control identifiers, where the identifier is a concatenation of control IDs starting from the top-level parent control and delimited with a dollar sign ($) character.

In your case you can maybe set VaryByCustom instead of VaryByControl and generate a cache key from the Test-property-value and vary it if it changes.

回答2:

To get a control participate in the full page life cycle it shall be added in the Init event or the CreateChildControls method rather than to add it on Load. Since VaryByControl needs fully qualified control identifiers to work it must be initialized before the page cycle begins.

Something similar to this:

protected override void OnInit(EventArgs e) {
    var testControl = LoadControl(@"TestControl.ascx");
    testControl.ID =  "TestControl";
    Suport.Controls.Add(testControl);
    base.OnInit(e);
}

protected override void OnLoad(EventArgs e) {
    TestControl testControl = GetTestControl("TestControl");
    if(testControl != null){ //If it is null it is cached and can not be changed
        testControl.Test = 242;
    }
    base.OnLoad(e);
}

private TestControl GetTestControl(string name) {
    var control = this.Suport.FindControl(name);
    var partialCachedControl = control as PartialCachingControl;
    if(partialCachedControl != null) {
        control = partialCachedControl.CachedControl;
    }
    return control as TestControl;
}

Since the output is cached per control you can not change the control until the cache is cleared. If you want to change the value and regenerate the content you either have to get the cache cleared or create a new control (with a new ID). One way to clear the cache is to use VaryByCustom instead and generates a cache key that changes if your Test-value is changing.

Also remember to implement INamingContainer interface on your test-control to avoid naming conflicts between the different objects. To do this, just add the interface to the control, like this:

public class TestControl: WebControl, INamingContainer {}

回答3:

You have to swap 2 lines in order to make your code work :

PartialCachingControl tc = (PartialCachingControl) LoadControl(@"Controls\TestControl.ascx");
Suport.Controls.Add(tc);
if (tc.CachedControl != null)
    ((TestControl)tc.CachedControl).Test = 67;

As soon as you add the control, the cached control is initialized.

E.G.

来源：https://stackoverflow.com/questions/6574528/how-to-loadcontrol-a-control-that-uses-varybycontrol-outputcache-specifying-val

标签

ASP.NET

caching

user-controls

runtime

loadcontrol