Develop Reference

ASP.Net Page Lifecycle and dynamic controls

I'm am a little bit stuck in the ASP.Net's page lifecycle. This is my first ASP.Net project after many years of doing React so I might be missing something;)
Simplified code:
protected void Page_Load(object sender, EventArgs e)
{
BuildView();
}
private void BuildView()
{
switch (pageViewMode.Value)
{
case "Overview": BuildOverview(); break;
case "Runs": BuildRunsOverview(); break;
}
}
private void BuildOverview()
{
var tilesContainer = new TilesContainer();
tilesContainer.OnTileClicked += (InfoTile targetTile) =>
{
pageViewMode.Value = targetTile.Value;
BuildView();
};
rootElement.Controls.Add(tilesContainer);
}
The problem is that the "OnTileClicked" event works only on the first load and not after the postback. I believe it has something to do with the page lifecycle and registering the events after the Control events ( https://learn.microsoft.com/en-us/previous-versions/aspnet/ms178472(v=vs.100)?redirectedfrom=MSDN ).
If it is really the case, how do I then dynamically build pages from the code behind? Should I really create all the controls ( BuildOverview() and BuildRunsOverview()) and then conditionally show or hide them?

'Should I really create all the controls ( BuildOverview() and BuildRunsOverview()) and then conditionally show or hide them?'
Answer is: yes.
You don't dynamically build pages from code behind - at least its not that well supported in asp.net pages.
In your case you need the TilesContainer on every postback and attach the event handler to it, else the event won't be called. So it would be easier to put all your controls in the markup (.aspx) and just set them to Visible = false/true depending on your code. Controls you set to Visible = false won't be rendered on the client side, so at least no overhead there.
If you use custom-controls (I assume your TilesContainer is a custom-control), then you need to implement the Visible-property the right way, e.g. if your TilesContainers main control is a Panel, override Visible and set the value there:
public override bool Visible
{
get { return base.Visible; }
// set all neccessary controls visibility here
set { this.pnlMain.Visible = base.Visible = value; }
}

Looping through controls on a page using a masterpage

I'm trying to perform an operation on every control on a page that is inherited from a masterpage. I don't know how to access the child pages controls. I have tried recursively getting to my controls like this:
private void checkControls(ControlCollection controlcollection)
{
foreach (Control control in controlcollection)
{
if (control.Controls.Count > 0)
{
Debug.WriteLine(control.GetType().ToString());
checkControls(control.Controls);
}
else
{
Debug.WriteLine(control.GetType().ToString());
}
}
The method is called like this:
protected void resettodefault()
{
checkControls(this.Page.Controls);
}
However, the only controls that are printed from this execution are:
ASP.site_master
System.Web.UI.LiteralControl
I would prefer to access my controls directly (without recursion). Otherwise, how can I modify my recursion to get to the desired page's controls?

I would suggest using a base page instead of a master page, this way your logic for iterating over controls (and whatever you will do with that afterwards) is not tied to which master page a page is using.
As far as getting all the controls on the page, because the controls are hierarchical, as is the HTML they represent, so iterating over them recursively makes sense. However if you are dead set on not recursively getting controls something like this should work:
IEnumerable<Control> GetAllControls()
{
var allControls = new List<Control>();
var currentControls = new Queue<Control>();
currentControls.Enqueue(this.Page);
while (currentControls.Count >0)
{
var c = currentControls.Dequeue();
if (!allControls.Contains(c))
{
allControls.Add(c);
if (c.Controls != null && c.Controls.Count > 0)
{
foreach (Control e in c.Controls)
{
currentControls.Enqueue(e);
}
}
}
}
return allControls;
}
The last thing to consider is the lifecycle of the page, and when you iterate over the controls. If you try to walk to control tree too early not all controls may exist.
EDIT: Updated code.
Update
For validation purposes I would highly recommend using the built in validation controls of asp.net. You can read more about them here. This has the added benefit of providing validation on the client, providing faster UI responses and easing the load off the servers.
For resetting all the textboxes. I would recommend creating a new class for this purpose, then calling upon that class when needed instead of messing with the master page:
public class UIControlsHelper
{
public static void ClearTextboxes(Page page)
{
GetAllControls(page)
.Where(x => typeof(TextBox).IsAssignableFrom(x.GetType())
.ToList()
.ForEach(x => (TextBox)x.Text = string.Empty);
}
IEnumerable<Control> GetAllControls(Page page)
// Same as above, but with the page parameter replaced.
}
}
And in any of your pages:
UIControlsHelper.ClearTextboxes(this);

To access the controls in your child page do the following steps:
1-declare a variable of the type you want to access. For example if you want to access a Label in your child page use:
Label lbl_child=this.ContentPlaceHolder1.findcontrol("your label id in child page") as Label;
Now you have your label and you are free to make changes on it. Every change on this control will be reflected on the child control.
ContentPlaceHolder1 is your contentplace holder id so change it with your content id.

public void ClearTextboxes(Page page) {
GetAllControls(page)
.Where(x => typeof(TextBox).IsAssignableFrom(x.GetType()))
.ToList()
.ForEach(x => ((TextBox)x).Enabled=false);
}

Dynamically change MasterPage and ContentPlaceHolderID of asp content tag?

I have a page which initially inherited from MastePage.master . And I want to use the same page but with different masterpage(MasterPage2.master) at some other place in my project. For that I am using the following code.
private void Page_PreInit(object sender, EventArgs e)
{
if (Request.QueryString["Update"].ToString() == "New")
{
this.MasterPageFile = "MasterPage2.master";
Content con = new Content();
con = (Content)this.FindControl("Content1");
this.Content1.ContentPlaceHolderID = "ContentPlaceHolder2";
}
}
I am also trying to set the asp content tag's ContentPlaceHolderID to ContentPlaceHolder2 which is from MasterPage2.master. Initially it was ContentPlaceHolder1.
But I am getting null value at con = (Content)this.FindControl("Content1");
Thanks

Page internally stores in private '_contentTemplateCollection' hashtable. it uses ContentPlaceHolderID property as key and stores special class (that will be used to build/initialize Content tag) as a value
- so to change ContentPlaceHolderID value (defined within markup) you need to modify this hashtable, remove old entry linked with old Id and add other entry with new Id
- you need to change ContentPlaceHolderId before creating master page otherwise an exception will be thrown in runtime
- best place to change Ids is Page 'preinit' event and if it is better to change Ids before change master page (if you will change master page at runtime)
To change ContentPlaceHolderID of Content tag, you can use following function in Page PreInit event
public static void AssignContentToNewPlaceHoldersWithinPage(Page pPage, string pOldId, string pNewId)
{
if (pPage == null || string.IsNullOrEmpty(pOldId) || string.IsNullOrEmpty(pNewId))
{
return;
}
// Try to get a reference to private hashtable using fasterflect free reflection library in codeplex (http://fasterflect.codeplex.com/)
// you can replace following line with standard reflection APIs
var lTmpObj = pPage.TryGetFieldValue("_contentTemplateCollection");
if (lTmpObj != null && lTmpObj is Hashtable)
{
var _contentTemplateCollection = lTmpObj as Hashtable;
if (_contentTemplateCollection.ContainsKey(pOldId) && !_contentTemplateCollection.ContainsKey(pNewId))
{
var lTemplate = _contentTemplateCollection[pOldId];
_contentTemplateCollection.Add(pNewId, lTemplate);
_contentTemplateCollection.Remove(pOldId);
}
}
}
function parameter are
pPage is reference to page instance contains content tag
pOldId is ContentPlaceHolderId property value in markup - the Id you want to change
pNewId is the new Id you want to use
I hope that my answer will be useful and I am sorry if my English language is not good

You can dynamically change the Master Page at runtime, but you need to use the same ContentPlaceHolder IDs. That way, your pages will work with either Master Page without adding extra code to change the IDs at runtime.
private void Page_PreInit(object sender, EventArgs e)
{
if (Request.QueryString["Update"].ToString() == "New")
{
this.MasterPageFile = "MasterPage2.master";
}
}
You can even test that your page will work with either Master Page in the Visual Studio design/markup view by changing the MasterPageFile in the <% Page %> directive in the .aspx markup.

The Master Page can be changed by overriding OnPreInit.
protected override void OnPreInit(EventArgs e)
{
base.OnPreInit(e);
MasterPageFile = "~/MasterPages/MyOther.Master";
}
But for the ContentPlaceHolders I would suggest to create new ContentPlaceHolders with the same name in both of your MasterPages.

Change panel "visible" property on MasterPage from Child pages

I want to show some panel with a label, both located on a MasterPage, from inside it's child pages.. I already did the coding on the MasterPage:
public class MyMaster : MasterPage
{
public void ShowPanel(string pMessage)
{
labelInside.Text = pMessage;
myPanel.visible = true;
}
}
Then I make the calls from child pages:
public void ShowPanel(string pMessage)
{
MyMaster masterPage = this.Master as MyMaster;
masterPage.ShowPanel(pMessage);
}
This "works" ok, but it won't show nothing, since I need the page to be "refreshed" in an "ajax-way" like an UpdatePanel, which I can't use because the Trigger is in another page, right?
I really need this to work.. even if you have another completely different way to do this, I would appreciate.

You must place your panel inside an UpdatePanel(UpdateMode conditional) and in ShowPanel call its Update method.

Have you considered having the masterpage just have a placeholder for the label, but having each child page put its own content label inside that placeholder, which it would then have full control over?

you can subClass your page, and expose a property say.. MyPage.FooVisible
than in your masterPage, you can:
myPage = this.Page as MyPage
if (myPage != null) myPage.FooVisble = false;
in your page you can handle that any way you like,
FooVisible {
set { SomeElement.Visible = value; }
}
pseudo code of course :)

Ensuring unique ID attribute for elements within ScriptControl

I'm creating a control based on ScriptControl, and I'm overriding the Render method like this:
protected override void Render(HtmlTextWriter writer)
{
RenderBeginTag(writer);
writer.RenderBeginTag(HtmlTextWriterTag.Div);
writer.Write("This is a test.");
writer.RenderEndTag();
RenderEndTag(writer);
}
My question is, what if I want to assign the div an ID attribute and have it be unique on the page, even if there are mulitple instances of my control?
I've seen other people's code that does this:
writer.AddAttribute(HtmlTextWriterAttribute.Id, this.ClientID + "_divTest");
That will prevent naming conflicts between instances of my control, but what if I've already created a div elsewhere on the page that coincidentally has the same ID?
I've also heard about implementing INamingContainer. Would that apply here? How could I use it?
UPDATE:
I've worked around this by overriding CreateChildControls and adding actual controls, as opposed to rendering HTML directly. In that case INamingContainer does its job. However, I'm still curious if there's a way to solve my original problem (unique IDs for directly rendered elements).

INamingController is a marker interface. Implementing it will guarantee you unique ids for each instance of your control.
http://msdn.microsoft.com/en-us/library/system.web.ui.inamingcontainer.aspx
public class MyScriptControl: ScriptControl, INamingContainer {
}

You won't want to create instances of controls just to get unique Ids, there's useless overhead/complexity in that approach. The Control.ID property may not be unique, but the Control.ClientID property will be unique. Therefore
writer.AddAttribute(HtmlTextWriterAttribute.Id, this.ClientID + "_divTest");
that attribute has to be unique unless you use the suffix "_divTest" twice in your custom control.

I am tried to realize your issue:
public class SC : ScriptControl
{
protected override IEnumerable<ScriptDescriptor> GetScriptDescriptors()
{
return null;
}
protected override IEnumerable<ScriptReference> GetScriptReferences()
{
return null;
}
}
//... Page code
protected void Page_PreRender(object sender, EventArgs e)
{
var sc = new SC();
var sc1 = new SC();
Page.Form.Controls.Add(sc);
Page.Form.Controls.Add(sc1);
}
But sc and sc1 have different ClientID. So it is not ASP.NET issue. Look over your realization. May be you generate ids for divs before adding ScriptControls to Page, or may be you try to create 2 divs in the scope of one ScriptControl, or may be you create ScriptConrol2 dynamicly on async-posback and it have the same id as ScriptControl1, that not added dynamicly on postback.