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Retrieving values from dynamically added controlsI have a custom control that I wrote (I inherit from
System.Web.UI.WebControls.CompositeControl). I dynamically add this control to my Page, but I was told that dynamically added controls do not survive postback. This seems to be true. However, this seems to make dynamically adding controls rather pointless to me, since if you cannot retrieve the values of the controls when you perform a postback, why add the controls in the firstplace? Can someone help me figure out how to retrieve the property values of a dynamically added control? Thanks. Nathan Sokalski wrote:
> I have a custom control that I wrote (I inherit from They do not survive postback on their own. You have to help them.> System.Web.UI.WebControls.CompositeControl). I dynamically add this > control to my Page, but I was told that dynamically added controls do > not survive postback. This seems to be true. However, this seems to > make dynamically adding controls rather pointless to me, since if you > cannot retrieve the values of the controls when you perform a > postback, why add the controls in the firstplace? Can someone help me > figure out how to retrieve the property values of a dynamically added > control? Thanks. You can do that by re-creating them dynamically after the postback. On top of that, you have to make sure that they get the same ID before and after the postback. If not, they will not respond to any events that they were supposed to handle. Usually, this means that in the page, you have to keep track of the number of controls that were added dynamically. -- Riki If you re-create dynamic controls in Page_PreInit event, they will get their
properties populated correctly in Page_Load event. Read through this: http://msdn2.microsoft.com/en-us/library/ms178472.aspx -- Show quoteEliyahu Goldin, Software Developer Microsoft MVP [ASP.NET] http://msmvps.com/blogs/egoldin http://usableasp.net "Nathan Sokalski" <njsokal***@hotmail.com> wrote in message news:e61d2Cp8HHA.536@TK2MSFTNGP06.phx.gbl... >I have a custom control that I wrote (I inherit from >System.Web.UI.WebControls.CompositeControl). I dynamically add this control >to my Page, but I was told that dynamically added controls do not survive >postback. This seems to be true. However, this seems to make dynamically >adding controls rather pointless to me, since if you cannot retrieve the >values of the controls when you perform a postback, why add the controls in >the firstplace? Can someone help me figure out how to retrieve the property >values of a dynamically added control? Thanks. > -- > Nathan Sokalski > njsokal***@hotmail.com > http://www.nathansokalski.com/ > On Sep 8, 8:23 pm, "Nathan Sokalski" <njsokal***@hotmail.com> wrote: I have a page with dynamically added controls that I retrieve the> I have a custom control that I wrote (I inherit from > System.Web.UI.WebControls.CompositeControl). I dynamically add this control > to my Page, but I was told that dynamically added controls do not survive > postback. This seems to be true. However, this seems to make dynamically > adding controls rather pointless to me, since if you cannot retrieve the > values of the controls when you perform a postback, why add the controls in > the firstplace? Can someone help me figure out how to retrieve the property > values of a dynamically added control? Thanks. > -- > Nathan Sokalski > njsokal...@hotmail.comhttp://www.nathansokalski.com/ values from. Basically, you just put the call to the dynamic control creation in the Page_Init event and don't check IsPostBack because you always want it to run. Populating the controls can be done in the Page_Load event, but in this case you will need to check IsPostBack. Then, you can create a procedure that can read the values of the controls and load them into an object for use by the rest of your code. Typically control generation will be done in a loop. So it is in this loop you must do 3 things: 1. Generate a unique name for each dynamic control. This can be done by using the index of the loop appended to a constant that can also be read later when the control value is required. For example "ControlName" + index. 2. Read the name of the control back after it is added to the page. This can be done by using the UniqueID property in ASP.NET 2.0 or the ID property in ASP.NET 1.1 or before. Usually you will add the controls to an HTML table and dynamically generate the rows and columns in the table. 3. Store the name of the control somewhere for use the next time the page is posted. I used ViewState for this. The 3rd item is the key really. After generating the controls and adding them to the page, I created a string with the UniqueID of each control like this example. The string was actually created inside the loop, after the loop is finished you need to store the names. Dim First as Boolean = True Dim strNames as String = "" For intCount as Integer = 0 to Whatever.Length 'Create your table row, table cell, and add the control to the page here. 'Note that you will not be able to get the correct ID until after the control, table row, and table cell 'have all been added to the page. 'Generate the unique name for the control. Dim ctrl as New DropDownList (or other control) ctrl.ID = "ControlName" + intCount 'Read the UniqueID from the control. ASP.NET 2.0 will screw up your naming convention 'if you use child controls or master pages, so UniqueID will actually get the name used 'in the output HTML. If First Then strNames = ctrl.UniqueID First = False Else strNames += "," + ctrl.UniqueID End If Next When you are done looping, strNames will look something like this. "ControlName0,ControlName1,ControlName2" This value is then stored under a known ViewState value: ViewState("ControlNames") = strNames Now, when reading the values of the controls (presumably after the page posts back) you will have a way to identify them. You can load the names into an array for use in the loop that retrieves them by using the Split method to change the string back into an array. strNames = ViewState("ControlNames") Dim Names() As String = strNames.Split(",") Then after you create the array, loop through it using the same zero based index in the same order as you used to create the controls. Then you can use Page.FindControl(Names(index)) to create an instance of the control to use to retrieve the properties of the control. Keep in mind that FindControl only works on the current naming container, so you may need to analyze your page to find out what the naming container of your dynamic controls are. It is also very critical that the loop you use to create the controls is indexed exactly the same way as the loop you use to retreive the values or you will not have a way to retrieve the controls. NightOwl888 Hi! Can anyone please explain this for a textbox.text value? After I click a
button, all the controls disappear, and also the textboxes and their values, which I need in the next process. Thank you. Show quote "NightOwl888" wrote: > On Sep 8, 8:23 pm, "Nathan Sokalski" <njsokal***@hotmail.com> wrote: > > I have a custom control that I wrote (I inherit from > > System.Web.UI.WebControls.CompositeControl). I dynamically add this control > > to my Page, but I was told that dynamically added controls do not survive > > postback. This seems to be true. However, this seems to make dynamically > > adding controls rather pointless to me, since if you cannot retrieve the > > values of the controls when you perform a postback, why add the controls in > > the firstplace? Can someone help me figure out how to retrieve the property > > values of a dynamically added control? Thanks. > > -- > > Nathan Sokalski > > njsokal...@hotmail.comhttp://www.nathansokalski.com/ > > > I have a page with dynamically added controls that I retrieve the > values from. Basically, you just put the call to the dynamic control > creation in the Page_Init event and don't check IsPostBack because you > always want it to run. > > Populating the controls can be done in the Page_Load event, but in > this case you will need to check IsPostBack. Then, you can create a > procedure that can read the values of the controls and load them into > an object for use by the rest of your code. > > Typically control generation will be done in a loop. So it is in this > loop you must do 3 things: > > 1. Generate a unique name for each dynamic control. This can be done > by using the index of the loop appended to a constant that can also be > read later when the control value is required. For example > "ControlName" + index. > 2. Read the name of the control back after it is added to the page. > This can be done by using the UniqueID property in ASP.NET 2.0 or the > ID property in ASP.NET 1.1 or before. Usually you will add the > controls to an HTML table and dynamically generate the rows and > columns in the table. > 3. Store the name of the control somewhere for use the next time the > page is posted. I used ViewState for this. > > The 3rd item is the key really. After generating the controls and > adding them to the page, I created a string with the UniqueID of each > control like this example. The string was actually created inside the > loop, after the loop is finished you need to store the names. > > Dim First as Boolean = True > Dim strNames as String = "" > For intCount as Integer = 0 to Whatever.Length > 'Create your table row, table cell, and add the control to the > page here. > 'Note that you will not be able to get the correct ID until after > the control, table row, and table cell > 'have all been added to the page. > > 'Generate the unique name for the control. > Dim ctrl as New DropDownList (or other control) > ctrl.ID = "ControlName" + intCount > > 'Read the UniqueID from the control. ASP.NET 2.0 will screw up > your naming convention > 'if you use child controls or master pages, so UniqueID will > actually get the name used > 'in the output HTML. > If First Then > strNames = ctrl.UniqueID > First = False > Else > strNames += "," + ctrl.UniqueID > End If > Next > > When you are done looping, strNames will look something like this. > "ControlName0,ControlName1,ControlName2" > > This value is then stored under a known ViewState value: > > ViewState("ControlNames") = strNames > > > Now, when reading the values of the controls (presumably after the > page posts back) you will have a way to identify them. You can load > the names into an array for use in the loop that retrieves them by > using the Split method to change the string back into an array. > > strNames = ViewState("ControlNames") > Dim Names() As String = strNames.Split(",") > > Then after you create the array, loop through it using the same zero > based index in the same order as you used to create the controls. > Then you can use Page.FindControl(Names(index)) to create an instance > of the control to use to retrieve the properties of the control. Keep > in mind that FindControl only works on the current naming container, > so you may need to analyze your page to find out what the naming > container of your dynamic controls are. > > It is also very critical that the loop you use to create the controls > is indexed exactly the same way as the loop you use to retreive the > values or you will not have a way to retrieve the controls. > > > NightOwl888 > > As the previous poster mentioned, the short of it is, you need to create the
dynamic controls in the Page_Init event. You also need to be sure you give them the same ID (I believe). If you do that, then later in the page lifecycle (like in Page_Load or any other events) the control will contain its postback value. If you're going to add controls to a page dynamically, it would really be a good idea to get a firm grasp on the page life-cycle - how controls are created in Page_Init, how they are populated with postback values, etc. Actually, it's a good idea to know that stuff even if you don't use dynamic controls. There are some pretty good articles out there on the "how's" and "why's" of dynamic controls. Here's a start: http://aspnet.4guysfromrolla.com/articles/092904-1.aspx Show quote > Hi! Can anyone please explain this for a textbox.text value? After I click > a > button, all the controls disappear, and also the textboxes and their > values, > which I need in the next process. On 9 Sep, 04:23, "Nathan Sokalski" <njsokal***@hotmail.com> wrote: I hope I'm not at cross purposes here but I don't think that is true.> I have a custom control that I wrote (I inherit from > System.Web.UI.WebControls.CompositeControl). I dynamically add this control > to my Page, but I was told that dynamically added controls do not survive > postback. This seems to be true. However, this seems to make dynamically > adding controls rather pointless to me, since if you cannot retrieve the > values of the controls when you perform a postback, why add the controls in > the firstplace? Can someone help me figure out how to retrieve the property > values of a dynamically added control? Thanks. I too have been faced with the problem of creating web server controls dynamically and then having to work out how to handle postback events, or (in the case of check boxes) how to detect their state. For me the answer was to read the Key/Value pairs contained in Request.Form For this to work it's important to assign a value to the ID field of the control when creating it, else it will indeed get lost. Admittedly I wasn't working with custom controls but I imagine the principle is the same based on inheritance from base classes. Phil Hall Create dynamic control each time (Postback or First time) in Page Init
event to load values for control from viewstate or let you use viewstate.Then store all these controls into a object array. Now In case of postback in Button Click event, you can loop through controls object array you made while creating these controls. Where you can get all chabged calues of these controls. For example: in VB .Net For Each ctrl As Object In objCtrls If (Not Nothing Is ctrl) Then 'Expecting all tab controls will have save button inside them. ctrl.Save() End If Next Hope it will help you, Lemme know if you need clarifications. Regards, AKS http://www.aksClassifieds.com http://forums.aksClassifieds.com  |
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