Vista - Re: HOW: Read dynamic control on postback

04-09-2009

Hello JP,

Quote:

> I think I finally got this thing figured out. Granted it takes a bit
> of code.
>
> Basically I'm generating the dynamic controls in the
> gridview.RowDataBound() Then in GridView.DataBound() if EVENTTARGET
> that generates the GridView is what fired the AJAX post back, I'm
> cycling though all the controls for each row in the given cell and
> adding them to a Control[row#,control object] type array so I can
> maintain all the properties that were set. I then store this array in
> a session.
>
> Then on post back, I check the page EVENTTARGET to ensure that the
> object that generated the full post back was the submit button
> otherwise I don't want to waste time cycling through the array.
>
> I make sure the session value is not null and convert it back to the
> Control[,] array. I cycling though the array OnPage_Load, I simply
> cycle though GridViewRows and do Controls.Add to the cell using the
> object stored in the array.
>
> So far seems to work. I have some other tweaks I need to make though
> but I've gotten over a major hurdle.
>
> You have been a huge help.

Instead of adding them to the session, I'd put it in the viewstate, as the
data is page specific.

It was a pleasure helping

.

Jesse

Quote:

>
> "Jesse Houwing" wrote:
>

Quote:

>> Hello JP,
>>

Quote:

>>> Ok, this might pose a problem then if the dynamic controls are in a
>>> GridView.
>>>
>>> In the page life cycle Page_Init occurs before Page_Load with
>>> viewsate becoming available just before Page_Load occurs.
>>>
>>> The way I understand it is that on postback ,the dynamic controls
>>> have be added to the back to the collection in the Page_Init method.
>>> Since this method occurs before the Page_Load method, there is no
>>> GridView object to add the controls back to because the postback
>>> data wont regenerate the gridview until it executes the Page_Load
>>> Method.
>>>

>> It's always tricky to find the right spot... At some point
>> EnsureChildControls(); is called on the page. After that it should be
>> in the right state. You can override EnsureChildControls to add the
>> controls where needed at the right time. The grid control will make
>> sure it will have empty rows added, no data just yet. That's the time
>> to ensure your textboxes get in there as well.
>>
>> JEsse
>>

Quote:

>>> "Jesse Houwing" wrote:
>>>
>>>> Hello JP,
>>>>
>>>>> So what you are saying is that after the user clicks submit
>>>>> (postback), I still have to add the control back to the
>>>>> collection, before I can see what the user typed? If thats true,
>>>>> how does the view state know that the properties belong to the
>>>>> dynamic control?
>>>>>
>>>> The value has been added to the viewstate in the same tree
>>>> structure as the controls were in. The control will get the right
>>>> values from the viewstate as long as you add it as follows:
>>>>
>>>> TextBox tb = new TextBox();
>>>> tb.ID = "id";
>>>> row.Add(tb);
>>>> e.g. It is important to set the ID before adding the control to the
>>>> tree.
>>>> Anything else, you need to set after adding the control to the
>>>> control tree, that way anything which was written from ViewState
>>>> will succesfully be read and applied, before any other changes are
>>>> done to the control.
>>>>
>>>>> I assume this is where the protected override void
>>>>> OnInit(EventArgs e) comes in to play? In this particular
>>>>> situation, I do want to maintain the value for postback solely for
>>>>> the purposes of storing it in the database, but I do not want to
>>>>> re-render the page after the postback.
>>>>>
>>>> The Grid usually has a RowCreated event, which will be fired when
>>>> the control tree is being recreated. That is the moment you can
>>>> safely add the control and re-apply eventsubscriptions for teh
>>>> specific control. This will also allow any event you subscribed to
>>>> to be fired after Page_Load.
>>>>
>>>> Then later in a databinding event, or in or after the Page_Load,
>>>> you can change any value in the control or remove it altogether.
>>>>
>>>> Jesse
>>>>
>>>>> "Jesse Houwing" wrote:
>>>>>
>>>>>> Hello JP,
>>>>>>
>>>>>> Did you re-add the control to the grid before reading it's value?
>>>>>> A dynamically added crontrol will need to be added back to the
>>>>>> control tree on every subsequent request, should you want to
>>>>>> access its value...
>>>>>>
>>>>>> Jesse
>>>>>>
>>>>>>> You are absolutely correct. I mistakenly typed my example in
>>>>>>> this message. This statement is inside a foreach loop that
>>>>>>> should have read as follows:
>>>>>>>
>>>>>>> foreach (GridViewRow gvr in gridQuestions.Rows)
>>>>>>> {
>>>>>>> //txtTransID is the dynamically generated control but this
>>>>>>> always
>>>>>>> returns null or error
>>>>>>> string a = ((TextBox)gvr.FindControl("txtTransID")).Text;
>>>>>>> }
>>>>>>> "Jesse Houwing" wrote:
>>>>>>>> Hello JP,
>>>>>>>>
>>>>>>>>> I created a page that has dynamically created TextBox or
>>>>>>>>> DropDownList controls.
>>>>>>>>>
>>>>>>>>> However once the text box is filled in and I submit the page,
>>>>>>>>> I cannot find the dynamic control. I have been all over the
>>>>>>>>> net looking for an answer. I read the article from
>>>>>>>>> 4GuysFromRolla but it still does not answer my question.
>>>>>>>>>
>>>>>>>>> How to I retrieve the values from a dynamically created
>>>>>>>>> control on postback?
>>>>>>>>>
>>>>>>>>> This was the name of the control I added to a GridView (AJAX
>>>>>>>>> call)
>>>>>>>>>
>>>>>>>>> TextBox controlTextBox = new TextBox();
>>>>>>>>> controlTextBox.EnableViewState = true;
>>>>>>>>> controlTextBox.ID = "txt" +
>>>>>>>>> drControls["controlName"].ToString();
>>>>>>>>> controlTextBox.MaxLength = 6;
>>>>>>>>> controlTextBox.Width = 150;
>>>>>>>>> controlTextBox.Enabled = true;
>>>>>>>>> controlTextBox.Visible = true;
>>>>>>>>> controlTextBox.Attributes.Add("runat", "server"); //just for
>>>>>>>>> the
>>>>>>>>> heck of it
>>>>>>>>> e.Row.Cells[2].Controls.Add(controlTextBox);
>>>>>>>>> (All is well at this point and the control is visible on the
>>>>>>>>> page)
>>>>>>>>> if(IsPostBack)
>>>>>>>>> {
>>>>>>>>> //Control never found
>>>>>>>>> string Answer=
>>>>>>>>> ((TextBox)GridView.FindControl("txtTransID")).Text;
>>>>>>>>> }
>>>>>>>>> I understand that the control itself (GUI representation)
>>>>>>>>> needs
>>>>>>>>> to
>>>>>>>>> be
>>>>>>>>> recreated, but should not the control properties be in the
>>>>>>>>> viewstate
>>>>>>>>> to access them?
>>>>>>>>> PLEASE HELP! Does anyone have a working example? I could care
>>>>>>>>> less
>>>>>>>>> that the controls get re-rendered on the postback as they get
>>>>>>>>> redirected to a different screen after the data saves, but I
>>>>>>>>> really
>>>>>>>>> need to just access the value
>>>>>>>> The control is added to a naming container (the grid), which
>>>>>>>> makes sure the control name is unique per row (each row will
>>>>>>>> contain the specified textbox).
>>>>>>>>
>>>>>>>> So you'll have to query the specific row of the grid control in
>>>>>>>> order to use FindControl.
>>>>>>>>
>>>>>>>> eg
>>>>>>>>
>>>>>>>> foreach (GridRow r in Grid.Rows)
>>>>>>>> {
>>>>>>>> r.FindControl("txtTransID");
>>>>>>>> }
>>>>>>>> should do the trick
>>>>>>>> --
>>>>>>>> Jesse Houwing
>>>>>>>> jesse.houwing at sogeti.nl
>>>>>> --
>>>>>> Jesse Houwing
>>>>>> jesse.houwing at sogeti.nl
>>>> --
>>>> Jesse Houwing
>>>> jesse.houwing at sogeti.nl

>> --
>> Jesse Houwing
>> jesse.houwing at sogeti.nl

--
Jesse Houwing
jesse.houwing at sogeti.nl

04-09-2009	#1 (permalink)
Jesse Houwing n/a posts	Re: HOW: Read dynamic control on postback Hello JP, Quote: > I think I finally got this thing figured out. Granted it takes a bit > of code. > > Basically I'm generating the dynamic controls in the > gridview.RowDataBound() Then in GridView.DataBound() if EVENTTARGET > that generates the GridView is what fired the AJAX post back, I'm > cycling though all the controls for each row in the given cell and > adding them to a Control[row#,control object] type array so I can > maintain all the properties that were set. I then store this array in > a session. > > Then on post back, I check the page EVENTTARGET to ensure that the > object that generated the full post back was the submit button > otherwise I don't want to waste time cycling through the array. > > I make sure the session value is not null and convert it back to the > Control[,] array. I cycling though the array OnPage_Load, I simply > cycle though GridViewRows and do Controls.Add to the cell using the > object stored in the array. > > So far seems to work. I have some other tweaks I need to make though > but I've gotten over a major hurdle. > > You have been a huge help. Instead of adding them to the session, I'd put it in the viewstate, as the data is page specific. It was a pleasure helping . Jesse Quote: > > "Jesse Houwing" wrote: > Quote: >> Hello JP, >> Quote: >>> Ok, this might pose a problem then if the dynamic controls are in a >>> GridView. >>> >>> In the page life cycle Page_Init occurs before Page_Load with >>> viewsate becoming available just before Page_Load occurs. >>> >>> The way I understand it is that on postback ,the dynamic controls >>> have be added to the back to the collection in the Page_Init method. >>> Since this method occurs before the Page_Load method, there is no >>> GridView object to add the controls back to because the postback >>> data wont regenerate the gridview until it executes the Page_Load >>> Method. >>> >> It's always tricky to find the right spot... At some point >> EnsureChildControls(); is called on the page. After that it should be >> in the right state. You can override EnsureChildControls to add the >> controls where needed at the right time. The grid control will make >> sure it will have empty rows added, no data just yet. That's the time >> to ensure your textboxes get in there as well. >> >> JEsse >> Quote: >>> "Jesse Houwing" wrote: >>> >>>> Hello JP, >>>> >>>>> So what you are saying is that after the user clicks submit >>>>> (postback), I still have to add the control back to the >>>>> collection, before I can see what the user typed? If thats true, >>>>> how does the view state know that the properties belong to the >>>>> dynamic control? >>>>> >>>> The value has been added to the viewstate in the same tree >>>> structure as the controls were in. The control will get the right >>>> values from the viewstate as long as you add it as follows: >>>> >>>> TextBox tb = new TextBox(); >>>> tb.ID = "id"; >>>> row.Add(tb); >>>> e.g. It is important to set the ID before adding the control to the >>>> tree. >>>> Anything else, you need to set after adding the control to the >>>> control tree, that way anything which was written from ViewState >>>> will succesfully be read and applied, before any other changes are >>>> done to the control. >>>> >>>>> I assume this is where the protected override void >>>>> OnInit(EventArgs e) comes in to play? In this particular >>>>> situation, I do want to maintain the value for postback solely for >>>>> the purposes of storing it in the database, but I do not want to >>>>> re-render the page after the postback. >>>>> >>>> The Grid usually has a RowCreated event, which will be fired when >>>> the control tree is being recreated. That is the moment you can >>>> safely add the control and re-apply eventsubscriptions for teh >>>> specific control. This will also allow any event you subscribed to >>>> to be fired after Page_Load. >>>> >>>> Then later in a databinding event, or in or after the Page_Load, >>>> you can change any value in the control or remove it altogether. >>>> >>>> Jesse >>>> >>>>> "Jesse Houwing" wrote: >>>>> >>>>>> Hello JP, >>>>>> >>>>>> Did you re-add the control to the grid before reading it's value? >>>>>> A dynamically added crontrol will need to be added back to the >>>>>> control tree on every subsequent request, should you want to >>>>>> access its value... >>>>>> >>>>>> Jesse >>>>>> >>>>>>> You are absolutely correct. I mistakenly typed my example in >>>>>>> this message. This statement is inside a foreach loop that >>>>>>> should have read as follows: >>>>>>> >>>>>>> foreach (GridViewRow gvr in gridQuestions.Rows) >>>>>>> { >>>>>>> //txtTransID is the dynamically generated control but this >>>>>>> always >>>>>>> returns null or error >>>>>>> string a = ((TextBox)gvr.FindControl("txtTransID")).Text; >>>>>>> } >>>>>>> "Jesse Houwing" wrote: >>>>>>>> Hello JP, >>>>>>>> >>>>>>>>> I created a page that has dynamically created TextBox or >>>>>>>>> DropDownList controls. >>>>>>>>> >>>>>>>>> However once the text box is filled in and I submit the page, >>>>>>>>> I cannot find the dynamic control. I have been all over the >>>>>>>>> net looking for an answer. I read the article from >>>>>>>>> 4GuysFromRolla but it still does not answer my question. >>>>>>>>> >>>>>>>>> How to I retrieve the values from a dynamically created >>>>>>>>> control on postback? >>>>>>>>> >>>>>>>>> This was the name of the control I added to a GridView (AJAX >>>>>>>>> call) >>>>>>>>> >>>>>>>>> TextBox controlTextBox = new TextBox(); >>>>>>>>> controlTextBox.EnableViewState = true; >>>>>>>>> controlTextBox.ID = "txt" + >>>>>>>>> drControls["controlName"].ToString(); >>>>>>>>> controlTextBox.MaxLength = 6; >>>>>>>>> controlTextBox.Width = 150; >>>>>>>>> controlTextBox.Enabled = true; >>>>>>>>> controlTextBox.Visible = true; >>>>>>>>> controlTextBox.Attributes.Add("runat", "server"); //just for >>>>>>>>> the >>>>>>>>> heck of it >>>>>>>>> e.Row.Cells[2].Controls.Add(controlTextBox); >>>>>>>>> (All is well at this point and the control is visible on the >>>>>>>>> page) >>>>>>>>> if(IsPostBack) >>>>>>>>> { >>>>>>>>> //Control never found >>>>>>>>> string Answer= >>>>>>>>> ((TextBox)GridView.FindControl("txtTransID")).Text; >>>>>>>>> } >>>>>>>>> I understand that the control itself (GUI representation) >>>>>>>>> needs >>>>>>>>> to >>>>>>>>> be >>>>>>>>> recreated, but should not the control properties be in the >>>>>>>>> viewstate >>>>>>>>> to access them? >>>>>>>>> PLEASE HELP! Does anyone have a working example? I could care >>>>>>>>> less >>>>>>>>> that the controls get re-rendered on the postback as they get >>>>>>>>> redirected to a different screen after the data saves, but I >>>>>>>>> really >>>>>>>>> need to just access the value >>>>>>>> The control is added to a naming container (the grid), which >>>>>>>> makes sure the control name is unique per row (each row will >>>>>>>> contain the specified textbox). >>>>>>>> >>>>>>>> So you'll have to query the specific row of the grid control in >>>>>>>> order to use FindControl. >>>>>>>> >>>>>>>> eg >>>>>>>> >>>>>>>> foreach (GridRow r in Grid.Rows) >>>>>>>> { >>>>>>>> r.FindControl("txtTransID"); >>>>>>>> } >>>>>>>> should do the trick >>>>>>>> -- >>>>>>>> Jesse Houwing >>>>>>>> jesse.houwing at sogeti.nl >>>>>> -- >>>>>> Jesse Houwing >>>>>> jesse.houwing at sogeti.nl >>>> -- >>>> Jesse Houwing >>>> jesse.houwing at sogeti.nl >> -- >> Jesse Houwing >> jesse.houwing at sogeti.nl -- Jesse Houwing jesse.houwing at sogeti.nl
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