I have a ASP.NET GridView that uses template columns and user controls to allow me to dynamically construct the datagrid. Now I'm implementing the event handler for inserting a row. To do that, I create an array of default values and add it to the data table which is acting as a data source. However, when my OnLoad event is fired on postback, all my template columns no longer have the user controls. My gridview ends up just being all blank with nothing in it and my button column disappears as well (which contains the add row, delete row and save buttons).
My row add event just does this:
public void AddDataGridRow()
{
List<object> defRow = new List<object>();
for (int i = 0; i < fieldNames.Count; i++)
{
defRow.Add(GetDefaultValueFromDBType(types[i]));
}
dt.Rows.Add(defRow);
}
It is fired from a button in a user control that's implement like this:
protected void Button1_Click(object sender, EventArgs e)
{
((Scoresheet)(this.Page)).AddDataGridRow();
}
My on load event does a bunch of stuff on first run to set the GridView up but I don't run that again by using the IsPostBack property to tell.
protected void Page_Load(object sender, EventArgs e)
{
if (!IsPostBack)
Initialize();
}
Anyone have any hints as to why my user controls are vanishing?
You have to add the controls to the grid on every page_load, not just if it's (!Postback)
Do you have the EnableViewState=true on the usercontrols and the GridView?
Is the AddDataGridRow() method called by Initialize()? You basically have two options:
Bind the grid on every postback and do not use viewstate (performace loss)
Bind the Grid only the first time (if (!IsPostBack)), and make sure that your user controls keep their viewstate.
From your code, it is not clear whether the user controls keep viewstate and what they have in them. It is not even clear what is the execution order of the methods you've shown. There is no binding logic, so even if you keep adding rows, the grid may still not be bound. Please elaborate a bit and show the whole page codebehind.
Related
I have an webforms ASPX page, which has a dynamically added user control. The user control has two DropDownLists, one is in an UpdatePanel as its items depend on the selection in the first DropDownList.
The problem is that if you do not change the value of the first DropDownList the value of the second DropDownList does not get saved. If you do change the value of the first DropDownList then it works fine.
This is how it works briefly...
The first time the page loads, the previous values are set. This happens in the main ASPX page Page_Load event where the user control is dynamically added and the initial values are set through a property of the user control. The property sets the selected value of the first DropDownList, triggers the SelectedIndexChanged event which populates items in the second DropDownList with choices based on the first DropDownList selection, and then selects the previous value of the second DropDownList.
Then in the main ASPX page, the user control is dynamically added again on post back in the PreLoad event.
Viewstate is fully enabled throughout.
I have debugged and on post back the second DropDownList has no Items. Even during the UpdatePanel partial post back the items collection is empty. However, if the first DropDownList is changed then the Items collection is correct - it's only if the second DropDownList is last populated on the initial load that the problem happens.
Here's the relevant parts of the code...
Any help greatly appreciated.
ASPX page:
protected void Page_PreLoad(object sender, EventArgs e)
{
if (Page.IsPostBack)
{
PopulateTemplateOptions();
}
}
protected void PopulateTemplateOptions(bool init = false)
{
//this is where the control is dynamically added
//If not post back then initial values are set by passing values to
//user control's TemplateOptions property
}
User control:
public string TemplateOptions
{
set
{
//this is where the initial values are set
}
}
protected void ddlEnquirySubjectDefault_SelectedIndexChanged(object sender, EventArgs e)
{
//this is where items are added to the second drop down list based on the selection in the first one.
}
(These are the only parts that are relevant, but there's another 7,000 lines of code I didn't include.)
Here are two of my ideas:
1) This line might be wrong in your code: if (Page.IsPostBack)
It must be if (!Page.IsPostBack), although I never used Page_PreLoad event so I am not sure if it is right.
2) Try to do what you want in Page_Init event instead. I use it on my projects, without problem.
I have a GridView with dynamically created image buttons that should fire command events when clicked. The event handling basically works, except for the very first time a button is clicked. Then, the postback is processed, but the event is not fired.
I have tried to debug this, and it seems to me, that the code executed before and after the first click is exactly the same as for any other clicks. (With the exception that in the first click, the event handler is not called.)
There is some peculiarity in that: The buttons which fire the event are created dynamically through databinding, i.e. databinding must be carried out twice in the page lifecycle: Once on load, in order to make the buttons exist (otherwise, events could not be handled at all), and once before rendering in order to display the new data after the events have been processed.
I have read these posts but they wouldn't match my situation:
ASP.NET LinkButton OnClick Event Is Not Working On Home Page,
LinkButton not firing on production server,
ASP.NET Click() event doesn't fire on second postback
To the details:
The GridView contains image buttons in each row. The images of the buttons are databound. The rows are generated by GridView.DataBind(). To achieve this, I have used the TemplateField with a custom ItemTemplate implementation. The ItemTemplate's InstantiateIn method creates the ImageButton and assigns it the according event handler. Further, the image's DataBinding event is assigned a handler that retrieves the appropriate image based on the respective row's data.
The GridView is placed on a UserControl. The UserControl defines the event handlers for the GridView's events. The code roughly looks as follows:
private DataTable dataTable = new DataTable();
protected SPGridView grid;
protected override void OnLoad(EventArgs e)
{
DoDataBind(); // Creates the grid. This is essential in order for postback events to work.
}
protected override void Render(HtmlTextWriter writer)
{
DoDataBind();
base.Render(writer); // Renews the grid according to the latest changes
}
void ReadButton_Command(object sender, CommandEventArgs e)
{
ImageButton button = (ImageButton)sender;
GridViewRow viewRow = (GridViewRow)button.NamingContainer;
int rowIndex = viewRow.RowIndex;
// rowIndex is used to identify the row in which the button was clicked,
// since the control.ID is equal for all rows.
// [... some code to process the event ...]
}
private void DoDataBind()
{
// [... Some code to fill the dataTable ...]
grid.AutoGenerateColumns = false;
grid.Columns.Clear();
TemplateField templateField = new TemplateField();
templateField.HeaderText = "";
templateField.ItemTemplate = new MyItemTemplate(new CommandEventHandler(ReadButton_Command));
grid.Columns.Add(templateField);
grid.DataSource = this.dataTable.DefaultView;
grid.DataBind();
}
private class MyItemTemplate : ITemplate
{
private CommandEventHandler commandEventHandler;
public MyItemTemplate(CommandEventHandler commandEventHandler)
{
this.commandEventHandler = commandEventHandler;
}
public void InstantiateIn(Control container)
{
ImageButton imageButton = new ImageButton();
imageButton.ID = "btnRead";
imageButton.Command += commandEventHandler;
imageButton.DataBinding += new EventHandler(imageButton_DataBinding);
container.Controls.Add(imageButton);
}
void imageButton_DataBinding(object sender, EventArgs e)
{
// Code to get image URL
}
}
Just to repeat: At each lifecycle, first the OnLoad is executed, which generates the Grid with the ImageButtons. Then, the events are processed. Since the buttons are there, the events usually work. Afterwards, Render is called, which generates the Grid from scratch based upon the new data. This always works, except for the very first time the user clicks on an image button, although I have asserted that the grid and image buttons are also generated when the page is sent to the user for the first time.
Hope that someone can help me understand this or tell me a better solution for my situation.
A couple problems here. Number one, there is no IsPostBack check, which means you're databinding on every load... this is bound to cause some problems, including events not firing. Second, you are calling DoDataBind() twice on every load because you're calling it in OnLoad and Render. Why?
Bind the data ONCE... and then again in reaction to events (if needed).
Other issue... don't bind events to ImageButton in the template fields. This is generally not going to work. Use the ItemCommand event and CommandName/CommandArgument values.
Finally... one last question for you... have you done a comparison (windiff or other tool) on the HTML rendered by the entire page on the first load, and then subsequent loads? Are they EXACTLY the same? Or is there a slight difference... in a control name or PostBack reference?
Well I think the event dispatching happens after page load. In this case, its going to try to run against the controls created by your first data-binding attempt. This controls will have different IDs than when they are recreated later. I'd guess ASP.NET is trying to map the incoming events to a control, not finding a control, and then thats it.
I recommend taking captures of what is in the actual post.
ASP.NET is pretty crummy when it comes to event binding and dynamically created controls. Have fun.
Since in my opinion this is a partial answer, I re-post it this way:
If I use normal Buttons instead of ImageButtons (in the exact same place, i.e. still using MyItemTemplate but instantiating Button instead of ImageButton in "InstantiateIn", it works fine.
If I assert that DoDataBind() is always executed twice before sending the content to the client, it works fine with ImageButtons.
Still puzzled, but whatever...
I renew parameters of my DataSource for GridView on Button and loads event Page_Load()
and After it (or with it) GridView renews itself.
I need to rename Header rows but there is no event after Page Load.
more information about details here :
[On Button Click] I change DataSource and Bind it (SqlDataSource1.DataBind(); ) Then sure Page gone to Refresh elements.
[On Page_Load] GridView is changing data, but if I can't change Headers there because it's looking like loads after this function :(
[one more Button] I can add new button with a function - rename headers and it works correct everytime
protected void Button2_Click(object sender, EventArgs e)
{
// Stack overflow
DataRow T;
if (go)
if (GridView2.HeaderRow.Cells.Count != 0)
for (int i = 0; i < SQF.SQF.Permission.Rows.Count; i++)
{
T = SQF.SQF.Permission.Rows[i];
GridView2.HeaderRow.Cells[i].Text = (string)T["Caption1"];
WebMsgBox.Show((string)T["Caption1"]);
}
}
Trouble : I no need one more button for it, I need to rename header rows after I click button to change Data but I have no idea where I can do it.
thank you.
Well you could use Gridview DataBound event, like that:
<asp:GridView runat="server" ID="SomeID" OnDataBound="GridVIew_OnDataBound" ... />
The DataBound event occurs right after the databinding process for that particular control has completed.
After Page_Load there is an event Page.PreRender.
Maybe it will suit you.
EDIT.
All events of your components, such as GridView, are fired between Page.Load and Page.PreRender. Consider using RowDataBound and RowUpdated events.
Here's the scenario:
-Gridview control
-Calendar control
I only want the calendar to show if a specific item is chosen in the drop down list which is in a gridview. When the grid view row is updated I want to change whether or not the calendar is visible. The calendar's visibility only shows correctly on the next post back.
Page_Load is called before events which are called before Render. There is no reason why you couldn't, in your event, check the value of the dropdownlist and set the Calendar control visible property, this would then knock into Render.
Try adding a check of IsPostBack before setting the loading your GridView. That will prevent you from overwriting it's values.
protected void Page_Load(object sender, EventArgs e) {
if(!IsPostBack) {
/*Populate your GridView*/
}
}
protected void GridView_RowUpdated(object sender, GridViewUpdatedEventArgs e)
{
/*show your calendar here if you need to*/
if(whatever) calendar.Visible = true;
}
This should work, if it doesn't then I'd recommend putting breakpoints in your Page_Load and RowUpdated methods and stepping through it, preferrably with a Watch on the gridview's datasource (it'll go red if it's changed) and a watch on calendar.Visible, to help you see if something has changed.
For the record, control events like OnRowUpdated will never fire before Page_Load unless explicitly called for some reason. Chances are you're just doing something where it's not updating the content of the GridView before it gets to the RowUpdated method, or it's overwriting the data in the GridView due to a lack of !IsPostBack check.
1) I noticed that if we don’t bind GridView to object data source control, then when user puts GridView into edit mode, we have to handle GridView.RowEditing event (else we get an exception ) and in this event put GridView’s row into editing mode. Is there a reason why GridView doesn’t automatically put a row into edit mode?
2) When we manually bind GridView to one of DataSet’s tables and user puts a row into edit mode, row’s columns will replace fields with text boxes. But for some reason these text boxes don’t display current field values, but instead they don’t display any text at all. What am I doing wrong?
3) I’ve also handled gridView.RowUpdated event, so I could put row back into non-edit mode, but to no effect. I even tried by pressing Edit button of some other row, but row still wouldn’t go out of edit mode. Any ideas what I’m doing wrong?
protected void gvwEmployees_RowUpdated(object sender, GridViewUpdatedEventArgs e)
{
e.KeepInEditMode = false;
}
Thanx
When not using a DataSource control with a GridView or other data-bound control which hide the complexity of the manual data-binding you must manually handle RowEditing, RowUpdating, and RowDeleting etc. With the built in data model and automatic binding the GridView handles these events for you.
You haven't posted your RowEditing code, but i suspect that you are not setting the GridViews EditIndex to the NewEditIndex and are not rebinding, this is probably why you are not seeing current data.
protected void gvwEmployees_RowEditing(object sender, GridViewEditEventArgs e)
{
GridView.EditIndex = e.NewEditINdex;
BindData();
}
The same is true for your RowUpdating event. You will have to manually update your data, then set the EditIndex to -1, this will put your GridView back into ReadOnly mode. Keep in mind that e.OldValues, e.NewValues and e.Keys properties of the GridViewUpdateEventArgs are not populated when binding manually. This mean you'll have to take care of the update yourself by using e.RowIndex which is the index of the edited row.
protected void gvwEmployees_RowUpdating(object sender, GridViewUpdateEventArgs e)
{
GridView.EditIndex = -1;
BindData();
}