In an ASP.NET page I have added two user control with a dropdownlist each one. The selection of a dropdownlist should be changed the query to the second user control.
What is the most efficient way to pass the selected value of dropdownlist to the second?
I initially thought of creating a public event (public string OnClientSelectedIndexChanged) while the first user control and outsource through a public string SelectedValue the selected value of the second user control:
public string SelectedValue
{
get
{
rcg.SelectedValue return;
}
set
{
rcg.SelectedValue = value;
}
}
rcg is the dropdownlist.
Could be corrected or have alternatives?
Thanks in advance
Alternative is maybe to use AJAX.
Surround the two dropdownlist with an ASP update panel and trigger this one with the first dropdownlist 'OnSelectedIndexChanged'. In the event's code you can bind your second dropdownlist..
Like this it is not necessary to reload the entire page for each first dropdownlist change..
Yes, you are on right track.
1: You expose an event from UC1(e.g. uc1ddlchanged) and a property from UC2 (e.g. uc1ddlSelectedValue).
2: In the OnSelectedIndexChanged of ddl1 in UC1 your raise the event uc1ddlchanged.
3: On your page that has UC1 and UC2 you handle this event and set the UC2.uc1ddlSelectedValue = UC1.SelectedValue
4: In the UC2 -> uc1ddlSelectedValue -> set{} you can set the value and rebind your ddl and or do any other thing needed to update the UC2.
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 checkboxlist control that I need to check the values of when a Submit button is clicked by the user onscreen(C#).
This checkboxlist is part of a user control that I am referencing within my page markup.
However, when I check the values of the checkboxlist within the code of the submit button, all of the values are gone (i.e it says there are no items at all in the checkboxlist control).
Anyone know why this would be happening? I am doing the exact same thing in code in another place with another checkboxlist user control and it works perfectly.
I don't have my exact code to hand but below is a simplified version of what I am doing.
Basically I am binding data to the Checkboxlist only when it is NOT a postback on the usedr control.
USER CONTROL WHICH CONTAINS ONLY THE CHECKBOXLIST CONTROL Page_Load()
If(!IsPostBack)
{
foreach(var item in myVals)
{
ListItem i = new ListItem();
i.Text = item.Text;
i.Value = item.Value;
i.Selected = false;
myCheckBoxListControl.Add(i);
}
}
Now I have a submit button function which checks the values in the checkboxlist...
SubmitButton_Click()
{
foreach(ListItem item in myCheckBoxListControl.Items)
{
// process each one here. The code never gets in here as there are never any items in the checkboxlist
}
}
Anyone know why the CheckboxList has lost all of its items by the time the submit button function gets executed? The checkboxlist has EnableViewState set to true.
I have a dynamically created bill of material with each line item being a dynamic user_control. the user_control has a textbox for quantity entry. When I click the submit button i'd like to get all the quantities from each textbox but the controls have all disappeard on the page load and the page shows zero controls.
I know you can turn on autopostback for the textbox then catch each individual text_changed_event but that doesn't seem efficient. I'd like to just loop through all of them when user clicks submit button, then take them back to the same bill of material page.
First of all the reason why controls disappear on postback is that they were added to your page dynamically and when postback occurred the information about the dynamic controls were lost and page had no information about these dynamic controls.
Now about getting the values from controls inside dynamic user controls, you have use the FindControl method or have to iterate through the Controls collection of user control to get the reference to TextBoxes.
An idea about how to do this:
//1. Using ID of user control
//inside button_click method
protected void btnSubmit_Click(...)
{
TextBox txt1 = idOfUserControl.FindControl(textBoxId);
}
//2. Using type of user control
//inside button_click method
protected void btnSubmit_Click(...)
{
foreach(Control c in Page.Controls)
if(c is YourUserControlClass)
{
YourUserControlClass control = (YourUserControlClass)c;
TextBox txt1 = c.FindControl(textBoxId);
}
}
So I have a ListView (assignmentsListView) in an UpdatePanel, being filtered by a DropDownList in the same UpdatePanel. The DropDownList has a list of persons in it and uses autopostback, and the ListView shows the tasks those persons are assigned to.
I am trying to use code similar to this:
protected void assignmentsListView_DataBound(object sender, EventArgs e)
{
string resFirstName = Utilities.getResourceFirstName(resDdl.SelectedValue);
if (assignmentsListView.Items.Count <= 0)
{
//Show error message
}
else
{
//Try to find the ImageButton in the ListView's header template.
ImageButton exportButton = (ImageButton)assignmentsListView.FindControl("ImageButton3");
//Register this button as a PostBack event in the Master Page
ScriptManager scriptManager = ScriptManager.GetCurrent(this.Page);
ScriptManager.RegisterPostBackControl(exportButton);
}
}
When I first load the page, the DropDownList shows the first person in the list, and the ListView correctly shows that persons tasks.
If I then select a person who I know has zero tasks, I get an error at the RegisterPostBackControl() method, saying the passed-in control cannot be null.
When debugging, at the RegisterPostBackControl method, it shows that the ListView Items collection has >0 elements in it (the number of elements matches the person selected before the current person).
What's going on? Any suggestions?
In Asp.Net Web Forms applications, the order of events are not always what you'd want. For your case, the new person selection is probably applied after this method is executed. The best thing you could do is force databindings in an earlier event (like Page_Init)
Given the following
public class MyControl : CompositeControl
{
private DropDownList myList;
protected override void CreateChildControls()
{
base.CreateChildControls();
myList = new DropDownList();
myList.AutoPostBack = true;
this.Controls.Add(myList);
if (!Page.IsPostBack)
{
myList.DataSource = MyBLL.SomeCollectionOfItems;
myList.DataBind();
}
}
}
I find that the items in the list persist properly, but when a different control is rendered and then this one is rendered again, the last selected item is not persisted. (The first item in the list is always selected instead)
Should the last selected item be persisted in ViewState automatically, or am I expecting too much?
I think this is a hidden ViewState issue. You create and bind a control in CreateChildControls. You should only create the control at this place. Move the binding code to the classes load event and use EnsureChildControls.
Here is the solution which is best recommended. It lies in understandng the Page Life Cycle correctly!! Postback Controls like Drop Down List restore their posted state (the selected item of a Drop Down List posted). It forgets its selected value because you are rebinding it in Page_Load event, which is after the Drop Down List has been loaded with posted value (because View State is loaded after Page_Init event and before Page_Load event). And in this rebinding in Page_Load event, the Drop Down List forgets its restored selected item. The best solution is to perform the Data Binding in the Page_Init event instead of Page_Load event.
Do something like the below...
Suppose Drop Down List name is lstStates.
protected void Page_Init(object sender, EventArgs e)
{
lstStates.DataSource = QueryDatabase(); //Just an example.
lstStates.DataTextField = "StateName";
lstStates.DataValueField = "StateCode";
lstStates.DataBind();
}
ASP.NET loads control's View State after Page_Init event and before Page_Load event, so Drop Down List's selectedIndex will not be affected, and you will get desired results magically!!