问题
On a page I have:
<asp:TextBox runat="server" ID="EmailTextBox" AutoPostBack="true" OnTextChanged="EmailTextBox_Changed" />
<asp:Button runat="server" ID="SearchButton" OnClick="AddButton_Click" Text="add" />
In EmailTextBox_Changed, it counts up how many emails can be found, before running the search.
The problem is, when you type something in EmailTextBox, and click on the button, you have to click twice to get the actual results up. This is because the first click is doing the "AutoPostBack" part from the text box, and then you have to click again to make the actual click postback to happen.
Without removing the "AutoPostBack=true", how can I stop it needing two clicks in these circumstances?
回答1:
I was looking for an answer to this issue as well. I ended up removing all autopostback=true and doing all the actions with JavaScript, same as you.
However, one of the things I experimented with before the JavaScript was something to maintain control focus after a postback. I noticed the hidden field I used to store the name of the control that had the last focus DID have the name of the search button (mine is a save button). So, while I'm still not sure how to get the 'search' function to fire 'automatically' like it should, which is basically to chain the postback events from both the textbox AND the button together one after another, I CAN know that the user clicked that save button before the postback happened (or tried to).
So, what you have on postback is your textbox event firing, and then the Page_Load method, or whatever page cycle method you want to use, where you can check to see what the last control to have focus was. With this, there are several ways you could implement a work around.
Off hand, you could add code in every event that fires from a control autopostback, like the textbox and the search button, to check the name of the focus control. If the control that had focus last is NOT the control's autopostback function we are running, we can set a page level bool called 'Run_Controls_Method' to TRUE, else, set it to false. This way we know we should run the control that had last focus postback method.
On page load, you could do something like:
if (Run_Controls_Method && hdfFocusControl.Value != "")
{
switch(hdfFocusControl.Value)
{
case "btnSearch":
btnSearch_OnClick(null, null);
break;
case etc.
}
}
The way I implement the hdfHasFocus is:
HTML:
<input id="hdfHasFocus" runat="server" type="hidden" />
HTML code behind:
protected void Page_PreRender(object sender,EventArgs e)
{
if (IsPostBack != true)
{
//Add the OnFocus event to all appropriate controls on the panel1 panel.
ControlManager.AddOnFocus(this.Controls,hdfHasFocus,true);
//other code...
}
ControlManager.SetFocus(this.Controls,hdfHasFocus.Value,true);
}
ControlManager.cs related code:
/// <summary>
/// Adds the onfocus event to the UI controls on the controls in the passed in control list.
/// </summary>
/// <param name="controls">The list of controls to apply this event.</param>
/// <param name="saveControl">The control whose .value will be set to the control.ID of the control which had focus before postback.</param>
/// <param name="Recurse">Should this method apply onfocus recursively to all child controls?</param>
public static void AddOnFocus(ControlCollection controls, Control saveControl, bool Recurse)
{
foreach (Control control in controls)
{
//To make the .Add a bit easier to see/read.
string action = "";
//Only apply this change to valid control types.
if ((control is Button) ||
(control is DropDownList) ||
(control is ListBox) ||
(control is TextBox) ||
(control is RadDateInput) ||
(control is RadDatePicker) ||
(control is RadNumericTextBox))
{
//This version ignores errors. This results in a 'worse case' scenario of having the hdfHasFocus field not getting a
// value but also avoids bothering the user with an error. So the user would call with a tweak request instead of
// and error complaint.
action = "try{document.getElementById(\"" + saveControl.ClientID + "\").value=\"" + control.ClientID + "\"} catch(e) {}";
//Now, add the 'onfocus' attribute and the built action string.
(control as WebControl).Attributes.Add("onfocus", action);
}
//The 'onfocus' event doesn't seem to work for checkbox...use below.
if (control is CheckBox)
{
//This version ignores errors. This results in a 'worse case' scenario of having the hdfHasFocus field not getting a
// value but also avoids bothering the user with an error. So the user would call with a tweak request instead of
// and error complaint.
action = "try{document.getElementById(\"" + saveControl.ClientID + "\").value=\"" + control.ClientID + "\"} catch(e) {}";
//In case there is already an attribute here for 'onclick' then we will simply try to add to it.
action = action + (control as WebControl).Attributes["onclick"];
//Now, add the event attribute and the built action string.
(control as WebControl).Attributes.Add("onclick", action);
}
//You don't seem to be able to easily work the calendar button wiht the keyboard, and it seems made for
// mouse interaction, so lets set the tab index to -1 to avoid focus with tab.
if (control is CalendarPopupButton)
{
(control as WebControl).Attributes.Add("tabindex", "-1");
}
//We also want to avoid user tab to the up and down spinner buttons on any RadNumericTextBox controls.
if (control is RadNumericTextBox)
{
(control as RadNumericTextBox).ButtonDownContainer.Attributes.Add("tabindex", "-1");
(control as RadNumericTextBox).ButtonUpContainer.Attributes.Add("tabindex", "-1");
}
//Recursively call this method if the control in question has children controls and we are told to recurse.
if ((Recurse) && (control.HasControls()))
{
AddOnFocus(control.Controls, saveControl, Recurse);
}
}
}
/// <summary>
/// Searches the ControlCollection passed in for a match on the ID name string passed in and sets focus on that control if it is found.
/// </summary>
/// <param name="controls">The collection of controls to search.</param>
/// <param name="FocusToID">The ID of the control to set focus on.</param>
/// <param name="recurse">Recursively search sub-controls in the passed in control collection?</param>
/// <returns>True means keep processing the control list. False means stop processing the control list.</returns>
public static bool SetFocus(ControlCollection controls, string FocusToID, bool recurse)
{
//Return if no control ID to work with.
if (string.IsNullOrEmpty(FocusToID) == true)
{ return false; }
//If we get here and don't have controls, return and continue the other controls if applicable.
if (controls.Count <= 0)
{ return true; }
foreach (Control control in controls)
{
//If this is the control we need AND it is Enabled, set focus on it.
if (((control is GridTableRow) != true) && //GridTableRow.ClientID throws an error. We don't set focus on a 'Row' anyway.
(control.ClientID == FocusToID) &&
((control as WebControl).Enabled))
{
control.Focus();
//return to caller. If we were recursing then we can stop now.
return false;
}
else
{
//Otherwise, see if this control has children controls to process, if we are told to recurse.
if ((recurse) && (control.HasControls()))
{
bool _continue = SetFocus(control.Controls, FocusToID, recurse);
//If the recursive call sends back false, that means stop.
if (_continue != true)
{ return _continue; }
}
}
}
//We are done processing all the controls in the list we were given...
// If we get here, then return True to the caller. If this was a recursive call, then
// the SetFocus in the call stack above will be told to continue looking since we
// didn't find the control in question in the list we were given.
return true;
}
回答2:
In fact, you don't have to click on the button to make the first event happen. Just 'leave' the textbox, i.e. with 'tabbing' out of it to make the AutoPostBack happen.
If you want to do both in a single postback just remove the Button and do the things you do in AddButton_Click also in the Textbox_Change event.
回答3:
Making it a client side check was the solution to this...there doesn't seem to be a way to prevent it otherwise
回答4:
Write below code in Page_Load event to prevent twice click
BtnSaveAndPrint.Attributes.Add("onclick", "return confirm('Are you sure you Want to Save & Print?');")
回答5:
You could avoid this by not doing it server side and using Javascript. You also didn't post your page load event. Are you checking if it post back or not ?
Another way you could do this is the event that happens on the click of the button can be called from the TextChanged event and get rid of the button all together.
回答6:
I had the same problem, I decided to move the click event code to the page load event and execute it in case of postback. And not to use a click event at all.
protected void Page_Load(object sender, System.EventArgs e)
{
if (IsPostBack)
{
// put code here
}
}
instead of :
public void ButtonClick(object sender, EventArgs e)
{
//...
}
来源：https://stackoverflow.com/questions/3189034/have-to-click-button-twice-in-asp-net-after-autopostback-textbox