I have a TextBox, which I use for both data input and display. A user can select items from a list and for each item there is a corresponding text which is displayed in the TextBox when the item is selected.
The user can edit this textbox, thus changing the list item's correponding text.
My problem is this: I use the TextChanged event to detect when the user enters some text and I update the internal variables in the event handler, however this event handler is called when I programmatically change the values of the textbox too. I want this handler only to be called when the User changes the textbox. How can I achieve this?
edit: I have the same problem a combo box as well.
The handler will always be called - no way disable it that I'm aware of. However you can simply set a flag in your class to indicate the you've programatically changed the state and should ignore the next event.
_updating = true;
_textBox.Text = "New Text";
...
_textBox_TextChanged( object sender, EventArgs e )
{
if( _updating ) { _updating = false; return; }
// Do something special with the new text.
}
You might also try creating your textbox control and overriding the Text property to provide your own custom logic.
class MyTextBox : TextBox
{
public overrides string Text{
get{ return base.Text; }
set{
if( value == Text ) return;
_updating = true;
base.Text = value;
_updating = false;
}
}
}
The TextChanged event is invoked whenever the TextBox changes its Text property, which can be achieved via modifying the Text property, or when the user directly changes the text, there are other events which are more likely usable for the scenario you are trying to achieve.
KeyPress: Raised whenever the user pulses a key
KeyDown: Raised whenever a Key is pulled down
KeyUp: Raised whenever a Key is pulled up (released)
Hope it helps
You could set a flag in the programatic updates, and in the event handler exit early if the flag is set.
But if you use databinding, then the variables and the gui are synchronized automatically, which avoids this problem all together.
Do you mean you want the second textbox to display something which depends on what's in the first textbox, but ONLY if the user did set it ?
Could you be more specific about what you are trying to achieve? It seems to me that your UI design may be confusing for the user, since the text in B is sometimes related to A, and sometimes not.
If you still want to do it, the typical way to go is to use an updating flag, as proposed in other answers.
Check for focus on the textbox. If it does not have focus, it means the user isn't editing it.
Related
Sometimes while the user is typing text in a DataGridViewTextBox you want to enable or disable a control, depending on the value being typed. For instance enable a button after you typed a correct value
Microsoft showed the way in an article about how to create a DataGridViewButtonCell that can be disabled.
This is their trick (it can also be seen in other solutions)
Make sure you get the event DataGridView.CurrentCellDirtyStateChanged
Upon receipt of this event, commit the changes in the current cell by calling:
DataGridView.CommitEdit(DataGridViewDataErrorContexts.Commit);
This commit will lead to the event DataGridView.CellValueChanged
Make sure you get notified when this event is raised
In your OnCellValueChanged function, check the validity of the changed value and decide
whether to enable or disable the corresponding control (e.g. button).
This works fine, except that the CommitEdit makes that the text is selected while in OnCellValueChanged. So if you want to type 64, you get notified when you type 6 and later when you type 4. But because the 6 is selected you don't get 64, but the 6 is replaced by 4.
Somehow the code must deselect the 6 in OnCellValueChanged before interpreting the value.
The property DataGridView.Selected doesn't do the trick, it doesn't deselect the text, but it deselects the cell.
So: how to deselect the text in the selected cell?
I think you need something that when the user is typing some text into the current cell, you need to know the current text (even before committing it) to check if some button need to be disabled. So the following approach should work for you. You don't need commit any thing, just handle the TextChanged event of the current editing control, the editing control is exposed only in the EditingControlShowing event handler, here is the code:
//The EditingControlShowing event handler for your dataGridView1
private void dataGridView1_EditingControlShowing(object sender,
DataGridViewEditingControlShowingEventArgs e){
var control = e.Control as TextBox;
if(control != null &&
dataGridView1.CurrentCell.OwningColumn.Name == "Interested Column Name"){
control.TextChanged -= textChanged_Handler;
control.TextChanged += textChanged_Handler;
}
}
private void textChanged_Handler(object sender, EventArsg e){
var control = sender as Control;
if(control.Text == "interested value") {
//disable your button here
someButton.Enabled = false;
//do other stuff...
} else {
someButton.Enabled = true;
//do other stuff...
}
}
Note that the conditions I used above can be modified accordingly to your want, it's up to you.
I have a few TextBoxes that are bound to a single CheckBox.
This is the logic associated with it:
If the Checkbox is checked, it will overwrite any existing text in the associated TextBoxes and make it '0'++
If all of the TextBoxes have a score of '0,' the CheckBox should
become disabled and checked.
If any of the TextBoxes then change from '0,' it will become
enabled and unchecked.
++ *Note:* The caveat to this is if the TextBox has a value of 'C.'
Okay, so the issue I have is implementing the caveat above when one of the associated TextBoxes has a value of 'C.' What I would like to have happen is loop through the TextBoxes and check to see if any are scored 'C.' If one is found, display a warning message to the user confirming if they want to proceed. If Yes is selected, all associated scores will be overwritten to '0.' If No is selected then the Checked event should be cancelled.
To accomplish this, I added Event Listeners for the CheckBox.PreviewMouseDown and CheckBox.Checked events. Here is the code for my CheckBox.PreviewMouseDown event listener:
private void NormalCheckBoxControl_PreviewMouseDown(object sender, MouseButtonEventArgs e)
{
CheckBox normalCheckBox = (CheckBox)sender;
bool showCorrespondingScoreWarningMsg = false;
//Get a Row to loop through the AssociatedAdqScore controls for each
ScoreControl tempScoreControl = new ScoreControl();
foreach (ScoreControl score in this.ScoreControlList)
{
if (score.ScoreTextBox.Text == "C")
{
showCorrespondingScoreWarningMsg = true;
}
}
if (showCorrespondingScoreWarningMsg)
{
MessageBoxResult msgResult = InformationBox.Show("WARNING: Proceeding will remove corresponding 'C' scores. Continue?", "Continue?", ButtonStyle.YesNo, IconStyle.Question);
if (msgResult == MessageBoxResult.No)
{
e.Handled = true;
}
}
}
This works if the user selects 'No,' however the issue I'm having is that when choosing 'Yes,' the CheckBox.Checked event still does not get fired. I have tried to manually set CheckBox.IsChecked = true; if if (msgResult == MessageBoxResult.Yes), but this breaks the bindings so that is not a viable solution.
Is there any way I can resolve this issue and proceed with the NormalCheckBoxControl_Checked(object sender, RoutedEventArgs e) event if the user selects 'Yes?'
I don't know of a "Checked" event, though there is a CheckedChanged event and also a CheckStateChanged event. I am used to .NET 2.0, so this may be a 3.0+ thing. Either way, I think I have manually called the event handler in instances like this without any problem.
You can manually call the event handler with null params (or known object & new event args):
NormalCheckBoxControl_Checked(null, null);
or
NormalCheckBoxControl_Checked(new object, new EventArgs());
This should manually kick off your routine, and unless you need them, then there's really no problem with providing dummy params. No need to raise an event and wait for it to bubble, just call the routine.
Of course, if there are other routines which rely on the event bubbling or if you have multiple handlers for the same event, then it might cause you a problem. Be aware of that, just in case.
I'm developing a simple WPF application where I want to use the text changed method for a specific text field. the thing is I implemented the method but, the method gets fired in very short period, like even after i enter one character. I want to check whether the text change is completed in order to go with the methods written in the text changed method.
private void searchBox_TextChanged(object sender, TextChangedEventArgs e)
{
if (...) // how to check whether the typing is finished?
{
// code goes here
}
}
I think you'll need the LostFocus event for this. As #SLaks comment says, you can't predict whether the user will press another key. Alternatively, you could databind the control - depending on what you're actually trying to do that may make more sense.
Instead of TextChanged, try monitoring the LostFocus event, which will fire when the user has left the textbox, either through pressing Enter/Tab or clicking somewhere else on the form.
Agree with LostFocus
UIElement.LostFocus Event
Question does not ask about binding but something to consider.
In binding the equivalent is UpdateSourceTrigger="LostFocus"
Binding.UpdateSourceTrigger Property
With binding you can get into more advanced validation UI effects.
How to: Implement Binding Validation
Is there any event that fire when the value of the textbox change from a peace of code and when the textbox is validated or lost the focus and the event don't fire on the key press,because I have a lot of calculation and It's not possible to do it on every key press
Use TextChanged for text changed.
Use LostFocus for when textbox looses focus.
Use Validating or Validated for validation.
Here is the order in which events are called for TextBox:
// Reference : http://msdn.microsoft.com/en-us/library/system.windows.forms.control.validated.aspx
1) Enter
2) GotFocus
3) Leave
4) Validating
5) Validated
6) LostFocus
This should help you decide where you want to put your code.
There's no event that will fulfill your requirement of being raised when the textbox's value is changed programmatically through code, but not when text is typed into it by the user. The TextChanged event is going to be raised either way (this is fairly intuitive—the text value is changing, and the computer doesn't know or care what is responsible for changing it). As the documentation for this event indicates:
User input or setting the Text property to a new value raises the TextChanged event.
If you need to run custom validation logic when you add text to your textbox in code, you will need to invoke whatever method contains the validation logic yourself. Extract it into a separate method, which you call from the Validating/Validated event handler and from all of the places in your code where you set the textbox's Text property.
As a supplement to the other answers that have already been posted, I strongly recommend using either the Validating (if you want to be able to cancel the validation) or Validated events to handle the textbox losing focus, rather than the somewhat more obviously named LostFocus event.
You can use the LostFocus or Validated events.
Use a member variable.
private bool _changeByCode;
public void DoSomeChanges()
{
_changeByCode = true;
textbox1.Text = "Hello";
_changeByCode = false;
}
public void Textbox1_Change(object source, EventArgs e)
{
if (_changeByCode)
return;
//do your validation here.
}
I have a check box and I have subscribed for the CheckedChanged event. The handler does some operations in there. I check and uncheck the checkbox programmatically (ex: chkbx_Name.Checked = true), and the CheckedChanged event gets fired.
I want this event to be fired only when I manually check or uncheck it. Is there any way to avoid firing of this event when i check/uncheck it programmatically?
unsubscribe the event before you set:
check1.CheckChanged -= check1_CheckChanged;
then you can programmatically set the value without the checkbox firing its CheckChanged event:
check1.Checked = true;
then re-subscribe:
check1.CheckChanged += check1_CheckChanged;
[EDIT: March 29, 2012]
The problem with Tanvi's approach is you need to catch all source of manual check or uncheck. Not that there's too many(it's only from mouse click and from user pressing spacebar), but you have to consider invoking a refactored event from MouseClick and KeyUp(detecting the spacebar)
It's more neat for a CheckBox(any control for that matter) to be agnostic of the source of user input(keyboard, mouse, etc), so for this I will just make the programmatic setting of CheckBox really programmatic. For example, you can wrap the programmatic setting of the property to an extension method:
static class Helper
{
public static void SetCheckProgrammatically(
this CheckBox c,
EventHandler subscribedEvent, bool b)
{
c.CheckedChanged -= subscribedEvent; // unsubscribe
c.Checked = b;
c.CheckedChanged += subscribedEvent; // subscribe
}
}
Using this approach, your code can respond neatly to both user's mouse input and keyboard input via one event only, i.e. via CheckChanged. No duplication of code, no need to subscribe to multiple events (e.g. keyboard, checking/unchecking the CheckBox by pressing spacebar)
No. Those property change events fire whenever the property value changes, regardless of whether this was done by your code, by the control's own code or databinding. It's all the same code path, usually.
What you can do, however, if your event handler resides in the same class as the code that changes the property value, is to introduce a private boolean field in the class which you use as an indicator of whether the current property change is triggered by your code or by the user. After your change you simply reset it. The event handler would then look at the field and decide of whether it should do anything or not:
class Foo : Form {
private bool checkedProgrammatically = false;
void someMethod() {
// ...
checkedProgrammatically = true;
checkBox1.Checked = true;
checkedProgrammatically = false;
// ...
}
private void checkBox1_CheckChanged(object sender, EventArgs e) {
if (checkedProgrammatically) return;
// ...
}
}
I'm sorry I can't just comment on Michael Buen's answer due to my being new here (no reputation), but for what it's worth I strongly prefer his solution to Johannes Rössel's for a couple of reasons.
1) the checkedProgrammatically variable is a little too close to global for me. There's nothing to stop another method accidentally setting it to true, causing all your events to stop.
2) you could end up with a lot of variables depending on the number of events you're dealing with. It would be easy to change the wrong one and the results can be difficult to debug.
3) it's more obvious what you're doing when you unsubscribe then resubscribe. All the logic is right there, and you don't need to change your event handlers to exit early depending on certain conditions.
I've used both methods extensively and I find Michael's a lot easier in the long run.
You can use the MouseClick event and in that check for the checked state of the checkbox.
This way it wont be triggered programatically, it would only be called when the user manually checks or unchecks the checkbox.
You can set boolean variable before changing value programiticaly, and check than reset that variable in checkedchanged event