I have a c# program set up that is supposed to accept a quantity input if a checkbox is checked. It then multiplies the quantity by the price and updates the appropriate label with the total cost.
However, when I run the program it does not update the label. I ran the debugger and the label's .text value in the system is correct but it still does not appear on the actual form.
Is there a label property in Visual Studio that prevents changes from being rendered?
here is the snippet responsible for updating the label.Text value
if (chkSesame.Checked)
{
intSesameQty = Convert.ToInt32(txtSesameQty.Text);
decSesameTotal = intSesameQty * decBAGEL_PRICE;
lblSesameSeedTotal.Text = decSesameTotal.ToString("c");
}
Without knowing more about the structure of your form, and how you are calling your code, it's hard to give you any other advice other than to attempt to call lblSesameSeedTotal.Refresh() after setting the text.
Calling Refresh (MSDN Control.Refresh link) effectively invalidates the control and forces the runtime to redraw the control, which, of course, includes updating its text.
There are lots of reasons why you may have to do this; redrawing is an expensive operation, so, in general, if you are handling an event elsewhere on the form, it may not update certain controls. This is especially true for labels and similar controls whose values tend to remain constant (e.g. a label for a textbox with the text: Enter Name Here doesn't really need to change).
Related
Hi I am working in WPF C# application and I am new.
In my application, there is a stack panel, lets call this stack panel as first stack panel. This stack panel has one text box whose width and height are not set. It has margin of 100. Its text wrapping is set to wrap.
User provides text information in to the text box. If user want more text box, then there is a button. Upon clicking this button, a new text box with previous text box properties appears in the first stack panel and user continuous typing.
The main goal is to show, the print preview of the first stack panel while user typing text into the text boxes of the first stack panel.
So what I did is: I have another stack panel, lets call this second stack panel beside to the first stack panel. There is function or method which is called upon each key press. This function or method, collects all the text from each text box from first stack panel into a list (of type string) and then it adds each string from the list as textblock (children) to second stackpanel. And once all the string from the list added to the second stackpanel, the textbox from the first stackpanel gets back focus so that user can able to continue typing text.
So far It is working fine. The problem is, as user adds more textboxes, it takes longer time to appear in the second stackpanel and set back the focus to the textbox from first stack panel.
To over come the situation, I used the following code:
private void OnPreviewKeyUp(object sender, KeyEventArgs e){
//code to collect text from each textbox from first stackpanel and add into a list of type string.
this.Dispatcher.Invoke(()=> {
ReloadTextInfoToPanel(textBoxTextList);
});
}
the above code, still taking same amount of time.
I even tried using
this.Dispatcher.InvokeAsync();
But same amount of time it is consuming.
What I want is, when user is typing in the text boxes of first stack panel then the function or method should be called independently, with out blocking the control.
I hope you have understood, what is the issue. Pardon my Bad English. Please guide me. Thanks in advance.
This is not a direct answer for your question, but I cannot make comments, but still want to try to help
You may consider updating the second panel every second or two (using a timer), instead of every key hit. This will lower the times of update significantly, but may not bother the user.
I´m trying to set textbox visible = false to avoid user from write on it manually but I still need it to write on it by using a bar code scanner, so I need it to get focused before use the scanner, what would be the better way to do it?
Your best option would be to simply validate that what's entered into the textbox is indeed a bar code. What happens when the scanner breaks down and the user still needs to enter a bar code? Limit it to numbers only.
If that's not an option and you find the scanner doesn't work with hidden or disabled textboxes, then set TabStop = false and Multiline = true, and try setting the text box size to 0x0. Or at least really tiny and make it the same colour as the background. In that case you'd want a label or something to then display the bar code or product info so the user knows the scanning worked.
Another possibility may be to set KeyPreview = true on your form. Then you can handle anything that looks like a bar code in the form's KeyPress event, no matter which control is focused. If numbers start coming in, capture them, and if it turns out not to be a bar code, just forward them to the focused control.
just simply set textbox property size to (0,0) with textbox visible = true
From the question, you want to achieve two things.
Make the textbox invisible before Scanning.
Lock the user from editing the textbox after bar code scanning.
Solution
Set the textbox visibility property to false before Scanning so that it does appear on the screen whatsoever.
Have an event handler after finishing scanning or at the end of your scanning method/function, change the Property of the textbox called Disabled to true.
Hope this helps.
If the purpose of hiding textbox is to not-allow user from editing it, then
you may set the ReadOnly property of texbox to true, then call the .Focus() method
before scanning the barcode. In my experience, after having installed the barcode
reader driver, softwares from accompanying CD, all you have to do is scan the
barcode and it will populate with the barcode-value in human readable format,
on any control in an application that can take user-input. I suggest to use
Readonly property of textbox instead of setting visible = false.
Suppose we inherit from WPF TextBox and then try to get text changes through overriding OnTextChanged.
Then we would notice when changes occurred, but the only information that we would have is:
Offset that this change occurred
Removed Length
Added Length
Can we get the accurate added text by using,
Text.Substring(Change.Offset, Change.AddedLength)
in OnTextChanged?
Text Change occurs in different conditions (such as user input, pasting text, or setting Text property in-code). Is there any possibility of conflicting changes coming into e.Changes?
Is this approach a trust way? If answer is No, Is there any other standard way(s) to get accurate changed text?
For a TextBox, this event occurs when its text changes; for a RichTextBox, this event occurs when any content or formatting changes (for example, images, table, or background color).
Can we get the accurate added text by using ... ?
Yes, you will always get accurate text in case of TextBox. You can make use of e.UndoAction to check for addition/deletion of text.
Read documentation here.
Is there any possibility of conflicting changes coming into e.Changes?
There won't be conflicting changes.
In general, the following will always be true:
The changes that occur result in the document being in a valid state.
The collection is ordered consecutively, related to where the change occurred in the control. For example, a TextChange object
that represents a change at position 2 is before a TextChange
object that represents a change at position 10.
Two TextChange objects do not represent an overlapping area. The value of Offset plus the value of AddedLength of one TextChange
object is always less than or equal to the value of Offset of the
next TextChange object in the collection. Likewise, the value of
Offset plus the value of RemovedLength of one TextChange object is
always less than or equal to the value of Offset of the next
TextChange object in the collection.
The collection reflects whatever changes occurred, even if there seems to be no net change. In the preceding example, neither the
first or fourth change results in a net change, because each simply
removed and re-added the and symbols, respectively. But
the symbols were actually removed and added, so they are included in
the collection.
More can be read here.
I made a short test program with one TextBox and one Label and I could not find the problems you describe. If I implement an TextChanged event for the TextBox like the following it works even if I paste something.The checking for null is needed because if the Textbox has an initial value the Initilialize method will trigger the change event before the label is created.
private void TextBox_TextChanged(object sender, TextChangedEventArgs e)
{
TextBox tbSource = (sender as TextBox);
if (lblOutput == null)
return;
lblOutput.Content = tbSource.Text;
}
I'm experiencing some weird behavior with the ComboBox.SelectionChangeCommitted event and am wondering if anyone has an explanation for it.
Somewhere in my event handler, I call MessageBox.Show. If I choose a new value in my ComboBox, and my code causes the MessageBox to pop up, I am seeing my selceted value get reverted back to its original value.
When debugging, I am seeing that the selected value is correct before MessageBox.Show. MessageBox.Show gives control back to the user until I click "Yes" or "No". After I have clicked one of the options, control returns to the debugger and the value of my ComboBox is reverted back to its original value before my change.
I am not programmatically setting the selected value elsewhere, so I'm at a loss as to why the value gets reverted. If the event handler does not pop the MessageBox, the selected does not get reverted.
Is it possible that the fact that I'm giving control back to the UI before I'm done handling the event has anything to do with it. If so, is there a clean way to get around it? Currently I'm capturing my selected value before I pop the MessageBox and then resetting it after, but I'd prefer to not have to resort to a "hack" to fix the issue.
The problem is likely that the act of displaying the message box causes the combo box drop-down menu to close, thus abandoning any uncommitted selection the user may have made.
It's basically the same thing as dropping down a combo box, highlighting an item in the list, and then pressing the Esc key. Notice that the highlighted item does not become the selected item because you never selected it before the combo box was dismissed. (You can try it easily yourself in the "Run" dialog.)
This is one of the many reasons why it's a bad idea to throw up message boxes all over the place (the other reasons include how visually jarring message boxes are to users, and that most of them don't even bother to read them anyway). Programmers who like to use message boxes as debugging aids are often bitten by this exact scenario when they try to debug UI code.
The solution is to either:
Defer validation until the entire form is committed/submitted, at which time you can show a message box without running the risk of abandoning any currently dropped-down combo boxes.
Find an alternative (i.e., non-modal) way of displaying the validation error. WinForms provides an ErrorProvider control that you can use for this purpose. The typical usage is showing a little warning or error icon next to the control with the invalid value; the user can hover over that icon to display a tooltip with more information about the exact error.
Or perhaps a combination of both approaches, allowing the user to get instant feedback but also ensuring that you never have to handle malformed input outside of the input form.
I was incorrect in my assumption that the subclass of ComboBox I was using did not add any relevant functionality. The issue ended up being due to a LostFocus event handler I was unaware of that caused the ComboBox to revert its value.
I could not recreate your issue using the code below which is essential what you are saying you are doing. The value in the combobox gets updated. You may get a better solution by posting the SelectionChangeCommitted code.
private void comboBox1_SelectionChangeCommitted(object sender, EventArgs e)
{
try
{
ComboBox cb = (ComboBox)sender;
string check1 = cb.Text;
MessageBox.Show("Messagebox check");
string check2 = cb.Text;
MessageBox.Show(check1 + "\n\n" + check2);
//check 1 and 2 show the old value. Once the method leaves then the value in the combobox is updated.
}
catch (Exception ex)
{
MessageBox.Show(ex.Message);
}
}
I have a Windows form (.NET 3.5) that contains a propertygrid control. The propertygrid control gets refreshed periodically do display any changes that may have occurred in the class which it represents. I want the refresh to only occur if the user is not currently editing a property in the grid. Is there a way to detect if the user is currently editing a control?
Yes - it's a little hacky but you can find out which subcontrol of the property grid is active, and make an educated guess based on what it is. The following seems to work:
bool isEditing = (propertyGrid.ActiveControl.GetType().Name != "PropertyGridView");
There probably is, but might I recommend having your type implement INotifyPropertyChanged instead of refreshing the grid on a timer? This way you would never have to call Refresh yourself; the display would automatically update the value displayed for each property whenever that property changed.
Of course, if your type has tons of properties, or if you're using your grid to dynamically display objects of many different types, this suggestion may not be practical. It's just a thought.
This is a fairly complex problem. I'd suggest a two fold approach:
Keep track of the last time the changed events fire.
Keep track of whether or not the control has focus.
If the control hasn't been modified within a certain threshold and has focus, or if the control doesn't have focus, I'd consider that to be sufficient to determine that it is not currently being edited.
You could hook up the OnLostFocus event. This way, the control would only get updated once it no longer had focus.
protected virtual void OnLostFocus( EventArgs e)