I'm writing a simple application with several controls on a Windows form. I need to monitor the state of buttons (enabled/disabled) according to the state of a textbox and a listbox.
For example, when the listbox is empty, buttons Delete, Delete All and Edit are to be disabled, or when either the textbox or the listbox is empty button Forward is disabled, and so on.
So, I put the change of these properties on Application.Idle event, so it goes something like this:
private void MainForm_Load(object sender, EventArgs e)
{
Application.Idle += new EventHandler(Application_Idle);
}
public void Application_Idle(object sender, EventArgs e)
{
CheckFillingFields(forwardBtn);
CheckFillingList(deleteBtn);
CheckFillingList(deleteAllBtn);
CheckFillingList(editBtn);
}
private void CheckFillingFields(object sender)
{
if (questionTxt.Text == "" || answersLst.Items.Count == 0)
(sender as Button).Enabled = false;
else
(sender as Button).Enabled = true;
}
private void CheckFillingList(object sender)
{
if (answersLst.Items.Count == 0)
(sender as Button).Enabled = false;
else
(sender as Button).Enabled = true;
}
So, the question is - is it acceptable to use Application.Idle in this case? Or should I make these properties dependable on user actions? (For example, when the user deletes an item from the listbox, I should check if it was the last one, and disable the corresponding buttons.)
Thanks a lot in advance, I really appreciate your help!
The simple answer is that, yes, the idle checking is bad and you should re-check the state of your controls on their change events, not "whenever possible".
Related
I created a windows forms like this
As you can see in selected changed event I disable button move to, it works correctly, problem starts when I try to
return an item it to main list, move to button keeps disable instead enable it again when I select item of first list. Someone knows
what occurs there?
Events:
private void lstTechUnnotified_SelectedIndexChanged(object sender, EventArgs e)
{
btnReturnTo.Enabled = false;
btnMoveTo.Enabled = true;
}
private void lstTechToNotified_SelectedIndexChanged(object sender, EventArgs e)
{
btnReturnTo.Enabled = true;
btnMoveTo.Enabled = false;
}
You need to make sure that there actually is an item being selected since ListBox.SelectedIndexChanged event gets fired even when there're no items selected - making the new SelectedIndex equal to -1. Also, from the way you asking, I expect you want to enable btnMoveTo when there's a selected item in lstTechUnnotified and otherwise, disable it - and the same for btnReturnTo and lstTechToNotified; if that's it, then the easy way is:
private void lstTechUnnotified_SelectedIndexChanged(object sender, EventArgs e)
{
btnMoveTo.Enabled = (lstTechUnnotified.SelectedIndex > -1);
}
private void lstTechToNotified_SelectedIndexChanged(object sender, EventArgs e)
{
btnReturnTo.Enabled = (lstTechToNotified.SelectedIndex > -1);
}
Though I'm not sure about your button names..
I am using a datagradview and I am wanting to prompt the user to save the current row before moving off I have been trying to use the following event but I seem to be in a circular loop when I hit my save event.
private void dgStock_SelectionChanged(object sender, EventArgs e)
{
if (isDirty == true)
{
isSavedFromRow = true;
btnSaveDetails_Click(sender, e);
isDirty = false;
}
}
The problem with the selection changed event is this happens once the row has changed so the user could think their saving the new row and not the current row.
I also seem to be caught in a circular loop some how has the messagebox box is getting fired numerious times I am only setting the isDirty to true if the user enters key down on my textboxes.
if (isDirty == true)
{
DialogResult _result = MessageBox.Show("Are you sure you wish to upate Live Product Information", "Save Changes", MessageBoxButtons.YesNo, MessageBoxIcon.Information);
if (_result == DialogResult.Yes)
{
updateStock();
_trackChanges.Clear();
isDirty = false;
}
}
This is me setting my dirty flag on key down felt this was best way to avoid the problem I seem to be having.
private void txtDescription_KeyDown(object sender, KeyEventArgs e)
{
isDirty = true;
btnSaveDetails.Enabled = true;
}
Your code sample suggests that your save stuff is defined in your save button click. If you change your structure to something like this
private void SaveClick(object sender, EventArgs e)
{
DoSaveStuff();
}
private void DoSaveStuff()
{
// Do your save stuff
}
i.e. pull your save stuff out into a method. You can call DoSaveStuff() whenever you need to save, e.g.
private void SelectionChanged(object sender, EventArgs e)
{
// Do stuff
if (condition)
{
DoSaveStuff();
}
}
The advantage of this approach is you're capturing the aspect of the behaviour you're interested in - the save stuff - rather than the whole button click. Furthermore, you click a button to save, your application doesn't, it simply saves in certain circumstances, e.g. when you click a button or when something changes.
As MSDN says the SelectionChangedEvent occurs whenever the selection has changed. So, whenever this happens you could check your original selection to see if it has changed and then save if it has. Maybe doing something like this
private void SelectionChanged(object sender, EventArgs e)
{
bool hasContentsChanged = // determine if your content has changed
if (hasContentsChanged)
{
DoSaveStuff();
}
}
An advantage of this approach is that you'd only have to save if it really had changed, i.e. if the original text != new text, rather than in all cases.
Most of my dropdown boxes use the SuggestAppend property, meaning when you start typing in the box, it will make a shortlist of the items that match your case. However, if I do this after opening the drawer, this happens:
I have tried using this method, but it closes both instead of just one:
private void cmbLoc_TextChanged(object sender, EventArgs e)
{
if (cmbLoc.Text != "")
{
cmbLoc.DroppedDown = false;
}
}
I am trying to have it so that when I type something into the text box, the original dropdown will disappear, and the SuggestAppend draw will appear. How can I manage this?
It worked if I used KeyDown. Try and tell if that helps
private void cmbLoc_KeyDown(object sender, KeyEventArgs e)
{
var comboBox = (ComboBox)sender;
comboBox.DroppedDown = false;
}
I have numeric buttons which when pressed display the number in different text boxes. Now my problem is that i want check which textbox has focus so that the number pressed will be entered in that textbox.
My Code:
private void btn_one_Click(object sender, EventArgs e)
{
if (txt_one.Focused==true)
{
txt_one.Text += btn_one.Text;
}
else if (txt_two.Focused==true)
{
txt_two.Text += btn_one.Text;
}
}
Now my problem is that the above code is not working what is wrong and what will be the solution? I even used something like this
private void btn_one_Click(object sender, EventArgs e)
{
if (txt_one.Focus()==true)
{
txt_one.Text += btn_one.Text;
}
else if (txt_two.Focus()=true)
{
txt_two.Text += btn_one.Text;
}
}
In both the above cases the text is entered in both the text boxes. Any solutions.
This problem is a little tricky (with my experience dealing with Enter, Focus, LostFocus, Leave events, all these things sometimes make your head ache a lot and you should avoid dealing with them if possible), at the time you click your Button, the current Focused control you can know is exactly the Button (ActiveControl is one short way to access it). So the solution is we have to record the track of focused TextBox, hold it in a reference and use it when needed. In fact if the control other than one of your TextBoxes is focused, we have to reset the variable lastFocused to null:
TextBox lastFocused;
//Enter event handler for all your TextBoxes
private void TextBoxes_Enter(object sender, EventArgs e){
lastFocused = sender as TextBox;
}
//Click event handler for your button
private void btn_one_Click(object sender, EventArgs e){
if(lastFocused != null) lastFocused.Text += btn_one.Text;
}
I have a tab control and 3 tabpages in it. ( C#)
if i am in tab 2, and edit a text box value
and then click tab 3, i need to validate what was enetered in the text box.
if correct i should allow to to switch to tab 3 else should remain in tab 2 it self
how do i achieve this?
iam curently handling the "leave" event of the tabpage2,
i validate the text box value there and if found invalid
i set as tabcontrol.Selectedtab = tabpage2; this does
the validation but switches to new tab! how could i restrict the navigation.
I am a novice to C#, so may be i am handling a wrong event!
Here is the relevant code:
private void tabpage2_Leave(object sender, EventArgs e)
{
if (Validatetabpage2() == -1)
{
this.tabcontrol.SelectedTab =this.tabpage2;
}
}
While the other approaches may work, the Validating event is designed specifically for this.
Here's how it works. When the SelectedIndex of the tab control changes, set the focus to the newly selected page and as well as CausesValidation = true. This ensures the Validating event will called if the user tries to leave the tab in any way.
Then do your normal validation in a page specific Validating event and cancel if required.
You need to make sure to set the initial selected tab page in the Form Shown event (Form_Load will not work) and also wire up the tab page specific validating events.
Here's an example:
private void Form_Shown(object sender, System.EventArgs e)
{
// Focus on the first tab page
tabControl1.TabPages[0].Focus();
tabControl1.TabPages[0].CausesValidation = true;
tabControl1.TabPages[0].Validating += new CancelEventHandler(Page1_Validating);
tabControl1.TabPages[1].Validating += new CancelEventHandler(Page2_Validating);
}
void Page1_Validating(object sender, CancelEventArgs e)
{
if (textBox1.Text == "")
{
e.Cancel = true;
}
}
void Page2_Validating(object sender, CancelEventArgs e)
{
if (checkBox1.Checked == false)
{
e.Cancel = true;
}
}
private void tabControl1_SelectedIndexChanged(object sender, System.EventArgs e)
{
// Whenever the current tab page changes
tabControl1.TabPages[tabControl1.SelectedIndex].Focus();
tabControl1.TabPages[tabControl1.SelectedIndex].CausesValidation = true;
}
You can use the TabControl Selecting event to cancel switching pages. Setting e.Cancel to true in the event stops the tabcontrol from selecting a different tab.
private bool _cancelLeaving = false;
private void tabpage2_Leave(object sender, EventArgs e)
{
_cancelLeaving = Validatetabpage2() == -1;
}
private void tabcontrol_Selecting(object sender, TabControlCancelEventArgs e)
{
e.Cancel = _cancelLeaving;
_cancelLeaving = false;
}