Using winforms, I have set the KeyPreview property to true and have event handles for the proper key events within the base form as well.
Within the forms that inherit from it, I set the AcceptButton property based on the requirements of the application.
There are certain cases in which I want the enter key to have functionality different than that of the AcceptButton.
I was hoping to capture the enter key press within my base form and check for the special cases where I do not want the AcceptButton event to fire.
It appears though, that the AcceptButton click is fired before any of the key events within my basef form. I could write functionality into the click events of the possible acceptbuttons, but, in my opinion, that would be a hack.
Any suggestions?
Thanks.
Another way to handle this is to override the form's ProcessDialogKey() method where you can suppress the accept and/or cancel buttons. For example, I have an application with a filter editor that filters a grid based on user input. I want the user to be able to hit the return key when the filter editor control has the focus to apply the filter. The problem is the accept button code runs and closes the form. The code below resolves the issue.
protected override bool ProcessDialogKey(Keys keyData)
{
// Suppress the accept button when the filter editor has the focus.
// This doesn't work in the KeyDown or KeyPress events.
if (((keyData & Keys.Return) == Keys.Return) && (filterEditor.ContainsFocus))
return false;
return base.ProcessDialogKey(keyData);
}
You can take this even further by dropping the following code in a base dialog form. Then you can suppress the accept button for controls in subclasses as necessary.
private readonly List<Control> _disableAcceptButtonList = new List<Control>();
protected override bool ProcessDialogKey(Keys keyData)
{
if (((keyData & Keys.Return) == Keys.Return) && (_disableAcceptButtonList.Count > 0))
{
foreach (Control control in _disableAcceptButtonList)
if (control.ContainsFocus)
return false;
}
return base.ProcessDialogKey(keyData);
}
protected virtual void DisableAcceptButtonForControl(Control control)
{
if (!_disableAcceptButtonList.Contains(control))
_disableAcceptButtonList.Add(control);
}
As our workaround, we captured the enter and leave event for the control that we wanted to have override the acceptbutton functionality. Inside the enter event, we held the current accept button in a private variable and set the acceptbutton to null. On leave, we would reassign the acceptbutton back to the private variable we were holding.
The KeyPreview events could have done something similar to the above. If anyone has a more elegant solution, I would still love to know.
Thanks.
Related
I have a Xamarin.Forms application which uses a TabbedPage, let's call it T, T consists of 3 ContentPage children A, B and C. Since the usere has the possibility to edit some data on tab B, I want to notify user before leaving tab in order to allow him to cancel the navigation change and save changes first or to discard changes and leave. So far I have managed to override OnBackButtonPressed() method and the navigation bar back button (which would exit TabbedPage). However I quickly noticed that I am still loosing changes when switching between tabs. I would like to override the click on new tab, so I could first present user with the leaving dialog and the skip the change or continue with it. What would be the best way to do this? I am currently working only on Android platform, so solutions on the platform level are also acceptible.
Thank you for your suggestions and feedback :)
I do not think there is an easy way to do this ,
you can use OnDissappearing and OnAppearing for the pages, that is as easy as it gets .
However I think you are using the wrong design.
Having tabs are ment to make it easier to navigate between pages, if you are going to notify the user when changing the tabs then it would be annoying . If I were you i would save the data for each page locally. so when you get back to the page you will have the data anyway.
So in the end I followed the advice of Ahmad and implemented the persisting of data on individual tabs so they are not lost when tabs are switched. (I no longer refresh input fields from data from model when OnAppearing is called).
But in order to know if there are some unsaved changes on my ChildB page, I had to implement the following procedures:
I created the method HandleExit on my ChildB page, which checks for unsaved changes in fields (at least one value in input fields is different from the ones in stored model) and the either prompts the user that there are unsaved changes (if there are some) or pops the navigation stack if there are no changes.
private async Task HandleExit()
{
if(HasUnsavedChanges())
{
var action = await DisplayAlert("Alert", "There are unsaved changes, do you want to discard them?", "Discard changes", "Cancel");
if(!action)
{
return;
}
}
await Navigation.PopAsync();
}
Since there are two ways on how user can return from Tabbed page (pressing the back button on device or pressing the back button in navigation bar, I had to:
A: override the back button method on my ChildB page, so it calls the HandleExit method. But since Navigation.PopAsync() needs to be called on UI thread, I had to explicitly execute the method on UI thread as written below:
protected override bool OnBackButtonPressed()
{
Device.BeginInvokeOnMainThread(new Action(async () =>
{
await HandleExit();
}));
return true;
}
B: Since there is no way to intercept the navigation bar back button on the ContentPage, I had to intercept the event on the platform level (Android) and then pass the event to the ContentPage if necessary via MessagingCenter. So first we need to intercept the event, when navigation bar button is pressed in one of the child pages and send the event via MessagingCenter. We can do that but adding the following method in our MainActivity.cs class:
public override bool OnOptionsItemSelected(IMenuItem item)
{
// check if the current item id
// is equals to the back button id
if (item.ItemId == 16908332)
{
// retrieve the current xamarin forms page instance
var currentpage = Xamarin.Forms.Application.Current.MainPage.Navigation.NavigationStack.LastOrDefault();
var name = currentpage.GetType().Name;
if(name == "ChildA" || name == "ChildB" || name == "ChildC")
{
MessagingCenter.Send("1", "NavigationBack");
return false;
}
}
return base.OnOptionsItemSelected(item);
}
Now whenever we will press the navigation bar back button in one of the child pages (ChildA, ChildB, ChildC) nothing will happen. But the button will work as before on the rest of the pages. For the second part of solution we need to handle the message from MessagingCenter, so we need to subscribe to it in our ChildB page. We can subsribe to the message topic in OnAppearing method as follows:
MessagingCenter.Subscribe<string>(this, "NavigationBack", async (arg) => {
await HandleExit();
});
Be careful to unsubscribe to the topic in OnDisappearing() otherwise strange things could happen, since there will be references left to your ContentPage even if you pop it from your navigation stack.
Now that we have handled both requests for back navigation in our ChildB page, we also need to handle them in all of remaining child pages (ChildA, ChildC), so they will know if there are unsaved changes in ChildB page, even if it is currently not selected. So the solution is again compraised of handling the device back button, and navigation bar back button, but first we heed a way to check if ChildB has unsaved changes when we are on one of the remaining pages, so we again write HandleExit method but this time it is as follows:
private async Task HandleExit()
{
var root = (TabbedPage)this.Parent;
var editPage = root.Children.Where(x => x.GetType() == typeof(ChildB)).FirstOrDefault();
if(editPage != null)
{
var casted = editPage as ChildB;
if (casted.HasUnsavedChanges())
{
var action = await DisplayAlert("Alert", "There are unsaved changes, do you want to discard them?", "Discard changes", "Cancel");
if (!action)
{
return;
}
}
}
await Navigation.PopAsync();
}
The only thing that remains now is to handle both navigation back events inside remaing child pages. The code for them is the same as in the actual ChildB page.
A: Handling the device back button.
protected override bool OnBackButtonPressed()
{
Device.BeginInvokeOnMainThread(new Action(async () =>
{
await HandleExit();
}));
return true;
}
B: Subscribing to topic from MessagingCenter
MessagingCenter.Subscribe<string>(this, "NavigationBack", async (arg) => {
await HandleExit();
});
If everthing has been done correctly, we should now be prompted with a dialog on any of the child pages if there are unsaved changes on the ChildB page. I hope this will help somebody in the future :)
We have a tool that is being integrated into our application. We have some strict borders around us too in that we cannot modify the application except for our extensions. I have searched here, I've searched the internet, but cannot find any postings about this problem.
I have a Windows Form that contains a ListView and our user requires we create a checkbox to Select/Deselect all. I have the event handler for when the check box state changes and call the routine to set everything to Selected.
private void SelectAllEventHandler(object sender, EventArgs e)
{
ChangeState(RadCapListView, SelectAllRadcap.Checked);
}
private void ChangeState(SWF.ListView control, bool state)
{
if (control.CheckBoxes)
{
control.Items.OfType<SWF.ListViewItem>().ToList()
.ForEach(item => item.Checked = state);
}
else
{
control.Items.OfType<SWF.ListViewItem>().ToList()
.ForEach(item => item.Selected = state);
}
control.Refresh();
}
Going into debug mode all items are marked as selected.
Also at the control level SelectedItems is properly updated.
The issue is that visually the control just will not highlight the selected items like we have our WPF forms doing. As you can see in the code I also tried to refresh the control hoping that would show items selected, but no joy.
Has anyone solved this problem in getting selected items to display properly?
Thank!
Instead of using control.Refresh(), try control.Focus().
I have a windows form with 6 textboxes. On the form load, by default, only one textbox will be displayed with the form size reduced. Once i enter the text into the textbox, my form size should increase and should display second textbox without any button click or textbox events. The intention behind it is that user doesn't put any extra effort to click button as it should be user friendly. Is there any possible ways of doing it?
No, it is impossible to do it without events, but possible without button clicks (which are actually producing events which should be handled)
So the most user friendly thing you can do is using events and where is no reason to avoid them. To achieve your functionality you have to
a) Set the Autosize property of the form to true
b) Handle the TextChanged event of your only textbox with following code:
private void textBox1_TextChanged(object sender, EventArgs e)
{
if(((TextBox)sender).Text.Length > 0)
{
TextBox tb = new TextBox();
tb.TextChanged += new EventHandler(textBox1_TextChanged);
this.Controls.Add(tb);
}
}
I have a CEdit box where a user can enter relevant information. As soon as he\she starts writing in the box, I need a notification so that I can call doSomething() to perform some other task. Does Windows provide a callback, and if so, how do I use it?
With MFC there's no callback as such, rather you do this by implementing a handler for the appropriate event. You need to handle one of two events: WM_CHAR or EN_CHANGE
Handle the dialog's EN_CHANGE for example duplicating in realtime the entered text elsewhere on the dialog. You need to firstly add an entry in the dialog's message map, and secondly override the appropriate handler:
BEGIN_MESSAGE_MAP(CstackmfcDlg, CDialog)
ON_EN_CHANGE(IDC_EDIT1, &CstackmfcDlg::OnEnChangeEdit1)
END_MESSAGE_MAP()
void CstackmfcDlg::OnEnChangeEdit1()
{
CString text;
m_edit.GetWindowText(text);
m_label.SetWindowText(text); // update a label control to match typed text
}
Or, handle the editbox class's WM_CHAR for example preventing input of certain characters, e.g. ignore anything other than a digit for numerical entry. Derive a class from CEdit, handle the WM_CHAR event of that class (not the dialog) and make your edit control an instance of that class.
BEGIN_MESSAGE_MAP(CCtrlEdit, CEdit)
ON_WM_CHAR()
END_MESSAGE_MAP()
void CCtrlEdit::OnChar(UINT nChar, UINT nRepCnt, UINT nFlags)
{
// Do nothing if not numeric chars entered, otherwise pass to base CEdit class
if ((nChar >= '0' && nChar <= '9') || VK_BACK == nChar)
CEdit::OnChar(nChar, nRepCnt, nFlags);
}
Note that you can use the VS IDE to put in stubs for the handler overrides by using the Properties bar with the mouse selection in the message map block.
EDIT: Added example code, and corrected explanation of WM_CHAR which I had wrong.
If you double click on the edit box in the resource editor it automatically creates the OnEnChanged event for you.
The following assumes that you have an MFC dialog application.
The class wizard can be started with a right-click:
Double-click the Control ID (has an icon with a small green plus) of the new edit control to add the corresponding member variable to the class.
The class and event wizards will update the class definition and add a CEdit member:
afx_msg void OnEnChangeEdit1(); // Added by event wizard
CEdit m_edit1; // member added by class wizard
The class wizard will update the function:
void CMFCApplication5Dlg::DoDataExchange(CDataExchange* pDX)
{
CDialogEx::DoDataExchange(pDX);
DDX_Control(pDX, IDC_EDIT1, m_edit1); // new variable added with class wizard
}
Double-clicking the control or right-clicking and selecting the add event wizard will update the message map and create the function declaration and definition:
BEGIN_MESSAGE_MAP(CMFCApplication5Dlg, CDialogEx)
ON_WM_SYSCOMMAND()
ON_WM_PAINT()
ON_WM_QUERYDRAGICON()
ON_EN_CHANGE(IDC_EDIT1, &CMFCApplication5Dlg::OnEnChangeEdit1) // new event handler added with wizard
END_MESSAGE_MAP()
Finally the code may be updated to interact with the edit control:
void CMFCApplication5Dlg::OnEnChangeEdit1()
{
// TODO: Add your control notification handler code here
CString text;
m_edit1.GetWindowText(text);
//m_edit1.SetWindowText(text);
}
I have a window I've created using UiBinder. I'm followings Sencha's HelloWorldUiBinder example and have placed a form inside the window. I wanted to know how to reset the form data after the widow has bee closed(hiden)?
I figured it out. All I did was add all of my fields to a List, then looped through that list in my closeWindow handler. Calling the rest() method. That clears all the data from my fields. I just need to figure out how to get my Radio buttons to select the default options when the window is reopened.
The code looks like this:
#UiHandler("closeButton")
public void onCloseButtonClicked(SelectEvent event){
for(Field<?> f : fields){
f.rest();
}
window.hide();
}