I'm trying to make a search feature where the user can hold in the control key and type some text to search.
I'm using the OnKeyDown/OnKeyUp to trap the control key.
Is there a easy way to check if the key parameter given to the onKeyUp/Down event is a litteral?
Or is it possible to convert the char given to OnKeyPressed while holding down the control key to the char it would have been if the control key where not pressed?
Edit:
I need a solution that can handle letters beyond the simple a..z range, like æ, ø å.
It looks like Delphi 2009 got a couple of useful methods in the TCharachter-class; e.g. function IsLetterOrDigit(C: Char): Boolean;
I'm stuck with delphi 2007, though...
The OnKeyDown & OnKeyPress Events have a number of Limitations.
Rather use a TApplicationEvents Component.
In it's OnShortCut Event hander use the following code
procedure TFormA.ApplicationEvents1ShortCut(var Msg: TWMKey; var Handled: Boolean);
begin
if (Msg.CharCode = Ord('B')) and (HiWord(Msg.KeyData) and KF_ALTDOWN <> 0) then
begin
Handled := True;
// Do what needs to be done;
end;
end;
This will trap ALT-B
have a look at Delphi - Using the TApplicationEvents OnShortCut event to detect Alt+C key presses for more info
You can convert the Key(Char) parameter from OnKeyPress event to it's ordinal value using Ord(Key) however, in the OnKeyDown event you can do the following
if CharInSet(Char(Key), ['A'..'Z']) then
do something
you might also want to play with ShiftState to check if ALT, CTRL and/or SHIFT key is down...
Here you have all the info:
Virtual Key Codes
Understanding and Processing Keyboard events in Delphi
Related
In a search form I have two components, a TEdit and and TDBGrid. The user enters text into the TEditand in the TEdit.OnChange event I search for matching items in a table using a query. These are displayed in a TDGrid. The event only triggers when the user has entered more than three characters in the TEdit.Textto cut down the overhead.
The problem occurs when the search has returned all possible records and the user wants to select one of the records displayed in the TDBGrid. While I told the users to use the Tab key (or the mouse) to switch from the TEdit to the TDBGrid, they use the return key to do this in another application and are insisting that they should be able to do the same thing in the application I'm altering/adding to. I can understand this, but the problem is that if I use
if (key = VK_RETURN) then key := VK_TAB;
in the TEdit.OnKeyUp event, the original value of the last key pressed in the TEdit is "remembered" as VK_RETURN and is passed to the TDBGrid's OnKeyUp event. Since I have other actions triggered in that event, I get undesired things happening as soon the the TDBGrid gains focus because they also want to select the correct row in the grid by pressing the return key again.
Therefore what I want to do is to "cancel" the key value passed to the TDBGrid from the TEdit. I tried using if (Sender = TEdit) then Key := VK_CANCEL; in the DGBrid's OnKeyUp event but I get a compiler "Incompatible types" error and I can't find anything to tell me how I should use it in this situation.
Is this possible? Or am I going about this the wrong way?
Thanks in advance!
I believe the following approach satisfies your needs and I suspect it to be the shortest such approach:
procedure TForm1.Edit1KeyPress(Sender: TObject; var Key: Char);
begin
if Key = #13 then
Key := #0;
end;
procedure TForm1.Edit1KeyUp(Sender: TObject; var Key: Word; Shift: TShiftState);
begin
if Key = VK_RETURN then
begin
PostMessage(Handle, WM_NEXTDLGCTL, 0, 0);
Key := 0;
end;
end;
This will make Enter, in Edit1, move focus to the next control. This is accomplished by posting the form a WM_NEXTDLGCTL message. The OnKeyPress handler is needed to suppress the "invalid input" message beep.
For bonus points, do
PostMessage(Handle, WM_NEXTDLGCTL, Ord(ssShift in Shift), 0);
instead to have Shift+Enter correspond to Shift+Tab.
I'm not quite sure I like this entire idea, though. I think I prefer to have Enter act on key down instead. The target control shoudn't care about this key up message.
Just to add to Andreas answer, I have used the same approach. There are 3 events you can play around with, onkeydown, onkeypress, onkeyup. At some point you will probably have to assign the key to null to avoid the "beep". The other thing to watch out for are unintended side effects, like moving 2 fields instead of one as has happened to me in the past.
Ran into a couple of problems using a code that only lets the user input alphabetical characters and a backspace.
When I compile my program using RAD studio 2010, apart from Vcl problems in the Uses clause, It compiles correctly, all working fine. However when I try and compile using XE5, I get an error: E2010 Incompatible types: 'Word' and 'AnsiChar'
If anyone can point me in the right direction it would be great!
Code below:
procedure TFRMStuTakeTest.DBEDTWord01KeyDown(Sender: TObject; var Key: Word; Shift: TShiftState);
begin
(*only return value if alphabetic *)
if Key in ['A'..'Z', 'a'..'z', #8] then
else
Key := #0;
end;
Sorry if there's something about procedures having to be from clean projects (i.e. unnamed/ not descriptive)
OnKeyDown is designed to deal with virtual key codes (those that are referred to using the VK_ constants), not individual letter and number keystrokes.
Use OnKeyPress to process individual characters, not OnKeyDown.
procedure TFRMStuTakeTest.DBEDTWord01KeyPress(Sender: TObject; var Key: Char);
begin
if not CharInSet(Key, ['A'..'Z','a'..'z', #8]) then
Key := #0;
end;
Better still, use the EditMask on the underlying TField, and set a valid mask for alpha characters using something like 'LLLLL;0;_', which would require 5 letters between '['A'..'Z','a'..'z']', and will handle all of the validations, editing keystrokes, and so forth.
YourTable.FieldByName('Word1').EditMask := 'LLLLL;0;_';
See the documentation for TField.EditMask for more information, and follow the link at the bottom to TEditMask for details about the mask characters. (There's an editor for the EditMask property in the Object Inspector; they're the same as those used by TMaskEdit, so you can drop one of those on your form and click the ... button on the right side of the EditMask property to access it.)
In my application, when I press CTRL + S, my form (with Key Preview enabled) captures this and saves the document. But when the focus is in, for example, an edit control, I get an annoying "Ding" sound, or in general, windows sounds. How do I avoid this sound?
Here's my form's capture of this key event...
procedure TForm1.FormKeyDown(Sender: TObject; var Key: Word;
Shift: TShiftState);
var
C: String;
begin
if not fChanging then
Modified;
if ssCtrl in Shift then begin
C:= LowerCase(Char(Key));
if C = 's' then begin
DoSave;
Key:= 0; //Tried this but didn't work
end else
if C = 'c' then begin
//Copy selected item(s)
end;
end;
end;
PS - Is there a more standard way of capturing these events? Because I'm sure I'm doing something wrong, and I'm sure there's another way I should be getting these key events without sounds.
A couple of things:
Try putting your code into FormKeyPress instead of FormKeyDown. This will make the Key := 0; code work... You will need to handle the CTRL checking manually though, by using something like GetKeyState() (I originally had GetAsyncKeyState() here, but as Rob Kennedy points out, GetKeyState() is a much better option).
Use an Action instead. Plop a TActionList on your form, double click on it, add an action and set it's hot key to CTRL-S. Add your save code to it's OnExecute event handler. This is the "proper" way to do it I believe.
Hope this helps.
Why don't you use Actions? That is the best way to handle shortcuts.
Here is some Delphi code to disable the system beep.
How can I change the TEdit's default error message when I use it in NumbersOnly mode. I mean this error:
Unacceptable character You can only type a number here
Is it possible to change this message ?
I don't know a direct way to change the value of that message (which is handled by Windows) but you can show your own message and then avoid to show the original windows hint ballon, using the Abort procedure in the OnKeyPress Event.
Check this sample
procedure TForm1.Edit1KeyPress(Sender: TObject; var Key: Char);
begin
if not (CharInSet(Key,['0'..'9',#8,#9])) then
begin
ShowHintMessage('Only numbers please');//you must write this function
Abort;//this will prevent which the original windows hint was shown
end;
end;
You must we aware which this code will be prevent the execution of the clipboard operations over the control.
Update
I Update the code to allow the Tab(#9) and Back space(#8) chars.
Looking at the VCL source, it looks like that message is generated by windows, rather than by Delphi. That is, the VCL is only wrapping the functionality that exists in windows. So it doesn't appear that it would be easy to modify the message.
In code I have developed some years ago I have been using this a lot to close the current form on pressing the Escape key at any moment:
procedure TSomeForm.FormKeyPress(Sender: TObject; var Key: Char);
begin
if key = #27 then close;
end;
This behaviour is defined for the TForm. The form's KeyPreview property is be set to True to let the form react to key presses before any other components. It all works perfectly well for the best part of the program, however, when the Escape key is pressed while a TEdit component is focused a sound (a ding sound used by Windows to signify invalid operation) is issued. It still works fine but I have never quite managed to get rid of the sound.
What's the problem with this?
Steps to recreate:
new VCL Forms application, set the form's KeyPreview to true
on the Events tab double-click the onKeyPress event and enter dummy code:
if key=#27 then ;
add a TListBox, TCheckBox, TEdit to the form and run the application
in the application try pressing Esc and NOTHING happens, as specified by the dummy code
focus the TEdit and press Esc. Nothing happens but the sound is played.
You get the ding because you left the ESC in the input. See how Key is a var? Set it to #0 and you eliminate the ding. That removes it from further processing.
procedure TSomeForm.FormKeyPress(Sender: TObject; var Key: Char);
begin
if key = #27 then
begin
key := #0;
close;
end;
end;
KeyPreview is just that, a preview of what will be passed to the controls unless you stop it.
Starting from Jim's answer (thanks Jim) I had to make it work for me. What I needed was to make a dropped down combobox close keeping the selected item and move to the next/previous control when TAB/shift+TAB was pressed. Everytime I did press TAB the annoying sound filled the room. My work arroud was using onKeyDown event to catch the shiftstate, declaring var aShift: boolean; in form's interface and use the following code:
procedure TForm2.StComboKeyDown(Sender: TObject; var Key: Word; Shift: TShiftState);
begin
if ssShift in Shift then aShift := true else aShift := false;
end;
procedure TForm2.StComboKeyPress(Sender: TObject; var Key: Char);
begin
if Key=char(VK_TAB) then
begin
Key := #0;
StCombo.DroppedDown := false;
if aShift
then previousControl.SetFocus
else nextControl.SetFocus;
end;
end;
Using the menu items and setting them to invisible, and using the shortcut, is a quick workaround that I've just stumbled across, but won't work if you need a shortcut that uses a character that is used in the first letter of an existing shortcut: For example for Alt+ENTER, you need to add something like this to the form create procedure:
MainMenu1.Items[0].ShortCut:=TextToShortCut('Alt+e');
However it's probably easier to use TActionList instead, and even though something like Alt+E is not listed you can add it.
It's an old thread... but anyway, here's a far better one: catching Alt-C!
Unlike ESC, Alt-C isn't serviced by KeyPress, so setting Key to #0 in KeyPress doesn't work, and the horrendous "ding!" is issued every time.
After hours of trying, here's the workaround I found:
- create a main menu option to service the request
- set its ShortCut to Alt+C - yes indeed, that is NOT one of the available ShortCut choices(!!)... but it does work anyway!
- do the processing in that menu option's OnClick
- you may even make in "in the background": you may set the menu option's Visible to false - as long as its Enabled stays true, it will be activated by Alt-C even though it will not be visible in the menu.
Hope that may help! And if you have something more elegant, please advise.