I've got this:
procedure Welcome(user: string; accesslevel: integer);
begin
if accesslevel>= 10 then btCustomers.Text = 'Customer overview';
end;
Though, while the button exists on the form, btCustomers is declared an 'undeclared identifier'. What am I missing?
P.S. I am aware that this should be handled by the form OnCreate, but the Welcome procedure gets called from an external form.
You could to pass a reference to the form so that the button can in turn be referenced.
procedure Welcome(form: TMyForm; user: string; accesslevel: integer);
begin
if accesslevel>= 10 then form.btCustomers.Text = 'Customer overview';
end;
However, any time you have a global scope function that takes as its first parameter a reference to an object, you have a candidate for a method of that object. So, add a method to TMyForm.
procedure TMyForm.Welcome(user: string; accesslevel: integer);
begin
if accesslevel>= 10 then btCustomers.Text = 'Customer overview';
end;
And call it like this:
MyForm.Welcome(user, accesslevel);
Related
I am adding components to a form at run time and I am also adding events that change properties of these components in a dictionary to call them later.
TEventBeforeInsert = function(var AComponent: TComponent; AForm: TForm): Boolean of Object;
TFieldBase = class
private
FEvent:TEventBeforeInsert;
....
function TFieldBase.EventBeforeInsert: TEventBeforeInsert;
begin
Result:=FEvent;
end;
function TFieldBase.EventBeforeInsert(AEvent: TEventBeforeInsert): TFieldBase ;
begin
FEvent:=AEvent;
Result:=Self;
end;
....
The Form Call
TFormBase.New
.addStringField
(
TFieldBase.New
.Enabled(True)
.Description('User')
.EventBeforeInsert(TEvents.New.EditFillUser), TTabsNames.Tab1
).Show();
The Form Class
TFormBase = class(TForm)
private
FDictionary: TDictionary<String, TEventBeforeInsert>;
...
function TFormBase.addStringField(AField: TFieldBase; ATab: TTabsNames): TFormBase;
var
FLink: TLinkControlToField;
FEdit: TEdit;
begin
Result := Self;
FEdit := TEdit.Create(Self);
FEdit.Visible := True;
FEdit.Parent := TPanel(PanelParent.FindComponent('PanelTab' + Ord(ATab).ToString));
FEdit.Enabled:=AField.Enabled;
if Assigned(AField.EventBeforeInsert) then
begin
FDictionary.Add(FEdit.Name,AField.EventBeforeInsert);
end;
end;
...
procedure TFormBase.rectInsertClick(Sender: TObject);
var
Item:String;
begin
for Item in FDictionary.Keys do
begin
if Not FDictionary.Items[Item](Self.FindComponent(Item),Self) then
Exit;
end;
end;
I'm having a problem here, when debugging I see the text property being changed correctly, but no changes are made to the form being displayed.
TEvents = class
...
function TEvents.EditFillUser(AComponent: TComponent;AForm: TForm): Boolean;
begin
TEdit(AComponent).Text:=IntToStr(0);
Result:=True;
end
I'm thinking it may be a problem that the variable is being passed by value ... Can someone help me?
Edit 1:
I've tried with the dictionary declared like this:
FDictionary: TDictionary<TComponent, TEventBeforeInsert>;
...
if Not FDictionary.Items[Item](Item,Self) then //call
And I also tried use TForm reference like this:
function TEvents.EditFillUser(AComponent: String;AForm: TForm): Boolean;
begin
TEdit(AForm.FindComponent(AComponent)).Text:=IntToStr(0);
Result:=True;
end
In TFormBase.addStringField(), you are not assigning a Name value to the newly create TEdit object before inserting it into FDictionary.. Only components created at design-time have auto-generated Names. Components created at run-time do not. So, you are tracking your objects using blank Names. If you want to track the objects by Name, you need to actually assign your own value to FEdit.Name, eg:
function TFormBase.addStringField(AField: TFieldBase; ATab: TTabsNames): TFormBase;
var
...
FEdit: TEdit;
FEvent: TEventBeforeInsert;
begin
...
FEdit := TEdit.Create(Self);
FEdit.Name := 'SomeUniqueNameHere'; // <-- for you to decide on...
...
FEvent := AField.EventBeforeInsert;
if Assigned(FEvent) then
FDictionary.Add(FEdit.Name, FEvent);
end;
However, in this particular case, I see no reason to use a TDictionary at all. Consider using a TList instead, then you don't need the Names at all. This will also boost the performance of the iteration in TFormBase.rectInsertClick() since it won't have to hunt for every TComponent object using FindComponent() anymore:
TFormBase = class(TForm)
private
type TEventBeforeInsertPair = TPair<TComponent, TEventBeforeInsert>;
FBeforeInsertEvents: TList<TEventBeforeInsertPair>;
...
public
constructor Create;
destructor Destroy; override;
...
end;
...
constructor TFormBase.Create;
begin
inherited;
FBeforeInsertEvents := TList<TEventBeforeInsertPair>.Create;
end;
destructor TFormBase.Destroy;
begin
FBeforeInsertEvents.Free;
inherited;
end;
function TFormBase.addStringField(AField: TFieldBase; ATab: TTabsNames): TFormBase;
var
...
FEdit: TEdit;
FEvent: TEventBeforeInsert;
begin
...
FEdit := TEdit.Create(Self);
...
FEvent := AField.EventBeforeInsert;
if Assigned(FEvent) then
FBeforeInsertEvents.Add(TEventBeforeInsertPair.Create(FEdit, FEvent));
end;
procedure TFormBase.rectInsertClick(Sender: TObject);
var
Item: TEventBeforeInsertPair;
begin
for Item in FBeforeInsertEvents do
begin
if not Item.Value(Item.Key, Self) then
Exit;
end;
end;
...
Also, your TEvents.EditFillUser() method does not match the definition of TEventBeforeInsert. The 1st parameter of TEventBeforeInsert is declared as passing the TComponent pointer by var reference (why?), but the 1st parameter of EditFillUser() is not doing that. Unless you want your event handlers to alter what the TComponent pointers are pointing at (which won't work the way you are currently using TEventBeforeInsert with TDictionary), then there is no reason to pass around the TComponent pointers by var reference at all:
TEventBeforeInsert = function(AComponent: TComponent; AForm: TForm): Boolean of Object;
Also, your use of TEvents.New appears to be a memory leak, as nobody is taking ownership of the newly created TEvents object (unless its constructor is adding the object to some internal list that we can't see). Same with TFieldBase.New. And even TFormBase.New (assuming there is no OnClose event that sets Action=caFree when the Form is closed). At some point, you need to call Free() any class object that you Create().
In Embarcadero Delphi XE7, I use a component which has a help-button.
In the component (which shows a message dialog), I specify a help context number. If the user clicks on the button, the help should show, but I get an error instead:
Project ... raised exception class $C00000FD with message 'stack overflow at 0x006f089e'.
The command executed when the user clicks on the button is:
Application.HelpContext(HelpContextNumber);
On Launch HTML Help as Separate Process, I read that I should attach an OnHelp event handler to the Application object.
I saved the Help unit but how do I attach it?
Application.OnHelp := ....?
The TApplication.OnHelp event is declared as a THelpEvent:
THelpEvent = function(Command: Word; Data: THelpEventData; var CallHelp: Boolean): Boolean of object;
So, you would need to declare a method in your Form like this:
type
TMyForm = class(TForm)
...
private
function MyOnHelpHandler(Command: Word; Data: THelpEventData; var CallHelp: Boolean): Boolean;
...
end;
And then you can assign that handler to the TApplication.OnHelp event at runtime, eg:
procedure TMyForm.FormCreate(Sender: TObject);
begin
Application.OnHelp := MyOnHelpHandler;
end;
procedure TMyForm.FormDestroy(Sender: TObject);
begin
Application.OnHelp := nil;
end;
function TMyForm.MyOnHelpHandler(Command: Word; Data: THelpEventData; var CallHelp: Boolean): Boolean;
begin
Result := ...;
end;
Alternatively, you can drop a TApplicationEvents component onto your Form at design-time, and then create an OnHelp event handler for it using the Object Inspector.
Delphi XE6 - I have a Unit (EMAIL1.pas) which does related processing. This is meant to be a standalone unit I can incorporate into multiple programs. My initial procedure is called GetDetailsFromEmailAddress. It has two parameters, an email address which I lookup and a "group of data" which will get updated, currently defined as a var. This can be a record or a class, I don't really care. It is just a group of related strings (firstname, last name, city, etc). Let's call this EmpRec.
My challenge is that this procedure creates an instance of a class (JEDI VCL HTMLParser) which uses a method pointer to call a method (TableKeyFound). This routine needs to update EmpRec. I do not want to change this code (HTMLPArser routine) to add additional parameters. There are several other procedures that my UNIT creates. All of them need to read/update EmpRec. How do I do this?
I need a way to "promote" the variable EmpRec which is passed in this one routine (GetDetailsFromEmailAddress) to be GLOBAL within this UNIT so that all the routines can access or change the various elements. How do I go about this? I do NOT really want to have to define this as a GLOBAL / Application wide variable.
Code sample below. So.. How does the routine TableKeyFoundEx get access to the EmpRec variable?
procedure GetDetailsFromEmailAddress(Email: string; var EmpRec: TEmpRec);
begin
...
// Now create the HTML Parser...
JvHtmlParser1 := TJvHTMLParser.Create(nil);
// On event KeyFoundEx, call Parsehandlers.TableKeyFoundEx;
JvHtmlParser1.OnKeyFoundEx := ParseHandlers.TableKeyFoundEx;
...
end.
procedure TParseHandlers.TableKeyFoundEx(Sender: TObject; Key, Results, OriginalLine: String; TagInfo: TTagInfo;
Attributes: TStrings);
begin
..
// NEED ACCESS to EmpRec here, but can't change procedure definition
end;
There are two different ways I would approach this:
use the parser's Tag property:
procedure GetDetailsFromEmailAddress(Email: string; var EmpRec: TEmpRec);
begin
...
JvHtmlParser1 := TJvHTMLParser.Create(nil);
JvHtmlParser1.OnKeyFoundEx := ParseHandlers.TableKeyFoundEx;
JvHtmlParser1.Tag := NativeInt(#EmpRec);
...
end;
procedure TParseHandlers.TableKeyFoundEx(Sender: TObject; Key, Results, OriginalLine: String; TagInfo: TTagInfo; Attributes: TStrings);
var
EmpRec: PEmpRec; // assuming PEmpRec = ^TEmpRec
begin
EmpRec := PEmpRec(TJvHTMLParser(Sender).Tag);
...
end;
use a little TMethod hack to pass the record DIRECTLY to the event handler:
// Note: this is declared as a STANDALONE procedure instead of a class method.
// The extra DATA parameter is where a method would normally pass its 'Self' pointer...
procedure TableKeyFoundEx(Data: Pointer: Sender: TObject; Key, Results, OriginalLine: String; TagInfo: TTagInfo; Attributes: TStrings);
var
EmpRec: PEmpRec; // assuming PEmpRec = ^TEmpRec
begin
EmpRec := PEmpRec(Data);
...
end;
procedure GetDetailsFromEmailAddress(Email: string; var EmpRec: TEmpRec);
var
M: TMethod;
begin
...
JvHtmlParser1 := TJvHTMLParser.Create(nil);
M.Code := #TableKeyFoundEx;
M.Data := #EmpRec;
JvHtmlParser1.OnKeyFoundEx := TJvKeyFoundExEvent(M);
...
end;
In addition to the two options that Remy offers, you could derive a sub-class of TJvHTMLParser.
type
PEmpRec = ^TEmpRec;
TMyJvHTMLParser = class(TJvHTMLParser)
private
FEmpRec: PEmpRec;
public
constructor Create(EmpRec: PEmpRec);
end;
....
constructor TMyJvHTMLParser.Create(EmpRec: PEmpRec);
begin
inherited Create(nil);
FEmpRec := EmpRec;
end;
When you create the parser, do so like this:
procedure GetDetailsFromEmailAddress(Email: string; var EmpRec: TEmpRec);
var
Parser: TMyJvHTMLParser;
begin
Parser := TMyJvHTMLParser.Create(#EmpRec);
try
Parser.OnKeyFoundEx := ParseHandlers.TableKeyFoundEx;
....
finally
Parser.Free;
end;
end.
And in your OnKeyFoundEx you cast Sender back to the parser type to gain access to the record:
procedure TParseHandlers.TableKeyFoundEx(Sender: TObject; ...);
var
EmpRec: PEmpRec;
begin
EmpRec := (Sender as TMyJvHTMLParser).FEmpRec;
....
end;
I used to drop TZipForge component on a form so I could use its event handlers. Now, I'm using several thread worker to extract some zip files, therefore I create an instance of the TZipForge class as a local variable. How do I make the event handlers without Event tab in Object Inspector?
To create a event hanlder manually yo must create a procedure with match with the declaration of the target event and then assign the Address of that procedure to the event of the class, for example if you want to create a event handle for the OnFileProgress event you must create a procedure like this inside of your class.
procedure FileProgress(Sender: TObject; FileName: string;
Progress: Double; Operation: TZFProcessOperation;
ProgressPhase: TZFProgressPhase; var Cancel: Boolean);
Check this sample
procedure TForm1.FileProgress(Sender: TObject; FileName: string;
Progress: Double; Operation: TZFProcessOperation;
ProgressPhase: TZFProgressPhase; var Cancel: Boolean);
begin
//do your stuff here
end;
procedure TForm1.FormCreate(Sender: TObject);
var
Archiver : TZipForge;
begin
Archiver := TZipForge.Create(nil);
try
Archiver.OnFileProgress:=FileProgress;//<- Here the event handler is assigned
Archiver.FileName := 'compressedfile.zip';
Archiver.OpenArchive(fmOpenRead);
try
Archiver.BaseDir := 'C\Foo';
Archiver.ExtractFiles('*.*');
finally
Archiver.CloseArchive();
end;
finally
Archiver.Free;
end;
end;
If I try to use a closure on an event handler the compiler complains with :
Incompatible types: "method pointer and regular procedure"
which I understand.. but is there a way to use a clouser on method pointers? and how to define if can?
eg :
Button1.Onclick = procedure( sender : tobject ) begin ... end;
Thanks!
#Button1.OnClick := pPointer(Cardinal(pPointer( procedure (sender: tObject)
begin
((sender as TButton).Owner as TForm).Caption := 'Freedom to anonymous methods!'
end )^ ) + $0C)^;
works in Delphi 2010
An excellent question.
As far as I know, it's not possible to do in current version of Delphi. This is much unfortunate since those anonymous procedures would be great to have for quickly setting up an object's event handlers, for example when setting up test fixtures in a xUnit kind of automatic testing framework.
There should be two ways for CodeGear to implement this feature:
1: Allow for creation of anonymous methods. Something like this:
Button1.OnClick := procedure( sender : tobject ) of object begin
...
end;
The problem here is what to put as the self pointer for the anonymous method. One might use the self pointer of the object from which the anonymous method was created, but then one can only create anonymous methods from an object context. A better idea might be to simply create a dummy object behind the scenes to contain the anonymous method.
2: Alternatively, one could allow Event types to accept both methods and procedures, as long as they share the defined signature. In that way you could create the event handler the way you want:
Button1.OnClick := procedure( sender : tobject ) begin
...
end;
In my eyes this is the best solution.
In previous Delphi versions you could use a regular procedure as event handler by adding the hidden self pointer to the parameters and hard typecast it:
procedure MyFakeMethod(_self: pointer; _Sender: TObject);
begin
// do not access _self here! It is not valid
...
end;
...
var
Meth: TMethod;
begin
Meth.Data := nil;
Meth.Code := #MyFakeMethod;
Button1.OnClick := TNotifyEvent(Meth);
end;
I am not sure the above really compiles but it should give you the general idea. I have done this previously and it worked for regular procedures. Since I don't know what code the compiler generates for closures, I cannot say whether this will work for them.
Its easy to extend the below to handle more form event types.
Usage
procedure TForm36.Button2Click(Sender: TObject);
var
Win: TForm;
begin
Win:= TForm.Create(Self);
Win.OnClick:= TEventComponent.NotifyEvent(Win, procedure begin ShowMessage('Hello'); Win.Free; end);
Win.Show;
end;
Code
unit AnonEvents;
interface
uses
SysUtils, Classes;
type
TEventComponent = class(TComponent)
protected
FAnon: TProc;
procedure Notify(Sender: TObject);
class function MakeComponent(const AOwner: TComponent; const AProc: TProc): TEventComponent;
public
class function NotifyEvent(const AOwner: TComponent; const AProc: TProc): TNotifyEvent;
end;
implementation
{ TEventComponent }
class function TEventComponent.MakeComponent(const AOwner: TComponent;
const AProc: TProc): TEventComponent;
begin
Result:= TEventComponent.Create(AOwner);
Result.FAnon:= AProc;
end;
procedure TEventComponent.Notify(Sender: TObject);
begin
FAnon();
end;
class function TEventComponent.NotifyEvent(const AOwner: TComponent;
const AProc: TProc): TNotifyEvent;
begin
Result:= MakeComponent(AOwner, AProc).Notify;
end;
end.