I'm learning OOP and I have created a basic program so far. I have create my own clas:
Type
Zombie = class
private
fLife : Integer;
fAge : Integer;
fHeight: String;
public
Constructor Create(pLife, pAge : Integer; pHeight : String);
Procedure SetLife(pLife : Integer);
function GetLife : Integer;
Procedure ShowLife;
end;
The procedure ShowLife does exactly what it says:
procedure Zombie.ShowLife;
begin
ShowMessage(inttostr(fLife));
end;
I'm trying to call this procedure on a Form but it says undeclared identifier:
procedure Tform1.ShowLifebtnClick(Sender: TObject);
begin
Zombies_Unit.ShowLife;
end;
I have included the unit in the user of the Form. How can I use methods on another form
You need to create and free the object before/after you use it. The pattern is like this:
MyZombie := TZombie.Create(10, 20, 30);
try
MyZombie.ShowLife();
finally
MyZombie.Free();
end;
You have to create an instance of your class and call the method of that object like
MyZombie := Zombie.create(20,15);
MyZombie.ShowLife;
...
MyZombie.free;
Sending from mobile, cannot format code.
EDIT/SUPPLEMENT:
As my short answer seems to be suitable to tech bad habits (I am sorry for that) I want to add the following advices to the asker:
Please use Try/Finally constructs to avoid that objects are not removed in case of an error occuring between create() and free() like Zdravko Danev's answer points out. It also makes sense to use common naming conventions to make your code easier to understand (e.g. TZombie as class name).
You must pay attention in one thing: Your class is in the same file of your form? If the answer is no, you must declare the unit name on uses of your form file like:
unit MyUnit;
interface
uses
Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,
Dialogs;
type
TMyForm = class(TForm)
private
{ Private declarations }
public
{ Public declarations }
end;
var
MyForm: TMyForm;
implementation
uses unitzombie; //The name unit where is your class
{$R *.dfm}
end.
After solving this little problem, you must create your object before calling this methods:
procedure Tform1.ShowLifebtnClick(Sender: TObject);
var
Zombi: Zombie;
begin
Zombi := Zombie.Create(5,10,15);
try
Zombi.ShowLife;
finally
Zombi.Free;
end;
end;
Related
I'm doing a simple class definition in Delphi and I wanted to use a TStringList in the class & it's constructor (so everytime you create an object, you pass it a StringList and it does some magic stuff to the StringList data, copying the string list to it's own internal string list). The problem I get is that when I try to declare what it "uses" before the class definition (so it knows how to handle the TStringList), it fails on compile. But without that, it doesn't know what a TStringList is. So it seems to be a scoping issue.
Below is a (very simplified) class definition, similar to what I'm trying to do. Can someone suggest how I can make this work and get the scoping right?
I tried adding the uses statements at the project level as well, but it still fails. I wonder what I need to do to get this right.
unit Unit_ListManager;
interface
type
TListManager = Class
private
lmList : TStringList;
procedure SetList;
published
constructor Create(AList : TStringList);
end;
implementation
uses
SysUtils,
StrUtils,
Vcl.Dialogs;
constructor TBOMManager.Create(AList : TStringList);
begin
lmList := TStringList.Create;
lmList := AListList;
end;
procedure SetPartsList(AList : TStringList);
begin
lmList := AListList;
ShowMessage('Woo hoo, got here...');
end;
end.
Kind Regards
You didn't show where exactly you were adding the unit reference, but I'm betting it was the wrong place. Take note of the additional code between interface and type.
I've also corrected your definition of the constructor, which you had placed in published instead of public. Only property items belong in the published section.
unit Unit_ListManager;
interface
uses
Classes,
SysUtils,
StrUtils,
Vcl.Dialogs;
type
TListManager = Class
private
lmList : TStringList;
procedure SetList;
public
constructor Create(AList : TStringList);
end;
implementation
constructor TListManager.Create(AList : TStringList);
begin
inherited Create; // This way, if the parent class changes, we're covered!
// lmList := TStringList.Create; This would produce a memory leak!
lmList := AListList;
end;
procedure TListManager.SetList;
begin
// You never provided an implementation for this method
end;
end.
For example, I have a couple of functions written for my form. Now, I need the exact same functions in another form. So, how can I share them between the two forms? Please, provide a simple example if possible.
Don't put them in your form. Separate them and put them in a common unit, and add that unit to the uses clause where you need access to them.
Here's a quick example, but you can see many of the Delphi RTL units (for instance, SysUtils) that do this. (You should learn to use the VCL/RTL source and the demo apps that are included in Delphi; they could answer many of the questions you've posted more quickly than waiting for an answer here.)
SharedFunctions.pas:
unit
SharedFunctions;
interface
uses
SysUtils; // Add other units as needed
function DoSomething: string;
implementation
function DoSomething: string;
begin
Result := 'Something done';
end;
end.
UnitA.pas
unit
YourMainForm;
uses
SysUtils;
interface
type
TMainForm = class(TForm)
procedure FormShow(Sender: TObject);
// other stuff
end;
implementation
uses
SharedFunctions;
procedure TMainForm.FormShow(Sender: TObject);
begin
ShowMessage(DoSomething());
end;
end.
In more recent versions of Delphi than Delphi 7, you can create the functions/methods in a record instead:
unit
SharedFunctions;
interface
uses
SysUtils;
type
TSharedFunctions = record
public
class function DoSomething: string;
end;
implementation
function TSharedFunctions.DoSomething: string;
begin
Result := 'Something done';
end;
end;
UnitB.pas
unit
YourMainForm;
uses
SysUtils;
interface
type
TMainForm = class(TForm)
procedure FormShow(Sender: TObject);
// other stuff
end;
implementation
uses
SharedFunctions;
procedure TMainForm.FormShow(Sender: TObject);
begin
ShowMessage(TSharedFunctions.DoSomething());
end;
end.
If you need forms. You could use inherited forms. Creating a form that inherit the functions of a parent form.
The most interesting. Any changes in the parent form is reflected a change in inherited forms. You even can inherit form controls (tbutton, tlabel, etc...).
In GUI Delphi7. Option "new form", option "inherited from a existing form".
Example:
//MainForm.pas
type
TMainForm = class(TForm)
procedure MiFunction();
.
.
end;
//ChilForm.pas
type
TChildForm = class(TMainForm)
.
.
end;
It is possible to have a parameter in a routine which can be in the same time either an type, either an string? I know I can accomplish this by overloading a routine, I ask if it possible to do it in another way.
Assume that I have this type - TTest = (t1,t2,t3). I want to have a routine which accepts a parameter of type TTest, but in the same time to be a String, so I can call it myproc(t1) or myproc('blabla')
You should use an overloaded function.
You already have the perfect solution to the problem and there is no need to look for a different way to do this. You could try with a single function that receives a Variant, but then that function will also receive anything which means that the following would also be legal:
myproc(0.5);
myproc(intf);
myproc(-666);
Using an overload allows you to maintain compile time type safety and there is absolutely no loss of generality in using an overload.
Even this can be easily accomplished with overloaded functions, considering it's a good exercise, based on David Hefferman's and Sertac Akyuz answers I made a small example to test both solutions. It is not perfect, it only shows both possibilities.
unit Unit4;
interface
uses
Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,
Dialogs;
type
ttest = (t1,t2);
TForm4 = class(TForm)
procedure FormCreate(Sender: TObject);
private
{ Private declarations }
public
{ Public declarations }
function my(aVar:Variant):String;
function MyUntype(const aVar):String;
end;
var
Form4: TForm4;
implementation
{$R *.dfm}
{ TForm4 }
procedure TForm4.FormCreate(Sender: TObject);
var aTestTypeVar : ttest;
aString : String;
begin
my(t1);
my(t2);
my('ssss');
//with untyped params
aString := 'aaaa';
MyUntype(aString);
aTestTypeVar := t1;
aString := IntToStr(Ord(aTestTypeVar));
MyUntype(aString);//can not be a numeral due to delphi Help
end;
function TForm4.my(aVar: Variant): String;
begin
showmessage(VarToStr(aVar));//shows either the string, either position in type
end;
function TForm4.MyUntype(const aVar): String;
begin
//need to cast the parameter
try
ShowMessage(pchar(aVar))
except
showmessage(IntToStr(Ord(ttest(aVar))));
end;
end;
end.
Also I know that Variants are slow and must be used only needed.
i can't figure out the formatting rules here .. too many lines of code in my example to add 4 spaces to each line, so here is the link to the code i need help with
http://nitemsg.blogspot.com/2011/01/heres-unit-written-in-delphi-7-that-you.html
The problem I have is that I don't know enough about delphi to use this code with a form.
I am a drag and drop programmer only.
An example with a showmessage('friendly name =' + ... ) when a USB device is detected is what I need.
cheers,
If you are only familiar with drag-and-drop programming, and don't know much about objects or other units, then you need to get yourself familiarized with using objects other than auto-created forms and the components you drop in them.
The code at this link is an entire unit. You need to create a new Unit in your project (File > New > Unit). It will look something like this:
unit Unit1;
interface
implementation
end.
Now when you save the unit, the name of the unit will automatically change to the filename (without the extension) like this:
unit MahUSB;
interface
implementation
end.
In this example, you should use the same unit name as that source you're trying to use. Save the unit as 'MahUSB.pas', and should be in the same folder as the rest of your project (or elsewhere, just a suggestion). Copy/Paste all the code from that website and replace everything in this unit now.
Now in order to actually use this, you need to create an instance of this object. ONLY ONE INSTANCE (I say that just because by the looks of this, there's no need for more than one).
Very important: Seeing as you are not familiar with objects, let me quickly explain something. Objects need to be created in order to work. At the same time, anything that's created also needs to be free'd when you're done with it. In this case, we will create this object when your application starts, and free the object when your application closes.
Now on your MAIN FORM (not any other forms) you need to put an event handler for both OnCreate and OnDestroy. You also need to declare a variable to represent this object. In the declaration of your main form, add a variable 'USB' with the type of this object. Make sure that goes under the 'private' or 'public' section, either one is ok. Also make sure you declare the "MahUSB" unit at the top of your main unit in the uses clause.
Declaring the object in your main form:
type
TForm1 = class(TForm)
private
USB: TUsbClass;
public
end;
Creating/freeing object when your app starts/closes:
procedure TForm1.FormCreate(Sender: TObject);
begin
USB:= TUsbClass.Create;
end;
procedure TForm1.FormDestroy(Sender: TObject);
begin
if assigned(USB) then USB.Free;
end;
Now we're not done yet. Now we need to add the event handlers. Notice at the top of this unit you got, there are two types called TOnDevVolumeEvent and TOnUsbChangeEvent. These are event types. The parameters in the event handlers must be identical to the parameters declared in these types. So now in your main form, declare these event handler procedures...
type
TForm1 = class(TForm)
procedure FormCreate(Sender: TObject);
procedure FormDestroy(Sender: TObject);
private
USB: TUsbClass;
procedure VolumeEvent(const bInserted : boolean; const sDrive : string);
procedure ChangeEvent(const bInserted : boolean;
const ADevType,ADriverName, AFriendlyName : string);
public
end;
Now just one more thing we have to do before this will work. The USB object needs to know what event handlers to use, therefore, we need to assign these procedures to the events. Upon your form's creation, we need to assign these events...
procedure TForm1.FormCreate(Sender: TObject);
begin
USB:= TUsbClass.Create;
USB.OnUsbChange:= Self.ChangeEvent;
USB.OnDevVolume:= Self.VolumeEvent;
end;
When all is said and done, your main form unit should look something like this:
unit uUSBTest;
interface
uses
Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,
Dialogs, MahUSB;
type
TForm1 = class(TForm)
procedure FormCreate(Sender: TObject);
procedure FormDestroy(Sender: TObject);
private
USB: TUsbClass;
procedure VolumeEvent(const bInserted : boolean; const sDrive : string);
procedure ChangeEvent(const bInserted : boolean;
const ADevType,ADriverName, AFriendlyName : string);
public
end;
var
Form1: TForm1;
implementation
{$R *.dfm}
procedure TForm1.ChangeEvent(const bInserted: boolean; const ADevType,
ADriverName, AFriendlyName: string);
begin
ShowMessage('Change event for "'+AFriendlyName+'"');
end;
procedure TForm1.VolumeEvent(const bInserted: boolean;
const sDrive: string);
begin
ShowMessage('Volume event for "'+sDrive+'\"');
end;
procedure TForm1.FormCreate(Sender: TObject);
begin
USB:= TUsbClass.Create;
USB.OnUsbChange:= Self.ChangeEvent;
USB.OnDevVolume:= Self.VolumeEvent;
end;
procedure TForm1.FormDestroy(Sender: TObject);
begin
if assigned(USB) then USB.Free;
end;
end.
And there you are! You will have these two event handler procedures where you can further handle either of those two events.
I have the following code which is working, but I don't understand it 100% (please see the comments from code):
unit Unit1;
interface
uses
Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,
Dialogs;
type
TMyRec=record
a:Integer;
b:String;
end;
TRecArray=array of TMyRec;
PRecArray = ^TRecArray;
TForm1 = class(TForm)
procedure FormCreate(Sender: TObject);
private
{ Private declarations }
public
v1:TRecArray;
procedure Test(a:PRecArray);
{ Public declarations }
end;
var
Form1: TForm1;
implementation
{$R *.dfm}
{ TForm1 }
procedure TForm1.FormCreate(Sender: TObject);
begin
SetLength(v1,3);
v1[0].b:='test1';//set the first value
Test(PRecArray(v1));//call method to change the value assigned before
end;
procedure TForm1.Test(a: PRecArray);
begin
ShowMessage(v1[0].b);//shows test1
try
a^[0].b:='test2' //this is raising an error...
except
end;
PRecArray(#a)^[0].b:='test3';//this is working...
ShowMessage(v1[0].b);//shows test3
end;
end.
I don't understand why 'a^[0].b:='test2' is raising an error.
Thank you!
Your 'Test' procedure expects a 'PRecArray', but you're passing a 'TRecArray' to it. Try calling it like
Test(#v1);//call method to change the value assigned before
Typecasting a 'TRecArray' to a 'PRecArray' will not make it a 'PRecArray'. (Note: your 'test3' will fail then of course.)
I see several things that are suspicious.
1
There is hardly ever a need to take a pointer to a dynamic array, as dynamic array variables are already pointers (well, references).
To pass such an array to a function or procedure, use var parameters:
procedure TForm1.Test(var a: TRecArray);
Now you don't have to use pointer syntax to access the array:
a[0].b := 'test2';
2
You call Test with:
Test(PRecArray(v1));
In your original, Test took a PRecArray, but you are not passing one (you are passing a TRecArray), so you should have done:
Test(#v1); // or Test(Addr(v1));
Applying my change above, where Test has a var parameter, simply use:
Test(v1);
3
Ok, this is probably not suspicous, but I'd like to plug my article Addressing Pointers, about pointers for Delphi programmers. It explains many of the issues you seem to have.
You could replace the
procedure TForm1.Test(a: TPointerArrayRec);
with
procedure TForm1.Test(var a: TArrayRec);
it's simpler and you don't have to use the deprecation dereference operator ^.