I have a datamodule for my frame, which uses a global instance.(dmData)
The data components are linked to the datasources on the dmData instance
now I want to use a datamodule instance that is private to a frame, because I want to have multiple instances of the form which contains the frame showing at the same time.
I can't figure out how to make that happen, either in code or in designing.
in the frame, I am creating the datamodule as dmLocalData := tdmData.Create(self), but in design I don't have the option to link dmLocalData, only the option to link to dmData(so all my data controls are blank (except for that ONE that has a local datasource that gets set in code)
I mean, in code, I could manually go through each component one by one and change the datasource, but thinking there really has to be a better way, the maintenance on that would be pretty much horrendous.
Any ideas about a better way?
Actually there is a way to avoid hand-wiring the controls for a dynamically created datamodule. In short - override the datamodules CreateNew constructor like this:
constructor TMainDM.CreateNew(AOwner: TComponent; Dummy: Integer);
begin
Dummy := -1;
inherited;
end;
This avoids that multiple instances of the datamodule get different names and thus the references are resolved as expected. As the datamodules are private to the frame anyway, there is no need for them to have globally unique names.
A much longer and more detailed explanation can be found in these two articles, which use a quite similar task as an example:
Tweaking DFM Loading (update)
Tweaking DFM Loading
Related
In DPR file:
Application.CreateForm(TMain, Main);
Application.CreateForm(TCommStatus, CommStatus);
But I get an error if I want to use CommStatus in Main, because it was not instanced yet. Then inside TMain I tried:
procedure TMainWindow.FormShow(Sender: TObject);
begin
Application.CreateForm(TCommStatus, CommStatus);
CommStatus.Expand(Self);
end;
I was trying to have my LOG window to be positioned and sized according to my MainWindow position and width. But as my LOG window is created after Main Window, I can't really call it in OnCreate(), even because there is no correct positioning data in OnCreate().
Don't use Application.CreateForm to create the CommStatus form at all. Create it yourself in your MainWindow.OnCreate:
proccedure TMainForm.FormCreate(Sender: TObject);
begin
CommStatus := TCommStatus.Create(Self);
CommStatus.Expand(Self);
end;
Don't forget to remove CommStatus from the auto-create forms list (in Project->Options->Forms).
I need to know if CommStatus is Assigned before execute CreateForm.
You answered your own question - use Assigned(), eg:
uses
..., CommStatusFormUnit;
if not Assigned(CommStatus) then
Application.CreateForm(TCommStatus, CommStatus);
Or:
uses
..., CommStatusFormUnit;
if not Assigned(CommStatus) then
CommStatus := TCommStatus.Create(Application);
Global variables, like the CommStatus variable in the CommStatusFormUnit unit, are zero-initialized at program startup, thus Assinged() will return False until the form is actually created, as long as you assign the new Form instance to the global variable (as the examples above do).
But CommStatus identifier does not exists until it. So I can't use Assigned(CommStatus).
Yes, it does exist, and yes, you can use Assigned(CommStatus). If you are having errors with it, then you are not using it correctly.
Expand(Self) should use Main position information to put CommStatus beside Main in the same left position, but it doesn't.
Then you are not handling the positioning logic correctly.
Another option is to create CommStatus first in your DPR. But without using Application.CreateFom (which would then incorrectly make CommStatus you main form).
This way you'll know it has definitely been created, and not have to worry.
I.e.
CommStatus := TCommStatus.Create(Application);
Application.CreateForm(TMain, Main);
However, that fact that you're trying to Expand CommStatus in the OnShow of your main form seems a little dubious to me. You've created a hidden dependency between the two forms, which is exactly one of the reasons globals are frowned upon.
One option to clean that up would be as follows:
CommStatus := TCommStatus.Create(Application);
Application.CreateForm(TMain, Main);
CommStatus.Expand(Main);
This way the relationship between the two is explicit and less error-prone.
I have a Form which has data aware controls bound to datasets in a datamodule. I need to create additional instances of both the form and datamodule in the same application.
I deleted the global variable that was automatically created when the data module was first added to the project. To my delight, controls in the designer could still be bound to datasets in the data module without this global variable. I'm assuming the IDE is parsing the dfm of the datamodule so the designer can still "see" the datamodule. (without the data module loaded in the IDE the list of data sources is empty)
When I create two instances of the form and two instances of the datamodule at runtime both instances of the form appear to be bound to only the first data module that was created. Inspecting the second instance of the data module reveals that the Name property has a number suffix that wasn't there at design time.
The form depends on a lot of datasets in the data module. Is there an easier way to bind the second form instance to the second data module's datasets without resorting to hand coded SomeControl.DataSource := Module2.dsSomeData for every single control?
I'm open to alternative suggestions as well. One solution would be to move the datasets to the form itself. Still it seems a shame if design time data binding only works on singletons.
Take a look at this question:
separate dataset instances using datamodules in delphi
Basically the answer is to create your DataModule, then your Form, then set the name of the created DataModule to an empty string. That will let the initial data binding happen but prevent other forms from seeing that Module.
In addition the next version that is created will still have the original name (no need for the numeric suffix).
I have a Form which has data aware controls bound to DataSets in a DataModule.
That is not possible. Indirectly, ok agreed, but there has to be a necessary DataSource in between. (From the rest of your question we have to distill the information that those DataSources are on the DataModule, but the question could certainly be more transparent about that.)
I deleted the global variable that was automatically created when the DataModule was first added to the project.
Good, stick to that custom!
To my delight, controls in the designer could still be bound to DataSets in the DataModule without this global variable. I'm assuming the IDE is parsing the dfm of the DataModule so the designer can still "see" the DataModule.
Same incorrectness/confusion between DataSource and DataSet, but you are partly right: for the IDE being able to find a DataModule, the following must be true:
The DataModule must be created/opened at least once during the session of the IDE (it may be closed afterwards during the session), see (*),
The unit of that DataModule must be present in the uses list of the Form unit.
When I create two instances of the Form and two instances of the DataModule at runtime, both instances of the Form appear to be bound to only the first DataModule that was created.
That is because you are depending on the automatic design time binding which does not work at runtime. That binding depends on the name of the DataModule. But this is not the only disadvantage of depending on design time binding, see (*).
Inspecting the second instance of the DataModule reveals that the Name property has a number suffix that wasn't there at design time.
Plus an underscore in front of that sequential number suffix. It seems to be by design. There cannot be multiple DataModules (nor Forms) with the same name, which is comparable with Components not capable of having the same name of that of a sibling or child Component. It is a little strange though, because when giving no Owner or even different Owners, the same rule still applies for DataModules and Forms, which is unlike default TComponent behaviour. I cannot find evidence nor an explanation in the RTL/VCL code. Maybe it has something to do with all DataModules and Forms being kept in the Screen variable. We just have to accept, but it is a no-problem.
The Form depends on a lot of DataSets in the DataModule. Is there an easier way to bind the second Form instance to the second DataModule's DataSets without resorting to hand coded SomeControl.DataSource := Module2.dsSomeData for every single control? ... One solution would be to move the DataSets to the Form itself.
Wherein dsSomedata being the DataSource!
Yes, there is an easier way. Instead of placing the DataSets on the Form, place the DataSources on the Form. Typically, a Form often has only a single or few DataSources compared to the number of data controls. That way the data control - DataSource binding remains intact (because both are read from the same DFM), and only the DataSet settings of the DataSources remain to be set manually:
TCustomerForm = class(TForm)
DataSource: TDataSource;
procedure FormCreate(Sender: TObject);
private
FData: TCustomerDataModule;
end;
procedure TCustomerForm.FormCreate(Sender: TObject);
begin
FData := TCustomerDataModule.Create(Self);
DataSource.DataSet := FData.Query;
end;
Or, when you want to create the Form from the DataModule:
TCustomerForm = class(TForm)
DataSource: TDataSource;
private
FData: TCustomerDataModule;
procedure SetData(Value: TCustomerDataModule);
public
property Data: TCustomerDataModule read FData write SetData;
end;
procedure TCustomerForm.SetData(Value: TCustomerDataModule);
begin
if FData <> Value then
begin
FData := Value;
DataSource.DataSet := FData.Query;
end;
end;
(*) In large projects with many Forms and DataModules, it is very common to not open every DataModule in the IDE, and (DataSource.)DataSet settings easily can get lost. Being dependent on the designtime binding by DataModule name then may result in your Forms never showing any data. This is a bug which is hard to foresee whithout checking every Form's (DataSource.)DataSet settings.
Doing it all in the above outlined manner ensures correct DataModule creation at runtime, and ensures all designtime capabilities and cleverness of the IDE providing DataSets, Fields, etc...
I have the same issue. I used the following solution.
My 2 instances of the form share the same DataModule instance. The 2 forms don't show up at the same time. I have the advantage, that the 2 forms show always the same data, since my data is in memory cached, with the TCLientDataSet.
e.g.
_dmSachkonto := TCachedDataModules.Instance.Add(TdmSachkonto) as TdmSachkonto;
TdmSachkonto is my DataModule.
I has a piece of code where I override TStringGrid's inplace editor and the hint window. For this, I created my own string grid based on TStringGrid and use a TEdit for inplace editor and a TPanel for tool tips. In TMyStringGrid.Create constructor I initialize them like this:
Constructor TMyStringGrid.Create();
Begin
inherited Create(AOwner);
MyEditor:= TEdit.Create(Self);
MyEditor.Parent := Self;
End;
In this case the owner (the main form) is freeing the controls. I used this for years and it worked.
The thing is that other people argue that the programmer should use NIL instead the Self when instantiation the child controls and later to manually free them in the Destroy destructor. It seems that the second alternative has gigantic advantage over the first one, especially when you dynamically create lots of child controls (not my case). Other problem with my code, they say, is that the child controls may be freed after an Application.ProcessMessages call while the application may still want to use them.
So, I should let my code unchanged or should I manually create and free the child controls?
There is a any Borland example of compound controls?
Delphi 7, Win XP
Reference: http://delphi.about.com/od/kbcurt/ss/dynamiccreateno.htm
Yes you can use your code without changing it.
There is a any Borland example of compound controls?
Best example is to check the implementation of TLabeledEdit.
It was creating the label in constructor
if Assigned(FEditLabel) then exit;
FEditLabel := TBoundLabel.Create(Self);
FEditLabel.FreeNotification(Self);
FEditLabel.FocusControl := Self;
There's no good reason to pass nil instead of Self in this situation. That AOwner parameter is there specifically for that reason. Take advantage of it.
There's a reason to pass nil when creating a control and manually destroy it, but for a completely different situation: if you're creating a control (typically a form) inside a function. This is a pretty common pattern, for example:
MyDialog := TMyDialog.Create(nil);
try
result := MyDialog.ShowModal;
finally
MyDialog.Free;
end;
There, you want to free it immediately instead of waiting around until the current form gets destroyed, which could be much later. But when it comes to sub-components, you usually want them to be destroyed at the same time as the parent component, not later, so pass Self to AOwner and let the VCL take care of it for you.
Considering that constructor, the grid instance is owned by Aowner (which is tipically a TForm or a TFrame). The inplace editor is owned and parented by the grid instance. I don't see how ProcessMessages would cause destruction of the child objects, since they will be destroyed in the destroying loop of TMyStringGrid. That's nothing I can see of wrong on that implementation - and I use that same design for the components I create. Ownership is there on VCL to easy our lifes when managing objects' lifetime. And is not the case where nil is recomended as owner, which is shown in Mason' answer.
In the pattern shown by Mason , the reason for the NIL is that, without a owner, the object destruction will not enter in a Notification loop. If you create a lot of components which destruction you handle manually, you want to make sure the owner is NIL, otherwise a lot of code get executed (without need) in each component construction/destruction.
Many moons ago, there was an excelent white paper on the web archive of (now defunct) eagle-software.com
In the unit below I have a variable declared in the IMPLEMENTATION section - local to the unit. I also have a procedure, declared in the TYPE section which takes an argument and assigns that argument to the local variable in question. Each instance of this TFrame gets passed a unique variable via passMeTheVar.
What I want it to do is for each instance of the frame to keep its own version of that variable, different from the others, and use that to define how it operates. What seems to be happening, however, is that all instances are using the same value, even if I explicitly pass each instance a different variable.
ie:
Unit FlexibleUnit;
interface
uses
//the uses stuff
type
TFlexibleUnit=class(TFrame)
//declarations including
procedure makeThisInstanceX(passMeTheVar:integer);
private
//
public
//
end;
implementation
uses //the uses
var myLocalVar;
procedure makeThisInstanceX(passMeTheVar:integer);
begin
myLocalVar:=passMeTheVar;
end;
//other procedures using myLocalVar
//etc to the
end;
Now somewhere in another Form I've dropped this Frame onto the Design pane, sometimes two of these frames on one Form, and have it declared in the proper places, etc. Each is unique in that :
ThisFlexibleUnit : TFlexibleUnit;
ThatFlexibleUnit : TFlexibleUnit;
and when I do a:
ThisFlexibleUnit.makeThisInstanceX(var1); //want to behave in way "var1"
ThatFlexibleUnit.makeThisInstanceX(var2); //want to behave in way "var2"
it seems that they both share the same variable "myLocalVar".
Am I doing this wrong, in principle? If this is the correct method then it's a matter of debugging what I have (which is too huge to post) but if this is not correct in principle then is there a way to do what I am suggesting?
EDIT:
Ok, so the lesson learned here is that the class definition is just that. Many classes can go in one unit and all instances of all classes in the Type section share the implementation section of the unit.
myLocalVar is a global variable, but only visible within the unit.
A local variable would be in a procedure/function, like
procedure makeThisInstanceX(passMeTheVar: integer);
var
myLocalVar: Integer;
begin
myLocalVar := passMeTheVar;
end;
if you want an instance variable, that is each frame has its own copy, put it in the class:
type
TFlexibleUnit = class(TFrame)
procedure makeThisInstanceX(passMeTheVar:integer);
private
myLocalVar: Integer;
...
end;
You are calling the makeThisInstanceX method as a class (static) method rather than creating an instance of the class and calling it as an object method. Take a look at this reference:
http://oreilly.com/catalog/delphi/chapter/ch02.html
frame / unit / class / control
I applaud your heroic attempt to better the code. However, judging by your questions and comments I regret to inform you that your understanding is very limited.
A frame is not a unit which is not a class. A frame is a class but not every class is a frame. A frame is a control but not every control is a frame. Units have interface and implementation (and initialization and finalization) sections. Classes have private and public (and protected and published) parts.
I did not put the last paragraph in to try to teach but to allow you to gauge your understanding level. A Delphi developer ought to have no problem with the paragraph. I'm not trying to make you feel bad or to show off - just trying to help. Perhaps Stack Overflow is not the right tool for you at this time.
As somebody just learning Delphi for the first time, I might be confused by some of the seemingly redundant features. But the product has a long history and each addition made sense at the time it was added. It was also easier to learn when you only had to learn it a piece at a time.
Our application used to make use of a common base form that all forms were meant to inherit from. I'd like to get rid of it for a number of reasons, ranging from the need to police that everyone uses it to several annoyances relating to Delphi's VFI implementation. It turns out that the bulk of the features it offered can be done in other, more reliable ways.
The one that I am not so sure about, is automatically positioning all forms in the center of their callers. So if I open Dialog A from my main form, it should be placed over the center of the main form. And if I then open Dialog B from Dialog A, it should be placed over the center of Dialog A and so on.
We used to take care of all this by setting the base form's Position property to poOwnerFormCenter and it worked great. But how do I do this app-wide?
I thought of using Screen.OnActiveFormChange, but I think this happens each time the form receives focus. I also thought of using Application.OnModalBegin but there doesn't seem to be an obvious way to find the form at the point this is called.
Has anyone tried this?
Well, obviously form inheritance is provided to solve exactly the problem you're trying to solve. Any solution is probably going to wind up mimicking form inheritance in some way.
Could you do something as simple as globally searching your code for "= class(TForm)" and replacing the TForm class with either your existing base form or a new, simplified base form class with only the functionality you need?
Failing that, you could try to modify the original TForm class itself to have the positioning behavior you want. Obviously, modifying the supplied classes is a little on the dangerous side.
If you are not going to go with a common base form, then I would suggest placing a non-visual component on each form. That component can inject the behaviors you want into the base form. If you want to have various different behaviors on different forms then give your component a role property that defines what role that form should have, and it can then inject different characteristics based on that role.
BTW, you can also have non-visual form inheritance, which is my preferred method of creating a common base class for all forms. It also has the advantage of adding properties to the form, and then based on those properties you can change the role or behavior of the form.
Without knowing more about your application, my advice would be to add the positioning code to each form individually - the advantages of not having a base class is that it makes it easier to have certain forms that do things slightly differently, and it keeps all the logic of a form together in one place.
I normally use the FormShow event for this, using the SetBounds() procedure.
With other non-form controls you can do the same thing by overriding the CMShowing message.
I took your idea of OnModalBegin and ran with it. The following is a "Hack", but it seems to work. To test simply drag around the form and click the button.
procedure TMainForm.Button1Click(Sender: TObject);
var
mForm: TForm;
begin
mForm := TForm.create(self);
mform.width := 300;
mform.height := 300;
mForm.ShowModal;
mForm.Free;
end;
procedure TMainForm.FormCreate(Sender: TObject);
begin
application.OnModalBegin := modalbegin;
end;
procedure TMainForm.FormShow(Sender: TObject);
begin
if Screen.FormCount>1 then begin
screen.forms[Screen.FormCount-1].left := round((screen.forms[Screen.FormCount-2].left + screen.forms[Screen.FormCount-2].width/2) - screen.forms[Screen.FormCount-1].width/2);
screen.forms[Screen.FormCount-1].top := round((screen.forms[Screen.FormCount-2].top + screen.forms[Screen.FormCount-2].height/2) - screen.forms[Screen.FormCount-1].height/2);
application.processmessages;
screen.forms[Screen.FormCount-1].Caption := inttostr(screen.forms[Screen.FormCount-1].top)+','+inttostr(screen.forms[Screen.FormCount-1].left);
end;
end;
procedure TMainForm.ModalBegin(Sender: TObject);
begin
if Screen.FormCount>=0 then
screen.forms[Screen.FormCount-1].OnShow := FormShow;
end;