How to automatically save the GUI to file? (Paradigm) - user-interface

The good (and bad) old Delphi taught us the "classic" way of building application because of the way we write code "behind" the IDE.
Based on this paradigm, I built some time ago a library that allows me to save/load the GUI to INI file with a single line of code.
LoadForm(FormName)
BAM! That's it! No more INI files!
The library only saves "relevant" properties. For example, for a TCheckBox it saves only its Checked property not also its Color or Top/Left. But it is more than enough.
Saving the form has no issues. However, I have "problems" during app initialization. They are not quite problems, but the initialization code is not that nice/elegant.
For example when I assign Checkbox1.Checked := True it will trigger the OnClick event (supposing that the checkbox was unchecked at design time). But assigning a False value (naturally) will not trigger the OnClick event.
Therefore, I have to manually call CheckBox1Click(Sender) after SaveForm(FormName) to make sure that whatever code is in CheckBox1Click, it gets initialized. But this raises another problem. The CheckBox1Click(Sender) might be called twice during application start up (once by SaveForm and once my me, manually).
Of course, in theory the logic of the program should be put in individual objects and separated from the GUI. But even if we do this, the initialization problem remains. You load the properties of the object from disk and you assign them to the GUI. When you set whatever value you have in your object to Checkbox1, it will (or not) call CheckBox1Click(Sender) which will set the value back into the object.
On app startup:
procedure TForm.FormCreate (Sender: TObject);
begin
LogicObject.Load(File); // load app logic
Checkbox1.Checked := LogicObject.Checked; // assign object to GUI
end;
procedure TForm.CheckBox1Click(Sender: TObject);
begin
LogicObject.Checked := Checkbox1.Checked;
end;
Probably the solution involves writing stuff like this for EVERY control on the form:
OldEvent := CheckBox1.OnClick;
CheckBox1.OnClick := Nil;
CheckBox1.Checked := something;
CheckBox1.OnClick := OldEvent;
Not elegant.
Question:
How do you solve this specific problem OR what is your approach when saving/restoring your GUI to/from disk?

This is one of the things which botthered me in some components from the beginning. What I know the are 3 options, except separating GUI and the business logic as #David said, which is not always an option.
As you wrote above, always unassign the events so they don't get triggered
Use non-triggered events such as OnMouseDown or OnMouseUp
Or a similar solution that I use and I think is the most elegant
Create a global variable FormPreparing which is set during initialization and check its value at the beginning of the events like below.
procedure TForm.FormCreate (Sender: TObject);
begin
FormPreparing := True;
try
LogicObject.Load(File); // load app logic
Checkbox1.Checked := LogicObject.Checked; // assign object to GUI
finally
FormPreparing := False;
end;
end;
procedure TForm.CheckBox1Click(Sender: TObject);
begin
if FormPreparing then
Exit;
LogicObject.Checked := Checkbox1.Checked;
end;

Related

How to refer to the current object in Delphi? [duplicate]

I am new to delphi and pascal and was wondering if there was a way to get/access a property of the component that the Sender is referencing within the procedure.
More specifically I would like to make a procedure that changes the caption property of a label, that label being the component that Sender is referencing.
I imagine that procedure looking something like:
procedure TForm1.LabelEdit(Sender: TObject);
begin
Sender.caption := 'Sample Text';
end;
Naturally this wouldn't work but can something like or something similar to this be done?
Although the example in your question doesn't really make sense (it incorrectly suggests that a TLabel has an OnEdit event), it is very much possible to use the Sender parameter to obtain information about the sender object.
Create a new VCL application and drop a number of TLabel controls on the form. Give them different captions (like Dog, Cat, Rabbit, Horse etc.).
Now select them all in the form designer and then use the Object Inspector to create a common OnClick handler for them. You can name it LabelClick (write LabelClick in the edit field next to OnClick and press Enter).
This will create the following empty method:
procedure TForm1.LabelClick(Sender: TObject);
begin
end;
It has a Sender parameter of type TObject. Now, depending on how this method is called, Sender can be any TObject (a button, a form, a bitmap, ...), or nil (no object at all).
But in our case, we expect this method mainly to be called in response to the labels being clicked on, and in these cases, the Sender will be the corresponding TLabel object.
Let's try to display the caption of the clicked label in a message box!
We try
procedure TForm1.LabelClick(Sender: TObject);
begin
ShowMessage(Sender.Caption); // won't compile!
end;
But this doesn't even compile! The problem is that TObject has no public Caption member. But TLabel does, so we can write
procedure TForm1.LabelClick(Sender: TObject);
begin
ShowMessage(TLabel(Sender).Caption);
end;
Here we are telling the compiler that we know Sender will always be a TLabel, and we ask it to assume that it is.
But this will crash or do other bad things if somehow this method is called with a non-TLabel Sender. So it is safer to do
procedure TForm1.LabelClick(Sender: TObject);
begin
ShowMessage((Sender as TLabel).Caption);
end;
This does the same, except that the compiler will now create code that checks at runtime that Sender really is a TLabel object. If not, the code will raise an exception. That's much better than the kind of memory corruption/AV issues you may get with the unsafe cast above.
Arguably even better is
procedure TForm1.LabelClick(Sender: TObject);
begin
if Sender is TLabel then
ShowMessage(TLabel(Sender).Caption);
end;
This will also test the type of Sender at runtime. If it is a label, we display its caption. Otherwise, we choose to do nothing. Notice that there is no point in using a safe (and slightly, slightly, slower) as cast here.
You cast Sender to the type that the event connects.
procedure TForm1.Button1Click(Sender: TObject);
begin
if Assigned(Sender) then
(Sender as TButton).Caption := 'Clicked';
end;
If you're sharing the event among different types of controls, you can test first to see what type it is:
procedure TForm1.ControlClick(Sender: TObject);
begin
if (Sender is TEdit) then
TEdit(Sender).Text := 'Clicked'
else if (Sender is TButton) then
TButton(Sender).Caption := 'Clicked';
end;
end;

Error handling in fphttpclient?

fphttpclient works fine with simple examples like
procedure ReadFromURL(theURL: string);
var
httpClient: TFPHTTPClient;
FileContents: String;
theStatusCode: integer;
begin
httpClient := TFPHTTPClient.Create(nil);
try
FileContents := httpClient.Get(theURL);
theStatusCode := httpClient.ResponseStatusCode;
if theStatusCode = 200 then
begin
; // do something
end
else
ShowMessage(IntToStr(theStatusCode));
finally
httpClient.Free;
end;
end;
but only, if the URL exists, so that the status code is 200. In other cases the code crashes at httpClient.Get with an exception of class EHTTPClient, ESocketError or EXC_BAD_ACCESS, although the procedure uses a try ... finally section (formulating it as try ... except doesn't change anything). Unfortunately, the exception is raised before the status code can be processed.
What is the recommended way to handle errors with fphttpclient? Is there any method to check for the existence of a resource (and, possibly, the correctness of an URL, too), before invoking the Get method?
Make sure the various events are assigned, so that the class knows what to do on password prompts, redirects etc.
Standard examples init the class like
With TFPHTTPClient.Create(Nil) do
try
AllowRedirect:=True;
OnRedirect:=#ShowRedirect;
OnPassword:=#DoPassword;
OnDataReceived:=#DoProgress;
OnHeaders:=#DoHeaders;
{ Set this if you want to try a proxy.
Proxy.Host:='ahostname.net.domain';
Proxy.Port:=80;
etc.
Please study examples and try to sort through your problems till you have reproducible cases. If then there is still a problem, please submit it to the bugtracker
In rare cases, checking the existences of headers with HEAD() can speed up e.g. sifting through lists of old urls

Problems creating a form in a jvPlugin dll and displaying it as a child of a control on the mail form

I'm trying to write a plugin system for my application based on jvPlugin. I create forms in the plugin dll, then reparent them into DevExpress docking controls. At first sight, it seems to work. The problem is that none of the controls on the dll forms ever receive focus. Also, when clicking on controls like TSplitter, a "Control 'xxx' has no parent window" exception is raised.
Here's how I'm doing it (condensed version).
The plugin host implements an IPluginHost interface
IPluginHost = interface
['{C0416F76-6824-45E7-8819-414AB8F39E19}']
function AddDockingForm(AForm: TForm): TObject;
function GetParentApplicationHandle: THandle;
end;
The plugin implments an IMyPlugin interface
IMyPlugin = interface
['{E5574F27-3130-4EB8-A8F4-F709422BB549}']
procedure AddUIComponents;
end;
The following event is called when the plugin is initialised:
procedure TMyPlugin.JvPlugInInitialize(Sender: TObject; var AllowLoad: Boolean);
var
RealApplicationHandle: THandle;
begin
if Supports(HostApplication.MainForm, IPluginHost, FPluginHost) then
begin
RealApplicationHandle := Application.Handle;
Application.Handle := FPluginHost.GetParentApplicationHandle; // Returns Application.Handle from the host application
try
FMyPluginForm:= TMyPluginForm.Create(Application); // Plugin host app owns the form
finally
Application.Handle := RealApplicationHandle;
end;
end;
end;
When the plugin host has loaded I call IMyPlugin.AddUIComponents in my plugin. It's implemented like this:
procedure TMyPlugin.AddUIComponents;
begin
// Add the docking form
FPluginHost.AddDockingForm(FMyPluginForm);
end;
AddDockingForm is implemented in the host like this:
function TfrmMyPluginHost.AddDockingForm(AForm: TForm): TObject;
var
DockPanel: TdxDockPanel;
begin
// Create a new dockpanel
DockPanel := TdxDockPanel.Create(Self);
DockPanel.Name := DPName;
DockPanel.Height := AForm.Height;
DockPanel.DockTo(dxDockSite1, dtBottom, 0);
DockPanel.AutoHide := TRUE;
// Rename the dock panel and parent the plugin
DockPanel.Caption := AForm.Caption;
DockPanel.Tag := Integer(AForm);
AForm.Parent := DockPanel;
AForm.BorderStyle := bsNone;
AForm.Align := alClient;
AForm.Show;
FDockedPluginFormList.Add(AForm);
Result := DockPanel;
end;
If I run the following function on any of the controls on the plugin form I see a list going all the way back to my host's main form. Yet TSplitters tell me they have no parent window. How can this be?
function TfrmMyPlugin.GetParents(WC: TWinControl): String;
begin
if (WC <> nil) and (WC is TWinControl) then
Result := WC.Name + ' [' + WC.ClassName + '] - ' + GetParents(WC.Parent);
end;
I must be missing something somewhere. Anybody got any good ideas?
Build both the plugin and the host application with runtime packages.
Without using runtime packages, the DLL uses a distinct copy of the RTL, VCL and any used units. For example, the DLL's TForm class is not the same as the host's TForm class (is operator fails across the host/DLL boundary and therefore a DLL control will not recognize host parent form as a valid instance of TForm), global variables like Application, Mouse, Screen are separate instances, you have two copies of RTTI, etc, etc.
The VCL was simply not designed to be used like this.
With runtime packages on, all the problems are solved and the plugin (either a runtime package itself or a DLL built with runtime packages) can integrate seamlessly with the host application using runtime packages.
We made it work using "runtime packages" adding "vcl,rtl,ourownpckg"
Where ourownpckg is a our-own-package created with all the DX dependencies and some other that we use across exe-plugins, including JVCL ones.
The three packages must be shiped along the exe
Hope it helps

Switch to the finish page in Inno Setup installation

I added a few custom pages to my setup. In one of this custom pages I do some checks. If this checks failed, I want switch to finish page. How can I do this?
I can not do this with ShouldSkipPage event function because:
function ShouldSkipPage(PageID: Integer): Boolean;
begin
// this will NEVER happened - see documentation below
if (PageID = wpInstalling) or (PageID = wpPreparing) or (PageID = wpWelcome) then
begin
// skip install - simply for example
result := True;
exit;
end;
resutl := false;
end;
From Inno Setup documentation:
The wizard calls this event function
to determine whether or not a
particular page (specified by PageID)
should be shown at all. If you return
True, the page will be skipped; if you
return False, the page may be shown.
Note: This event function isn't called
for the wpWelcome, wpPreparing, and
wpInstalling pages, nor for pages that
Setup has already determined should be
skipped (for example,
wpSelectComponents in an install
containing no components).
I'm sorry, i did not understand why you cannot use ShouldSkipPage.
The usual way of doing it is in ShouldSkipPage:
function ShouldSkipPage(curPageId : Integer) : Boolean;
begin
{For a certain condition, skip to wpFinished}
if (SomeCondition and (curPageId <> wpFinished)) then
Result := True
{Probably more checks}
else
Result := False
end;
If I understand you correctly, you are performing a check, and if it fails, you want to skip wpWelcome, wpPreparing, and wpInstalling (and perhaps more custom pages).
I assume that you also want to skip the actions performed when these pages are shown, specifically, you don't want to perform the installation step.
If that is the case, you should cancel the installation, not continue it without performing the actual installation steps. You can do it in InitializeSetup, for example:
Procedure InitializeSetup();
VAR
Check: Integer;
BEGIN
// perform you check here, set the variable according to it's result
IF (Check <> 0) THEN
// abort installation
Return False;
ELSE
Return True;
END;
Edit
In response to your comment: The easiest solution would be to show a message box with the result of your check, instead of a complete wizard page. If that is not enough for your purposes I would suggest the following approach:
Perform your check in InitializeSetup and store the result in a global variable.
Create a new wizard page (lets call it CheckResult) to display the results of your check, it should be displayed directly after wpWelcome.
In that page's OnNextButtonClick just call CancelButtonClick, that way the installation is always aborted when this page is displayed
Now is the time to modify ShouldSkipPage ;-) If the global check variable indicates that everything is ok, skip your CheckResult page, so that the installation is not aborted automatically
This should work, but if you somehow can, follow the KISS principle and go with the message box approach.

Determine if flash OCX is installed?

What is the best way to determine if the flash ocx is installed in Innosetup (or any installer for that matter). I don't want to attempt to install it myself, I will simply force the user to go to the flash site and install, I just want to make sure that the flash.ocx (version 9+) is installed.
Is it enough to check for HKEY_CLASSES_ROOT\ShockwaveFlash.ShockwaveFlash and check that CurVer >= 9? Is there a better way to test for this?
Add a function in the code section to check whether you can create an instance of the Flash control, like so:
function IsFlashInstalled(): boolean;
var
V: Variant;
begin
try
V := CreateOleObject('ShockwaveFlash.ShockwaveFlash.9');
Result := True;
except
Result := False;
end;
end;
Check out the various examples in the Inno Setup package on how to use your own function to show a message box to the user, cancel the installation, open the Flash site in the default browser or whatever you want to do.
Easy way without Try/Except
function IsFlashInstalled: Boolean;
var ClassID : TCLSID;
begin
Result := Succeeded(CLSIDFromProgID('ShockwaveFlash.ShockwaveFlash', ClassID));//Use CreateComObject() instead...
end;

Resources