I am using TcxGridDBBandedTableView and have two columns of type TcxGridDBBandedColumn.
vwABC : TcxGridDBBandedTableView
vwABCField1 : TcxGridDBBandedColumn
vwABCField2 : TcxGridDBBandedColumn
When I change anything in vwABCField1, vwABCField2 values should get cleared. For this I am using OnEditValueChanged property of vwABCField1 like this:
procedure TMyForm.vwABCField1PropertiesEditValueChanged(Sender: TObject);
begin
vwABCField2.EditValue := '';
end;
While debugging, when I come to vwABCField2.EditValue := ''; statement, I never return back and get trapped in infine loop and after some time I get stackoverflow error.
vwABCField2.EditValue := ''; is calling vwABCField1PropertiesEditValueChanged procedure again and again recursively infinite time. I don't know why. I have not declared anything on OnEditValueChanged event of vwABCField2.
Update
If I write anything else in the above function instead of vwABCField2.EditValue := '';, it will be called only once. For example
procedure TMyForm.vwABCField1PropertiesEditValueChanged(Sender:TObject);
begin
ShowMessage("hi");
end;
works fine. So I suspect that culprit is vwABCField2.EditValue := ''; statement.
As in the official documentation is stated:
Do not change the edit value in your OnEditValueChanged event handler, as this can result in stack overflow. Use this event to get notification that the edit value has changed.
Because when you change the edit value in this event, of course, your editvalue is changed and therefore calling the OnEditValueChanged event again and again and ...
Related
I am using a TEdit to allow the user to enter a number, e.g. 10.
I convert the TEdit.Text to an integer and a calculation procedure is called.
In this calc procedure, a check was built-in to make sure no numbers below 10 are processed.
Currently I use the OnChange event. Suppose the user wants to change '10' into e.g.'50'. But as soon as the '10' is deleted or the '5' (to be followed by the 0) is typed, I trigger my warning that the minimum number is 10. I.e. the program won't wait until I have fully typed the 5 and 0.
I tried OnEnter, OnClick, OnExit, but I seem not to overcome this problem. The only solution is to add a separate button that will trigger the calculation with the new number. It works, but can I do without the button?
Use a timer for a delayed check, e.g.:
procedure TForm1.Edit1Change(Sender: TObject);
begin
// reset the timer
Timer1.Enabled := false;
Timer1.Enabled := true;
end;
procedure TForm1.Timer1Timer(Sender: TObject);
begin
Timer1.Enabled := false;
// do your check here
end;
Setting the timer to 500 ms should be fine for most users.
And as David suggested in the comments to the question: Do not show an error dialog, use something less intrusive instead, e.g. an error message in a label near the edit or change the background color. And also: Do not prevent the focus to be moved away from that control and do not play a sound, that's also very annoying.
For our in house software we set the background of a control to yellow if there is an error and display the error message of the first such error in the status bar and also as a hint of the control. If you do that, you probably don't even need to have the delay.
Thanks, for your help. I tried the timer option, but could not get that to work. I now have this code, which works (almost - see below), but requires the used to always type a CR:
procedure Calculate;
begin
// this is my calculation procedure
ShowMessage('calculation running correctly');
end;
procedure TForm1.Edit1KeyPress(Sender: TObject; var Key: Char);
var
N : integer;
begin
if Key = #13 then
begin
N := StrtoInt(Edit1.Text);
if N<10 then ShowMessage('<10!') else
if N>100 then ShowMessage('>100!') else Calculate;
end;
end;
I used the ShowMessage() here only to see if the sample code worked. In the real program I have left that out, as you all suggested.
I also included the 'turn yellow on wrong entry' (thanks David). The only issue is that if the user runs this I get a beep from my computer. I can't see what went wrong. But what is causing the beep?
I'm making a multi-device application in Delphi XE8 which uses LiveBindings to a dataset.
There are a number of LB-specific Actions for FMX, including TFMXBindNavigateDelete. I'm trying to use this in a button-click handler like this:
Button Click Code:
procedure TForm1.Button1Click(Sender: TObject);
begin
if cdsOrdersSTATUS.Value='READY' then
begin
ShowMessage('Your Order Is Already READY/PENDING!');
end
else
begin
TAction(ActionList1.Actions[0]).Execute; //Not working,why?
end;
end;
The first (and only) item in ActionList1's Actions is my FMXBindNavigateDelete1.
The problem is, even if the code TAction(ActionList1.Actions[0]).Execute executes, the current dataset record is not deleted, so apparently
TFMXBindNavigateDelete's Action has no effect. Why is this, and how can I make it work?
Pic. ActionList1:
Actually, I think this is a good question and doesn't deserve the downvote.
I can reproduce your problem. I put two buttons on the FMX form. I set
Button1's OnClick to your Button1Click and Button2's Action to LiveBindingsBindNavigateDelete1.
Clicking Button2 pops up the standard 'Delete record?' confirmation and deletes the current record
if I answer "Yes", as expected.
However, when clicking Button1, even if your else block executes, the 'Delete record?' confirmation
does not appear, so the record has no chance of being deleted.
The reason is in the code
function TCustomAction.Execute: Boolean;
begin
Result := False;
if Supported and not Suspended then
begin
Update;
if Enabled and AutoCheck then
if (not Checked) or (Checked and (GroupIndex = 0)) then
Checked := not Checked;
if Enabled then
Result := ((ActionList <> nil) and ActionList.ExecuteAction(Self)) or
((Application <> nil) and Application.ExecuteAction(Self)) or inherited Execute or
((Application <> nil) and Application.ActionExecuteTarget(Self));
end;
end;
The Enabled property seems by default to be set to False during the call to
Update so the if Enabled then ... never executes. I haven't managed to find
a way to get Enabled set to True during the call to Update. Perhaps someone else knows how to do that.
In the case of Button2, execution then passes to TComponent.ExecuteAction and
it is the call to Action.ExecuteTarget(Self) in it which results in the
record-deletion routine executing.
So, from that, your problem seemed to me to become how to adjust the code so that
TComponent.ExecuteAction gets executed, in other words, how to associate the
Action with a component. The answer was fairly obvious.
All that's needed is this
procedure TForm1.Button1Click(Sender: TObject);
begin
if cdsOrdersSTATUS.Value='READY' then
begin
ShowMessage('Your Order Is Already READY/PENDING!');
end
else
begin
Button1.ExecuteAction(LiveBindingsBindNavigateDelete1); // <- this works
//LiveBindingsBindNavigateDelete1.Execute; //Not working,why?
end;
end;
I didn't understand exactly what you wanted to do but if you trigger the action by it's index, you can do something like this:
TAction(ActionList1.Actions[0]).Execute;
This question already has answers here:
Reference object instance created using "with" in Delphi
(9 answers)
Closed 8 years ago.
Is there a way to refer to a dinamicaly created object in "with" segment to let's say pass this object somewhere else?
I have a simple code like this
var
someObject: TSomeObject;
begin
someObject := TSomeObject.Create;
try
someObject.someProperty := 1;
SomeOtherProcedure(someObject);
finally
someObject.Free;
end;
end;
there is a variable that is being passed to SomeOtherProcedure. Now I am trying to drop someObject variable and use "with" segment to have something like this
begin
with TSomeObject.Create do
try
someProperty := 1
SomeOtherProcedure( < what goes here ?? > );
finally
Free;
end;
end;
I do not want to have something like
var
someObject: TSomeObject;
begin
someObject := TSomeObject.Create;
with someObject do
(...)
Is this even possible to refer to an object that is being created in "With"?
Thanks!
No you can't and use of the With statement (especially in cases like the one you illustrated) should be avoided as it can cause more problems than it solves.
Consider the following code :-
Procedure TMyForm1.btnProcessClick(Sender : TObject);
Begin
With TMyForm2.Create(Nil) Do
Begin
Try
Caption := 'Processing....';
DoSomeProcessing;
DoSomeMoreProcessing;
Finally
Free;
End;
End;
End;
Supposing TMyForm1 also has a method called DoSomeProcessing? Which one will get called? Which form caption will change to say 'Processing...'? It's not immediately clear the method that will be called. The situation becomes even more complicated when you start referencing properties. Don't expect the Debugger to be able to help you either. Now all of this might not cause you too much of an issue now when the code is still fresh, but what about 6 months or a year later? You have caused yourself a whole load of grief all to save yourself a bit of typing.
I am working on the application which has two listboxes.I load the two listboxes with values and when i keep on clicking the items from the list box i get the following error while debugging.
Running the exe causes the application to close.Sometimes i get the "Access Violation" message.
so what should I do to get rid of this error from my aaplication?
EDIT
..
The main form has timer that refresh all the controls
timer_RefreshCOntrol (intervali 1).
whenver the editBox_one is modified(value)
this function is called
Procedure TStringSetting.SetValue (const AValue : String);
Begin
...
If FValueControl <> Nil then
Begin
FValueControl.OnChange := VoidNotifyEvent;
FValueControl.Text := NewValue;
FValueControl.OnChange := EditChange; //<--here the stackoverflow error comes....
end;
end;
Procedure EditChange (Sender: TObject);
Begin
Value := FValueControl.Text;
If Not EditIsValid then FValueControl.Font.Color := clRed
else If Dirty then FValueControl.Font.Color := clBlue
else FValueControl.Font.Color := clWindowText;
If #OldCustomEditChange <> Nil then OldCustomEditChange(Sender);
end;`
the EditChange (Sender: TObject); <--keeps geting called and the stackoverflow error comes
EditChange is assigned to the editbox on FormCreate
EDIT2
I am not the original developer.I just handled code sometimes back, major refactoring is not possible.
edit 3
The call stack value but what is the "???"
EDIT 4
after going through #Cosmin Prund and #david
i got the place where the infinity call start
Procedure TFloatSetting.EditChange (Sender: TObject);
Begin
SkipNextOnChange := True;
Inherited EditChange(Sender);
IfValidThenStore(FValueControl.Text);
Inherited EditChange(Sender); {<-------This is where it start}
end;
Procedure TStringSetting.EditChange (Sender: TObject);
Begin
Value := FValueControl.Text;
If Not EditIsValid then FValueControl.Font.Color := clRed
else If Dirty then FValueControl.Font.Color := clBlue
else FValueControl.Font.Color := clWindowText;
If #OldCustomEditChange <> Nil then OldCustomEditChange(Sender); {<---this keeps calling Procedure TFloatSetting.EditChange (Sender: TObject);}
end;
Based in the posted call stack it's obvious why the error is happening: TStringSetting.EditChange triggers TFloatSetting.EditChange and that in turn triggers TStringSetting.EditChange. The loop goes on like this until all stack space is exhausted.
Here are some tips on why that might happen, and tips on how to debug and fix it:
Maybe the controls involved trigger the OnChange event handler when the Value is changed progrmatically. If the two editors are supposed to display the same data in two formats and you're using the respective OnChange event handlers to keep them in sync, this might be the cause.
Maybe you're directly calling one event handler from the other.
Ways to debug this:
You should first try the breakpoint solution, as suggested by paulsm4. If the stack overflow happens every time one of the OnChange handlers is called, this solution would easily work.
Comment-out the code for one of the event handlers. Run the program, the error should no longer appear. Un-comment the code in tiny (but logical) amounts, test and repeat. When the error shows up again, you know you fund the line that's causing the error. If you can't figure it out yourself, edit the question, add the code and mark the line that you just found out it's giving you trouble.
If the controls you're using are triggering the OnChange event handler when there value is changed programatically, you should make your event handlers non-reentrant: that would stop the infinite recursive loop for sure. I almost always assume controls trigger OnChange or equivalent events when properties are changed from code and always protect myself from re-entry using something like this:
// Somewhere in the private section of your form's class:
FProcessingEventHandler: Boolean;
// This goes in your event handler
procedure TYourForm.EventHandler(Sender:TObject);
begin
if FProcessingEventHandler then Exit; // makes code non-reentrant
FProcessingEventHandler := True;
try
// old code goes here ...
finally FProcessingEventHandler := False;
end;
end;
Suggestions:
Set a breakpoint in EditChange and OldCustomEditChange to see who's calling them. Each invocation. Clearly, only EditChange should ever call OldCustomEditChange.
Look in your .dfm to make sure EditChange is only assigned to one event (not multiple events) and OldCustomEditChange isn't assigned at all.
You report a non-terminating recursive call sequence to EditChange. Looking at the code of EditChange there are two candidates for a recursive call:
OldCustomEditChange being equal to EditChange, or calling a function that in turn calls EditChange.
An event handler that responds to changes to FValueControl.Font by calling EditChange.
These are the only opportunities for the code in EditChange to call itself.
It is easy to see how both of these possibilities leads to the non-terminating recursive function call and eventually the stack overflow. Of the two candidates my bet is number 1. I would study carefully what happens when OldCustomEditChange is called.
To debug a stack overflow of this nature simply open the call stack window and look at the long sequence of calls. You will typically see a pattern with one function calling itself, possibly via one or more intermediate functions.
I have never asked questions in any community as I always solved problems by myself or could find them online. But with this one I came to dead end and need Help!
To make it very clear – I converted a simple app, found elsewhere to make it use a Tthread object.
The idea is simple – the app checks online using webservice, through THTTPRIO component, weather and put the results in Memo1 lines.
Clicking on Button1 we get it done in standard way – using THTTPRIO put on the Form1 (it's called here htt as in original app) and using main and only thread.
procedure TForm1.Button1Click(Sender: TObject);
var
wf:WeatherForecasts;
res:ArrayOfWeatherData;
i:integer;
begin
wf:=(htt as WeatherForecastSoap).GetWeatherByPlaceName(edit1.Text);
if wf.PlaceName<> '' then
res:=wf.Details;
memo1.Lines.Add('The min and max temps in Fahrenheit is:');
memo1.Lines.Add(' ');
for i:= 0 to high(res) do
begin
memo1.Lines.Add(res[i].Day+' - '+ ' Max Temp. Fahr: '+res[i].MaxTemperatureF+' - '+'Min Temp Fahr: '+res[i].MinTemperatureF);
end
end;
Clicking on Button2 – we use class TThread
procedure TForm1.Button2Click(Sender: TObject);
var WFThread:WeatherThread;
begin
WFThread := WeatherThread.Create (True);
WFThread.FreeOnTerminate := True;
WFThread.Place := Edit1.Text;
WFThread.Resume;
end;
In Execute procedure in WeatherThread1 unit I put this code:
procedure WeatherThread.Execute;
begin
{ Place thread code here }
GetForecast;
Synchronize (ShowWeather);
end;
...and the GetForecast code:
procedure WeatherThread.GetForecast;
var
HTTPRIO: THTTPRIO;
wf:WeatherForecasts;
res:ArrayOfWeatherData;
i:integer;
begin
HTTPRIO := THTTPRIO.Create(nil);
HTTPRIO.URL := 'http://www.webservicex.net/WeatherForecast.asmx';
HTTPRIO.WSDLLocation := 'http://www.webservicex.net/WeatherForecast.asmx?WSDL';
HTTPRIO.Service := 'WeatherForecast';
HTTPRIO.Port := 'WeatherForecastSoap';
wf:=(HTTPRIO as WeatherForecastSoap).GetWeatherByPlaceName(Place);
if Lines=nil then Lines:=TStringList.Create;
if wf.PlaceName<> '' then
res:=wf.Details;
Lines.Clear;
for i:= 0 to high(res) do
begin
Lines.Add(res[i].Day+' - '+ ' Max Temp. Fahr: '+res[i].MaxTemperatureF+' - '+'Min Temp Fahr: '+res[i].MinTemperatureF);
end;
end;
Procedure ShowWeather shows results in Form1.Memo1.
And now there is a problem: In main thread, clicking Button1, everything works fine. But of course when HTTPRIO component communicates – it freezes the form.
With Button2 I put the code in separate thread but it does NOT WANT TO WORK! Something strange happens. When I start application – and click Button2, there is an error when using HTTPRIO component. But it works for a while when I click FIRST Button1 and AFTER THAT Button2 (but it works for a while, 5-7 clicks only).
I suppose I do something wrong but cannot figure out where the problem is and how to solve it. It looks like the code in threaded unit is not thread-safe, but it should be. Please help how to make HTTPRIO work in a thread!!!
You can find zipped full code here.
When I run your code in Delphi 2007, madExcept shows an exception CoInitialize has not been called.
After adding the call to CoInitialize in the execute method, the webservice gets called without problems.
Possible fix
procedure TWeatherThread.Execute;
begin
CoInitialize(nil);
try
...
finally
CoUninitialize;
end;
end;
A long shot, but I'm missing calls to Synchronize here:
You should never update your GUI directly from your thread code.
You should embed those calls inside a method, and call that method using the TThread.Synchronize method for this.
Delphi about has a nice demo on this.
Since Delphi 4, it includes a demo called sortthds.pas in the ...\demos\threads subdirectory that shows the same.
--jeroen
You may be clouding the issue by doing the dynamic RIO creation (RIO objects have a strange lifetime) and threading together, and comparing that outcome to the straightforward Button1. I'd make another button that calls GetForecast without threads. See if that works. If it bombs, then your problem isn't threading.