I want to do a check on a ListBox if it is empty, like:
if {Listbox.Items is empty} then
begin
Listbox.Items.Add('Item');
end else
begin
//do somthing else
end;
The part of the check if Listbox.Items or if Listbox are/is empty is a little hard for me. I tried to figure out a way how to do it, but I failed as I am still a beginner with Delphi. How can I implement that in Delphi XE5?
if listbox.items.count = 0 then
// it's empty
In Access VBA there is no ".items.count" property on a Listbox
I tried Me.ListBox.ListCount and .ListIndex to see if the List was empty.
ListCount was always 1 and ListIndex always -1 whether the list was empty or not (in my case).
To overcome that I used:
If Me.ListBox.ItemData(0) = "" then
Do Something
End If
This worked for me - hope this helps someone
I would reverse your if statement.
Personally I like the most code in the true part of my statement and the shorter code in the false part. For some reason it makes more sense to me.
So the code would look like:
If Listbox.items.count > 0
begin
//Do something else
end
else
Listbox.items.add('item');
Also if your true, or false, part only contains 1 line of code you don't need a begin..end. It's not wrong to have them but in my opinion it makes code easier to read if they aren't there ;)
Related
I personally don't know how a built in function can be indexed as "nil" butthis error appeared and it haulted my nextbot's movement. heres my code that is causing this
if (!self:GetPlayerVisible() and chasing_timer > chasing_time) then
self.stopchasing = true
self.enraged = false
print("Chase stopped")
print("Increasing escaped chases count, new:", self.escapedchases)
self.escapedchases = self.escapedchases + 1
end
I tried replacing the "!" with "not" but it did nothing.
I don't know what self is but that table does not contain an element GetPlayerVisible. Hece you may not call it. Calling nil values doesn't make sense.
Ask yourself why you think this function exists. Typical reasons are typos, indexing the wrong table or not having implemented a function yet.
To avoid this error you basically have two options. Make sure you call something that exists, or don't call it.
(Delphi 6 with TChart, Win XP)
I'm getting erratic behavior trying to clear the points from a point series, and of course, this code used to work.
Basically, this part of my program generates 5 data points and plots them. When I try to clear them using OSC_Series.Clear I get a "List index out of bounds [0]" error.
I checked to make sure there was nothing odd about the values I was plotting. All is good there. Then I tried different things to try to isolate and work around the problem.
Here's some code.
type
TksGraph_DataFrm = class(TForm)
.
.
.
private
OSC_Series: TPointSeries
public
end;
procedure TksGraph_DataFrm.cat7AnalysisInitialize(var P:TTest_Project);
begin
// Do a bunch of stuff.
// Set up the analysis data points series.
OSC_Series:=TPointSeries.Create(self);
AnalysisChart.AddSeries(OSC_Series);
with OSC_Series do
begin
Title:='';
HorizAxis:=aBothHorizAxis;
VertAxis:=aBothVertAxis;
SeriesColor:=clRed;
Pointer.Brush.Color:=clYellow;
Pointer.HorizSize:=4;
Pointer.VertSize:=4;
Pointer.Style:=psRectangle;
Pointer.Visible:=true;
LinePen.Color:=clBlack;
LinePen.Width:=1;
Linepen.Visible:=true;
ShowInLegend:=false;
XValues.Order:=LoNone;
end;
end;
procedure TksGraph_DataFrm.cat7AnalysisRefresh(var P:TTest_Project);
var X,Y:single;
begin
X:= some value
Y:= some value
// Plot the result.
OSC_Series.AddXY(X,Y);
showmessage(
'Count = '+inttostr(OSC_Series.Count)+#13+
'X = '+FloatToStr(X)+#13+
'Y = '+FloatToStr(Y)+#13+
'Plot-X = '+FloatToStr(OSC_Series.XValue[OSC_Series.Count-1])+#13+
'Plot-Y = '+FloatToStr(OSC_Series.YValue[OSC_Series.Count-1]));
end;
Here is the routine I to use to reset the series. I'm including code that does and does not work.
procedure TksGraph_DataFrm.cat7AnalysisClear(var P:TTest_Project);
var i:integer;
begin
// This should work, but it gives me the list out of bounds error
// unless the count is 0.
OSC_Series.Clear;
// This does not work, for obvious reasons. I get a "list out of
// bounds [3] for this one.
for i:=0 to OSC_Series.Count - 1 do OSC_Series.Delete[0];
// It seems this should work, but again I get the out of bounds [0]
// error.
repeat
OSC_Series.Delete(0);
until OSC_Series.Count = 0;
// This works. Don't ask me why.
showmessage('A - '+inttostr(OSC_Series.Count));
OSC_Series.Clear;
showmessage('B - '+inttostr(OSC_Series.Count));
// This also works.
sleep(2000);
OSC_Series.Clear;
// This does not work.
sleep(1000);
OSC_Series.Clear;
end;
I'm stumped, obviously.
This smells like the code is working with an object (OSC_Series) which has been destroyed and the memory then re-used for something else. When you then use the stale reference to that memory you get unexpected and unpredictable results.
Where is OSC_Series free'd ?
I would check all such places and make sure that you do not attempt to use the OSC_Series reference after it has been free'd.
Note also that since the series is owned by the form it could be that the form itself is contriving to executing code in events after it has destroyed its owned components (including this series).
OK, dumb and not dumb.
I experimented with where I put the showmessage statement. I found I could only avoid the error if that statement came after the OSC_Series.Clear statement. I kept moving that statement back until it was after the call to the AnalysisRefresh routine, which is in a button's OnClick event handler. This means that none of the code in the refresh, enable, or update routines was causing this.
Stepping back a bit, if the AnalysisRefresh routine fails the user is shown a message. After that box is closed OSC_Series.Clear is called. If I close the box by pressing SPACE or ENTER on the keyboard... no error. If I use the mouse, error.
The chart behind the mouse has an OnMouseMove event where I display the mouse position on a status bar. I also display a hint if the mouse is near a plotted point. After clicking the message box with a mouse to close it the OnMouseMove event is called and by the time it gets to where it can display the hint, the plotted point is gone, and... error.
So, it seemed like an almost random error, but it wasn't. The trigger was just somewhere else entirely. That's you my try/except block wasn't catching the error. EurekaLog was catching it, but in a different procedure far, far away. (Deltics' answer was pretty close.)
Thanks for your help and suggestions.
Dang it if some days I can push hundreds of lines of code with no problems, then something like this pops up and it costs me near two days.
I have downloaded opensource delphi twain component (TDelphiTwain).
The interesting thing is, that when placed and saved on the form it creates bad dfm entry for itself.
object DelphiTwain: TDelphiTwain
OnSourceDisable = DelphiTwainSourceDisable
OnSourceSetupFileXfer = DelphiTwainSourceSetupFileXfer
TransferMode = ttmMemory
SourceCount = 0
Info.MajorVersion = 1
Info.MinorVersion = 0
Info.Language = tlDanish
Info.CountryCode = 1
Info.Groups = [tgControl, tgImage, tgAudio, MinorVersion]
Info.VersionInfo = 'Application name'
Info.Manufacturer = 'Application manufacturer'
Info.ProductFamily = 'App product family'
Info.ProductName = 'App product name'
LibraryLoaded = False
SourceManagerLoaded = False
Left = 520
Top = 136
end
The problem is with the line:
Info.Groups = [tgControl, tgImage, tgAudio, MinorVersion]
There are only three possible elements:
tgControl, tgImage and tgAudio
It adds MinorVersion everytime I Save the form.
When the app is run I get the error that there is invalid property for Info.Groups.
When i rmeove the bad part manually and without leaving dfm file the app starts ok.
I looked in the internet and there was one inquire regarding these strange issue, unfortunately it hasn't been resolved.
I think that there is some sort of memory corruption. In the post in teh internet, strange signs were displayed ...
Has anyone worked with that component or could give me some hint how this could be fixed?
The error seems to be in TTwainIdentity.GetGroups where result is not initialized. You can try to change the code by replacing
Include(Result, tgControl);
with
Result := [tgControl];
You have to recompile the package to make this change work inside the IDE.
I don't know the component, but I think the problem lies in the TTwainIdentity.GetGroups method. It starts like this:
begin
Include(Result, tgControl);
This means that it assumes that Result is initialized to an empty set. However, Result may contain garbage, and not necessarily an empty set. Change this method to look like this:
function TTwainIdentity.GetGroups(): TTwainGroups;
{Convert from Structure.SupportedGroups to TTwainGroups}
begin
Result := [tgControl];
if DG_IMAGE AND Structure.SupportedGroups <> 0 then
Include(Result, tgImage);
if DG_AUDIO AND Structure.SupportedGroups <> 0 then
Include(Result, tgAudio);
end;
Some result types will not throw a compiler warning about not being initialized, but that doesn't mean they are empty. Same goes, for instance, for strings.
See also: http://qc.embarcadero.com/wc/qcmain.aspx?d=894
But still, it is odd that this happens. Apparently, Delphi tries to find the name of the given item in the set and accidentally finds the name of another property. It seems to me that quite some checks in writing the dfm are missing if this happens. :)
I'm trying to get a handle on how OOP is done in Lua, and I thought I had a simple way to do it but it isn't working and I'm just not seeing the reason. Here's what I'm trying:
Person = { };
function Person:newPerson(inName)
print(inName);
p = { };
p.myName = inName;
function p:sayHello()
print ("Hello, my name is " .. self.myName);
end
return p;
end
Frank = Person.newPerson("Frank");
Frank:sayHello();
FYI, I'm working with the Corona SDK, although I am assuming that doesn't make a difference (except that's where print() comes from I believe). In any case, the part that's killing me is that inName is nil as reported by print(inName)... therefore, myName is obviously set to nil so calls to sayHello() fail (although they work fine if I hardcode a value for myName, which leads me to think the basic structure I'm trying is sound, but I've got to be missing something simple). It looks, as far as I can tell, like the value of inName is not being set when newPerson() is called, but I can't for the life of me figure out why; I don't see why it's not just like any other function call.
Any help would be appreciated. Thanks!
Remember that this:
function Person:newPerson(inName)
Is equivalent to this:
function Person.newPerson(self, inName)
Therefore, when you do this:
Person.newPerson("Frank");
You are passing one parameter to a function that expects two. You probably don't want newPerson to be created with :.
Try
Frank = Person:newPerson("Frank");
This has been driving me crazy for hours and its probably very obvious to someone ...
Can anyone see why this is printing out even though its reporting as being false?
<g:if test="${className == 'SRep'}">
${className == 'SRep'}
</g:if>
If classname==SRep then its correct. However if classname <> SRep it still prints out false? I don't understand how this can be.
If I use ?showSource=true, the if statement looks like this:
if(true && ("false")) {
printHtmlPart(29)
}
else {
printHtmlPart(30)
}
Anyone see anything obvious?
Thanks
John
your code looks fine but im not sure what 'className' is, perhaps it's not being returned or returning wrong type etc:
i would display the output in the GSP of className just to see what it is
e.g. add this anywhere in your GSP:
${className} //displays the value
you may also want to check the object type, in your case i think it should be string
so check what you have:
${className?.class} //displays the type of object