Saving Icons to Stream

[sggaunt]

I adapted a function to write some object properties (in a TList) to a File stream

I think it should be possible to save Any properties in this way, it works OK for Integers, strings (fixed length) even simple enumerated types but if I Use the same method for an Icon (ObjectIco is a TIcon), it dosent work.


procedure TThings.WriteToStream(Fs : TFileStream );
begin
Fs.WriteBuffer(XPos, Sizeof(Xpos));
Fs.WriteBuffer(YPos, Sizeof(Ypos));
Fs.WriteBuffer(ObjectIco, Sizeof(ObjectIco));
end;

Does anyone know the correct way to do this ??
Steve.

 

[halfyawn]

procedure TThings.WriteToStream(Fs : TFileStream );
begin
Fs.WriteBuffer(XPos, Sizeof(Xpos));
Fs.WriteBuffer(YPos, Sizeof(Ypos));
ObjectIco.SaveToStream(fs);
end;

 

[sggaunt]

Tried that, It did seem to be saving OK? (the resulting file was larger), But I couldnt get it to reload with the equivalent ObjectIco.Loadfromstream (Horrible access violation crash).
Is there some creation issue here?

Steve

 

[towerbase]

Can you post the code that you used both to save and load the x, y positions and the icon?

Andrew

 

[sggaunt]

Ok You ased for it:-

I thought you might need a bit more background so
The objects are made part of a TList so we can use the Savetostream methods

The code is based on PCPlus Tutorial on how to save mixed objects.


TObjectList = Class(TList)
procedure AddObject(Index: integer;
ObjectName: TextStr; // a fixed length string
status: Integer;
Moveable: Boolean;
Position: Integer;
Ten: Tenses;
Text: array of TStringList;
XPos,YPos: integer;
Image: TIcon);
procedure SaveObjects(fname : string );
procedure LoadObjects(fname: string);
end;

TThings = class(TObject)
objectico: TIcon;
Index: integer;
ObjectName: TextStr;
Status: integer;
Moveable: Boolean;
Position: integer;
Tense: Tenses;
Text: array[0..5] of TstringList; // we will have to save the length of the strings!!
XPos: integer;
YPos: integer;
procedure WriteToStream( Fs: TFileStream );
procedure ReadFromStream(Fs: TFileStream);
constructor CreateFromStream(Fs : TFileStream );
private

public

constructor make(item: integer; obj: TextStr; place: integer; stat: integer;
m: boolean; ten: tenses;
Txt: array of TstringList;
x,y:integer;
Image: TIcon);

end;

In the implementation these procedures do the TThing Load/save :-


procedure TThings.WriteToStream(Fs : TFileStream );
var A, B, C: integer;
LineofText: TextStr;
begin
// Here we cannont attempt to save the string list array so we must extratct
// the text and store it as a simple strings

Fs.WriteBuffer(Index, Sizeof(Index));
Fs.WriteBuffer(ObjectName, Sizeof(ObjectName));
Fs.WriteBuffer(Status, Sizeof(Status));
Fs.WriteBuffer(Moveable, Sizeof(Moveable));
Fs.WriteBuffer(Position, Sizeof(Position));
Fs.WriteBuffer(Tense, Sizeof(Tense));

C := 0;
for a := 0 to 5 do
begin
C := text[a].count;
Fs.WriteBuffer(C, Sizeof(C)); // store number of strings on each page
for b := 0 to C - 1 do
begin
LineofText := Text[a].strings;
Fs.WriteBuffer(LineofText, sizeof(LineofText));
end;

end;

Fs.WriteBuffer(XPos, Sizeof(Xpos));
Fs.WriteBuffer(YPos, Sizeof(Ypos));
ObjectIco.SaveToStream(Fs);



end;

procedure TThings.ReadFromStream(Fs: TFileStream);
var A,B,C: integer;
LineofText: TextStr;
begin
Fs.ReadBuffer(Index, sizeof(Index));
Fs.ReadBuffer(ObjectName, sizeof(ObjectName));
Fs.ReadBuffer(Status, Sizeof(Status));
Fs.ReadBuffer(Moveable, sizeof(Moveable));
Fs.ReadBuffer(Position, Sizeof(Position));
Fs.ReadBuffer(Tense, Sizeof(Tense));

// As you can see I also had a problem with the TStringlist field and got round it by
// extracting it to Fixed length strings. The sring list is implictly created here I thought // this might be a clue but doing simular diddnt seem to work with the Icon type.

C := 0;
for A := 0 to 5 do
begin
Fs.ReadBuffer(C, Sizeof(C));
Text[a] := Tstringlist.create;
for b := 0 to C - 1 do
begin
Fs.ReadBuffer(LineofText, sizeof(LineofText));
Text[a].Add(LineofText);
end;
end;

Fs.ReadBuffer(XPos, Sizeof(Xpos));
Fs.ReadBuffer(YPos, Sizeof(Ypos));

ObjectIco.LoadFromStream(Fs); // Here lieth the crash.

end;


At the TList level these are the procedures called by the main form Load/save Actions
If it seems over complex? This is because the other modules have 2 Types of object (none with icons or the like) and the writetostream Procedures are virtual so looping through the TList only need to make one call.
I intend to add this module into the main TList (when I can get it to work).

procedure TObjectList.SaveObjects(Fname : string );
var Fs : TFileStream;
I : integer;
begin
// create a File stream object
Fs := TFileStream.Create(Fname, fmCreate);
try
for i := 0 to ObjList.Count - 1 do
// cast The ObjectList object to a TThing
TThings(ObjList).WriteToStream(Fs);
finally;
Fs.Free;
end;
end;

procedure TObjectList.LoadObjects(Fname : string );
var Fs : TFileStream;
begin
Fs := TFileStream.Create(Fname, fmOpenRead);
try
//read in the object data and create each object as we read it.
while Fs.Position < Fs.Size do
begin
ObjList.Add(TThings.CreateFromStream(Fs));
inc(NumberOfObjects);
end;
finally;
Fs.Free;
end;
end;

The constructer works fine and I am able to create the icons in memory no problem with these two lines

ObjectIco := TIcon.Create;
ObjectIco.Assign(Image);

Where image is a Tcon Passed in from a TImage as Image.picture.icon.

Steve..

 

[towerbase]

Thanks (!)

A couple of points I don't understand in your code. How does this line work?

  LineofText := Text[a].strings;

LineOfText is (presumably) an array of char and strings is not.

However, I suspect that in your ReadFromStream method whilst you are creating your TStringLists with

  Text[a] := Tstringlist.create;

there is no equivalent creation of ObjectIco and this would cause it to crash at

  ObjectIco.LoadFromStream(Fs); // Here lieth the crash.

If you stop the debugger at this line, does ObjectIco have a value of nil?

Andrew

 

[sggaunt]

Cheers Andrew

Something got lost in the cut and paste the string list thing should read

LineofText := Text[a].strings;

After I posted I tried :-

ObjectIco := TIcon.Create;
ObjectIco.LoadFromStream(Fs);

Which Now Works!! (I am sure I tried this before?, I must be suffering from one of the same problems as MerryMadDad.)

There is still a problem though, as you can see this is supposed to save a list of Objects, and looking at the saved file It does.

But now when I read back it only seems to read 1 object

while Fs.Position < Fs.Size do

This loop is only executing Once no matter how many objects are saved and Fs.Position goes from 0 to the File size in one step. again before adding the icon this seemed to work Ok.??

Steve

 

[sggaunt]

Failed to copy correctly again I see

LineofText := Text[a].strings;

steve

 

[sggaunt]

LineofText := Text[a].strings(square bracket b square bracket);
for some reason this editor wont accept the second set of brackets

 

[towerbase]

The reason the editor won't accept the second set of square brackets surrounding the b is that it interprets this as a command to format the following text in bold!

I haven't time to look at your problem until tomorrow. Maybe someone else can help meanwhile?

Andrew

 

[sggaunt]

??

 

[towerbase]

I suspect that ObjectIco.LoadFromStream loads the entire stream from the current position. I guess you will need to save the length of the icon in the stream before saving the icon. Then when reading it back use a stream.Read to get the length of the icon and then read the icon with the read length.

Andrew

 

[sggaunt]

Cheers Andrew
Sounds feasible, I will it.

Steve