20th Chapter-Development Delphi Object Type Data management function (five) (2)

20.3.1.4 DFM file and standard text file (TXT file) of the mutual conversion

In the Delphi visual design environment, programmers are allowed to browse and modify the DFM file content in the Code Editor by text. When you open the DFM file directly with the File/open command, or when you select the view as Text command on the pop-up menu of the Form Design window, information in the form of text appears in the editor. Let's call this text form a form design script. Delphi provides this kind of script editing function is to Delphi visual design a big supplement. Of course, this script editing ability is limited, for example, can not arbitrarily add and delete parts in the script, because the code and DFM scripts are closely linked, arbitrary additions and modifications can lead to inconsistencies. However, there is no such limitation in the dynamically generated DFM file, and the application of DFM dynamic generation technology will be introduced later.

In fact, the DFM file content is binary data, its script is automatically transformed through the Delphi development environment, and Delphi VCL in the Classes Library unit in the binary flow of the document DFM and its script of the mutual transformation process. They are objectbinarytotext and objecttextbinary, Objectresourcetotext and Objecttexttoresource.

The objectbinarytotext process converts parts stored in binary streams into text-based representations, which can be processed using text-processing functions, and can be searched and substituted using text editors, which can then be converted to parts in binary streams.

The main program for the Objectbinarytotext process is this:

Procedure Objectbinarytotext (Input, Output:tstream);

Var

Nestinglevel:integer;

Saveseparator:char;

Reader:treader;

Writer:twriter;

Procedure Writeindent;

Const

Blanks:array[0..1] of Char = ';

Var

I:integer;

Begin

For I: = 1 to NestingLevel do writer.write (Blanks, SizeOf (blanks));

End

Procedure Writestr (const s:string);

Begin

Writer.write (S[1], Length (S));

End

Procedure newline;

Begin

Writestr (#13 #10);

Writeindent;

End

Procedure Convertheader;

Begin

...

End

Procedure Convertbinary;

Begin

...

End

Procedure Convertvalue;

Begin

...

End

Procedure Convertproperty;

Begin

...

End

Procedure Convertobject;

Begin

...

End

Begin

NestingLevel: = 0;

Reader: = Treader.create (Input, 4096);

Saveseparator: = DecimalSeparator;

DecimalSeparator: = '. ';

Try

Writer: = Twriter.create (Output, 4096);

Try

Reader.readsignature;

Convertobject;

Finally

Writer.free;

End

Finally

DecimalSeparator: = Saveseparator;

Reader.free;

End

End

The Convertobject procedure called in the procedure is a recursive process that converts each part in the DFM file into text. Because of the ownership of the parts, the parts are nested, and recursion is the best way:

Procedure Convertobject;

Begin

Convertheader;

INC (NestingLevel);

While does reader.endoflist do convertproperty;

Reader.readlistend;

While does reader.endoflist do convertobject;

Reader.readlistend;

Dec (NestingLevel);

Writeindent;

Writestr (' End ' #13 #10);

End

The Neststinglevel variable represents the nesting level of the part. Writeindent is the space before the start character of each line is written, and the Convertheader process is the inheritance flag information that handles the part. The converted header message text has two forms.

Inherited Testform1:ttestform[2]

Or:

Object Testform1:ttestform

The former is ffinherited and Ffchildpos, and there are no places behind it.

The Convertproperty process is used to convert attributes.

Procedure Convertproperty;

Begin

Writeindent;

Writestr (READER.READSTR);

Writestr (' = ');

Convertvalue;

Writestr (#13 #10);

End

The Writeindent statement writes the space before the property name, and the WRITESTR (READER.READSTR) statement writes the property name Convertvalue The process converts the property value to a string based on the type of the property and then writes to the stream.

The function of objecttexttobinary process is opposite to objectbinarytotext, the TXT file is converted to a part in binary stream, and as long as the writing of TXT file content conforms to DFM script syntax, Objecttexttobinary can convert any program generated TXT file into a part, this function also for DFM file dynamic generation and edit laid the foundation. The main procedures for the objecttexttobinary process are as follows:

Procedure Objecttexttobinary (Input, Output:tstream);

Var

Saveseparator:char;

Parser:tparser;

Writer:twriter;

...

Begin

Parser: = Tparser.create (Input);

Saveseparator: = DecimalSeparator;

DecimalSeparator: = '. ';

Try

Writer: = Twriter.create (Output, 4096);

Try

Writer.writesignature;

Convertobject;

Finally

Writer.free;

End

Finally

DecimalSeparator: = Saveseparator;

Parser.free;

End

End

The process and structure of the program is similar to Objectbinarytotext. Convertobject is also a recursive process:

Procedure Convertobject;

Var

Inheritedobject:boolean;

Begin

Inheritedobject: = False;

If Parser.tokensymbolis (' inherited ') then

Inheritedobject: = True

Else

Parser.checktokensymbol (' OBJECT ');

Parser.nexttoken;

Convertheader (Inheritedobject);

While isn't Parser.tokensymbolis (' end ') and

Not Parser.tokensymbolis (' OBJECT ') and

Not Parser.tokensymbolis (' inherited ') do convertproperty;

Writer.writelistend;

While not Parser.tokensymbolis (' end ') does convertobject;

Writer.writelistend;

Parser.nexttoken;

End

The task of converting the DFM file to the DFM scripting language is accomplished by the Objectresourcetotext and Objexttexttoresource two processes.

Procedure Objectresourcetotext (Input, Output:tstream);

Begin

Input.readresheader;

Objectbinarytotext (Input, Output);

End

The Objecttexttoresource process is more complex because the DFM file resource header contains the inheritance flag information, so after calling Objecttexttobinary, it reads the flag information and writes the resource header.

Procedure Objecttexttoresource (Input, Output:tstream);

Var

Len:byte;

Tmp:longint;

Memorystream:tmemorystream;

Memorysize:longint;

HEADER:ARRAY[0..79] of Char;

Begin

MemoryStream: = tmemorystream.create;

Try

Objecttexttobinary (Input, MemoryStream);

Memorysize: = memorystream.size;

Fillchar (header, SizeOf (header), 0);

Memorystream.position: = SizeOf (Longint); {Skip Header}

Memorystream.read (Len, 1);

If Len and $F 0 = $F 0 Then

Begin

If Ffchildpos in Tfilerflags ((Len and $F 0)) Then

Begin

Memorystream.read (Len, 1);

Case Tvaluetype (Len) of

Vaint8:len: = 1;

Vaint16:len: = 2;

Vaint32:len: = 4;

End

Memorystream.read (TMP, Len);

End

Memorystream.read (Len, 1);

End

Memorystream.read (Header[3], Len);

Strupper (@Header [3]);

Byte ((@Header [0]) ^): = $FF;

Word (@Header [1]) ^): = 10;

Word (@Header [Len + 4]) ^): = $1030;

Longint ((@Header [Len + 6]) ^): = Memorysize;

Output.write (Header, Len + 10);

Output.write (memorystream.memory^, memorysize);

Finally

Memorystream.free;

End

End