Delphi XE5 - strange behavior help needed - multithreading

Question

I'm working on TLogger class that is logging my application logs to file...
I have to way of getting Logs from File to TMemo:
1. assign TMemo to TLogger class then, assign True to DisplayInMemo property, then just call GetLogFromFile();
2. call GetLogsFromFile(); then Self.Memo1.Text := TLogger.LogsResult;
Below... Commented solution works fine... Uncommented solution works only every 2 click on button 4
procedure TForm1.Button4Click(Sender: TObject); // get log.file to memo
begin
// automatic forwarding logs from File to TMemo - it works!
//logger.DisplayMemo := Self.Memo1;
//logger.DisplayInMemo := True;
//logger.GetLogsFromFile();
// tested - half-automatic method of formwarding logs to TMemo - works every 2 clicks :(
logger.DisplayInMemo := False;
logger.GetLogsFromFile();
Self.Memo1.Text := logger.LogsResult;
end;
Whole TLogger implementation:
unit Logger;
interface
uses
System.IOUtils, System.TypInfo, System.SysUtils, FMX.Forms, FMX.Dialogs, System.Classes, FMX.Graphics, FMX.ExtCtrls, LoggerThread, FMX.Memo;
type
TLogger = class
private
FileName : String; // name of file to log
FilePath : String; // path to app / log-file
LStringResult : String; // result of thread log.file reading
LLoggerMemo : TMemo; // copy of memo - place where GetLogsFromFile put results
LDisplayInMemo : Boolean; // bool - if True GetLogsFromFile puts results to DisplayMemo, otherwise waiting in LogsResult
NewLoggerThread : TLoggerThread; // thread object - created in Create()
procedure GetLogsFromFileThreadTerminateHandler(sender: TObject);
public
constructor Create(); overload; // open or create 'development.log'
constructor Create(LogFileName : String); overload; // open or create LogFileName for logging
destructor Destroy(); overload; // cleaner of TLogger object
// main procedures
procedure Log(LogString : String); // add line to log file
procedure GetLogsFromFile(); // get all logs from log file to string
// settings, reading results,
property DisplayInMemo : Boolean read LDisplayInMemo write LDisplayInMemo; //bool - if True GetLogsFromFile puts results to DisplayMemo, otherwise waiting in LogsResult
property LogsResult : String read LStringResult write LStringResult; //string results after Getters from TLogger usage
property DisplayMemo : TMemo read LLoggerMemo write LLoggerMemo; // sets TMemo where results will be put if DisplayInMemo set to True
end;
implementation
constructor TLogger.Create();
begin
{$IFDEF Android}
FilePath := TPath.GetDownloadsPath + System.SysUtils.PathDelim;
{$ELSE}
FilePath := ExtractFilePath(ParamStr(0));
{$ENDIF}
FileName := 'development.log';
LDisplayInMemo := False;
// inherited
inherited Create;
end;
constructor TLogger.Create(LogFileName : String);
begin
{$IFDEF Android}
FilePath := TPath.GetDownloadsPath + System.SysUtils.PathDelim;
//TPath.Combine(TPath.GetDocumentsPath,'test.txt'); // to have / \ auto-change
{$ELSE}
FilePath := ExtractFilePath(ParamStr(0));
{$ENDIF}
FileName := LogFileName;
LDisplayInMemo := False;
// inherited
inherited Create;
end;
destructor TLogger.Destroy();
begin
inherited Destroy;
end;
// adds a sigle line to log file with date time
procedure TLogger.Log(LogString : String);
begin
NewLoggerThread := TLoggerThread.Create(True);
NewLoggerThread.FreeOnTerminate := True;
NewLoggerThread.Log := LogString; //log to write - date time then added in execute
NewLoggerThread.LoggerInstruction := TLoggerInstruction.liLogToFile; //set instuction for thread - LogToFile
NewLoggerThread.FileName := FileName; //file to write
NewLoggerThread.FilePath := FilePath; //path to file
try
NewLoggerThread.Start;
except
NewLoggerThread.Free();
end;
end;
// results String with LogFile content
procedure TLogger.GetLogsFromFile();
begin
NewLoggerThread := TLoggerThread.Create(True);
NewLoggerThread.FreeOnTerminate := True;
NewLoggerThread.OnTerminate := GetLogsFromFileThreadTerminateHandler;
NewLoggerThread.FileName := FileName; //file to write
NewLoggerThread.FilePath := FilePath; //path to file
NewLoggerThread.LoggerInstruction := TLoggerInstruction.liGetLogsFromFile; //set instuction for thread - GetLogFromFile
try
NewLoggerThread.Start;
except
NewLoggerThread.Free();
end;
end;
procedure TLogger.GetLogsFromFileThreadTerminateHandler(sender: TObject);
begin
LStringResult := (Sender as TLoggerThread).StringResult;
if LDisplayInMemo then
LLoggerMemo.Text := (Sender as TLoggerThread).StringResult;
end;
end.
As you can see only difference is in LDisplayInMemo: if is True TMemo fills with logs... when is False I need 2 clicks on Button 4 to get results in TMemo...
procedure TLogger.GetLogsFromFileThreadTerminateHandler(sender: TObject);
begin
LStringResult := (Sender as TLoggerThread).StringResult;
if LDisplayInMemo then
LLoggerMemo.Text := (Sender as TLoggerThread).StringResult;
end;
Any ideas? To be honest I have no idea what's the reason of diffenerce in working of both solutions :( I also tried ProcessMessages after Self.Memo1.Text := logger.LogsResult;

Answer 1

The reason the following code only works the second time you click the button is that your code to actually get the log information runs in another thread... it's asynchronous!
logger.DisplayInMemo := False;
logger.GetLogsFromFile();
Self.Memo1.Text := logger.LogsResult; //This line runs AT THE SAME TIME you're getting logs!
NOTE: You're reading the value of logger.LogsResult before it gets a value from your LoggerThread.
When you click the button a second time, the thread has finished running (the first time), and you're now able to read a value.
The reason your commented section works, is that you are only assigning the memo text when the thread terminates - i.e. finished doing it's work.