| Description |
Normally, you would allow the callback method of an asynchronous read to be called. If you need to wait until this happens in the main thread of operation, then call EndRead.
The AsynResult parameter should be supplied with the value returned by the BeginRead you want to wait for.
It will return the number of bytes read, unless the stream end was reached.
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| Microsoft MSDN Links |
System.IO
System.IO.FileStream
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| A simple example |
// Full Unit code.
// -------------------------------------------------------------
// Create a new WinForm application, double click the form to
// create an OnLoad event, and then replace the WinForm unit
// with this text.
unit WinForm;
interface
uses
System.Drawing, System.Collections, System.ComponentModel,
System.Windows.Forms, System.Data;
type
TWinForm = class(System.Windows.Forms.Form)
\{REGION 'Designer Managed Code'\} // Note that REGION and ENREGION should be prefixed by a dollar sign
strict private
///
/// Required designer variable.
///
Components: System.ComponentModel.Container;
///
/// Required method for Designer support - do not modify
/// the contents of this method with the code editor.
///
procedure InitializeComponent;
procedure TWinForm_Load(sender: System.Object; e: System.EventArgs);
{ENDREGION}
strict protected
///
/// Clean up any resources being used.
///
procedure Dispose(Disposing: Boolean); override;
private
{ Private Declarations }
public
constructor Create;
end;
[assembly: RuntimeRequiredAttribute(TypeOf(TWinForm))]
implementation
\{REGION 'Windows Form Designer generated code'\}
///
/// Required method for Designer support -- do not modify
/// the contents of this method with the code editor.
///
procedure TWinForm.InitializeComponent;
begin
//
// TWinForm
//
Self.AutoScaleBaseSize := System.Drawing.Size.Create(5, 13);
Self.ClientSize := System.Drawing.Size.Create(292, 266);
Self.Name := 'TWinForm';
Self.Text := 'WinForm';
Include(Self.Load, Self.TWinForm_Load);
end;
{ENDREGION}
procedure TWinForm.Dispose(Disposing: Boolean);
begin
if Disposing then
begin
if Components <> nil then
Components.Dispose();
end;
inherited Dispose(Disposing);
end;
constructor TWinForm.Create;
begin
inherited Create;
//
// Required for Windows Form Designer support
//
InitializeComponent;
//
// TODO: Add any constructor code after InitializeComponent call
//
end;
procedure TWinForm.TWinForm_Load(sender: System.Object; e: System.EventArgs);
program Project1;
{$APPTYPE CONSOLE}
uses
System.IO,
System.Runtime.Remoting.Messaging;
var
Stream : System.IO.FileStream;
ByteArray : Array of Byte;
AsyncRes : IAsyncResult;
Index : Integer;
procedure ReadDone(AsyncResult : IAsyncResult);
var
Index : Integer;
begin
Console.WriteLine('Read is finished :');
Console.WriteLine;
// Display our array contents
for Index := 0 to Length(ByteArray)-1 do
Console.WriteLine(ByteArray[Index].ToString);
end;
begin
// Create our File Stream
Stream := System.IO.FileStream.Create('C:\DelphiBasics.txt', FileMode.Create);
// Write to the stream
Stream.WriteByte(1);
Stream.WriteByte(2);
Stream.WriteByte(3);
Stream.WriteByte(4);
Stream.WriteByte(5);
Stream.WriteByte(6);
Stream.WriteByte(7);
Stream.WriteByte(8);
Stream.WriteByte(9);
// Move to the start of the stream
Stream.Seek(0, SeekOrigin.Begin);
// Declare our array to hold the returned data
SetLength(ByteArray, 12);
// Read from the stream asynchronously
AsyncRes := Stream.BeginRead(ByteArray, 0, 10, ReadDone, TObject.Create);
// Wait for the read to end
Console.WriteLine;
Console.WriteLine('Waiting in main thread for read to complete');
Console.WriteLine;
Stream.EndRead(AsyncRes);
// Display our array contents
for Index := 0 to Length(ByteArray)-1 do
Console.WriteLine(ByteArray[Index].ToString);
// Close the file stream
Stream.Close;
Console.Readline;
end.
end. | | Hide full unit code | Read is finished :
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Waiting in main thread for read to complete
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