Delphi Handle Exception

初在Delphi里进行处理错误时，最常用的做法是try….except ….end. 例如：

复制代码try raise Exception.Create('Error Message'); except on e:Exception do begin ShowMessage(e.Message); end; end;

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try
    raise Exception.Create('Error Message');
  except
    on e:Exception do
    begin
      ShowMessage(e.Message);
    end;

  end;

 

而现在要说的是另外的一种做法:

复制代码var ExceptionObj : TObject; begin { Simulate an access violation. } try System.Error(reAccessViolation); except ExceptionObj := ExceptObject; if ExceptionObj <> nil then begin MessageDlg(ExceptionObj.ToString, mtError, [mbOK], 0); end; end; end;

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var
  ExceptionObj : TObject;
begin
  { Simulate an access violation. }
  try
    System.Error(reAccessViolation);
  except
    ExceptionObj := ExceptObject;
    if ExceptionObj <> nil then
    begin
      MessageDlg(ExceptionObj.ToString, mtError, [mbOK], 0);
    end;
  end;
end;

在上面的代码，使用了ExceptObject这个对象，这个对象是在System单元中定义的，用于返回当前正在处理的错误对象，如果没有发生错误，其值为nil。当错误变量（在try..except里定义的）不可访问时，ExceptObject就显得很有用，例如当错误处理代码调用一个函数进行错误处理时。

需要注意的是，当错误处理完毕后，ExceptionObject返回的将是nil。还有可能会用到的一个函数是AcquireExceptionObject。这个函数返回当前except 对象的指针，这个函数的作用是为了防止当前的except对象被释放掉。AcquireExceptionObject是通过引用计数进行操作的。

 

下面是delphi的错误处理的代码：

复制代码procedure TForm2.btIOErrorClick(Sender: TObject); var ExceptionObj : TObject; begin { Try to write something onto the console--it will raise an exception. } try WriteLn('This will generate an error because there is no' + ' console attached!'); except ExceptionObj := ExceptObject; if ExceptionObj = nil then MessageDlg('No exception', mtError, [mbOK], 0) else begin MessageDlg(ExceptionObj.ToString, mtError, [mbOK], 0); end; end; end; {$OVERFLOWCHECKS ON} {$OPTIMIZATION OFF} {$HINTS OFF} procedure TForm2.btOverflowErrClick(Sender: TObject); var b : Cardinal; ExceptionPtr : Pointer; begin { Simulate an overflow. Note: Enable the overflow checking and disable optimizations, because the Delphi compiler will not compile this code otherwise. } ExceptionPtr := nil; try b := $FFFFFFFF; b := b * b; except ExceptionPtr := AcquireExceptionObject; end; // Check exception. if ExceptionPtr = nil then MessageDlg('No exception', mtError, [mbOK], 0) else begin MessageDlg(TObject(ExceptionPtr).ToString, mtError, [mbOK], 0); ReleaseExceptionObject; end; end; {$HINTS ON} {$OPTIMIZATION ON} {$OVERFLOWCHECKS OFF} procedure TForm2.btRuntimeErrorClick(Sender: TObject); var ExceptionObj : TObject; begin { Simulate an access violation. } try System.Error(reAccessViolation); except ExceptionObj := ExceptObject; if ExceptionObj = nil then MessageDlg('No exception', mtError, [mbOK], 0) else begin MessageDlg(ExceptionObj.ToString, mtError, [mbOK], 0); end; end; end;

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procedure TForm2.btIOErrorClick(Sender: TObject);
var
  ExceptionObj : TObject;
begin
  {
  Try to write something onto the console--it will raise an
  exception.
  }
  try
  WriteLn('This will generate an error because there is no' +
          ' console attached!');
  except
    ExceptionObj := ExceptObject;
    if ExceptionObj = nil then
      MessageDlg('No exception', mtError, [mbOK], 0)
    else
    begin
      MessageDlg(ExceptionObj.ToString, mtError, [mbOK], 0);
    end;
  end;
end;
 
{$OVERFLOWCHECKS ON}
{$OPTIMIZATION OFF}
{$HINTS OFF}
procedure TForm2.btOverflowErrClick(Sender: TObject);
var
  b : Cardinal;
  ExceptionPtr : Pointer;
begin
  {
  Simulate an overflow. Note: Enable the overflow
  checking and disable optimizations, because the Delphi
  compiler will not compile this code otherwise.
  }
  ExceptionPtr := nil;
  try
    b := $FFFFFFFF;
    b := b * b;
  except
    ExceptionPtr := AcquireExceptionObject;
  end;
 
  // Check exception.
  if ExceptionPtr = nil then
    MessageDlg('No exception', mtError, [mbOK], 0)
  else
  begin
    MessageDlg(TObject(ExceptionPtr).ToString, mtError, [mbOK], 0);
    ReleaseExceptionObject;
  end;
end;
{$HINTS ON}
{$OPTIMIZATION ON}
{$OVERFLOWCHECKS OFF}
 
procedure TForm2.btRuntimeErrorClick(Sender: TObject);
var
 
  ExceptionObj : TObject;
  begin
  { Simulate an access violation. }
  try
    System.Error(reAccessViolation);
  except
    ExceptionObj := ExceptObject;
    if ExceptionObj = nil then
      MessageDlg('No exception', mtError, [mbOK], 0)
    else
    begin
      MessageDlg(ExceptionObj.ToString, mtError, [mbOK], 0);
    end;
  end;
end;