Delphi 資料庫記錄修改與異常保護：DisableControls/EnableControls 效能優化、Try...Finally 確保資源釋放完整實作範例

修改記錄潛在風險與 Try...Finally 解決方案

程式執行 Post 寫入磁碟時若磁碟未就緒會發生異常。異常發生時應用程式暫停彈出錯誤對話框，使用者點擊後程式繼續執行至不可預期位置。此時表單所有控制項已與 TTable 失去連接（因前置 DisableControls），導致顯示資料與資料庫脫節。

Object Pascal Try...Finally 解決此問題：Try 區塊含可能產生異常程式碼，Finally 區塊含即使發生異常也必須執行陳述式。本例 Finally 僅含 EnableControls：

with Table do
begin
  DisableControls;           { 修改期間切斷控制項連接 }
  try
    First;                   { 指標移至第一筆 }
    while not EOF do
    begin
      <讀取欄位值到變數>
      <適當修改>
      Edit;                  { 進入編輯狀態 }
      <寫回修改值>
      Post;                  { 寫入資料庫 }
      Next;                  { 下一筆 }
    end;
    EnableControls;
  finally                    { 異常發生時執行 }
    EnableControls;          { 恢復控制項功能 }
  end;
end;

關鍵區別：Try...Finally 為異常保護（確保 Finally 執行讓程式繼續）；Try...Except 為異常處理（採取對應處理）。切勿混淆。

完整程式範例：客戶資料表地址欄位大小寫轉換

unit Unit26;
interface
uses Windows, Messages, SysUtils, Classes, Graphics, Controls, Forms,
  Dialogs, StdCtrls, Grids, DBGrids, ExtCtrls, DB, DBTables, Buttons;
type
  TForm1 = class(TForm)
    DataSource1: TDataSource;
    CustomerTable: TTable;
    Panel1: TPanel;
    DBGrid1: TDBGrid;
    Panel2: TPanel;
    UpperCaseFirstAddBtn: TButton;
    UpperCaseSecondAddBtn: TButton;
    MixedCaseFirstAddBtn: TButton;
    MixedCaseSecondAddBtn: TButton;
    BitBtn1: TBitBtn;
    procedure ForceCase(TargetField: string; ToUpper: Boolean);
    procedure UpperCaseFirstAddBtnClick(Sender: TObject);
    procedure MixedCaseFirstAddBtnClick(Sender: TObject);
    procedure UpperCaseSecondAddBtnClick(Sender: TObject);
    procedure MixedCaseSecondAddBtnClick(Sender: TObject);
    procedure FormCreate(Sender: TObject);
  private
    { Private declarations }
  public
    { Public declarations }
  end;
var Form1: TForm1;
implementation
const
  Upper = True;
  Mixed = False;
{$R *.DFM}
function IsUpper(Ch: Char): Boolean;
begin
  Result := (Ch >= 'A') and (Ch <= 'Z');
end;
procedure TForm1.ForceCase(TargetField: string; ToUpper: Boolean);
var
  WorkBuffer: string;
  I: Integer;
begin
  with CustomerTable do
  begin
    DisableControls;
    try
      First;
      while not EOF do
      begin
        WorkBuffer := FieldByName(TargetField).AsString;
        if ToUpper then
          for I := 1 to Length(WorkBuffer) do
            WorkBuffer[I] := UpCase(WorkBuffer[I])
        else
        begin
          for I := 1 to Length(WorkBuffer) do
            if IsUpper(WorkBuffer[I]) then
              WorkBuffer[I] := Chr(Ord(WorkBuffer[I]) + 32);
          WorkBuffer[1] := UpCase(WorkBuffer[1]);
        end;
        Edit;
        FieldByName(TargetField).AsString := WorkBuffer;
        Post;
        Next;
      end;
    finally
      EnableControls;
    end;
  end;
end;
procedure TForm1.UpperCaseFirstAddBtnClick(Sender: TObject);
begin
  ForceCase('Addr1', Upper);
end;
procedure TForm1.MixedCaseFirstAddBtnClick(Sender: TObject);
begin
  ForceCase('Addr1', Mixed);
end;
procedure TForm1.UpperCaseSecondAddBtnClick(Sender: TObject);
begin
  ForceCase('Addr2', Upper);
end;
procedure TForm1.MixedCaseSecondAddBtnClick(Sender: TObject);
begin
  ForceCase('Addr2', Mixed);
end;
procedure TForm1.FormCreate(Sender: TObject);
begin
  CustomerTable.Open;
end;
end.

四按鈕分別處理 Addr1/Addr2 全大寫或首字大寫其餘小寫。ForceCase 統一邏輯：DisableControls → Try...Finally 保護 EnableControls → 遍歷記錄修改欄位值。