delphi - 按标题搜索标签

Question

我试图弄清楚如何通过标签的标题搜索标签:

for I := ComponentCount - 1 downto 0 do
begin
  if Components[i] is TLabel then
    if Components[i].Caption = mnNumber then
    begin
      Components[i].Left := Left;
      Components[i].Top := Top + 8;
    end;
end;

我收到错误:未声明的标识符:“Caption”。
我该如何解决这个问题？

Answer 1

迭代Components[]是错误的方法。这只会产生表单所拥有的组件。您将错过任何动态添加的、不属于表单的组件或属于框架的组件。

您应该使用Controls[]。然而，这只产生第一代 child 。如果有更深的父/子嵌套，那么您需要递归。那是更多的工作。我使用一些助手来使其变得简单。我已将它们包含在这个单元中:

unit ControlEnumerator;

interface

uses
  System.SysUtils, System.Generics.Collections, Vcl.Controls;

type
  TControls = class
  private
    type
      TEnumerator<T: TControl> = record
        FControls: TArray<T>;
        FIndex: Integer;
        procedure Initialise(WinControl: TWinControl; Predicate: TFunc<T, Boolean>);
        class function Count(WinControl: TWinControl; Predicate: TFunc<T, Boolean>): Integer; static;
        function GetCurrent: T;
        function MoveNext: Boolean;
        property Current: T read GetCurrent;
      end;
      TEnumeratorFactory<T: TControl> = record
        FWinControl: TWinControl;
        FPredicate: TFunc<T, Boolean>;
        function Count: Integer;
        function Controls: TArray<T>;
        function GetEnumerator: TEnumerator<T>;
      end;
  public
    class procedure WalkControls<T: TControl>(WinControl: TWinControl; Predicate: TFunc<T, Boolean>; Method: TProc<T>); static;
    class function Enumerator<T: TControl>(WinControl: TWinControl; Predicate: TFunc<T, Boolean>=nil): TEnumeratorFactory<T>; static;
    class function ChildCount<T: TControl>(WinControl: TWinControl; Predicate: TFunc<T, Boolean>=nil): Integer; static;
  end;

implementation

{ TControls.TEnumerator<T> }

procedure TControls.TEnumerator<T>.Initialise(WinControl: TWinControl; Predicate: TFunc<T, Boolean>);
var
  List: TList<T>;
  Method: TProc<T>;
begin
  List := TObjectList<T>.Create(False);
  Try
    Method :=
      procedure(Control: T)
      begin
        List.Add(Control);
      end;
    WalkControls<T>(WinControl, Predicate, Method);
    FControls := List.ToArray;
  Finally
    List.Free;
  End;
  FIndex := -1;
end;

class function TControls.TEnumerator<T>.Count(WinControl: TWinControl; Predicate: TFunc<T, Boolean>): Integer;
var
  Count: Integer;
  Method: TProc<T>;
begin
  Method :=
    procedure(Control: T)
    begin
      inc(Count);
    end;
  Count := 0;
  WalkControls<T>(WinControl, Predicate, Method);
  Result := Count;
end;

function TControls.TEnumerator<T>.GetCurrent: T;
begin
  Result := FControls[FIndex];
end;

function TControls.TEnumerator<T>.MoveNext: Boolean;
begin
  inc(FIndex);
  Result := FIndex<Length(FControls);
end;

{ TControls.TEnumeratorFactory<T> }

function TControls.TEnumeratorFactory<T>.Count: Integer;
begin
  Result := TEnumerator<T>.Count(FWinControl, FPredicate);
end;

function TControls.TEnumeratorFactory<T>.Controls: TArray<T>;
var
  Enumerator: TEnumerator<T>;
begin
  Enumerator.Initialise(FWinControl, FPredicate);
  Result := Enumerator.FControls;
end;

function TControls.TEnumeratorFactory<T>.GetEnumerator: TEnumerator<T>;
begin
  Result.Initialise(FWinControl, FPredicate);
end;

class procedure TControls.WalkControls<T>(WinControl: TWinControl; Predicate: TFunc<T, Boolean>; Method: TProc<T>);
var
  i: Integer;
  Control: TControl;
  Include: Boolean;
begin
  if not Assigned(WinControl) then begin
    exit;
  end;
  for i := 0 to WinControl.ControlCount-1 do begin
    Control := WinControl.Controls[i];
    if not (Control is T) then begin
      Include := False;
    end else if Assigned(Predicate) and not Predicate(Control) then begin
      Include := False;
    end else begin
      Include := True;
    end;
    if Include then begin
      Method(Control);
    end;
    if Control is TWinControl then begin
      WalkControls(TWinControl(Control), Predicate, Method);
    end;
  end;
end;

class function TControls.Enumerator<T>(WinControl: TWinControl; Predicate: TFunc<T, Boolean>): TEnumeratorFactory<T>;
begin
  Result.FWinControl := WinControl;
  Result.FPredicate := Predicate;
end;

class function TControls.ChildCount<T>(WinControl: TWinControl; Predicate: TFunc<T, Boolean>): Integer;
begin
  Result := Enumerator<T>(WinControl, Predicate).Count;
end;

end.

现在你可以这样解决你的问题:

var
  lbl: TLabel;
....
for lbl in TControls.Enumerator<TLabel>(Form) do
  if lbl.caption=mnNumber then
  begin
    lbl.Left := Left;
    lbl.Top := Top + 8;
  end;

或者您可以使用谓词将标题测试放入迭代器中:

var
  Predicate: TControlPredicate;
  lbl: TLabel;
....
Predicate := function(lbl: TLabel): Boolean
  begin
    Result := lbl.Caption='hello';
  end;
for lbl in TControls.Enumerator<TLabel>(Form, Predicate) do
begin
  lbl.Left := Left;
  lbl.Top := Top + 8;
end;