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copied!<p><strong>Delphi 7 version</strong> Here's an example of how to achieve that. I used Delphi2010 to implement it but it should work in Delphi7 at least as I used TypInfo unit directly.</p> <pre><code>unit Unit1; interface uses Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms, Dialogs, StdCtrls; type TForm1 = class(TForm) ListBox1: TListBox; Edit1: TEdit; Button1: TButton; procedure FormCreate(Sender: TObject); procedure Button1Click(Sender: TObject); private { Private declarations } FList: TList; procedure DoSort(PropName: String); procedure DoDisplay(PropName: String); public { Public declarations } end; var Form1: TForm1; implementation {$R *.dfm} uses TypInfo; var PropertyName: String; type TPerson = class private FName: String; FAge: Integer; published public constructor Create(Name: String; Age: Integer); published property Name: String read FName; property Age: Integer read FAge; end; { TPerson } constructor TPerson.Create(Name: String; Age: Integer); begin FName := Name; FAge := Age; end; function ComparePersonByPropertyName(P1, P2: Pointer): Integer; var propValueP1, propValueP2: Variant; begin propValueP1 := GetPropValue(P1, PropertyName, False); propValueP2 := GetPropValue(P2, PropertyName, False); if VarCompareValue(propValueP1, propValueP2) = vrEqual then begin Result := 0; end else if VarCompareValue(propValueP1, propValueP2) = vrGreaterThan then begin Result := 1; end else begin Result := -1; end; end; procedure TForm1.FormCreate(Sender: TObject); begin FList := TList.Create; FList.Add(TPerson.Create('Zed', 10)); FList.Add(TPerson.Create('John', 20)); FList.Add(TPerson.Create('Mike', 30)); FList.Add(TPerson.Create('Paul', 40)); FList.Add(TPerson.Create('Albert', 50)); FList.Add(TPerson.Create('Barbara', 60)); FList.Add(TPerson.Create('Christian', 70)); Edit1.Text := 'Age'; DoSort('Age'); // Sort by age DoDisplay('Age'); end; procedure TForm1.Button1Click(Sender: TObject); begin DoSort(Edit1.Text); DoDisplay(Edit1.Text); end; procedure TForm1.DoSort(PropName: String); begin PropertyName := PropName; FList.Sort(ComparePersonByPropertyName); end; procedure TForm1.DoDisplay(PropName: String); var i: Integer; strPropValue: String; begin ListBox1.Items.Clear; for i := 0 to FList.Count - 1 do begin strPropValue := GetPropValue(FList[i], PropName, False); ListBox1.Items.Add(strPropValue); end; end; end. </code></pre> <p>BTW, I used a simple form with a <em>listbox</em>, an <em>edit</em> and a <em>button</em>. The listbox shows the contents of the list (FList) sorted. The button is used to sort the list according to what the user has typed in the editbox.</p> <p><strong>Delphi 2010 version</strong> (uses references to methods)</p> <pre><code>unit Unit2; interface uses Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms, Dialogs, StdCtrls; type TForm2 = class(TForm) ListBox1: TListBox; Edit1: TEdit; Button1: TButton; procedure FormCreate(Sender: TObject); procedure Button1Click(Sender: TObject); private { Private declarations } FList: TList; FPropertyName: String; { << } procedure DoSort(PropName: String); procedure DoDisplay(PropName: String); function CompareObjectByPropertyName(P1, P2: Pointer): Integer; { << } public { Public declarations } end; var Form2: TForm2; implementation {$R *.dfm} uses TypInfo; type TPerson = class private FName: String; FAge: Integer; published public constructor Create(Name: String; Age: Integer); published property Name: String read FName; property Age: Integer read FAge; end; { TPerson } constructor TPerson.Create(Name: String; Age: Integer); begin FName := Name; FAge := Age; end; /// This version uses a method to do the sorting and therefore can use a field of the form, /// no more ugly global variable. /// See below (DoSort) if you want to get rid of the field also ;) function TForm2.CompareObjectByPropertyName(P1, P2: Pointer): Integer; { << } var propValueP1, propValueP2: Variant; begin propValueP1 := GetPropValue(P1, FPropertyName, False); propValueP2 := GetPropValue(P2, FPropertyName, False); if VarCompareValue(propValueP1, propValueP2) = vrEqual then begin Result := 0; end else if VarCompareValue(propValueP1, propValueP2) = vrGreaterThan then begin Result := 1; end else begin Result := -1; end; end; procedure TForm2.FormCreate(Sender: TObject); begin FList := TList.Create; FList.Add(TPerson.Create('Zed', 10)); FList.Add(TPerson.Create('John', 20)); FList.Add(TPerson.Create('Mike', 30)); FList.Add(TPerson.Create('Paul', 40)); FList.Add(TPerson.Create('Albert', 50)); FList.Add(TPerson.Create('Barbara', 60)); FList.Add(TPerson.Create('Christian', 70)); Edit1.Text := 'Age'; DoSort('Age'); // Sort by age DoDisplay('Age'); end; procedure TForm2.Button1Click(Sender: TObject); begin DoSort(Edit1.Text); DoDisplay(Edit1.Text); end; procedure TForm2.DoSort(PropName: String); begin FPropertyName := PropName; { << } FList.SortList(CompareObjectByPropertyName); { << } /// The code above could be written with a lambda, and without CompareObjectByPropertyName /// using FPropertyName, and by using a closure thus referring to PropName directly. /// Below is the equivalent code that doesn't make use of FPropertyName. The code below /// could be commented out completely and just is there to show an alternative approach. FList.SortList( function (P1, P2: Pointer): Integer var propValueP1, propValueP2: Variant; begin propValueP1 := GetPropValue(P1, PropName, False); propValueP2 := GetPropValue(P2, PropName, False); if VarCompareValue(propValueP1, propValueP2) = vrEqual then begin Result := 0; end else if VarCompareValue(propValueP1, propValueP2) = vrGreaterThan then begin Result := 1; end else begin Result := -1; /// This is a catch anything else, even if the values cannot be compared end; end); /// Inline anonymous functions (lambdas) make the code less readable but /// have the advantage of "capturing" local variables (creating a closure) end; procedure TForm2.DoDisplay(PropName: String); var i: Integer; strPropValue: String; begin ListBox1.Items.Clear; for i := 0 to FList.Count - 1 do begin strPropValue := GetPropValue(FList[i], PropName, False); ListBox1.Items.Add(strPropValue); end; end; end. </code></pre> <p>I marked with <code>{ << }</code> the main changes.</p>

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