Delphi XE2 之 FireMonkey 入門(26) – 資料繫結: TBindingsList: TBindExprItems

如果要給一對 "原始檔控制" 和 "目標控制項" 寫多個運算式, 使用 TBindExpression 就不如 TBindExprItems 了.

TBindExprItems 中的運算式又分兩組: FormatExpressions、ClearExpressions, 後者是在斷開綁定時的運算式.

樣本設想:
1、TrackBar1 為源, 把其 Value 值綁定給 Edit1.Text 和 Edit1.Width 和 Label1.Text;
2、斷開綁定時, 在 Edit1 中顯示 "已斷開綁定".

先在表單上添加: TrackBar1、Edit1、Label1、BindingsList1、CheckBox1, 然後啟用 TrackBar1、ChengkBox1 和表單的預設事件:

unit Unit1;interfaceuses  System.SysUtils, System.Types, System.UITypes, System.Classes, System.Variants,  FMX.Types, FMX.Controls, FMX.Forms, FMX.Dialogs, Data.Bind.EngExt,  Fmx.Bind.DBEngExt, Data.Bind.Components, FMX.Edit;type  TForm1 = class(TForm)    TrackBar1: TTrackBar;    Edit1: TEdit;    Label1: TLabel;    BindingsList1: TBindingsList;    CheckBox1: TCheckBox;    procedure FormCreate(Sender: TObject);    procedure TrackBar1Change(Sender: TObject);    procedure CheckBox1Change(Sender: TObject);  end;var  Form1: TForm1;implementation{$R *.fmx}var  bindExprItems: TBindExprItems;procedure TForm1.FormCreate(Sender: TObject);begin  bindExprItems := TBindExprItems.Create(BindingsList1);  with bindExprItems do  begin    ControlComponent := Edit1;    //目標控制項    SourceComponent := TrackBar1; //原始檔控制    {把 TrackBar1.Value 綁定到 Edit1.Text}    with FormatExpressions.AddExpression do    begin      ControlExpression := 'Text';      SourceExpression := 'Value';    end;    {把 TrackBar1.Value 綁定到 Edit1.Width}    with FormatExpressions.AddExpression do    begin      ControlExpression := 'Width';      SourceExpression := 'Value';    end;    {把 TrackBar1.Value 綁定到 Label1.Text}    with FormatExpressions.AddExpression do    begin      ControlExpression := 'Owner.Label1.Text'; //Owner      SourceExpression := 'Value';    end;    {當要斷開綁定時...}    with ClearExpressions.AddExpression do    begin      ControlExpression := 'Self.Text';  //這裡的 Self 是指目標控制項本身, 可省略      SourceExpression := '"已斷開綁定"';    end;    Active := True;  end;  CheckBox1.IsChecked := True;  TrackBar1.Max := ClientWidth;end;procedure TForm1.TrackBar1Change(Sender: TObject);begin  BindingsList1.Notify(Sender, 'Value');end;procedure TForm1.CheckBox1Change(Sender: TObject);begin  bindExprItems.Active := TCheckBox(Sender).IsChecked;end;end.