DevExpress控件擴展之表達式編輯器

業務需求：

業務工作中經常需要對表格中的數據進行處理，包括過濾、復合計算等。過濾需要有過濾條件，復合計算需要計算公式。這兩種場景都需要一個表達式編輯器。GridControl自帶過濾條件的表達式編輯器，我們要做的就是把這個編輯器拿出來，獨立於GridControl，進而可以綁定到其它控件上。

實現原理：

找到表達式編輯器內部類UnboundColumnExpressionEditorForm，這是一個窗口類。我們將其邊框設置為None，Dock屬性設置為Fill，拖放到控件上，使其看上去像個控件，並公布出獲取表達式字符串的方法。

代碼片段：

public class UnboundExpressionPanel : PanelControl {
      public UnboundExpressionPanel() : base() {
          BorderStyle = DevExpress.XtraEditors.Controls.BorderStyles.NoBorder;
          StartEdit(new GridColumn());
      }

      object[] arguments;
      protected object[] Arguments { get { return arguments; } }

      MyUnboundColumnExpressionEditorForm form = null;
      protected MyUnboundColumnExpressionEditorForm Form { get { return form; } }

      private GridColumn fUnboundColumn;
      public GridColumn UnboundColumn {
          get { return fUnboundColumn; }
          set {
              if (fUnboundColumn == value) return;
              StartEdit(value);
          }
      }

      protected MyUnboundColumnExpressionEditorForm CreateForm(params object[] arguments)
      {
          return new MyUnboundColumnExpressionEditorForm(arguments[0], null);
      }

      protected void ApplyExpression(string expression) {
          if (Arguments == null) return;
          ((GridColumn)Arguments[0]).UnboundExpression = expression;
      }

      public void StartEdit(params object[] arguments) {
          if (arguments.Length < 1) return;
          GridColumn unboundColumn = arguments[0] as GridColumn;
          if (unboundColumn == null) return;
          fUnboundColumn = unboundColumn;
          DestroyForm();
          this.arguments = arguments;
          this.form = CreateForm(arguments);
          if (form == null) return;
          form.Dock = DockStyle.Fill;
          form.TopLevel = false;
          form.FormBorderStyle = FormBorderStyle.None;
          form.Closing += new CancelEventHandler(form_Closing);
          form.buttonCancel.Click += new EventHandler(buttonCancel_Click);
          form.buttonOK.Text = "Apply";
          Controls.Add(form);
          form.Visible = true;
      }

      void buttonCancel_Click(object sender, EventArgs e)
      {
          if (form != null) form.Close();
      }

      void form_Closing(object sender, CancelEventArgs e)
      {
          e.Cancel = true;
          if (this.arguments == null || this.form == null) return;
          if (form.DialogResult == DialogResult.OK)
          {
              ApplyExpression(form.Expression);
          }
          else
          {
              form.ResetMemoText();
          }
      }

      public void DestroyForm()
      {
          if (form != null) form.Dispose();
          form = null;
      }
  }

  public class MyUnboundColumnExpressionEditorForm : UnboundColumnExpressionEditorForm
  {
      public MyUnboundColumnExpressionEditorForm(object contextInstance,
          IDesignerHost designerHost)
          : base(contextInstance, designerHost) { }

      private string GetExpressionMemoEditText()
      {
          GridColumn column = ContextInstance as GridColumn;
          return null == column ? string.Empty : column.UnboundExpression;
      }

      public void ResetMemoText()
      {
          ExpressionMemoEdit.Text = GetExpressionMemoEditText();
      }
  }

下載地址：

http://pan.baidu.com/s/1sjn24cH