DevExpress控件扩展之表达式编辑器

业务需求：

业务工作中经常需要对表格中的数据进行处理，包括过滤、复合计算等。过滤需要有过滤条件，复合计算需要计算公式。这两种场景都需要一个表达式编辑器。GridControl自带过滤条件的表达式编辑器，我们要做的就是把这个编辑器拿出来，独立于GridControl，进而可以绑定到其它控件上。

实现原理：

找到表达式编辑器内部类UnboundColumnExpressionEditorForm，这是一个窗口类。我们将其边框设置为None，Dock属性设置为Fill，拖放到控件上，使其看上去像个控件，并公布出获取表达式字符串的方法。

代码片段：

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();

      }

  }

下载地址：

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