What is wrong with using the Usage block in Webcontrols?

Question

I have the following code that uses a block using on TableHeaderCell , LiteralControl , HyperLink and GridViewRow ( try..finally ). The code works like indentation. Is there a problem / trap in disposing of controls with the using block as shown below? If so, can you provide any msdn link where the trap data will be listed?

  protected void grdTransactions_RowCreated(object sender, GridViewRowEventArgs e) { if (e != null) { if (e.Row.RowType == DataControlRowType.Header) { GridViewRow newHeaderRow = null; try { newHeaderRow = new GridViewRow(-1, -1, DataControlRowType.Header, DataControlRowState.Normal); using (TableHeaderCell cellFirst = new TableHeaderCell()) { cellFirst.ColumnSpan = 1; cellFirst.Text = "FIRST"; newHeaderRow.Cells.Add(cellFirst); } using (TableHeaderCell cellAssociate = new TableHeaderCell()) { GetTableCell(cellAssociate,"tableColGroupAssociate", 4, "associateHide", "Associate Transaction Info"); newHeaderRow.Cells.Add(cellAssociate); } newHeaderRow.Cells.Add(cellAssociate); ((GridView)sender).Controls[0].Controls.AddAt(0, newHeaderRow); } finally { if (newHeaderRow != null) { newHeaderRow.Dispose(); newHeaderRow = null; } } } } } 

Helper Method

  private static void GetTableCell(TableHeaderCell cellAssociate, string cssClassName, int colSpan, string hideClassName, string displayName) { cellAssociate.ColumnSpan = colSpan; cellAssociate.CssClass = cssClassName; using (LiteralControl ltlText = new LiteralControl()) { ltlText.Text = displayName; cellAssociate.Controls.Add(ltlText); } using (HyperLink lnkHide = new HyperLink()) { lnkHide.Text = SupportToolUIResource.HideLinkText; lnkHide.CssClass = hideClassName; lnkHide.Target = SupportToolUIResource.HideLinkTarget; cellAssociate.Controls.Add(lnkHide); } } 

Link

• Why do I need to call dispose on ASP.NET controls?

Answer 1

Thanks to @Tim Medora for the explanation and link. Why do I need to call dispose on ASP.NET controls? .

Some interesting points:

• What we need to do is make sure that new controls are added to the Controls' collection so that it is deleted when the page is placed.
• Management objects implement the IDisposable interface. Each parent control can call Dispose on all of its children.
• Any correctly written object that implements IDisposable and has state data that is actually cleared during the dispose process should raise an ObjectDisposedException if any of its public / protected / internal properties or methods are available after they have been deleted. (Assume an invalid state after a call to Dispose.) Some types will ignore this rule if they really have nothing to clean up and don't have to worry about an invalid state.

Conclusion

No need to use the "using" block for webcontrols. In addition, this can cause problems if the using block is used in webcontrols.

Answer 2

Even if you are "done" with the control, the page will gain access to the control when it displays, so getting rid of them during construction does not make much sense. In one of your examples, you use one of the controls you control, which also makes no sense.

Call Dispose when you are done using the control. Dispose of the method leaves the control in an unusable state. After this method, you must free all references to the control so that the memory of this activity can be disposed of by garbage collection.

The description of the Disposed event raised by the control also indicates the intended use:

Occurs when the server control is freed from memory, the last stage of the server control life cycle when the ASP.NET page requested.

Source: http://msdn.microsoft.com/en-us/library/system.web.ui.control.dispose.aspx
Source: http://msdn.microsoft.com/en-us/library/system.web.ui.control.disposed.aspx
See Also: fooobar.com/questions/513998 / ...

So, in theory:

• Build a control tree.
• The page starts rendering.
• The page looks at the controls added to the tree.
• The controls have been deleted.
• Potential problems.

Here is the implementation of IDisposable (from Control ). Notice how this changes the container and event values.

 public virtual void Dispose() { if (this.Site != null) { IContainer container = (IContainer)this.Site.GetService(typeof(IContainer)); if (container != null) { container.Remove(this); EventHandler eventHandler = this.Events[Control.EventDisposed] as EventHandler; if (eventHandler != null) { eventHandler(this, EventArgs.Empty); } } } if (this._occasionalFields != null) { this._occasionalFields.Dispose(); } if (this._events != null) { this._events.Dispose(); this._events = null; } } 

When to remove

This does not mean that you should not dispose of your resources; if control must manage resources, it is certainly free. The control may be accessing the database; I would wrap the database code inside the using block inside the control.

In practicality, this style creates a large block of code for something that can be expressed more simply.

 using (LiteralControl ltlText = new LiteralControl()) { ltlText.Text = displayName; cellAssociate.Controls.Add(ltlText); } // could become cellAssociate.Controls.Add( new LiteralControl { Text = displayName } );