Simple .NET/ASP.NET PDF document editor web control SDK

// Raise the event when the worker starts. This is done by posting a message // to the captured synchronization context. do worker.DoWork.Add(fun args -> syncContext.Post(SendOrPostCallback(fun _ -> triggerStarted(DateTime.Now)), state=null) ... /// The Started event gets raised when the worker starts. It is /// raised on the GUI thread (i.e. in the synchronization context of /// the thread where the worker object was created). // It has type IEvent<DateTime> member x.Started = started The simple way to raise additional events is often wrong. For example, it is tempting to simply create an event, arrange for it to be triggered, and publish it, as you would do for a GUI control. However, if you do that, you will end up triggering the event on the background worker thread, and its event handlers will run on that thread. This is dangerous, because most GUI objects (and many other objects) can be accessed only from the thread they were created on; this is a restriction enforced by most GUI systems. One of the nice features of the BackgroundWorker class is that it automatically arranges to raise the RunWorkerCompleted and ProgressChanged events on the GUI thread. We have shown how to achieve this in Listing 13-3. Technically speaking, the extended IterativeBackgroundWorker object has captured the synchronization context of the thread where it was created and posts an operation back to that synchronization context. A synchronization context is just an object that lets you post operations back to another thread. For threads such as a GUI thread, this means posting an operation will post a message through the GUI event loop.

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The procedure do_rel_update updates one column of all rows in the table components_rel: 126 127 128 129 130 131 procedure do_rel_update as begin update components_rel set component_name = component_name || ' or update'; end do_rel_update;

To round off this section on the BackgroundWorker design pattern, we show the full code required to build a small application with a background worker task that supports cancellation and reports progress. Listing 13-4 shows the full code. Listing 13-4. Connecting an IterativeBackgroundWorker to a GUI open System.Drawing open System.Windows.Forms let form = new Form(Visible=true,TopMost=true) let panel = new FlowLayoutPanel(Visible=true, Height = 20, Dock=DockStyle.Bottom, BorderStyle=BorderStyle.FixedSingle) let progress = new ProgressBar(Visible=false, Anchor=(AnchorStyles.Bottom ||| AnchorStyles.Top), Value=0)

So we ll take a look at the data access controls in the first part of this chapter, drilling specifically into the SqlDataSource and ObjectDataSource controls (see Table 11-1) They may not represent the end of writing code to get to data sources, but in many cases they are a great.

The procedure do_rel_child_update updates one column of all rows in the child table parts_rel: 133 134 135 136 137 138 139 140 141 142 procedure do_rel_child_update as begin for i in 1..g_num_of_child_updates loop update parts_rel set part_desc = part_desc || ' updated' where part_id = i; end loop; end do_rel_child_update; The procedure do_nt_update updates one column of all rows in the table components_nt: 144 145 146 147 148 149 procedure do_nt_update as begin update components_nt set component_name = component_name || ' or update'; end do_nt_update;

let text = new Label(Text="Paused", Anchor=AnchorStyles.Left, Height=20, TextAlign= ContentAlignment.MiddleLeft) panel.Controls.Add(progress) panel.Controls.Add(text) form.Controls.Add(panel) let fibOneStep (fibPrevPrev:bigint,fibPrev) = (fibPrev, fibPrevPrev+fibPrev) // Run the iterative algorithm 500 times before reporting intermediate results // Burn some additional cycles to make sure it runs slowly enough let rec RepeatN n f s = if n <= 0 then s else RepeatN (n-1) f (f s) let rec BurnN n f s = if n <= 0 then f s else ignore (f s); BurnN (n-1) f s let step = (RepeatN 500 (BurnN 1000 fibOneStep)) // Create the iterative worker. let worker = new IterativeBackgroundWorker<_>(step,(1I,1I),100) worker.ProgressChanged.Add(fun (progressPercentage,state)-> progress.Value <- progressPercentage) worker.WorkerCompleted.Add(fun (_,result) -> progress.Visible <- false; text.Text <- "Paused"; MessageBox.Show(sprintf "Result = %A" result) |> ignore) worker.WorkerCancelled.Add(fun () -> progress.Visible <- false; text.Text <- "Paused"; MessageBox.Show(sprintf "Cancelled OK!") |> ignore) worker.WorkerError.Add(fun exn -> text.Text <- "Paused"; MessageBox.Show(sprintf "Error: %A" exn) |> ignore) form.Menu <- new MainMenu() let workerMenu = form.Menu.MenuItems.Add("&Worker") workerMenu.MenuItems.Add(new MenuItem("Run",onClick=(fun _ args -> text.Text <- "Running"; progress.Visible <- true; worker.RunWorkerAsync())))

The procedure do_nt_child_update updates one column of all rows in the child table parts_nt (the hidden table containing the nested table data). Note that owing to a bug in Oracle 10g Release 1 and Oracle9i Release 2, because of which the nested_table_get_refs hint does not work in static SQL, the update fails unless you use dynamic SQL, as follows: 151 152 153 154 155 156 157 158 159 160 161 procedure do_nt_child_update as begin for i in 1..g_num_of_child_updates loop execute immediate 'update /*+ nested_table_get_refs */ parts_nt' || ' set part_desc = part_desc|| :1 ' || ' where part_id = :2 ' using 'updated', i; end loop; end do_nt_child_update; The procedure do_or_delete deletes all rows in components_or_view: 163 164 165 166 167 procedure do_or_delete as begin delete components_or_view; end do_or_delete;

way to dramatically speed a development effort. The ObjectDataSource adheres to a layered architecture better, whereas the SqlDataSource may prove itself suitable only for prototyping and quick fixes. Table 11-1. Data Source Controls in ASP .NET 2.0

workerMenu.MenuItems.Add(new MenuItem("Cancel",onClick=(fun _ args -> text.Text <- "Cancelling"; worker.CancelAsync()))) form.Closed.Add(fun _ -> worker.CancelAsync()) When run in F# Interactive, a window appears as in Figure 13-1.