I have just been notified my Cinch MVVM article won the best overall article of the month for July 2009 over at www.codeproject.com which is obviously very nice.
The article is question can be located right here, if you fancy a gander
Month: August 2009
A Look At Tasks In The System.Threading.Tasks VS2010 Namespace
I had a bit of time today to look at the System.Threading.Tasks VS2010 Namespace, and I started throwing a bit of code together and wrote an article about which you can read over at
http://www.codeproject.com/KB/threads/TPLTasks.aspx
But if you just want a quick overview, what the Tasks in the System.Threading.Tasks VS2010 Namespace are all about (from what I read anyhow), is a replacement for queuing work items up using the currently available ThreadPool. The issue with the current ThreadPool is that
- Work items can’t return a value
- Can not cancel tasks
- No waiting on work items
- Composing a group of items in a structured way
- Handling exceptions thrown concurrently or any other richer construct built on top of it
So Tasks are there to help out in this area. Let’s have a quick look at how to do some common things such as
Run A Task That Returns A Value
1: /// <summary>
2: /// This handler shows you to use a Task that
3: /// doesn't use any state inside the Task
4: ///
5: /// This Task blocks the calling thread until the
6: /// Task completes
7: /// </summary>
8: private void TaskFactWithReturnValue_Click(object sender,
9: RoutedEventArgs e)
10: {
11: Func<ObservableCollection<String>> obtainTaskResults
12: = TaskWithResults;
13: Task<ObservableCollection<String>> task =
14: Task.Factory.StartNew<ObservableCollection<String>>
15: (obtainTaskResults,
16: TaskCreationOptions.DetachedFromParent);
17: items.Clear();
18: task.Wait(); //Blocks while waiting for Task to complete
19: items = task.Result;
20: lstItems.ItemsSource = items;
21: MessageBox.Show("TaskFactWithReturnValue DONE");
22: }
23:
24: /// <summary>
25: /// Runs the Tasks Func delegate, which returns
26: /// a list of ObservableCollection String
27: /// </summary>
28: private ObservableCollection<String> TaskWithResults()
29: {
30: ObservableCollection<String> results =
31: new ObservableCollection<string>();
32: for (int i = 0; i < 10; i++)
33: {
34: results.Add(String.Format(
35: "TaskFactWithReturnValue Item {0}", i));
36: }
37: return results;
38:
39: }
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And we can even chain tasks together using a technique called Continuations, here is an example of that:
1: /// <summary>
2: /// This handler shows you to use a Task that will
3: /// use 2 chained Tasks the first Task accepts some
4: /// State, and the 2nd Task in the chain doesn't
5: /// ONLY when both Tasks have completed is the work
6: /// considered done
7: ///
8: /// This Task blocks the calling thread until the
9: /// 2 chained Task complete
10: /// </summary>
11: private void TaskContinue_Click(object sender,
12: RoutedEventArgs e)
13: {
14: //SYNTAX EXAMPLE 1
15: #region SYNTAX EXAMPLE 1
16: Func<Object, ObservableCollection<String>>
17: obtainTaskResultsFunc =
18: TaskWithResultsWithState;
19: Task<ObservableCollection<String>> task =
20: Task.Factory.StartNew(obtainTaskResultsFunc,
21: new ObjectState<Int32>
22: {
23: CurrentTask = "TaskState",
24: Value = 2
25: });
26:
27: Func<Task, ObservableCollection<String>>
28: contineResultsFunc = ContinueResults;
29: Task<ObservableCollection<String>>
30: continuationTask =
31: task.ContinueWith<ObservableCollection<String>>
32: (contineResultsFunc,
33: TaskContinuationOptions.OnlyOnRanToCompletion);
34:
35: continuationTask.Wait();
36: items.Clear();
37: items = continuationTask.Result;
38: #endregion
39:
40: //SYNTAX EXAMPLE 2
41: #region SYNTAX EXAMPLE 2
42: //Task<ObservableCollection<String>> taskAll =
43: // Task.Factory.StartNew((o) =>
44: // {
45: // return TaskWithResultsWithState(o);
46: // }, new ObjectState<Int32>
47: // {
48: // CurrentTask = "TaskState",
49: // Value = 2
50: // }).ContinueWith<ObservableCollection
51: // <String>>((previousTask) =>
52: // {
53: // return ContinueResults(
54: // previousTask);
55: // },TaskContinuationOptions.
56: // OnlyOnRanToCompletion);
57:
58:
59: //taskAll.Wait();
60: //items.Clear();
61: //items = taskAll.Result;
62: #endregion
63:
64:
65: lstItems.ItemsSource = items;
66: MessageBox.Show("TaskContinue DONE");
67: }
68:
69:
70:
71: /// <summary>
72: /// Runs the Tasks Func delegate, which returns a list
73: /// of ObservableCollection String
74: /// </summary>
75: private ObservableCollection<String>
76: TaskWithResultsWithState(Object o)
77: {
78: var state = o as ObjectState<Int32>;
79: ObservableCollection<String> results =
80: new ObservableCollection<string>();
81: for (int i = 0; i < state.Value; i++)
82: {
83: results.Add(String.Format("{0} Item {1}",
84: state.CurrentTask, i));
85: }
86: return results;
87:
88: }
89:
90: /// <summary>
91: /// Runs the Contination Tasks Func delegate,
92: /// which returns a list
93: /// of ObservableCollection String
94: /// </summary>
95: private ObservableCollection<String>
96: ContinueResults(Task originalTask)
97: {
98:
99: Task<ObservableCollection<String>> taskOriginal
100: = originalTask as Task<ObservableCollection<String>>;
101:
102: ObservableCollection<String> results =
103: new ObservableCollection<string>();
104:
105: ObservableCollection<String> orginalResults =
106: taskOriginal.Result as
107: ObservableCollection<String>;
108:
109: foreach (var item in orginalResults)
110: results.Add(item);
111:
112: for (int i = 0; i < 10; i++)
113: results.Add(
114: String.Format(
115: "ContinueResults Item {0}", i));
116:
117: return results;
118: }
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As I say I go through all this a lot more in my article, which is available at the following Url should you want to know more:
Cinch (My MVVM framework) Part 6 is out
I just published part VI of my MVVM framework series over at http://www.codeproject.com .
Here is the link
http://www.codeproject.com/KB/WPF/CinchVI.aspx
This time I talk about
What the demo app looks like, and pointing you at all the relevant parts that cover the demo app, as discussed in all the previous Cinch articles.
Enjoy
Cinch (My MVVM framework) Part 5 is out
I just published part III of my MVVM framework series over at http://www.codeproject.com .
Here is the link
http://www.codeproject.com/KB/WPF/CinchV.aspx
This time I talk about
Unit testing using the Cinch framework
Enjoy
Cinch (My MVVM framework) Part 4 is out
I just published part III of my MVVM framework series over at http://www.codeproject.com .
Here is the link
http://www.codeproject.com/KB/WPF/CinchIV.aspx
This time I talk about
Developing Models Using Cinch
Developing ViewModels Using Cinch
* Choosing a ViewModel Base Class
* ViewModelBase Class
* How To Use The Exposed Services
o EventLogger service
o MessageBox service
o Open File service
o Save File service
o Popup window service
* Background Tasks
* Mode Support
Enjoy
