HttpWebRequest load image from rss with UI freezing (windows phone) - C# Discussion Boards

30-Mar-11 2:30

There are a few things here. First of all, the return type from number would be int[] not int - the two are not comparable. Secondly, you don't return _number[], you return _number. Finally, why use an array at all? Arrays have the nasty habit of becoming complicated to manage - why not look into a generic List? So this becomes:

class TestClass
{
  public TestClass()
  {
    Number = new List<int>();
  }
  public List<int> Number { get; set; }
}

I'm not a stalker, I just know things. Oh by the way, you're out of milk.

Forgive your enemies - it messes with their heads

Re: How to write a class, where one of its attributes is an Array?

nstk3-Apr-11 23:02

nstk

3-Apr-11 23:02

Is this a different list than an ArrayList?

http://msdn.microsoft.com/en-us/library/system.collections.arraylist%28v=VS.100%29.aspx

Re: How to write a class, where one of its attributes is an Array?

David198730-Mar-11 2:46

David1987

30-Mar-11 2:46

class Testclass
{
    private int[] _number;
    public int[] number
    {
        get { return _number; }
        set { _number = value; }
    }
}

number will be null unless you initialize it somehow.

Re: How to write a class, where one of its attributes is an Array?

#realJSOP30-Mar-11 7:16

#realJSOP

30-Mar-11 7:16

This is all you need:

public class TestClass
{
    public int[] Numbers { get; set; }
}

However, I would probably use a List<int> in the following form:

public class NumbersList : List<int>
{
    // You don't have to put anything in the class if you don't want/need 
    // to. It's just to clean up the allocation and type references because 
    // typing "private NumbersList numbers; is cleaner than typing 
    // "private List<int> numbers;" (at least, that's the way I see it).
}

...which would allow you then to do this:

public class TestClass
{
    public NumbersList Numbers { get; set; }
}

...as well as being much more flexible than a mere array.

".45 ACP - because shooting twice is just silly" - JSOP, 2010
-----
You can never have too much ammo - unless you're swimming, or on fire. - JSOP, 2010
-----
"Why don't you tie a kerosene-soaked rag around your ankles so the ants won't climb up and eat your candy ass." - Dale Earnhardt, 1997

Re: How to write a class, where one of its attributes is an Array?

davidnz30-Mar-11 10:21

davidnz

30-Mar-11 10:21

Ditto what others have said regarding arrays.

Personally I'd only use an int[] if it is being initialised once, and then will not have elements added or removed. That could be useful for certain specific applications.

For example...

public class Simple
{
    private int[] _int = { 1, 2, 3, 4, 5 };
    public int[] MyInt { get { return _int; } }
}



    private static void TestSimple()
    {
        Simple s = new Simple();
        s.MyInt[0] += 1;
    }

...is fine. But as others have said if the size of the array is to be dynamic (items being added) I'd use say a List<int> probably.

Re: How to write a class, where one of its attributes is an Array?

nstk2-Apr-11 4:40

nstk

2-Apr-11 4:40

Thank you all for your help. This is a great forum indeed!

I will definately use a List, as there will be numbers of unknown quantity and value in the beginning of the programme.

HttpWebRequest load image from rss with UI freezing (windows phone)

peter_piper30-Mar-11 2:09

Re: HttpWebRequest load image from rss with UI freezing (windows phone)

30-Mar-11 2:09

Hello
I'm some kind of new to c# and tried out a tutorial to download some comic images from an rss feed.
Now I want to optimize the program, so that the UI-Thread isn't blocked anymore. I've read that I should use Backgroundworker und HttpWebRequest instead of WebClient.

Problem: I tried out backgroundworker and httpwebrequest instead of webclient, but the UI is still freezing and I don't really understand why.

Hope somebody can explain me, what I'm doing wrong.

public class FailsViewModel :INotifyPropertyChanged
    {

        static int i = 0;
        public FailsViewModel()
        {
            
            this.Fails = new ObservableCollection<FailViewModel>();

            InitializeBackgoundWorker();
            LoadFailsAsync();
            //_bw.RunWorkerAsync(); // ->bw_DoWork*/
        }

        private void InitializeBackgoundWorker() 
        {
            _bw = new BackgroundWorker();
            _bw.WorkerReportsProgress = true;
            _bw.WorkerSupportsCancellation = true;
            _bw.DoWork += new DoWorkEventHandler(bw_DoWork);
            _bw.ProgressChanged += new ProgressChangedEventHandler(bw_ProgressChanged);
            _bw.RunWorkerCompleted += new RunWorkerCompletedEventHandler(bw_RunWorkerCompleted);
        }

        public void LoadFailsAsync()
        {
                    
                    var request = (HttpWebRequest)WebRequest.Create(new Uri("http://schabus.knor.net/rss"));
            
                    request.BeginGetResponse(r =>
                    {
                        var httpRequest = (HttpWebRequest)r.AsyncState;
                        var httpResponse = (HttpWebResponse)httpRequest.EndGetResponse(r);
                        
                        using (var reader = new StreamReader(httpResponse.GetResponseStream()))
                        {
                            var response = reader.ReadToEnd();

                            //With backgroundworker
                            _bw.RunWorkerAsync(response); //-->doWork 

                            //Without backgroundworker (Load items async then let then let the UI Show the Images)
                            /*Collection<FailViewModel> c = LoadItems(response);

                            Deployment.Current.Dispatcher.BeginInvoke(() =>
                                {
                                    for (int i = 0; i < c.Count; i++)
                                    {
                                        this.Fails.Add(c.ElementAt(i));
                                        //MessageBox.Show("\nTitle: " + Fails.ElementAt(i).Title);
                                        Thread.Sleep(1);
                                    }
                                    MessageBox.Show("fertig - bw_RunWorkerCompleted");
                                });
                             */
                        }
                    }, request);

                    /*
                    WebClient client = new WebClient();
                    client.DownloadStringCompleted += new DownloadStringCompletedEventHandler(client_DownloadStringCompleted);
                    client.DownloadStringAsync(new Uri ("http://schabus.knor.net/rss", UriKind.Absolute));
                    */
        }


        private Collection<FailViewModel> LoadItems(string e)
        {
            Collection<FailViewModel> fvmc = new Collection<FailViewModel>();

            XElement xel = XElement.Parse(e);

            Collection<FailViewModel> fails = new Collection<FailViewModel>();

            var items = xel.Descendants(XName.Get("item"));

            foreach (var item in items)
            {
                var desc = item.Descendants(XName.Get("encoded", "http://purl.org/rss/1.0/modules/content/")).SingleOrDefault();
                var title = item.Descendants(XName.Get("title")).SingleOrDefault();

                if (desc != null && title != null)
                {
                    string url = desc.Value.Substring(desc.Value.IndexOf("src=\"") + 5);
                    string localUrl = url.Substring(0, url.IndexOf("\""));
                    string absoluteUrl = "http://schabus.knor.net" + localUrl;

                    //add item
                    FailViewModel fvm = new FailViewModel();
                    fvm.Title = title.Value;
                    fvm.Uri = new Uri(absoluteUrl, UriKind.Absolute);
                    fvmc.Add(fvm);
                }
            }
            return fvmc;
        }

        private Collection<FailViewModel> LoadItems_WebRequest(DownloadStringCompletedEventArgs e)
        {
            Collection<FailViewModel> fvmc = new Collection<FailViewModel>();

            XElement xel = XElement.Parse(e.Result);

            Collection<FailViewModel> fails = new Collection<FailViewModel>();
 
            var items = xel.Descendants(XName.Get("item"));

            foreach (var item in items)
            {
                var desc = item.Descendants(XName.Get("encoded", "http://purl.org/rss/1.0/modules/content/")).SingleOrDefault();
                var title = item.Descendants(XName.Get("title")).SingleOrDefault();

                if (desc != null && title != null)
                {
                    string url = desc.Value.Substring(desc.Value.IndexOf("src=\"") + 5);
                    string localUrl = url.Substring(0, url.IndexOf("\""));
                    string absoluteUrl = "http://schabus.knor.net" + localUrl;

                    //add item
                    FailViewModel fvm = new FailViewModel();
                    fvm.Title = title.Value;
                    fvm.Uri = new Uri(absoluteUrl, UriKind.Absolute);
                    fvmc.Add(fvm);
                }
            }
            return fvmc;
        }
        
        #region Properties
        
        private BackgroundWorker _bw = null;

        public volatile bool isComplete = false;
        private ObservableCollection<FailViewModel> _Fails = default(ObservableCollection<FailViewModel>);
        public ObservableCollection<FailViewModel> Fails
        {
            get
            {
                return _Fails;
            }
            set
            {
                _Fails = value;
                OnPropertyChanged("Fails");
            }
        }

        private FailViewModel _SelectedFail = default(FailViewModel);
        public FailViewModel SelectedFail
        {
            get
            {
                return _SelectedFail;
            }
            set
            {
                _SelectedFail = value;
                OnPropertyChanged("SelectedFail");
            }
        }
    #endregion

        protected virtual void OnPropertyChanged(string propertyName)
        { 
            if(this.PropertyChanged != null)
                this.PropertyChanged(this, new PropertyChangedEventArgs(propertyName));
        }

        public event PropertyChangedEventHandler PropertyChanged;

        #region BackgroundWorker
        private void bw_DoWork(object sender, DoWorkEventArgs e)
        {
            BackgroundWorker worker = sender as BackgroundWorker;
            //ohne bgw 
            e.Result = LoadItems((string)e.Argument);//LoadItems((string)e.Result);
            
            //LoadItems((DownloadStringCompletedEventArgs)e.Argument);
        }

        void client_DownloadStringCompleted(object sender, DownloadStringCompletedEventArgs e)
        {
                    //back to ui thread
                    ((WebClient)sender).DownloadStringCompleted -= client_DownloadStringCompleted;

                    if (e.Error == null && e.Cancelled == false)
                    {           
                        MessageBox.Show("DSC-" + (i++) +"\n"+e.Result  );
                        //param e : String in xml
                        _bw.RunWorkerAsync(e); // ->bw_DoWork
                    }
            
        }
        //läuft wieder im UI thread ab!
        private void bw_RunWorkerCompleted(object sender, RunWorkerCompletedEventArgs e)
        {
            //add
            Collection<FailViewModel> c = e.Result as Collection<FailViewModel>;

            for(int i=0; i<c.Count;i++)
            {
                this.Fails.Add(c.ElementAt(i));
                //MessageBox.Show("\nTitle: " + Fails.ElementAt(i).Title);
                Thread.Sleep(1);
            }
            
            MessageBox.Show("fertig - bw_RunWorkerCompleted"); //shown *two times* at beginning!!
            //clean
            _bw.DoWork -= bw_DoWork;
            _bw.ProgressChanged -= bw_ProgressChanged;
            _bw.RunWorkerCompleted -= bw_RunWorkerCompleted;
        }

        private void bw_ProgressChanged(object sender, ProgressChangedEventArgs e)
        {
            MessageBox.Show("Progress");
        }
        #endregion

Luc Pattyn30-Mar-11 3:18

Re: HttpWebRequest load image from rss with UI freezing (windows phone)

30-Mar-11 3:18

I didn't study all that in detail, however I noticed you still have a LoadFailsAsync method running on the main thread, so I guess the problem is there. I would perform all web communication in synchronous mode inside the DoWork handler, once you are using an extra thread (or BGW) there no longer is a need to go asynchronously and things should become simpler...

Smile | :)

Luc Pattyn [Forum Guidelines] [My Articles] Nil Volentibus Arduum

Please use <PRE> tags for code snippets, they preserve indentation, improve readability, and make me actually look at the code.

peter_piper30-Mar-11 3:42

Re: HttpWebRequest load image from rss with UI freezing (windows phone)

30-Mar-11 3:42

Got already an implementation like that, where the the LoadFailsAsync- method calls the web communication asynchronously with HttpWebRequest and load the images inside it. (commentented out code in the LoadFailsAsync() above)
But got also the same effect.

public void LoadFailsAsync()
{
            var request = (HttpWebRequest)WebRequest.Create(new Uri("http://schabus.knor.net/rss"));

            request.BeginGetResponse(r =>
            {
                var httpRequest = (HttpWebRequest)r.AsyncState;
                var httpResponse = (HttpWebResponse)httpRequest.EndGetResponse(r);

                using (var reader = new StreamReader(httpResponse.GetResponseStream()))
                {
                    var response = reader.ReadToEnd();

                    //Without backgroundworker (Load items async then let then let the UI Show the Images)
                    Collection<FailViewModel> c = LoadItems(response);

                    Deployment.Current.Dispatcher.BeginInvoke(() =>
                        {
                            for (int i = 0; i < c.Count; i++)
                            {
                                this.Fails.Add(c.ElementAt(i));
                                //MessageBox.Show("\nTitle: " + Fails.ElementAt(i).Title);
                                Thread.Sleep(1);
                            }
                            MessageBox.Show("fertig - bw_RunWorkerCompleted");
                        });
                }
            }, request);
}

Luc Pattyn30-Mar-11 3:54

Re: HttpWebRequest load image from rss with UI freezing (windows phone)

30-Mar-11 3:54

what a mess. That isn't synchronous at all, every Begin, End, Async word points to an asynchronous implementation which is harder to get right and most often meaningless when running on a separate thread or BGW.

Frown | :(

Luc Pattyn [Forum Guidelines] [My Articles] Nil Volentibus Arduum

Please use <PRE> tags for code snippets, they preserve indentation, improve readability, and make me actually look at the code.

peter_piper4-Apr-11 3:03

Re: HttpWebRequest load image from rss with UI freezing (windows phone)

4-Apr-11 3:03

thank you Luc so far, but I think synchronous HttpWebRequest / WebClient methods aren't supportet for WP7. So it was unfortunately impossible for me to use BackGroundWorker with synchronous HttpWebRequest-methods.

So I write it completely new but it's still freezing the UI.
How Luc told me I tried to avoid any use of nested asyn mehtods/threads.

My Idea was to use HttpWebRequest to download it asynyhronous (without other threads... because HttpWebRequest is already asynchronous)

hope the code is better structured then the code above Smile | :)

   public class ComicsViewModel : INotifyPropertyChanged
    {
        public ComicsViewModel()
        {
            if (!DesignerProperties.IsInDesignTool)
            {
                this.ComicList = new ObservableCollection<ComicViewModel>();

                /**** load with WebRequest ***********/
                this.IsReading = true;
                LoadComicsRss2();
                /************************************/
            }
        }

        private void LoadComicsRss2() 
        {
            Uri uri = new Uri("http://schabus.knor.net/rss", UriKind.Absolute);
            HttpWebRequest req = HttpWebRequest.CreateHttp(uri);

            req.BeginGetResponse(HandleGetComicsResponse, req);
        }

        private void HandleGetComicsResponse(IAsyncResult result)
        {
            HttpWebRequest state =  (HttpWebRequest)result.AsyncState;
            using (var response = state.EndGetResponse(result))
            {
                using (var streamReader =  new StreamReader(response.GetResponseStream()))
                {
                    var data = streamReader.ReadToEnd();

                    Deployment.Current.Dispatcher.BeginInvoke(() => { this.ComicList.Clear(); });

                    XElement xel = XElement.Parse(data);

                    var items = xel.Descendants(XName.Get("item"));

                    foreach (var item in items)
                    {
                        var desc = item.Descendants(XName.Get("encoded",
                            "http://purl.org/rss/1.0/modules/content/")).SingleOrDefault();

                        var title = item.Descendants(XName.Get("title")).SingleOrDefault();

                        if (desc != null && title != null)
                        {
                            string url = desc.Value.Substring(desc.Value.IndexOf("src=\"") + 5);
                            string localUrl = url.Substring(0, url.IndexOf("\""));
                            string absoluteUrl = "http://schabus.knor.net" + localUrl;

                            // Add Comic to list
                            ComicViewModel vm = new ComicViewModel();
                            vm.Title = title.Value;
                            vm.Uri = new Uri(absoluteUrl, UriKind.Absolute);

                            Deployment.Current.Dispatcher.BeginInvoke(() => { this.ComicList.Add(vm);});
                        }
                    }
                }
            }
            Deployment.Current.Dispatcher.BeginInvoke(() => { this.IsReading = false; });
        }

}

    <phone:PhoneApplicationPage.Resources>

        <DataTemplate x:Key="ComicViewModelTemplate">
    		<StackPanel>
    			<TextBlock Text="{Binding Title}" HorizontalAlignment="Center"/>
    			<Image Source="{Binding Uri}"/>
    		</StackPanel>
    	</DataTemplate>
           
    </phone:PhoneApplicationPage.Resources>

<Grid x:Name="LayoutRoot" Background="Transparent" DataContext="{Binding Source={StaticResource ComicsViewModelDataSource}}">
        <Grid.RowDefinitions>
            <RowDefinition Height="Auto"/>
            <RowDefinition Height="*"/>
        </Grid.RowDefinitions>
        <Grid x:Name="ContentPanel" Grid.Row="1" Margin="12,0,12,0">

            <ListBox Margin="10,0" ItemTemplate="{StaticResource ComicViewModelTemplate}" ItemsSource="{Binding ComicList}" SelectedItem="{Binding SelectedComic, Mode=TwoWay}">
            	<Custom:Interaction.Triggers>
            		<Custom:EventTrigger EventName="SelectionChanged">
            			<ic:NavigateToPageAction TargetPage="/ComicPage.xaml"/>
            		</Custom:EventTrigger>
            	</Custom:Interaction.Triggers>
            </ListBox>

        </Grid>

</Grid>

Luc Pattyn4-Apr-11 4:57

Re: HttpWebRequest load image from rss with UI freezing (windows phone)

4-Apr-11 4:57

Hi Peter,

1.
I'm not familiar with WP7, and am unaware of what .NET parts are missing over there, sorry.

2.
"it's still freezing the UI" isn't informative enough: is it just dead for a while and in the end produces all the output hoped for? does it do anything at all? or is it just dead permanently right from the start?

3.
I still see a foreach loop with a BeginInvoke inside. That could go wrong in at least two ways: either the BeginInvoke for some reason is blocking, turning the whole loop in a long operation, hence freezing the GUI for a long while. Or all those Invokes get queued or even launched somehow, possibly overloading the system.

Suggestions:
- add logging with timestamps, so you KNOW what is happening;
- reduce the loop to just one or two iterations.

In general: when in trouble, simplify, improve observability, get the facts.

Smile | :)

Luc Pattyn [Forum Guidelines] [My Articles] Nil Volentibus Arduum

Please use <PRE> tags for code snippets, they preserve indentation, improve readability, and make me actually look at the code.

peter_piper12-Apr-11 4:12

sort generic list collection

12-Apr-11 4:12

2. I meant the UI wasn't responsive for some time minute

luckily I found my answer in those two Links here:

http://tinyurl.com/28zb9x3
http://tinyurl.com/636qz5z

anyways thank you Luc!

arkiboys29-Mar-11 23:41

29-Mar-11 23:41

A generic list i.e. mResults has several fields and records...
Fields are such as field1, field2, field3, etc...

How can I sort this list by Field2? Is it easier with LINQ?
Thanks

Pete O'Hanlon29-Mar-11 23:56

29-Mar-11 23:56

Well, the LINQ approach is fairly easy:

var sortedList = from res in mResults
  order by res.Field2
  select res;

I'm not a stalker, I just know things. Oh by the way, you're out of milk.

Forgive your enemies - it messes with their heads

arkiboys30-Mar-11 0:18

30-Mar-11 0:18

This is what I am using but there is an error:

var sortedList = from res in mResults  
     order by res.Field2  
     select res;

return (List<ClassName>)sortedList

Error is:
Unable to cast object of type 'System.Linq.OrderedEnumerable`2[ProjectName.ClassName,System.String]' to type 'System.Collections.Generic.List`1[ProjectName.ClassName]'.

Shameel30-Mar-11 0:28

Shameel

30-Mar-11 0:28

Try this code, I didn't test it though

return sortedList.ToList<ClassName>();

arkiboys30-Mar-11 0:39

30-Mar-11 0:39

The error has gone but:
at present I have the mResult being returned in a method.
i.e. return mResult;

Now I am using the linq code you sent i.e.

internal static List<Classname> mResult

private void MethodName()
{
...
...
//return mResult;

            //sort the list by field2 is ascending order...
            var sortedList = from res in mResult
                             orderby res.field2
                             select res;
            return sortedList.ToList<ClassName>();
}

Questioin:
How can I declare the var sortedList to be something like:
internal static var sortedList
and then in the LINQ code I do not use the var to declare?
Thanks

Pete O'Hanlon30-Mar-11 1:01

30-Mar-11 1:01

You don't use the implicit var. You declare the sortedList as a List<ClassName> and then your query becomes:

sortedList = (from res in mResult
  orderby res.field2
  select res).ToList();

I'm not a stalker, I just know things. Oh by the way, you're out of milk.

Forgive your enemies - it messes with their heads

arkiboys30-Mar-11 1:04

30-Mar-11 1:04

I see.
Thank you all.

davidnz30-Mar-11 0:48

davidnz

30-Mar-11 0:48

If you mean you already have an instance of List<mResults>, assigned to a variable say list...

list.Sort((i, j) => { return i.Field2.CompareTo(j.Field2); });

should work.

davidnz30-Mar-11 1:02

davidnz

30-Mar-11 1:02

Actually, I think you mean your list is called mResults, so in that case I would do...

mResults.Sort((i, j) => { return i.Field2.CompareTo(j.Field2); });

Luc Pattyn30-Mar-11 1:19

30-Mar-11 1:19

This article[^] tells you how to do it without LINQ.

Smile | :)

Luc Pattyn [Forum Guidelines] [My Articles] Nil Volentibus Arduum

Please use <PRE> tags for code snippets, they preserve indentation, improve readability, and make me actually look at the code.

Pete O'Hanlon30-Mar-11 1:55

30-Mar-11 1:55

Nah. It's crap. Poke tongue | ;-P

Only kidding - it's a good article.

A small critique - the plural of criterion is criteria, so you have s singular of "the criterion is...", where the plural would be "Multiple sort criteria are easy to implement". A criterium is actually a bike race.

I'm not a stalker, I just know things. Oh by the way, you're out of milk.

Forgive your enemies - it messes with their heads