I am trying to implement the MVVM patter for my WP7 Silverlight app and I am running into a problem with the async JSON Rest call. I moved into my ViewModel class the following two methods that were on my WP7 app Page.
public void FetchGames()
{
ObservableCollection<Game> G = new ObservableCollection<Game>();
//REST call in here
var webClient = new WebClient();
Uri uri = new Uri("http://www.somewebsite.com/get/games/league/" + league);
webClient.OpenReadCompleted += new OpenReadCompletedEventHandler(OpenReadCompletedGames);
webClient.OpenReadAsync(uri);
}
private void OpenReadCompletedGames(object sender, OpenReadCompletedEventArgs e)
{
DataContractJsonSerializer ser = null;
ser = new DataContractJsonSerializer(typeof(ObservableCollection<Game>));
Games = ser.ReadObject(e.Result) as ObservableCollection<Game>;
this.IsDataLoaded = true;
}
Now the problem is that because it is an async call the following code does not work. The following code is on my app Page.
protected override void OnNavigatedTo(System.Windows.Navigation.NavigationEventArgs e)
{
base.OnNavigatedTo(e);
if (NavigationContext.QueryString.TryGetValue("league", out league))
{
try
{
App.gViewModel.league = league;
App.gViewModel.FetchGames();
if(App.gViewModel.IsDataLoaded)
{
lbTeams.ItemsSource = App.gViewModel.Games;
}
}
catch ()
{
//error logging in here
}
}
}
Stepping thru the code shows that FetchGames is called then hits the next line ( if(App.gViewModel.IsDataLoaded)
) before the async call is finished. So IsDataLoaded is always false and I cant bind the listbox on the page.
Doing a lot of googleing I have some possible solutions but I am unable convert them to my particular problem. One is like this and it has to do with continuation passing style'. I couldn't get it to work tho and would greatly appreciate some help.
Thanks!
void DoSomethingAsync( Action<string> callback ) {
HttpWebRequest req; // TODO: build your request
req.BeginGetResponse( result => {
// This anonymous function is a closure and has access
// to the containing (or enclosing) function.
var response = req.EndGetResponse( result );
// Get the result string and call the callback
string resultString = null; // TODO: read from the stream
callback(resultString);
}, null );
}
This can be resolved by moving
lbTeams.ItemsSource = App.gViewModel.Games;
to the end of the OpenReadCompletedGames method. You'll need to use the Dispatcher to update the UI from here.
Dispatcher.BeginInvoke( () => { lbTeams.ItemsSource = App.gViewModel.Games; } );
Related
I am trying to parse some pois from a xml download from a server and I saw that it is done after the program continues in the main thread. I haven't found a way to solve it because I need it.
using System.Threading;
namespace XML_Parser
{
class XMLParserPOI_Wiki
{
private static XMLParserPOI_Wiki objSingle = new XMLParserPOI_Wiki();
public static XMLParserPOI_Wiki ObjSingle
{
get { return objSingle; }
set { objSingle = value; }
}
private List<POI> places;
public List<POI> Places
{
get { return places; }
}
private XMLParserPOI_Wiki()
{
}
public void parseWikitude(string url)
{
places = new List<POI>();
WebClient wc = new WebClient();
wc.DownloadStringCompleted += HttpsCompleted;
wc.DownloadStringAsync(new Uri(url));
}
private void HttpsCompleted(object sender, DownloadStringCompletedEventArgs e)
{
if (e.Error == null)
{
XDocument xdoc = XDocument.Parse(e.Result, LoadOptions.None);
XNamespace ns = "http://www.opengis.net/kml/2.2";
XNamespace ns2 = "http://www.openarml.org/wikitude/1.0";
var placemarkers = xdoc.Root.Descendants(ns + "Placemark");
places =
(from query in xdoc.Root.Descendants(ns + "Placemark")
select new POI
(
...
)).ToList();
System.Diagnostics.Debug.WriteLine("Lista");
System.Diagnostics.Debug.WriteLine(places.Count);
}
}
}
}
In my main class:
XMLParserPOI_Wiki parserXML = XMLParserPOI_Wiki.ObjSingle;
parserXML.parseWikitude("http://myurl.php");
System.Diagnostics.Debug.WriteLine("Lista de pois");
System.Diagnostics.Debug.WriteLine(parserXML.Places.Count);
for (int i = 0; i < parserXML.Places.Count; i++)
{
System.Diagnostics.Debug.WriteLine(parserXML.Places[i].getName());
}
It prints Lista de POis and 0, before Lista and X (number of pois)
I guess I should freeze main thread but I tried a couple of times with some examples and they didn't work.
Can you point me to any tutorial about this? More than get an answer I want to understand how to deal with this kind of operations
First of all, you don't want to block (freeze) the UI thread EVER!
This is called asynchronous programming. There are two things you can do to solve your problem (I recommend option 2!):
Use the classic callback model. You basically call some long operation on a background thread and give a function to it, to execute when the long operation is done. Here's how to do it in your case.
At the end of the HttpsCompleted method, invoke what you need on the UI Thread using:
Deployment.Current.Dispatcher.BeginInvoke(delegate() {
//The code here will be invoked on the UI thread
});
If you want to make the parseWikitude method reusable, you should pass an Action to it. This way you can call it from multiple places and tell it what to do on the UI thread when the parsing is done. Something like this:
public void parseWikitude(string url, Action callback) {
places = new List<POI>();
WebClient wc = new WebClient();
wc.DownloadStringCompleted += HttpsCompleted;
wc.DownloadStringAsync(new Uri(url), callback);
}
private void HttpsCompleted(object sender, DownloadStringCompletedEventArgs e)
{
if (e.Error == null)
{
...
var callback = (Action)e.UserState;
Deployment.Current.Dispatcher.BeginInvoke(callback);
}
}
//And then when you use it, you do it like that
parserXML.parseWikitude("http://myurl.php", delegate() {
//The code here will be executed on the UI thread, after the parsing is done
});
Use the (rather) new asnyc pattern in .NET. You should read about this, as it is one of the best features of .NET if you ask me. :) It basically does the callback thing automatically and makes the code a lot easier to read/maintain/work-with. Once you get used to it, that is.
Here's an example:
public Task<List<POI>> parseWikitude(string url) {
TaskCompletionSource<List<POI>> resultTaskSource = new TaskCompletionSource<List<POI>>();
WebClient wc = new WebClient();
wc.DownloadStringCompleted += HttpsCompleted;
wc.DownloadStringAsync(new Uri(url), resultTaskSource);
return resultTaskSource.Task;
}
private void HttpsCompleted(object sender, DownloadStringCompletedEventArgs e)
{
if (e.Error == null)
{
//If needed, run the code here in a background thread
//...
var resultTaskSource = (TaskCompletionSource<List<POI>>)e.UserState;
resultTaskSource.SetResult(places);
}
}
//And when you need to use it, do it like that (note, this must be invoked in an async method!)
var places = await parser.parseWikitude("http://myurl.php");
//The code here will be executed on the same thread when the parsing is done, but the thread will not be blocked while the download is happening.
So, these are the two ways you can handle it. Option one is old-school, classic and easy. Option two is the new and cool way of doing async stuff. It really is a must-know. Simplifies a lot of things once you get used to it.
P.S. Sorry if I got carried away. :D
I am preparing to using Timeglider to create a timeline. One requirement is the data has to be in JSON format. One requirement for me is it needs to be client side as I do not have access to the servers or central admin.
When I try to do http://webname/_vti_bin/ListData.svc/listname I get an error for access permissions however when I issue it http://webname/subsite/_vti_bin/ListData.svc/listname I have no problem pulling data.
My situation is the list is on the TLD. I tried to follow this post How to retrieve a json object from a sharepoint list but it relates to SP 2007.
To implement pure JSON support in SharePoint 2007, 2010 and so on have a look at this project, http://camelotjson.codeplex.com/. It requires the commercial product Camelot .NET Connector to be installed on the server.
If you don't like to go commercial you can resort to the sp.js library, here is a small example I wrote, enjoy!
// Object to handle some list magic
var ListMagic = function () {
/* Private variables */
var that = this;
var clientContext = SP.ClientContext.get_current();
var web = clientContext.get_web();
var lists = web.get_lists();
/**
* Method to iterate all lists
*/
that.getLists = function () {
clientContext.load(lists);
clientContext.executeQueryAsync(execute, getFailed);
function execute() {
var listEnumerator = lists.getEnumerator();
while (listEnumerator.moveNext()) {
var l = listEnumerator.get_current();
// TODO! Replace console.log with actual routine
console.log(l.get_title());
}
}
function getFailed() {
// TODO! Implement fail management
console.log('Failed.');
}
};
/**
* Method to iterate all fields of a list
*/
that.getFields = function (listName) {
// Load list by listName, if not stated try to load the current list
var loadedList = typeof listName === 'undefined' ? lists.getById(SP.ListOperation.Selection.getSelectedList()) : that.lists.getByTitle(listName);
var fieldCollection = loadedList.get_fields();
clientContext.load(fieldCollection);
clientContext.executeQueryAsync(execute, getFailed);
function execute() {
var fields = fieldCollection.getEnumerator();
while (fields.moveNext()) {
var oField = fields.get_current();
// TODO! Replace console.log with actual routine
var listInfo = 'Field Title: ' + oField.get_title() + ', Field Name: ' + oField.get_internalName();
console.log(listInfo);
}
}
function getFailed() {
// TODO! Implement fail management
console.log('Failed.');
}
};
/**
* Method to get a specific listitem
*/
that.getListItem = function (itemId) {
var loadedList = lists.getById(SP.ListOperation.Selection.getSelectedList());
var spListItem = loadedList.getItemById(itemId);
clientContext.load(spListItem);
clientContext.executeQueryAsync(execute, getFailed);
function execute() {
// TODO! Replace console.log with actual routine
//spListItem.get_fieldValues()
console.log(spListItem.get_fieldValues()["Title"]);
}
function getFailed() {
// TODO! Implement fail management
console.log('Failed.');
}
};
/**
* Method to fake an init (optional)
*/
that.init = function () {
// Run any init functionality here
// I.e
that.getFields("Tasks");
};
return that;
};
// In case of no jquery use window.onload instead
$(document).ready(function () {
ExecuteOrDelayUntilScriptLoaded(function () {
var sp = new ListMagic();
sp.init();
}, 'sp.js');
});
Personally, I make HttpHandlers. I install them in the SharePoint isapi folder and the GAC and I can call them just like you might the owssvr.dll. http://servername/_vti_bin/myhttphandelr.dll
Pass it querystring variables or call it from jquery ajax. You can use the httpcontext and make a spcontext from it and have access to all sorts of information from the current location in SharePoint. Then you can javascriptserialize the objects and pass them as JSON. Looking for some code... Hang on... I can't put all the code but this should get you close. I use this to add a submenu to the context menu to allow a user to delete or rename a file if they uploaded it to a library and it is version 1.0 and to collect a file from a library and create a eml file with the selected file(s) as an attachment(s). We don't give our users delete privileges normally. Point being, you can now create a class with just the information you need from SharePoint and pass it as JSON. The only downfall I have with this, is iisreset is required if you make any changes to the dll.
I task schedule a iisreset every night at midnight anyway to keep it fresh and free from memory bloat. I come in the next day and my changes are there. The cool thing is, the spcontext has information about the current location in SharePoint from where it is called. So, http://servername/_vti_bin/myhttphandelr.dll vs http://servername/subsite/library/_vti_bin/myhttphandelr.dll
I might add. Don't try to serialize SharePoint objects. One they are huge, complex objects. Two, I don't think they are marked serializable. Just make you own class and populate it with the values you need from the SharePoint objects.
using System;
using System.Collections.Generic;
using System.Runtime.InteropServices.ComTypes;
using System.Web;
using System.Web.Script.Serialization;
using ADODB;
using interop.cdosys;
using Microsoft.SharePoint;
namespace owssvr2
{
public class OWSsvr2 : IHttpHandler, System.Web.SessionState.IRequiresSessionState
{
private string cmd;
ctx ctx = new ctx();
private string currentuser;
private SPContext SPcontext;
private HttpContext cntx;
public bool IsReusable
{
get { return false; }
}
public void ProcessRequest(HttpContext context)
{
SPcontext = SPContext.GetContext(context); <-- Gets spcontext from the httpcontext
cntx = context;
ctx = GetData(context.Request); <-- I parse some information from the request to use in my app
cmd = ctx.Cmd;
ctx.User = context.User.Identity.Name;
currentuser = context.User.Identity.Name;
switch (cmd)
{
case "Delete":
Delete();
context.Response.Redirect(ctx.NextUsing);
break;
case "HasRights":
HasRights();
JavaScriptSerializer javaScriptSerializer = new JavaScriptSerializer();
string serEmployee = javaScriptSerializer.Serialize(ctx);
context.Response.Write(serEmployee);
context.Response.ContentType = "application/json; charset=utf-8";
break;
case "Rename":
Rename(context);
//context.Response.Redirect(context.Request["NextUsing"]);
break;
case "SendSingleFile":
try
{
context.Response.Clear();
context.Response.ClearHeaders();
context.Response.BufferOutput = true;
ADODB.Stream stream = SendSingleFile(context.Request["URL"]);
stream.Type = StreamTypeEnum.adTypeBinary;
stream.Position = 0;
context.Response.ContentType = "application/octet-stream";
context.Response.AddHeader("content-disposition", "attachment;filename=Email.eml");
IStream iStream = (IStream)stream;
byte[] byteArray = new byte[stream.Size];
IntPtr ptrCharsRead = IntPtr.Zero;
iStream.Read(byteArray, stream.Size, ptrCharsRead);
context.Response.BinaryWrite(byteArray);
context.Response.End();
}
catch(Exception ex) {context.Response.Write(ex.Message.ToString()); }
break;
case "SendMultiFile":
try
{
//SendMultiFile(context.Request["IDs"]);
context.Response.Clear();
context.Response.ClearHeaders();
context.Response.BufferOutput = true;
ADODB.Stream stream = SendMultiFile(context.Request["IDs"]);
stream.Type = StreamTypeEnum.adTypeBinary;
stream.Position = 0;
context.Response.ContentType = "application/octet-stream";
context.Response.AddHeader("content-disposition", "attachment;filename=Email.eml");
IStream iStream = (IStream)stream;
byte[] byteArray = new byte[stream.Size];
IntPtr ptrCharsRead = IntPtr.Zero;
iStream.Read(byteArray, stream.Size, ptrCharsRead);
context.Response.BinaryWrite(byteArray);
context.Response.End();
}
catch(Exception ex) {context.Response.Write("There was an error getting the files. </br>" + ex.Message.ToString()); }
break;
case "FileInfo":
JavaScriptSerializer javaScriptSerializer1 = new JavaScriptSerializer();
string serEmployee1 = javaScriptSerializer1.Serialize(FileInfo(context));
context.Response.Write(serEmployee1);
context.Response.ContentType = "application/json; charset=utf-8";
break;
case "UsersInGroups":
UsersInGroups ug = new UsersInGroups(context, context.Request["job"],context.Request["groups"]);
break;
}
}
I just wrote a simple windows 8 form that post to web service api. It works fine. But my challenge is been able to determine when the post operation was a success and a failure. I dont know how to return a value cos aysnc Task is not allowing a return type.
//This class does the post to web service
public class B2cMobileuserService : IB2cMobileuserService
{
private string RegisterUserUrl = RestfulUrl.RegisterMobileUser;
private readonly HttpClient _client = new HttpClient();
public async Task RegisterMobileUser(B2cMobileuserView user)
{
var jsonString = Serialize(user);
var content = new StringContent(jsonString, Encoding.UTF8, "application/json");
var result = await _client.PostAsync(RegisterUserUrl, content);
}
}
//This class calls the one above
public class WebserviceProcessor
{
//declaring all the service objects that would be used
IB2cMobileuserService mobileuserService = null;
public WebserviceProcessor() {
mobileuserService = new B2cMobileuserService();
}
//This method is going to post values to the web serever
public async void RegisterUser(B2cMobileuserView mobileuser) {
mobileuserService.RegisterMobileUser(mobileuser);
}
}
//Then the code below is from my .xaml user interface that calls the class that sends to webservice
private void Button_Click(object sender, RoutedEventArgs e)
{
B2cMobileuserView user = new B2cMobileuserView();
user.Name = name.Text;
user.Email = email.Text;
user.PhoneType = "Windows Mobile";
user.BrowserType = "None";
user.CountryName = "Nigeria";
user.UserPhoneID = phone.Text;
Serviceprocessor.RegisterUser(user);
progressBar.Visibility = Visibility.Visible;
}
Please I dont know how to return a value cos when I try I get the error that says async method must be void.
I need to set a way to know when the post was a success based on the return value from the web service.
To ensure the POST was successful, call HttpResponseMessage.EnsureSuccessStatusCode:
public async Task RegisterMobileUser(B2cMobileuserView user)
{
var jsonString = Serialize(user);
var content = new StringContent(jsonString, Encoding.UTF8, "application/json");
var result = await _client.PostAsync(RegisterUserUrl, content);
result.EnsureSuccessStatusCode();
}
If you want to return a value, use a Task<T> return type instead of Task.
On a side note, avoid async void; use async Task instead of async void unless the compiler forces you to write async void:
//This method is going to post values to the web serever
public Task RegisterUser(B2cMobileuserView mobileuser) {
return mobileuserService.RegisterMobileUser(mobileuser);
}
Also, you should name your asynchronous methods ending in *Async:
//This method is going to post values to the web serever
public Task RegisterUserAsync(B2cMobileuserView mobileuser) {
return mobileuserService.RegisterMobileUserAsync(mobileuser);
}
You may find my async intro and MSDN article on async best practices helpful.
I have a valid URL for a remote JPEG which I'm trying to load in the background. But I find I never get control back after invoking the BitmapImage() constructor. My question is, should this approach work, or should I pitch it all, load up BcpAsync project from NuGet and start working with WebClient asynch methods?
A sample URL for which it fails is
http://image.weather.com/images/maps/current/garden_june_720x486.jpg
It is valid. .UpdateAsync() references it from AppViewModel.Instance, it's not explicitly referenced here.
Here's the background agent:
protected override async void OnInvoke(ScheduledTask task)
{
AppViewModel.LoadData();
await AppViewModel.Instance.RemoteImageProxy.UpdateAsync();
AppViewModel.Instance.ImageUrl = AppViewModel.Instance.RemoteImageProxy.LocalFileUri;
AppViewModel.Instance.UpdateCount++;
PinnedTile.Update();
}
AppViewModel.SaveData();
#if DEBUG
ScheduledActionService.LaunchForTest(task.Name, TimeSpan.FromSeconds(AppViewModel.Instance.BgAgentInterval));
#endif
NotifyComplete();
}
Here's the invoked method:
public Task<double> UpdateAsync() {
LastCheckedTime = DateTime.UtcNow;
CompletionTask = new TaskCompletionSource<double>();
// Not usually called on UI thread, not worth optimizing for that case here.
Deployment.Current.Dispatcher.BeginInvoke(() => { //todo determine whether System.Windows.Deployment.Dispatcher can be called from main app, or just bgAgent.
HelperImageControl = new Image();
HelperImageControl.Loaded += im_Loaded;
HelperImageControl.ImageFailed += im_ImageFailed;
HelperImageControl.ImageOpened += im_ImageOpened;
// breakpoint here
HelperImageControl.Source = new BitmapImage(SourceUri);
// stepping over the function, control does not return here. Nor are any of the above events fired.
});
return CompletionTask.Task; // this will be completed in one of the subsequent control events...
}
You need to call CompletionTask.SetResult(); to return control back to the caller method.
This works (I'm returning 100 in case of successful download because you set the task to return double).
TaskCompletionSource<double> CompletionTask;
public Task<double> UpdateAsync()
{
CompletionTask = new TaskCompletionSource<double>();
Deployment.Current.Dispatcher.BeginInvoke(() =>
{
var HelperImageControl = new Image();
var bmp = new BitmapImage();
bmp.ImageOpened += bmp_ImageOpened;
bmp.ImageFailed += bmp_ImageFailed;
bmp.CreateOptions = BitmapCreateOptions.None;
bmp.UriSource = new Uri("http://image.weather.com/images/maps/current/garden_june_720x486.jpg", UriKind.Absolute);
HelperImageControl.Source = bmp;
});
return CompletionTask.Task;
}
void bmp_ImageFailed(object sender, ExceptionRoutedEventArgs e)
{
CompletionTask.SetException(e.ErrorException);
}
void bmp_ImageOpened(object sender, RoutedEventArgs e)
{
CompletionTask.SetResult(100);
}
I have a list of theaters and I created a secondary tile from my application to navigate directly to specific theater. I pass the id of the theater in query string :
I load the theaters from a WCF service in the file "MainViewModel.cs"
In my home page, I have a list of theaters and I can navigate to a details page.
But when I want to navigate from the tile, I have an error...
The Tile :
ShellTile.Create(new Uri("/TheaterDetails.xaml?selectedItem=" + theater.idTheater, UriKind.Relative), tile, false);
My TheaterDetails page :
public partial class TheaterDetails : PhoneApplicationPage
{
theater theater = new theater();
public TheaterDetails()
{
InitializeComponent();
}
protected override void OnNavigatedTo(NavigationEventArgs e)
{
if (!App.ViewModel.IsDataLoaded)
{
App.ViewModel.LoadData();
}
if (DataContext == null)
{
string selectedIndex = "";
if (NavigationContext.QueryString.TryGetValue("selectedItem", out selectedIndex))
{
int index = int.Parse(selectedIndex);
theater = (from t in App.ViewModel.Theaters
where t.idTheater == index
select t).SingleOrDefault();
DataContext = theater;
....
....
....
The error :
https://dl.dropboxusercontent.com/u/9197067/error.png
Like if the data were not loaded...
Do you have an idea where the problem come from ?
The solution could be easy but I am a beginner... Maybe it's because I load the data asynchronously and the application doesn't wait until it's done...
Thanks
EDIT :
My LoadData() method :
public void LoadData()
{
client.GetTheatersCompleted += new EventHandler<ServiceReference1.GetTheatersCompletedEventArgs>(client_GetTheatersCompleted);
client.GetTheatersAsync();
// Other get methods...
this.IsDataLoaded = true;
}
private void client_GetTheatersCompleted(object sender, ServiceReference1.GetTheatersCompletedEventArgs e)
{
Theaters = e.Result;
}
You should check to see which variable is actually null. In this case it looks to be Theaters (otherwise the error would have thrown earlier).
Since Theaters is populated from a web call it is most likely being called asynchronously, in other words when you return from LoadData() the data is not yet there (it's still waiting for the web call to come back), and is waiting for the web service to return its values.
Possible solutions:
Make LoadData() an async function and then use await LoadData(). This might require a bit of rewriting / refactoring to fit into the async pattern (general introduction to async here, and specific to web calls on Windows Phone here)
A neat way of doing this that doesn't involve hacks (like looping until the data is there) is to raise a custom event when the data is actually populated and then do your Tile navigation processing in that event. There's a basic example here.
So the solution that I found, thanks to Servy in this post : Using async/await with void method
I managed to use async/await to load the data.
I replaced my LoadData() method by :
public static Task<ObservableCollection<theater>> WhenGetTheaters(ServiceClient client)
{
var tcs = new TaskCompletionSource<ObservableCollection<theater>>();
EventHandler<ServiceReference1.GetTheatersCompletedEventArgs> handler = null;
handler = (obj, args) =>
{
tcs.SetResult(args.Result);
client.GetTheatersCompleted -= handler;
};
client.GetTheatersCompleted += handler;
client.GetTheatersAsync();
return tcs.Task;
}
public async Task LoadData()
{
var theatersTask = WhenGetTheaters(client);
Theaters = await theatersTask;
IsDataLoaded = true;
}
And in my page :
protected override async void OnNavigatedTo(NavigationEventArgs e)
{
if (!App.ViewModel.IsDataLoaded)
{
await App.ViewModel.LoadData();
}