I have list that is bound to a view when it loads which works fine. I also have a timer that calls a service to check for any new items to add to the list. The problem occurs when I try and add new items to the list I get a error that it needs to be done on the UI thread.
I am attempting to add the items to an ObservableCollection as Below:
private ObservableCollection<ChatMessageViewModel> _items;
public MyViewModel(IMvxMessenger messenger, IMyService myService) : base (messenger)
{
_myService = myService;
_timer = new Timer(GetLatestItems,null, 1000,10000);
}
public async void GetLatestItems()
{
var newItems = await _myService.GetNewMessages();
if (newItems != null && newItems.Count > 0)
{
foreach (var item in newItems)
{
Items.Add(item);
}
}
}
ObservableCollection/INotifyCollectionChanged must be used synchronously - so you must use it on the UI thread.
Timer uses a ThreadPool thread.
To marshall the call back onto the UI, try something like:
public MyViewModel(IMvxMessenger messenger, IMyService myService) : base (messenger)
{
_myService = myService;
_timer = new Timer(GetLatestItems,null, 1000,10000);
}
public async void GetLatestItems()
{
var newItems = await _myService.GetNewMessages();
InvokeOnMainThread(() => {
if (newItems != null && newItems.Count > 0)
{
foreach (var item in newItems)
{
Items.Add(item);
}
}
});
Related
How do you model bind an array from the URI with GET in ASP.NET Core 1 Web API (implicitly or explicitly)?
In ASP.NET Web API pre Core 1, this worked:
[HttpGet]
public void Method([FromUri] IEnumerable<int> ints) { ... }
How do you do this in ASP.NET Web API Core 1 (aka ASP.NET 5 aka ASP.NET vNext)? The docs have nothing.
The FromUriAttribute class combines the FromRouteAttribute and FromQueryAttribute classes. Depending the configuration of your routes / the request being sent, you should be able to replace your attribute with one of those.
However, there is a shim available which will give you the FromUriAttribute class. Install the "Microsoft.AspNet.Mvc.WebApiCompatShim" NuGet package through the package explorer, or add it directly to your project.json file:
"dependencies": {
"Microsoft.AspNet.Mvc.WebApiCompatShim": "6.0.0-rc1-final"
}
While it is a little old, I've found that this article does a pretty good job of explaining some of the changes.
Binding
If you're looking to bind comma separated values for the array ("/api/values?ints=1,2,3"), you will need a custom binder just as before. This is an adapted version of Mrchief's solution for use in ASP.NET Core.
public class CommaDelimitedArrayModelBinder : IModelBinder
{
public Task BindModelAsync(ModelBindingContext bindingContext)
{
if (bindingContext.ModelMetadata.IsEnumerableType)
{
var key = bindingContext.ModelName;
var value = bindingContext.ValueProvider.GetValue(key).ToString();
if (!string.IsNullOrWhiteSpace(value))
{
var elementType = bindingContext.ModelType.GetTypeInfo().GenericTypeArguments[0];
var converter = TypeDescriptor.GetConverter(elementType);
var values = value.Split(new[] { "," }, StringSplitOptions.RemoveEmptyEntries)
.Select(x => converter.ConvertFromString(x.Trim()))
.ToArray();
var typedValues = Array.CreateInstance(elementType, values.Length);
values.CopyTo(typedValues, 0);
bindingContext.Result = ModelBindingResult.Success(typedValues);
}
else
{
// change this line to null if you prefer nulls to empty arrays
bindingContext.Result = ModelBindingResult.Success(Array.CreateInstance(bindingContext.ModelType.GetElementType(), 0));
}
return TaskCache.CompletedTask;
}
return TaskCache.CompletedTask;
}
}
You can either specify the model binder to be used for all collections in Startup.cs:
public void ConfigureServices(IServiceCollection services)
{
// Add framework services.
services.AddMvc().AddMvcOptions(opts =>
{
opts.ModelBinders.Insert(0, new CommaDelimitedArrayModelBinder());
});
}
Or specify it once in your API call:
[HttpGet]
public void Method([ModelBinder(BinderType = typeof(CommaDelimitedArrayModelBinder))] IEnumerable<int> ints)
ASP.NET Core 1.1 Answer
#WillRay's answer is a little outdated. I have written an 'IModelBinder' and 'IModelBinderProvider'. The first can be used with the [ModelBinder(BinderType = typeof(DelimitedArrayModelBinder))] attribute, while the second can be used to apply the model binder globally as I've show below.
.AddMvc(options =>
{
// Add to global model binders so you don't need to use the [ModelBinder] attribute.
var arrayModelBinderProvider = options.ModelBinderProviders.OfType<ArrayModelBinderProvider>().First();
options.ModelBinderProviders.Insert(
options.ModelBinderProviders.IndexOf(arrayModelBinderProvider),
new DelimitedArrayModelBinderProvider());
})
public class DelimitedArrayModelBinderProvider : IModelBinderProvider
{
public IModelBinder GetBinder(ModelBinderProviderContext context)
{
if (context == null)
{
throw new ArgumentNullException(nameof(context));
}
if (context.Metadata.IsEnumerableType && !context.Metadata.ElementMetadata.IsComplexType)
{
return new DelimitedArrayModelBinder();
}
return null;
}
}
public class DelimitedArrayModelBinder : IModelBinder
{
public Task BindModelAsync(ModelBindingContext bindingContext)
{
if (bindingContext == null)
{
throw new ArgumentNullException(nameof(bindingContext));
}
var modelName = bindingContext.ModelName;
var valueProviderResult = bindingContext.ValueProvider.GetValue(modelName);
var values = valueProviderResult
.ToString()
.Split(new char[] { ',' }, StringSplitOptions.RemoveEmptyEntries);
var elementType = bindingContext.ModelType.GetTypeInfo().GenericTypeArguments[0];
if (values.Length == 0)
{
bindingContext.Result = ModelBindingResult.Success(Array.CreateInstance(elementType, 0));
}
else
{
var converter = TypeDescriptor.GetConverter(elementType);
var typedArray = Array.CreateInstance(elementType, values.Length);
try
{
for (int i = 0; i < values.Length; ++i)
{
var value = values[i];
var convertedValue = converter.ConvertFromString(value);
typedArray.SetValue(convertedValue, i);
}
}
catch (Exception exception)
{
bindingContext.ModelState.TryAddModelError(
modelName,
exception,
bindingContext.ModelMetadata);
}
bindingContext.Result = ModelBindingResult.Success(typedArray);
}
return Task.CompletedTask;
}
}
There are some changes in the .NET Core 3.
Microsoft has split out the functionality from the AddMvc method (source).
As AddMvc also includes support for View Controllers, Razor Views and etc. If you don't need to use them in your project (like in an API), you might consider using services.AddControllers() which is for Web API controllers.
So, updated code will look like this:
public void ConfigureServices(IServiceCollection services)
{
services.AddControllers()
.AddMvcOptions(opt =>
{
var mbp = opt.ModelBinderProviders.OfType<ArrayModelBinderProvider>().First();
opt.ModelBinderProviders.Insert(opt.ModelBinderProviders.IndexOf(mbp), new DelimitedArrayModelBinderProvider());
});
}
I'm trying to retrieve user data from Parse (xamarin.ios using c#). I'm using an async method with await. My challenge is,each time I navigate to the tableView in the app, which should populate the user data in question,the table is always empty.
I would like to wait until the results have been returned before proceeding with the other portion of code.I have tried to use the ContinueWith() function but constantly ran into a build error -
Cannot implicitly convert type 'void' to System.Collections.Generic.IEnumerable<Parse.ParseObject>
My Questions:
Is this the best way to wait for the result?
How do I solve the build error?
Here is my current implementation:
public async void retrieveData(string username)
{
try
{
this.requests.ClearRequests();
refreshed = false;
var query = ParseObject.GetQuery("Requests").WhereEqualTo("username", username);
IEnumerable<ParseObject> results = await query.FindAsync().ContinueWith(t =>{
if(results != null)
{
foreach(ParseObject parseObject in results)
{
UserRequest request = new UserRequest();
request.objectId = parseObject.ObjectId;
request.make = parseObject.Get<string> ("item1");
request.model = parseObject.Get<string> ("item2");
request.year = parseObject.Get<string> ("item3");
request.userName = parseObject.Get<string> ("username");
this.requests.addRequest (request);
}
refreshed = true;
}
});
}
catch(ParseException e) {
Console.WriteLine (e.Message + e.StackTrace);
}
}
You shouldn't need a ContinueWith...that's what the await should handle.
await waits on a Task and then brings back the result with the proper return type. ContinueWith returns a Task, so you would have to grab the Result from the task to make it usable.
For more on this type of thing, you may want to check out Difference between await and ContinueWith
You can try something like this.
public async void retrieveData(string username, )
{
try
{
this.requests.ClearRequests();
refreshed = false;
var query = ParseObject.GetQuery("Requests").WhereEqualTo("username", username);
IEnumerable<ParseObject> results = await query.FindAsync();
if(results != null)
{
foreach(ParseObject parseObject in results)
{
UserRequest request = new UserRequest();
request.objectId = parseObject.ObjectId;
request.make = parseObject.Get<string> ("item1");
request.model = parseObject.Get<string> ("item2");
request.year = parseObject.Get<string> ("item3");
request.userName = parseObject.Get<string> ("username");
this.requests.addRequest (request);
}
refreshed = true;
}
//This is your refresh method for your TableView
this.RefreshTableView();
//or, if in iOS
NSNotificationCenter.DefaultCenter.PostNotificationName("resultsRetrieved", null);
}
catch(ParseException e) {
Console.WriteLine (e.Message + e.StackTrace);
}
}
To show the results in the tableView, I would recommend moving the refreshing of the tableView to a separate method that gets triggered synchronously after the results have been retrieved and parsed. This is shown with the this.RefreshTableView() call above.
If in iOS on Xamarin, another option is to post a notification to the NSNotificationCenter (the Xamarin documentation for which is here). Use the PostNotificationName part seen above instead and then add an observer in the ViewControllers that you want to be dependent on the data. This is done as follows:
Make a notificationToken object:
NSObject notificationToken;
Then in your setup method (you could put this inside of your ViewDidLoad):
void Setup ()
{
notificationToken = NSNotificationCenter.DefaultCenter.AddObserver ("resultsRetrieved", RefreshData);
}
Make your RefeshData method:
void RefreshData (NSString notifString)
{
this.tableView.ReloadData();
}
And then, make sure you dispose of the notification observer when you tear down the class
void Teardown ()
{
NSNotificationCenter.DefaultCenter.RemoveObserver (notificationToken);
}
I had a similar issue so started using callbacks. I'm using them in Xamarin.Android, pretty sure they're available in Xamarin.iOS.
Method that starts the task method - Note I am passing in a method of this class as a parameter
private async void updatedData()
{
await Utils.DataTasks.getNewLiveTips(populateTipsList);
}
Method that calls for data from server
public class DataTasks
{
public static async Task getAllData(Action<IEnumerable<ParseObjects>> callback) {
var query = new ParseQuery<ParseObjects>().OrderByDescending("updatedAt").Limit(5);
IEnumerable<ParseObjects> parseTips = await query.FindAsync();
foreach (var tip in parseTips)
{
// Save data to DB if needed
}
callback(parseTips);
}
Method I passed as parameter in the first instance is now called
private void populateTipsList(IEnumerable<ParseObjects> results)
{
mAdapter = new TipAdapter(this.Activity, results);
mRecyclerView.SetAdapter(mAdapter);
refresher.Refreshing = false;
}
Is it possible to delete entity while same is still in plugin update transaction?
It seems following code is not working. I need to delete entity when its get updated and some other circumstances
Something like:
protected void ExecutePosAnnotationtUpdate(LocalPluginContext localContext)
{
if (localContext == null)
{
throw new ArgumentNullException("localContext");
}
if (localContext.PluginExecutionContext.Depth > 1) return;
Entity postEntityImage = null;
if (localContext.PluginExecutionContext.PostEntityImages.Contains("PostImage"))
{
if (localContext.PluginExecutionContext.PostEntityImages["PostImage"] != null)
{
postEntityImage = localContext.PluginExecutionContext.PostEntityImages["PostImage"];
}
}
Entity preEntityImage = null;
if (localContext.PluginExecutionContext.PreEntityImages.Contains("PreImage"))
{
if (localContext.PluginExecutionContext.PreEntityImages["PreImage"] != null)
{
preEntityImage = localContext.PluginExecutionContext.PreEntityImages["PreImage"];
}
}
if ((bool)postEntityImage.Attributes["isdocument"])
{
if ( some condition )
localContext.OrganizationService.Delete(postEntityImage.LogicalName, postEntityImage.Id);
}
}
`
Since you're updating, the record is there in Target.
public void Execute(IServiceProvider serviceProvider)
{
var context = (IPluginExecutionContext)serviceProvider.GetService(typeof(IPluginExecutionContext));
var serviceFactory = (IOrganizationServiceFactory)serviceProvider.GetService(typeof(IOrganizationServiceFactory));
var service = serviceFactory.CreateOrganizationService(context.UserId);
var target = context.InputParameters["Target"] as Entity;
var condition = /* whatever */
if(condition)
{
service.Delete(target.LogicalName, target.Id);
}
}
Works as expected when attached to Update message, Post-Operation, Asynchronous. Works inside the Sandbox, also.
Records will not disappear at once, it takes some time (~20 seconds on my on-premise playground). If you make it Synchronous it will still work but alerts are going to come up because data disappears while being handled by the CRM during the update.
I am using MVVMCross 3.2.2 as part of an iOS/Android app. One of my screens has multiple views that are displayed depending upon the selection in a Tab bar like row of buttons. Different data is displayed in each of these these views individual UITableView. The data binding works perfectly.
I also have a menu, that has a "profile" selection. Changing the profile fires an MvxMessage that my HomeView receives and then uses the message to set the ViewModel up to filter the data to be displayed. This all seems to work perfectly and the data is displayed correctly.
If I do something in the HomeView that displays another view using ShowViewModel(). When I return back to the home view the binding no longer works properly when a profile changes is made. The message gets handled, the data gets filtered, but a call to ReloadDataTable on the UITableView does not change the data.
ViewModel
#region Groupings
public IList<Group> Groups{
get { return _groupService.GetAll(); }
}
public void SetupSubGroups(Group group)
{
if (group == null)
{
_groups = new ObservableCollection<Group> ();
if (_profileService.SelectedProfile != null)
{
var grp = _groupService.GetByGroupName (_profileService.SelectedProfile.Name);
if (grp == null)
grp = new Group { Name = _profileService.SelectedProfile.Name };
_groups.Add (grp);
}
}
else
{
var litsOfGroups = _groupService.GetSubGroups (group);
foreach (var grp in litsOfGroups)
_groups.Add (grp);
}
RaisePropertyChanged(() => AvailableGroups);
}
private ObservableCollection <Group> _groups;
public ObservableCollection<Group> AvailableGroups {
get { return _groups; }
}
#endregion
ViewController
public override void ViewDidLoad ()
{
base.ViewDidLoad ();
var groupSource = new GroupTableViewDataSource (TableViewGroups);
TableViewGroups.Source = groupSource;
_localViewModel.SetupSubGroups (null);
_bindingSet = this.CreateBindingSet<HomeViewController, HomeViewModel> ();
_bindingSet.Bind (groupSource).To (vm => vm.AvailableGroups);
_bindingSet.Apply ();
TableViewReportTags.ReloadData ();
NavigationController.NavigationBarHidden = false;
}
private void OnProfileChanged(ProfileChangedMessage message)
{
_localViewModel.SetupSubGroups (null);
TableViewGroups.ReloadData ();
}
private HomeViewModel _localViewModel { get { return ViewModel as HomeViewModel; } }
Any ideas what I can look at, or change would be really useful. I have spend many hours on this, and have made no progress.
I got some questions regarding the use of threads, specially when you have to wait for a thread to be finished so you can perform other operations.
In my app, I use threads for operations such as http connections or when I read from or write to a RecordStore.
For example in the following class that I use to initialize my thread, I retrieve some customers from a webservice using the method called HttpQueryCustomers.
public class thrLoadCustomers implements Runnable {
private RMSCustomer mRMSCustomer;
private String mUrl;
public thrLoadCustomers(RMSCustomer rmsCust, String url) {
mRMSCustomer = rmsCust;
mUrl = url;
}
public void run() {
String jsonResultados = "";
try {
jsonResultados = HttpQueryCustomers();
} catch (IOException ex) {
//How to show a message from here??
} catch (SecurityException se) {
//How to show a message here??
} catch (NullPointerException npe) {
//How to show a message from here??
}
if (!jsonResultados.equals("")) {
try {
mRMSCustomer.save(jsonResultados);
} catch (RecordStoreException ex) {
//How to show a message from here???
}
}
}
public String HttpQueryCustomers() throws IOException,SecurityException,NullPointerException {
StringBuffer stringBuffer = new StringBuffer();
HttpConnection hc = null;
InputStream is = null;
System.out.println(mUrl);
try {
hc = (HttpConnection) Connector.open(mUrl);
if (hc.getResponseCode() == HttpConnection.HTTP_OK) {
is = hc.openInputStream();
int ch;
while ((ch = is.read()) != -1) {
stringBuffer.append((char) ch);
}
}
} finally {
is.close();
hc.close();
}
String jsonData = stringBuffer.toString();
return jsonData.toString();
}
}
Notice in the above class that I pass a parameter called rmsCust of the type RMSCustomer
RMSCustomer is a class that I use to handle all the operations related to RMS:
public class RMSCustomer {
private String mRecordStoreName;
private Customer[] mCustomerList;
public RMSCustomer(String recordStoreName) {
mRecordStoreName = recordStoreName;
}
public Customer[] getCustomers() {
return mCustomerList;
}
public Customer get(int index) {
return mCustomerList[index];
}
public void save(String data) throws RecordStoreException,JSONException,NullPointerException {
RecordStore rs = null;
int idNuevoRegistro;
String stringJSON;
try {
rs = RecordStore.openRecordStore(mRecordStoreName, true);
JSONArray js = new JSONArray(data);
//Set the size of the array
mCustomerList = new Customer[js.length()];
for (int i = 0; i < js.length(); i++) {
JSONObject jsObj = js.getJSONObject(i);
stringJSON = jsObj.toString();
idNuevoRegistro = addRecord(stringJSON, rs);
//Add a new Customer to the array
mCustomerList[i] = initializeCustomer(stringJSON, idNuevoRegistro);
}
} finally {
if (rs != null) {
rs.closeRecordStore();
}
}
}
public int addRecord(String stringJSON, RecordStore rs) throws JSONException,RecordStoreException {
byte[] raw = stringJSON.getBytes();
int idNuevoRegistro = rs.addRecord(raw, 0, raw.length);
return idNuevoRegistro;
}
public Customer initializeCustomer(String stringJSON, int idRecord) throws JSONException {
Customer c = new Customer();
JSONObject jsonObj = new JSONObject(stringJSON);
// Set Customer properties
//...
return c;
}
}
This class is used to show a list of customer and ,as you can see, it extends the List class and receives an array of Customers as a parameter.
public class ListCustomers extends List {
private final Customer[] mData;
public static ListCustomers create(Customer[] data) {
int i = 0;
for (; i < data.length; i++) {
if (data[i] == null) {
break;
}
}
String[] names = new String[i];
for (int j = 0; j < i; j++) {
names[j] = data[j].name;
}
return new ListCustomers(names, data);
}
protected ListCustomers(String names[], Customer[] data) {
super("List of Customer", IMPLICIT, names, null);
mData = data;
}
public Customer getSelectedObject() {
return mData[this.getSelectedIndex()];
}
}
Finally this is how I call the thread from the MIDlet (using all the 3 previous classes) when I want to show a List of Customers:
private void showCustomerList(String url) {
showWaitForm();
if (scrCustomerList == null) {
rmsCustomers = new RMSCustomer("rmsCustomers");
thrLoadCustomers load = new thrLoadCustomers(rmsCustomers, url);
Thread t = new Thread(load);
t.start();
try {
t.join();
} catch (InterruptedException ex) {
}
scrCustomerList = ListCustomers.create(rmsCustomers.getCustomers());
scrCustomerList.addCommand(cmdSelect);
scrCustomerList.addCommand(cmdBack);
scrCustomerList.setCommandListener(this);
}
mDisplay.setCurrent(scrCustomerList);
}
Now here's the problems I have :
The showWaitForm() doesn't work (it sets a form with a Gauge as the
Current form)
I don't know how to show all the exceptions that might be thrown from
within the thrLoadCustomers class.
I don't know whether using t.join() is the best choice
The last question is about something the book I'm reading says :
Threads, in particular, can be a scarce commodity. The MSA
specification requires that an application must be allowed to create
ten threads. Just because you can doesn’t mean you should. In general,
try to use the fewest resources possible so that your application will
run as smoothly as possible
This is the first time a use threads, and in my app I might have up to 10 threads (classes). However, I will only execute once thread at the time, will I be going against what the previous quotation says??
I hope I'm not asking too many questions. Thank you very much for your help.
P.D Much of the code I posted here wouldn't have been possible with the help of Gregor Ophey
Question #1 is about a different problem not related to threading, and for which very little code is shown. I'd suggest you to post a new dedicated question with proper explanation of the issue.
Questions #2 and #3: You could define a wrapper class like this:
public class WSResult {
private boolean success; //true if the WS call went ok, false otherwise
private String errorMessage; //Error message to display if the WS call failed.
private Object result; //Result, only if the WS call succeeded.
private boolean completed = false;
//TODO getter and setters methods here
}
In your screen, you can create an instance of result and wait for it:
WSResult result = new WSResult();
//Start thread here
new Thread(new LoadCustomersTask(result)).start();
//This is old school thread sync.
synchronized(result){
while(!result.isCompleted()){
result.wait();
}
}
//Here the thread has returned, and we can diaplay the error message if any
if(result.isSuccess()){
} else {
//Display result.getErrorMessage()
}
Then your runnable would be like this:
class LoadCustomersTask implements Runnable {
private final WSResult result;
public LoadCustomersTask(WSResult res){
result = res;
}
public void run(){
//Do the WS call
//If it went well
result.setSuccess(true);
result.setResult(jsonResultados);
//Else
result.setSuccess(false);
result.setErrorMessage("Your error message");
//In any case, mark as completed
result.setcompleted(true);
//And notify awaiting threads
synchronized(result){
result.notifyAll();
}
}
}
You can also do it with thread.join, but wait/notify is better because you not making the screen depend on the particular thread where the runnable runs. You can wait/notify on the result instance, as shown, or on the runnable if it is intended for a single use.
Question #4: Yes threads must not be abused, specially in JavaME where programs usually run in single core CPUs with a frecuency in the order of MHz. Try not to have more than 1-3 threads running at the same time. If you really need to, consider using a single thread for running all background tasks (a blocking queue).