With reference to .Net Maui: How to read/write (get/set) a global object from any content page (MVVM)
I now have a need to pass an object that is rather a large (>500Mb), it is an OpenMap extract, a RouterDb object (Itinero http://docs.itinero.tech/index.html)
Though I am trying to use MVVM some packages (Mapsui) use code behind so I am left with a mixture of ViewModel and Codebehind. I can overcome the limitation of not having any kind of global object reference by using the MessagingCenter which works remarkably well.
I am wondering if this mechanism can handle the passing of large objects (megabytes) or if internally it simply passes a reference to the object. I suspect from my experiments that it is trying to pass a copy of the object and failing, as I end up with a null object.
Here's the code
MessagingMarker.cs - just a placeholder class
namespace RouteIt.Models;
public class MessagingMarker
{
}
In my MainPageViewModel.cs
//Takes about 10seconds to load
using (var stream = new FileInfo(#"C:\Users\Gordon\source\repos\RouteIt\Resources\Raw\gb.routerdb").OpenRead())
{
routerDb = RouterDb.Deserialize(stream);
}
//send message to codebehind containing object or reference?
MessagingCenter.Send(new MessagingMarker(), "RouterDbLoaded", routerDb);
and in my receiving MainPage.xaml.cs constructor
MessagingCenter.Subscribe<MessagingMarker, RouterDb>(this, "RouterDbLoaded", (sender, arg) =>
{
routerDb = arg;
});
router = new(routerDb);
Any thoughts? (And yes perhaps I need to re-struture my app, but at this stage I don't want to really, one day Mapsui might support mvvm apparently.)
As always thanks for at least reading :)
Related
I am some need help understanding the latest recommended approach to wire up and use reactiveui for a WPF project.
In doing research on the internet on reactiveui I came across various (few) posts spanning a long time period during which the library evolved with the unfortunate result that some of these how-to articles now refer to older ways of doing things which are no longer applicable
I am trying to understand the recommended way to wire up commands (usually to invoke web service which returns a DTO) and I’ve found multiple ways mentioned to do it.
My current understanding is that
// this is the first thing to do
MyCommand = ReactiveCommand.Create()
// variations to wire up the delegates / tasks to be invoked
MyCommand.CreateAsyncTask()
MyCommand.CreateAsyncFunc()
MyCommand.CreateAsyncAction()
// this seems to be only way to wire handler for receiving result
MyCommand.Subscribe
// not sure if these below are obsolete?
MyCommand.ExecuteAsync
MyCommand.RegisterAsyncTask()
Could someone try to explain which of these variations is the latest API and which are obsolete, with perhaps a few words about when to use each of them
The changes on the ReactiveCommand API are documented in this blog post:
http://log.paulbetts.org/whats-new-in-reactiveui-6-reactivecommandt/
The first option - ReactiveCommand.Create() - just creates a reactive command.
To define a command which asynchronously returns data from a service you would use :
MyCommand = ReactiveCommand.CreateAsyncTask(
canExec, // optional
async _ => await api.LoadSomeData(...));
You may use the Subscribe method to handle data when it is received:
this.Data = new ReactiveList<SomeDTO>();
MyCommand.Subscribe(items =>
{
this.Data.Clear();
foreach (var item in items)
this.Data.Add(item);
}
Though, the simplest thing is to use instead the ToProperty method like this:
this._data = MyCommand
.Select(items => new ReactiveList<SomeDTO>(items))
.ToProperty(this, x => x.Data);
where you have defined an output property for Data:
private readonly ObservableAsPropertyHelper<ReactiveList<SomeDTO>> _data;
public ReactiveList<SomeDTO> Data
{
get { return _data.Value; }
}
I am facing the following problem,
I have an object called "data". It has three properties, one of it being itemRendererData. The "itemRendererData" is an ArrayCollection of objects having many properties one of which is the property "imageURL" (datatype:String).
I am working in flex. I have defined the view and the item renderer properly. The view has the data. I am supposed to get the images from the url specified by imageURL property.
In the itemRenderer, I have declared, source
source = {data.itemRendererData.imageURL}
But the images are not being displayed.
Use a the FlexEvent.DATA_CHANGE handler rather than binding, which is actually the proper way to handle this and gives you far more control.
public function CustomItemRenderer() {
this.addEventListener(FlexEvent.DATA_CHANGE, this.dataChangeHandler);
this.addEventListener(FlexEvent.CREATION_COMPLETE, this.creationCompleteHandler);
}
private function creationCompleteHandler(e:FlexEvent) {
if (this.data) {
this.image.source = this.data.itemRendererData.imageURL;
}
}
private function dataChangeHandler(e:FlexEvent) {
if (this.data && this.initialized) {
this.image.source = this.data.itemRendererData.imageURL;
}
}
You will notice that I have a handler for FlexEvent.CREATION_COMPLETE as well. This is because the data is actually set before the components are created. So the first time a renderer is loaded, this.image is null and this.image.source will error out.
If that doesn't work, you also need to make sure that the Image/BitmapImage is not a direct child of the renderer. I never did figure out why this was, but adding it as a child of Group fixed that issue where the image was being set but not rendering. Again, I have no idea why this was and I tested for a few hours trying to figure it out.
As an added tip, avoid MXML-based ItemRenderers in mobile applications. They are noticeably slower than pure-AS3 renderers.
Here is what I am trying to do. In my WP7 app, I am loading a page that has two StackPanels. StackPanel1 is "Collapsed" and StackPanel2 is "Visible". On load of the page, I am kicking off an HttpWebRequest and then processing the BeginGetResponse asynchronously. At this point I just want to swap the Visibility of the two StackPanels. However, since the BeginGetResponse is run Asynchronously, I am no longer in the UI thread and cannot manipulate these StackPanel controls. If I try to reference them, of course, I get "An object reference is required for the non-static field, method, or property 'blah.StackPanel1'"
This all makes sense and I get why.
Here are some things I have tried:
Delegates, but any way I sliced it, I needed a static reference to my controls. fail.
I tried to create a static reference to my page class and then use that to reference my controls in the BeginGetResponse. This compiled, but I got a UnauthorizedAccessException 'invalid cross-thread access.' at run-time when I tried to reference the controls.
Searching and searching and searching.
Using Deployment.Current.Dispatcher.BeginInvoke to run on the UI thread.
How can I statically reference these controls?
OR is there a better way to do what I'm doing?
EDIT:
Here is my HttpWebRequest
if (NetworkInterface.GetIsNetworkAvailable())
{
HttpWebRequest httpWebRequest = HttpWebRequest.CreateHttp("http://urlThatWorks.com");
httpWebRequest.Method = "GET";
httpWebRequest.BeginGetResponse((asyncresult) =>
//do processing of my return here
//then here is the problem
StackPanel1.Visibility = System.Windows.Visibility.Visible;
StackPanel2.Visibility = System.Windows.Visibility.Collapsed;
}, httpWebRequest);
}
ANOTHER EDIT:
And here is how I tried with Deployment.Current.Dispatcher.BeginInvoke
httpWebRequest.BeginGetResponse((asyncresult) =>
//do processing of my return here
Deployment.Current.Dispatcher.BeginInvoke(() =>
{
StackPanel1.Visibility = System.Windows.Visibility.Visible;
StackPanel2.Visibility = System.Windows.Visibility.Collapsed;
});
}, httpWebRequest);
You don't really want a static reference, you want a thread-safe way of accessing them.
You can execute it on the UI thread by:
Deployment.Current.Dispatcher.BeginInvoke(()=> SomeMethod);
or
Deployment.Current.Dispatcher.BeginInvoke(()=> { // code });
I'm using Linq and having trouble doing something that I believe should be trivial. I want to return data from one layer so it can be used independently of linq in another layer.
Suppose I have a Data Access Layer. It knows about the entity framework and how to interact with it. But, it doesn't care who accesses it. The one interesting requirement I have is that the queries in the entity framework return projected data that is not part of the Entity Model itself. Please don't ask me to change this part of the requirement and make POCOs for each return type, as it is not the best design given the problem I am trying to solve. Below is an example.
public class ChartData
{
public function <<returnType??>> GetData()
{
MyEntities context = new MyEntities();
var results = from context.vManyColumnsOfData as v
where v.CompanyName = "acme"
select new {Year = v.SalesYear, Income = v.Income};
return ??;
}
}
Then, I would like to have an ASP.Net UI layer be able to call into the Data Access Layer to get the data in order to bind it to a control. The UI layer should have no notion of where the data came from. It should only know that it has the data it needs to bind. Below is an example.
protected void chart_Load(object sender, EventArgs e)
{
// set some chart properties
chart.Skin = "Default";
...
// Set the data source
ChartData dataMgr = new ChartData();
<<returnType?>> data = dataMgr.GetData();
chart.DataSource = data;
chart.DataBind();
}
What is the best way to send linq projected data back to another layer?
If you don't need to use the projected type statically, just return IEnumerable<object>.
Please don't ask me to change this part of the requirement and make
POCOs for each return type, as it is not the best design given the
problem I am trying to solve.
I feel like I should rightly ignore this, as the best thing to do is to return a defined type. Anonymous types are useful when they are wholly contained within the method that creates them. Once you start passing them around, it is time to go ahead and give them the proper class treatment.
However, to live within your imposed limitations, you can return IEnumerable<object> from the method and use that or var at the callsite and rely upon the dynamic binding of the control to get at the data. It's not going to help you if you need to deal with the object programmatically, but it will serve fine for databinding.
You can not return an anonymous type, so basically for this you will need POCO's even though you don't want them.
"not the best design given the problem I am trying to solve"
Could you explain what you are trying to achieve a little more? It might be possible to return some type of list containing a dictionary of items (ie rows and columns). Think something like an untyped dataset (yuck)
Your GetData method can use IEnumerable (the "old" non-generic interface) as its return type.
Any dynamic resolution (e.g. ASP.NET or XAML bindings) should work as expected, which seems to be what you want to do.
However, if you want to use the results in your code, you will probably have to resort to .NET 4's dynamic keyword.
The following example can be run in LINQPad (in "C# Program" mode) and illustrates this:
void Main()
{
var v = GetData();
foreach (dynamic element in v)
{
((string)element.Name).Dump();
}
}
public IEnumerable GetData()
{
return from i in Enumerable.Range(1, 10)
select new
{
Name = "Item " + i,
Value = i
};
}
Keep in mind that, design-wise, coding like this will make most people frown and can affect performance.
I am writing unittest for void method actually that method load the collection in
ViewData["CityList"] method is
public void PopulateCityCombo() {
IEnumerable<Cities> c= service.GetCities();
ViewData["CityList"] = c.Select(e => new Cities{ ID = e.ID, Name = e.Name});
}
now i do not know how to unit test using Moq since controller method is void and not returning data, can any one tell i will achive that.
On a side note, I would shy away from using ViewData within controller methods as per your example. The ViewData dictionary approach is fast and fairly easy to implement, however it can lead to typo's and errors that are not caught at compile time. An alternative would be to use the ViewModel pattern which allows you to use strongly-typed classes for the specific view you need to expose values or content within. Ultimately giving you type safe and compile time checking along with intellisense.
Switching to the ViewModel pattern would allow you to call the PopulateCityCombo() method from your controller to populate a ViewModel that in turn would passed to the corresponding view.
From there you would need to inject a mock service layer into your controllers constructor from your unit test.
// arrange
var mock = new Mock<servicelayer>();
mock.Setup(x=>x.GetCities()).Returns(expectedData);
var controller = new YourController(mock.Object);
// act
var result = controller.ControllerMethod() as ViewResult;
var resultData = (YourViewModel)result.ViewData.Model;
// assert
// Your assertions