I am trying to do a simple override and load some data when my page loads, I am using the following code in the code behind page.
namespace XYZ
{
public partial class MainPage : ContentPage
{
private Label results;
private Label groupResults;
public MainPage()
{
InitializeComponent();
results = new Label();
groupResults = new Label();
}
protected override void OnAppearing()
{
base.OnAppearing();
storeIdTxt.Text = Settings.StoreIdSetting;
}
}
}
If I uncomment the override things works just fine, the error I am getting seems to be a generic one attached here
my settings class is fairly simple as follows
using System;
using System.Collections.Generic;
using System.Text;
using Plugin.Settings;
using Plugin.Settings.Abstractions;
namespace NWMPosNG.Helpers
{
/// <summary>
/// This is the Settings static class that can be used in your Core solution or in any
/// of your client applications. All settings are laid out the same exact way with getters
/// and setters.
/// </summary>
public static class Settings
{
private static ISettings AppSettings
{
get
{
return CrossSettings.Current;
}
}
#region Setting Constants
private const string SettingsKey = "settings_key";
private static readonly string SettingsDefault = string.Empty;
private const string StoreId = null;
private static readonly string StoreIdDefault = "0";
#endregion
public static string GeneralSettings
{
get
{
return AppSettings.GetValueOrDefault(SettingsKey, SettingsDefault);
}
set
{
AppSettings.AddOrUpdateValue(SettingsKey, value);
}
}
public static string StoreIdSetting
{
get
{
return AppSettings.GetValueOrDefault(StoreId, StoreIdDefault);
}
set
{
AppSettings.AddOrUpdateValue(StoreId, value);
}
}
}
}
I narrowed down the issue to when I access the saved data using
storeIdTxt.Text = Settings.StoreIdSetting;
But I don't understand why that causes the crash.
You are using the Settings Plugin from James Montemagno. Which is pretty much a KeyValuePair that is stored on the local device across sessions.
In your case:
AppSettings.GetValueOrDefault(StoreId, StoreIdDefault);
Translates to:
AppSettings.GetValueOrDefault(null, "0");
Which crashes because 'null' can't be a key. That's why setting the key (StoreId) prevents the crash from happening.
This line was the culprit
private const string StoreId = null;
I don't really understand why but setting this to a non NULL value makes the crash go away
Related
I am creating my first Blazor web application for self education purposes. There is a simple database with data. Dataset is currently rather small. However while clicking on page link it takes some 1-2 seconds to load. Just wondering that how long it would take if dataset would consist of larger amount of items. Is there a way to load page first and then populate the data?
public class EmployeesBase : ComponentBase:
[Inject]
protected IRepository Repository { get; set; }
protected List<BlazorCompanyManager.Data.Employee> employees;
protected override void OnInitialized()
{
this.employees = this.Repository.GetEmployees();
}
public interface IRepository:
using System;
using System.Collections.Generic;
using System.Linq;
using System.Threading.Tasks;
namespace BlazorCompanyManager.Data
{
public interface IRepository
{
public List<Employee> GetEmployees();
public Employee GetEmployee(Guid id);
public bool UpdateEmployee(Employee employee);
public void AddEmployee(Employee employee);
public void DeleteEmployee(Guid id);
}
}
public class Repository : IRepository:
protected readonly ApplicationDbContext dbContext;
public Repository(ApplicationDbContext db)
{
this.dbContext = db;
}
public List<Employee> GetEmployees()
{
return this.dbContext.EmployeeTable.ToList();
}
I have tried to make it work with OnInitializedAsync and other override methods, but got no success so far. Could anyone give some idea on how it can be done?
You''re running an async code block synchronously, thus blocking the UI thread.
this.dbContext.EmployeeTable.ToList()
should look like this:
public async ValueTask<List<Employee>> GetEmployeesAsync()
{
using var dbContext = this.DBContext.CreateDbContext();
var list = await dbContext
.EmployeeeTable
.ToListAsync()
?? new List<TRecord>();
return list;
}
To do this you also need to move to an IDbContextFactory in your Repository. You can no longer rely on a single DbContext.
protected virtual IDbContextFactory<MyDbContext> DBContext { get; set; } = null;
public xxxxxRepository(IConfiguration configuration, IDbContextFactory<MyDbContext> dbContext)
=> this.DBContext = dbContext;
Startup/Program
var dbContext = configuration.GetValue<string>("Configuration:DBContext");
services.AddDbContextFactory<MyDbContext>(options => options.UseSqlServer(dbContext), ServiceLifetime.Singleton);
You component initialization then looks like this.
protected async override void OnInitializedAsyc()
{
this.employees = await this.Repository.GetEmployeesAsync();
}
Data loading will be dependant on your data server, but the UI will be responsive. You may need to consider paging as the data set grows - you can only display so many rows at once so why fetch them all at once!
I'm trying do upgrade Unity from version 3.0.1304.1 to the latest, 5.11.1. Unsurprisingly, there are some issues (3.0.1304.1 is quite old). The code below accomplished two things:
Use a ContainerControlledLifetimeManager for all classes deriving from some base class X, without specifying that for every class derived from X.
Use the default constructor when resolving for all classes deriving from base class Y, without specifying that for every class derived from Y.
Unity documentation is scarce nowadays, and lacks examples. I've read the upgrade notes and regular documentation but I can't make this work with the new version.
So far I have:
Replaced IConstructorSelectorPolicy with ISelect<ConstructorInfo>
Replaced IBuilderContext with BuilderContext (or ref BuilderContext in the PreBuildUp function)
But what to do with the LifetimeManagerFactory? Should I derive IOCConstructorSelectorPolicy from ISelect<ConstructorInfo> and should IOCConstructorSelectorPolicy.SelectConstructor then be replaced by Select (as per the ISelect interface) and how to implement this Select function?
I know this is a very long shot, and I'll post this on the unity github as well (as a request for documentation of sorts), but hopefully there is someone who can give me some pointers.
/// <summary>
/// This class merely exists for readability: avoid having to write the class it derives from.
/// </summary>
public class IOCConfigLifetimeExtension : DefaultLifetimeManagerExtension<ContainerControlledLifetimeManager, X>
{}
/// <summary>
/// An IOC strategy to use a specific LifetimeManager (<typeparamref name="TLifetimeManager"/>) for subclasses of <typeparamref name="TBaseClass"/>.
/// </summary>
public class DefaultLifetimeManagerExtension<TLifetimeManager, TBaseClass> : UnityContainerExtension where TLifetimeManager : LifetimeManager, new()
{
protected override void Initialize()
{
var theFactory = new LifetimeManagerFactory(Context, typeof(TLifetimeManager));
Context.Strategies.Add(new DefaultLifetimeManagerStrategy(theFactory, TypePredicate), UnityBuildStage.TypeMapping);
}
private bool TypePredicate(Type type)
{
return typeof (TBaseClass).IsAssignableFrom(type);
}
}
public class DefaultLifetimeManagerStrategy : BuilderStrategy
{
public DefaultLifetimeManagerStrategy(LifetimeManagerFactory factory, Predicate<Type> typePredicate)
{
mFactory = factory;
mTypePredicate = typePredicate;
}
public override void PreBuildUp(IBuilderContext context)
{
if (context.Existing == null) {
var theLifetime = context.Policies.GetNoDefault<ILifetimePolicy>(context.BuildKey, false);
if (theLifetime == null && mTypePredicate(context.BuildKey.Type)) {
theLifetime = mFactory.CreateLifetimePolicy();
context.PersistentPolicies.Set(theLifetime, context.BuildKey);
}
}
}
private readonly LifetimeManagerFactory mFactory;
private readonly Predicate<Type> mTypePredicate;
}
/// <summary>
/// A Unity extension that prioritizes the default constructor for classes derived of Y when available, otherwise the default resolve method is used.
/// </summary>
public class IOCExtension : UnityContainerExtension
{
protected override void Initialize()
{
var theDefaultConstructorSelectorPolicy = Context.Policies.Get<IConstructorSelectorPolicy>(null);
Context.Policies.SetDefault<IConstructorSelectorPolicy>(new IOCConstructorSelectorPolicy(theDefaultConstructorSelectorPolicy));
}
public class IOCConstructorSelectorPolicy : IConstructorSelectorPolicy
{
public IOCConstructorSelectorPolicy(IConstructorSelectorPolicy defaultConstructorSelectorPolicy)
{
mDefaultConstructorSelectorPolicy = defaultConstructorSelectorPolicy;
}
public SelectedConstructor SelectConstructor(IBuilderContext context, IPolicyList resolverPolicyDestination)
{
Type theType = context.BuildKey.Type;
if (typeof(DataNode).IsAssignableFrom(theType)) {
ConstructorInfo theDefaultConstructorInfo = theType.GetConstructor(Type.EmptyTypes);
if (theDefaultConstructorInfo != null && theDefaultConstructorInfo.IsPublic) {
return new SelectedConstructor(theDefaultConstructorInfo);
}
}
return mDefaultConstructorSelectorPolicy.SelectConstructor(context, resolverPolicyDestination);
}
private readonly IConstructorSelectorPolicy mDefaultConstructorSelectorPolicy;
}
}
I have a xamarin forms app.
There are 2 classes with data, one of the pages is filling the data.
The problem is: I'm creating new view, that should use data from both classes.
The only way i'm familiar with is to set a class as a bindingContext to pass data between pages, and it's working fine with ONE class, because apparently there couldn't be 2 bindingContext at the same time.
EXAMPLE:
1st class (all the classes are filled on the previous page. just accept that they are filled)
public class Buildings : INotifyPropertyChanged
{
public event PropertyChangedEventHandler PropertyChanged;
private string _id;
public string Id
{
get { return _id; }
set
{
_id = value;
PropertyChanged?.Invoke(this, new PropertyChangedEventArgs("Id"));
}
}
}
2nd class
public class Flats : INotifyPropertyChanged
{
public event PropertyChangedEventHandler PropertyChanged;
private string _num;
public string Num
{
get { return _num; }
set
{
_num = value;
PropertyChanged?.Invoke(this, new PropertyChangedEventArgs("Num"));
}
}
}
new view:
public partial class HouseView
{
private Flats _flats;
private Buildings _buildings;
public HouseView()
{
InitializeComponent();
}
private void HouseView_OnBindingContextChanged(object sender, EventArgs e)
{
var building = BindingContext as Building;
//var flat = BindingContext as Flat;
//_flat = flat;
_building = building;
var buildingInfo = await Rest.GetHouseInfo(_building.Id, _flat.Num); //function that will return info on a current house;
// rest code
}
}
Maybe there is no need for binding context, because i'm just passing the parameters, not changing them in a view? I guess the solution can be pretty simple, and i cant figure it out....
What you are missing is understanding the concept of ViewModel, and it's relation with the views.. In this case what you need is a 3rd class (ViewModel) that handles your 2 previous class:
public class HouseViewModel : INotifyPropertyChanged
{
public Flats Flats { get; set; }
private Buildings Buildings { get; set; }
}
Also using OnBindingContextChanged is just messy and will take some performance from your app .. try to prepare your data before on your VM, so the view knows as little as possible in how to get/handle data.
There is simple way to transfer data between pages in Xamarin forms.
Add new class to the main project called Transporter.cs, and this class should be static.
Inside this class, add the variables to transfer data between other pages; then you can simply access any variable by using Transporter.Variable.
Example:
public static Transporter
{
public static string x;
}
> Now, in each page, you can simply access (set or get) the value:
Transporter.x=MyName.Text;
>In another page:
MySecondName.Text=Transporter.x;
Note: MyName is an entry field in the first page, and MySecondName is an entry field in the second page.
Also, you can define any type of variables like (Lists, int, object... etc).
I want to change my session proviced to statically typed - I just hate typing strings because of many many errors I do.
What technology am I using? ASP.NET MVC via EXT.NET MVC
I was trying to do that using web.config but the problem is that after add session state to it visual is not going to compile my code because of that session should be using strings as keys.
I want to use session by enums such as :
public enum SessionEnum{Model}
public class Bar{
void foo(){
Session[SessionEnum.Model] = "blah";
}
}
I am aware that I can create wrapper converting enums to strings but it's not very satisfying solution for me.
public class StorageWrapper{
public object this[SessionEnum enum]{ get{return Session[enum.toString()]}; //+set
}
What I did was create static object for base class for all of my controllers and then I was able to use it across them but after closing and opening the page again I wasn't able to get values from it. I guess I should serialize them somehow but I have no idea how.
Is there any way to do that?
EDIT
My session now looks like this :
[Serializable]
public abstract class DataWrapper<T> : HttpSessionStateBase
{
Dictionary<T, object> Dictionary { get; set; } = new Dictionary<T, object>();
public object this[T a]
{
get
{
try
{
return Dictionary[a];
}
catch
{
return null;
}
}
set { Dictionary[a] = value; }
}
}
[Serializable]
public class SessionWrapper : DataWrapper<SessionNames>
{}
public enum SessionNames { Model, Login, LastOpenedFile }
It's very simple.
Create a UserSession object which does everything you want (holds your values as enum etc), instantiate it, then put it in the session.
var US = new UserSession();
US.stuff = somestuff;
Session["UserSess"] = US
Then you can just always use Session["UserSess"].stuff;
Mmmm, wouldn't you use static const string instead of an enum?
using System.Web;
public static class SessionEnum
{
public static const string Model = "_Session_Model";
public static const string Login = "_Session_Login";
public static const string LastOpenedFile = "_Session_LastOpenedFile ";
}
class test
{
void test()
{
Session[SessionEnum.Model] = "blah";
}
}
suppose i have one static method and i need to access viewstate from that method...how could i do so...i know it is not possible but there must be some way out.
[WebMethod]
public static string GetData(int CustomerID)
{
string outputToReturn = "";
ViewState["MyVal"]="Hello";
return outputToReturn;
}
You can get the reference to the page via HttpContext.CurrentHandler. But since Control.ViewState is protected you can't access it (without using reflection) as opposed to the Session which is accessible via HttpContext.Current.Session.
So either don't use a static method, use the Session or use this reflection approach:
public static string CustomerId
{
get { return (string)GetCurrentPageViewState()["CustomerId"]; }
set { GetCurrentPageViewState()["CustomerId"] = value; }
}
public static System.Web.UI.StateBag GetCurrentPageViewState()
{
Page page = HttpContext.Current.Handler as Page;
var viewStateProp = page?.GetType().GetProperty("ViewState",
BindingFlags.FlattenHierarchy |
BindingFlags.Instance |
BindingFlags.NonPublic);
return (System.Web.UI.StateBag) viewStateProp?.GetValue(page);
}
However, this won't work if called via WebService, because then it's outside of Page-Lifecycle.
You might be able use [WebMethod(EnableSession=true)] for your PageMethod, and use Session instead of ViewState. Remember, with a static PageMethod no instance of the Page class is ever created, so nice things like ViewState simply are not there and there is no way to make them be there.
I tried this and worked for me:
Create a class conteining the properties of the viewState you want to access to
In the constructor pass the real ViewState
Create a static instance of the class but not initialize it
In the PageLoad initialize Not static class and the static one
Access the ViewState using static class properties
public class Repository
{
public int a
{
get
{
if (_viewState["a"] == null)
{
return null;
}
return (int)_viewState["a"];
}
set
{
_viewState["a"] = value;
}
}
public StateBag _viewState;
public Repository(StateBag viewState)
{
_viewState = viewState;
}
}
static Repository staticRepo;
protected void Page_Load(object sender, EventArgs e)
{
Repository repo = new Repository(ViewState);
staticRepo = repo;
}
public static void testMethod()
{
int b = staticRepo.a;
}