();
```
### StatisticsService Implementation
```csharp
using System.Linq;
using ViewInjectSample.Interfaces;
namespace ViewInjectSample.Model.Services
{
public class StatisticsService
{
private readonly IToDoItemRepository _toDoItemRepository;
public StatisticsService(IToDoItemRepository toDoItemRepository)
{
_toDoItemRepository = toDoItemRepository;
}
public int GetCount() => _toDoItemRepository.List().Count();
public int GetCompletedCount() =>
_toDoItemRepository.List().Count(x => x.IsDone);
public double GetAveragePriority()
{
var items = _toDoItemRepository.List();
if (items.Count() == 0) return 0.0;
return items.Average(x => x.Priority);
}
}
}
```
---
## Populating Lookup Data
### Vấn đề truyền thống
Rendering form với dropdown lists thường yêu cầu controller:
1. Request data access services cho mỗi tập options
2. Populate model hoặc ViewBag với các options
### Giải pháp: Inject Service vào View
```csharp
public class ProfileController : Controller
{
public IActionResult Index()
{
// Chỉ cần truyền profile instance
var profile = new Profile
{
Name = "Rick",
FavColor = "Blue",
Gender = "Male",
State = new State("Ohio", "OH")
};
return View(profile);
}
}
```
```cshtml
@using System.Threading.Tasks
@using ViewInjectSample.Model.Services
@model ViewInjectSample.Model.Profile
@inject ProfileOptionsService Options
Update Profile
Update Profile
Name: @Html.TextBoxFor(m => m.Name)
Gender: @Html.DropDownList("Gender",
Options.ListGenders().Select(g =>
new SelectListItem { Text = g, Value = g }))
State: @Html.DropDownListFor(m => m.State!.Code,
Options.ListStates().Select(s =>
new SelectListItem { Text = s.Name, Value = s.Code }))
Fav. Color: @Html.DropDownList("FavColor",
Options.ListColors().Select(c =>
new SelectListItem { Text = c, Value = c }))
```
### ProfileOptionsService
```csharp
namespace ViewInjectSample.Model.Services
{
public class ProfileOptionsService
{
public List ListGenders()
{
return new List() { "Female", "Male" };
}
public List ListStates()
{
return new List
{
new State("Alabama", "AL"),
new State("Alaska", "AK"),
new State("Ohio", "OH")
};
}
public List ListColors()
{
return new List() { "Blue", "Green", "Red", "Yellow" };
}
}
}
```
> **Lưu ý:** Unregistered type sẽ throw exception tại runtime vì service provider được query nội bộ qua `GetRequiredService`.
---
## Overriding Services
### Default Fields có sẵn
View có sẵn các default fields:
| Field | Mô tả |
| ----------- | --------------- |
| `Html` | HTML Helpers |
| `Component` | View Components |
| `Url` | URL Helpers |
### Override Html Helper
Sử dụng `@inject` để override default HTML Helpers với phiên bản custom:
```cshtml
@using System.Threading.Tasks
@using ViewInjectSample.Helpers
@inject MyHtmlHelper Html
My Helper
Test: @Html.Value
```
---
## So sánh: Controller DI vs View DI
```mermaid
flowchart TD
A["Dependency Injection"] --> B["Controller DI"]
A --> C["View DI (@inject)"]
B --> B1["✅ Controller nhận services"]
B1 --> B2["Business logic"]
C --> C1["✅ View nhận services"]
C1 --> C2["Localiztion"]
C1 --> C3["Lookup data"]
C1 --> C4["Statistics"]
```
| Tiêu chí | Controller DI | View DI (@inject) |
| --------------- | --------------------------- | ---------------------- |
| **Mục đích** | Business logic, data access | View-specific services |
| **Cú pháp** | Constructor injection | `@inject` directive |
| **Testability** | Cao | Thấp hơn |
| **Khuyến nghị** | ✅ Ưu tiên dùng | Hạn chế, chỉ khi cần |
---
## Tài liệu tham khảo
- [Dependency injection into controllers](https://learn.microsoft.com/en-us/aspnet/core/mvc/controllers/dependency-injection)
- [Configuration in ASP.NET Core](https://learn.microsoft.com/en-us/aspnet/core/fundamentals/configuration)
- [Views in ASP.NET Core MVC](https://learn.microsoft.com/en-us/aspnet/core/mvc/views/overview)
- [Getting Lookup Data Into Your View](https://blog.simontimms.com/2015/06/09/getting-lookup-data-into-you-view/)