.NET Core依赖注入构造传参后Razor组件空引用异常求助

Root Causes #

• The [Inject] property is private, so Blazor's DI system can't set its value via reflection.
• You're calling myService.DoWork() in the component constructor, which runs before Blazor injects dependencies into the component.

Step-by-Step Fixes #

1. Correct the Injected Property Accessibility #

Blazor requires public properties for dependency injection. Update your component code to make the property public:

[Inject]
public MyService MyService { get; set; }

(PascalCase is standard for public properties, but the critical change is adding the public modifier.)

2. Move Service Usage to a Lifecycle Method #

Use Blazor's OnInitialized or OnInitializedAsync methods—these run after dependencies are injected, making it safe to call service methods:

public WeatherForecast()
{
    // Avoid service calls here
}

protected override void OnInitialized()
{
    MyService.DoWork(); // Service is now properly injected
}

If DoWork is asynchronous, use the async lifecycle method:

protected override async Task OnInitializedAsync()
{
    await MyService.DoWorkAsync();
}

3. Improve Service Registration (Optional but Recommended) #

Instead of directly instantiating MyService, use a factory function to resolve dependencies (like configuration) through the service provider. This is more flexible if your service needs other dependencies later:

// Retrieve service address from configuration (e.g., appsettings.json)
var serviceAddress = builder.Configuration["ServiceAddress"];

// Register the service with a factory
builder.Services.AddSingleton<MyService>(sp => 
{
    // Resolve other required services here using sp.GetRequiredService<T>() if needed
    return new MyService(serviceAddress);
});

Verification #

After applying these changes:

• Confirm serviceAddress is correctly populated in Program.cs (check your configuration if using appsettings).
• Run the app again—the NullReferenceException should be resolved.

内容的提问来源于stack exchange，提问作者Cal