Problem with on Initialize() method

Question

User887623398 posted

Hello,

I'm trying to learn blazor from a tutorial.

When I write this statement in may page:

protected override void OnInit()
{
    customers = customerManager.SelectAll();
}

and after that explains:

You are basically overriding OnInit() method of ComponentBase class (Blazor components inherit from ComponentBase class). Inside, you call SelectAll() method and store the return value into customers member.

I see red lines under OnInit( ) method. And visual studio suggests OnInitialize().

Is this method correct? So what are these red lines?

Should I add specific name space?

Saeed

Answer 1

User753101303 posted

Hi,

Try OnInitialized instead. The tutorial you are using is based on an older preview version.

Answer 2

User887623398 posted

All code cames here:

public class Customer
{
    [Key]
    [Required]
    [StringLength(5, MinimumLength = 5)]
    public string CustomerID { get; set; }

    [Required]
    [StringLength(30)]
    public string CompanyName { get; set; }

    [Required]
    [StringLength(30)]
    public string ContactName { get; set; }

    [Required]
    [StringLength(15)]
    public string Country { get; set; }

}

public class AppDbContext:DbContext
{

    public AppDbContext(
DbContextOptions<AppDbContext> options) : 
base(options)
    {

    }
    public DbSet<Customer> Customers { get; set; }
}

public class CustomerManager
{
    private AppDbContext db;

    public CustomerManager(AppDbContext db)
    {
        this.db = db;
    }

    public List<Customer> SelectAll()
    {
        return db.Customers.ToList();
    }

    public Customer SelectByID(string id)
    {
        return db.Customers.Find(id);
    }

    public string Update(Customer obj)
    {
        db.Update(obj);
        db.SaveChanges();
        return "Success!";
    }
}

Answer 3

User753101303 posted

I meant

protected override void OnInitialized() // was OnInit in an early preview and the name was changed since then
{
    customers = customerManager.SelectAll();
}

From https://devblogs.microsoft.com/aspnet/asp-net-core-and-blazor-updates-in-net-core-3-0-preview-8/ : "In Razor components rename OnInit to OnInitialized and OnInitAsync to OnInitializedAsync"

Not sure if the turorial mention the exact version but it is outdated. I often prefer to favor the official documentation https://docs.microsoft.com/en-us/aspnet/core/tutorials/build-your-first-blazor-app?view=aspnetcore-3.1 and using tutorials with caution especially if no version at all is mentioned.