如何为静态类中的静态对象的属性赋值？

Question

I have this assignment:

Counts.btnCountViewsAvg.BtnCount = 123;

Here are the classes that I use:

public static class Counts
{
    public static BtnCountViews btnCountViewsAvg;
}

public class BtnCountViews // this class used in many places
{
    public int BtnCount { get; set; }
    public int Views { get; set; }
}

What I would like to do is to assign 123 to BtnCount but it says cannot assign to a null. When I check the btnCountViewsAvg is null. I used static as I only want to have one Counts class in the application.

Can someone give me some advice on how I can assign a value to Counts.btnCountViewsAvg.BtnCount

Answer 1

It is your Counts.btnCountViewsAvg that is null. You need to instantiate that before being able to set the BtnCount property.

To instantiate the value you need to do the following:

Counts.btnCountViewsAvg = new BtwCountViews();

Furthermore you could instantiate using the object initialiser it like so:

Counts.btnCountViewsAvg = new BtwCountViews { BtnCount = 123 };

In order to ensure that btnCountViewsAvg is only created once you could do the following:

public static class Counts
{
    public readonly static BtnCountViews btnCountViewsAvg = new BtnCountViews();
}

Or to follow on from Jon Skeets suggestion with using a property rather than a public field this would be a better approach:

public static class Counts
{
    public static ButtonCountViews ButtonCountViewsAvg { get; } = new ButtonCountViews();
}

Note I renamed your class to remove the abbreviation.

Answer 2

You have two options:

• Create new object only once

   public static class Counts { public static BtnCountViews btnCountViewsAvg = new BtnCountViews(); } 

• Or create it every time you need it:

   Counts.btnCountViewsAvg = new BtnCountViews() { BtnCount = 123 }; 

Answer 3

You, probably, want something like this: create an instance of BtnCountViews with BtnCount = 123 and assign it to static field:

public static class Counts
{
    // we create a instance: new btnCountViewsAvg() 
    // then we set up a property of this instance: { BtnCount = 123, }
    public static BtnCountViews btnCountViewsAvg = new btnCountViewsAvg() {
      BtnCount = 123,
    };
}