为什么我无法从其他文件访问表单属性？

Question

I'm very new to C# and I couldn't figure out reaching variables, form properties and some other methods that reside in one file, from another file. I feel like, this should be as simple as an #include directive, but couldn't find a way.

This is the code in file Form1.cs created by auto when I create a new Windows Form app in VS. I can reach class definitions that reside in another file named Class1.cs ; no problem here:

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows.Forms;

namespace reach_test {
    public partial class Form1 : Form {
        public Form1() {
            InitializeComponent();
        }
        private void Form1_Load(object sender, EventArgs e) {
            Class1 formName = new Class1(); // this line compiles OK.
            formName.someMethod();          // this line compiles OK.
            this.Text = "Some Header";      // this line compiles OK.
        }
    }
}

And this is the code in Class1.cs file, which I added after. I can not reach, for example, Form1.Text property, which reside in file Form1.cs :

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace reach_test {
    public class Class1 {
        public string myText;
        public Class1() {
            myText = "Windows Header";
        }
        public void someMethod() {
            Form1.Text = myText; // this line does not compile!
        }
    }
}

Error message is: An object reference is required for the non-static field, method, or property 'System.Windows.Forms.Control.Text.get'

Answer 1

According to your code Form1 is a class name and so static properties only can be accesses in such a manner. Text property is not declared as being static , that's why you have to create an instance :

  Form1 myForm = new Form1(); // <- myForm is an instance of Form1 class

  myForm.Text = myText;

  // Probably, you want to do it as well...
  myFrom.Show();

Answer 2

When you say

    Form1.Text = myText; // this line does not compile!

You are trying to Call ClassName.PropertyName in your Class1 which is wrong, because it should be InstanceName.PropertyName . More over you don't have access to Form1's instance from your Class1.

The best thing you can do is

public class Class1 {
    public string myText;
    public Class1() {
        myText = "Windows Header";
    }
}
private void Form1_Load(object sender, EventArgs e) {
    Class1 formName = new Class1(); 
    this.Text = formName.myText;     
}

If you really want to set the Form1.Text within Class1 then you should pass your Form1's instance to Class1 like below.

public class Class1 {
    private string _myText;
    private Form _form1;
    public Class1(Form form1) {
        _myText = "Windows Header";
        _form1 = form1;
    }
    public DoSomething(){
        _form1.Text = _myText;
    }
}
private void Form1_Load(object sender, EventArgs e) {
    Class1 formName = new Class1(); 
    formName.DoSomething();     
}

Answer 3

In C# Windows Form application each Forms is a class, if you want to access Form's property you must create an object like this:

 Form1 myForm = new Form1();
myForm.Show()

then set public property

  myForm.Text = "My text";

But i advice change you'r code to this:

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace reach_test {
    public class Class1 {
        public string myText;
        public Class1() {
            myText = "Windows Header";
        }
        public string someMethod() {
           return myText; 
        }
    }
}

then set Form1.Text :

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows.Forms;

namespace reach_test {
    public partial class Form1 : Form {
        public Form1() {
            InitializeComponent();
        }
        private void Form1_Load(object sender, EventArgs e) {
            Class1 formName = new Class1(); // this line compiles OK.
           this.text= formName.someMethod();          // this line compiles OK.
        }
    }
}