Windows Button

12y1.3kVisual Basic .NET

What is reason for if we move the Button button1 = new Button(); within the constructor. Program is not working. Problem is highlighted.

Why is it called button1 is a private field?

using System;
using System.Windows.Forms;
using System.Drawing;

public class WindowWithButton : Form
{
//Button button1 = new Button();

public WindowWithButton()
{
Button button1 = new Button();

this.Size = new Size(300, 300);

this.Text = "Window Object With Button";
button1.Text = "Press";

this.Controls.AddRange(new System.Windows.Forms.Control[] { this.button1 });

this.button1.Location = new Point(100, 50);
}

public static void Main()
{
Application.Run(new WindowWithButton());
}
}

5 Replies

Know the answer? Post it — somebody with the same question will find it here.

Vulpes12y ago
Accepted answer
If there's no 'this', the compiler first looks to see if there's a local variable or parameter called button1.

If there isn't, it then looks to see if there's a field or property called button1 and, if there is, it uses that.

If there had been both a field AND a local variable called button1, then the latter would have 'won'.
12y ago
Thank you for your explanation.
12y ago
Please explain the reason why button1.Text = "Press"; is working without 'this' even though Button button1 = new Button(); is outside the constructor method.
Vulpes12y ago
The reason why it's no longer working is because you're preceding button1 with 'this' in a couple of lines. The compiler is therefore still expecting button1 to be a field rather than a local variable.

If you remove 'this', where highlighted, it will work fine:

using System;
using System.Windows.Forms;
using System.Drawing;

public class WindowWithButton : Form
{
//Button button1 = new Button();

public WindowWithButton()
{
Button button1 = new Button();

this.Size = new Size(300, 300);

this.Text = "Window Object With Button";
button1.Text = "Press";

this.Controls.AddRange(new System.Windows.Forms.Control[] { button1 });

button1.Location = new Point(100, 50);
}

public static void Main()
{
Application.Run(new WindowWithButton());
}
}
Pradeep Shet12y ago
Hi,

Because object of button is with in the scope of Constructor.
-Object created with in the scope is local to the block. Once it is out of constructor it will forget the object.
- if you create the Button object out side the constructor, it is local to class and any methods or properties can access that object with in class.
- If you specify public access specifier then it is accessible to all inheriting class as well.

Hope this answered your query. If yes plz mark it answered. Thank you.