Windows Button

Question

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());
}
}

Vulpes · 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'.

Maha · Answer

Thank you for your explanation.

Maha · Answer

Please explain the reason why button1.Text = Press ; is working without ' this' even though Button button1 = new Button (); is outside the constructor method.

Vulpes · Answer

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 Shet · Answer

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.