Always dispose a form

I'm pretty sure your conclusion (that not immediately deallocating your form was causing a memory leak) is incorrect. Perhaps you have another reference to your form or something like that that is causing it to stay around. Or maybe there is some funky event stuff you have hooked up that is keeping the references alive. The garbage collector should collect the form references just fine.

I just created a test application to see if I could reproduce the memory issue you were having, and I could not. Basically, the application showed the same form a hundred times in a row, with memory going up and down, not increasing. I created two forms... the main form with just one button on it. When that button is clicked, it initiates the logic to launch the second form 100 times in a row. The second form has several hundred controls on it (buttons/labels/textboxes), so it is consuming some memory. If you care to challenge my findings, here is the code for the first form:

C#

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

namespace DeleteMe_TestMemoryUsageFromForms
{
	// This form is in charge of showing the other form.
	public partial class Form1 : Form
	{
		public Form1()
		{
			InitializeComponent();
		}

		private void button1_Click(object sender, EventArgs e)
		{
			Thread t = new Thread(new ThreadStart(delegate()
			{
				// Show the other form 100 times.
				for (int i = 0; i < 100; i++)
				{
					this.Invoke(new ThreadStart(delegate()
					{
						(new TestForm()).ShowDialog();
					}));
				}
			}));
			t.Start();
		}
	}
}

Here is the code for the second form:

C#

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


namespace DeleteMe_TestMemoryUsageFromForms
{
	// This form has several hundred controls on it.
	public partial class TestForm : Form
	{
		Thread stopMe;

		public TestForm()
		{
			InitializeComponent();
			stopMe = new Thread(new ThreadStart(delegate()
			{
				// Wait 1/10th of a second, then close.
				System.Threading.Thread.Sleep(100);
				this.Invoke(new ThreadStart(delegate()
				{
					this.Close();
				}));
			}));
			stopMe.Start();
		}
	}
}

The first form just has a button on it and the second form has several hundred controls.

Visual Studio is an excellent GUIIDE.

One of the weaknesses in the design of .net is that an object that subscribes to events from another object and fails to explicitly unsubscribe from them will never fall out of scope as long as that object remains live. While a simple boring form might be garbage-collected if it goes out of scope, a more complex form may well attach some event hooks (including, ironically, the parent form's Disposing event handler); those hooks will not be released without a proper dispose, and will prevent garbage-collection from cleaning up the objects.

The content also seems a little light to be worth an article, though the point you make is certainly well-taken.

Actually, I think my preference is to have a form which is meant to be used as a dialog have a static/shared procedure which will take care of everything.

supercat9 wrote:
a little light to be worth an article

FYI, pretty sure the new Tips/Tricks section (in which this article is placed) is for "articles" just like this that are very small (too small to be a full blown article).

Visual Studio is an excellent GUIIDE.

Always dispose a form

License

Comments and Discussions