Changing opacity in form with trackbar in C# don't works, why?

Question

I have (for fun) make a form in C#, with a trackbar. I want to change the Opacity of the form with it, so I wrote this:

private void trackBar1_Scroll(object sender, EventArgs e)
{
    progressBar1.Value = trackBar1.Value;
    System.Windows.Forms.Form.ActiveForm.Opacity = trackBar1.Value;
    label2.Text = trackBar1.Value.ToString();
}

When I start the program, the opacity will be 100% if the trackbar is in value 1 to 100, and if i drag the trackbar to 0, the form becomes fully transparant.

can you only get 100% Opacity or 0% Opacity when a form is started, or is what i want also possible?

I think opacity is a value between 0 and 1. – wgraham Aug 20 '13 at 19:10 — wgraham, Aug 20 '13 at 19:10

score 4 · Accepted Answer · answered Aug 20 '13 at 19:11

4

Use this:

System.Windows.Forms.Form.ActiveForm.Opacity = ((double)(trackBar1.Value) /100.0)

You can have different degrees of opacity. For example 0.5 will give you 50% opacity.

answered Aug 20 '13 at 19:11

AlexDev

4,049
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King King · Answer 2 · 2013-08-20T19:38:44.780

4

The value of System.Windows.Forms.Form.Opacity is between 0.0 and 1.0, to get the percentage of the opacity you can multiply it with 100, so 1 means fully opaque and 0 means fully transparent.

For the trackbar, you should convert its Value to the corresponding value between 0.0 and 1.0, so you should do something like this:

yourForm.Opacity = (double)trackBar1.Value/trackBar1.Maximum;

edited Aug 20 '13 at 19:38

answered Aug 20 '13 at 19:17

King King

61,710
16
105
130

score 3 · Answer 3 · answered Aug 20 '13 at 19:10

3

Divide the number by 100. It should be a double between 0 and 1

((double)trackBar1.Value) / 100

answered Aug 20 '13 at 19:10

Jonesopolis

25,034
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Slight correction: opacity should be a `double` not a `decimal`. See: http://msdn.microsoft.com/en-us/library/system.windows.forms.form.opacity.aspx – wgraham Aug 20 '13 at 19:11
Can't it be between 0 and 100? or is there just a "TRANSPARANT" or "NOT TRANSPARANT" – Thijmen Minecraft Aug 20 '13 at 19:11
it is between 0 and 100, it's just a percentage - 25% = .25 – Jonesopolis Aug 20 '13 at 19:12
Or did you mean `System.Windows.Forms.Form.ActiveForm.Opacity = trackBar1.Value/100;` ? That don't work also by the way. – Thijmen Minecraft Aug 20 '13 at 19:14
that line should be exactly as AlexDev's answer has it – Jonesopolis Aug 20 '13 at 19:15

score -1 · Answer 4 · answered May 20 '21 at 12:42

-1

private void trackBar1_Scroll(object sender, EventArgs e) { label1.Text =trackBar1.Value.ToString()+ "%";

        Opacity=trackBar1.Value / 100.00;
        
    }

answered May 20 '21 at 12:42

Oussama Essabi

1

1

a bit more explanation of your solution would be great, in that case it's simply because opacity is a value between 0 and 1. – TinoZ May 20 '21 at 12:54

Changing opacity in form with trackbar in C# don't works, why?

4 Answers4