Dim.Auto Deep Dive

The Dim.Auto type is a type of Dim that automatically sizes the view based on its content. This is useful when you want to size a view based on the content it contains. That content can either be the Text, the SubViews, or something else defined by the view.

Like all Dim types, Dim.Auto is used to set the Width or Height of a view.

The DimAutoStyle enum defines the different ways that Dim.Auto can be used to size a view. The DimAutoStyle enum has the following values:

Text - The view is sized based on the Text property and TextFormatter settings.
Content - The view is sized based on either the ContentSize or the Subviews property. If ContentSize is null, the view is sized based on the size of the subviews (the Subview with the largest relvant dimension plus location will dictate the size). If ContentSize is not null, the view is sized based on the ContentSize property.
Auto - The view is sized based on both Text and Content, whichever is larger.

Using Dim.Auto

Dim.Auto is defined as:

public static Dim Auto (DimAutoStyle style = DimAutoStyle.Auto, Dim min = null, Dim max = null)

To use Dim.Auto, set the Width or Height property of a view to Dim.Auto (DimAutoStyle.Text) or Dim.Auto (DimAutoStyle.Content).

For example, to create a View that is sized based on the Text property, you can do this:

View view = new ()
{
    Text = "Hello, World!",
    Width = Dim.Auto (DimAutoStyle.Text),
    Height = Dim.Auto (DimAutoStyle.Text),
};

Note, the built-in Label view class does precisely this in its constructor.

To create a View that is sized based on its Subviews, you can do this:

View view = new ()
{
    Width = Dim.Auto (DimAutoStyle.Content),
    Height = Dim.Auto (DimAutoStyle.Content),
};
view.Add (new Label () { Text = "Hello, World!" });

In this example, the View will be sized based on the size of the Label that is added to it.

Specifying a miniumum size

You can specify a minimum size by passing a Dim object to the min parameter. For example, to create a View that is sized based on the Text property, but has a minimum width of 10 columns, you can do this:

View view = new ()
{
    Text = "Hello, World!",
    Width = Dim.Auto (DimAutoStyle.Text, min: Dim.Absolute (10)),
    Height = Dim.Auto (DimAutoStyle.Text),
};

Specifying a maximum size

NOT YET IMPLEMENTED

Limitations

Dim.Auto is not always the best choice for sizing a view. For example, if you want a view to fill the entire width of the Superview, you should use Dim.Fill () instead of Dim.Auto (DimAutoStyle.Content).

Dim.Auto is also not always the most efficient way to size a view. If you know the size of the content ahead of time, you can set the Width and Height properties to Dim.Absolute (n) instead of using Dim.Auto.

TODO: Verify accuracy of the following paragraphs

Some Pos and Dim types are not compatible with Dim.Auto. For example, you cannot use Dim.Auto (DimAutoStyle.Content) with Subviews that use Dim.Fill () or Dim.Percent (n) because the size of the Subview is not known until the layout is computed.

Pos types that are relative to the size of the view, such as Pos.Percent (n) are not compatible with Dim.Auto because the size of the view is not known until the layout is computed. However, Pos.Center () and Pos.AnchorEnd () are compatible with Dim.Auto because they are relative to the size of the view's Superview.

Building Dim.Auto friendly View

It is common to build View classes that have a natrual size based on their content. For example, the Label class is a view that is sized based on the Text property. Another example is Slider which is size based on the number of options it has, it's orientation, etc...

Developers using these views shouldn't need to know the details of how the view is sized, they should just be able to use the view and have it size itself correctly.

For example, a vertical Slider with 3 options may be created like this:

List<object> options = new () { "Option 1", "Option 2", "Option 3" };
Slider slider = new (options)
{
    Orientation = Orientation.Vertical,
    Type = SliderType.Multiple,
};
view.Add (slider);

Note the developer does not need to specify the size of the Slider, it will size itself based on the number of options and the orientation.

Views like Slider do this by setting Width and Height to Dim.Auto (DimAutoStyle.Content) in the constructor and and setting the ContentSize property to the size that the view should be in the LayoutStarted event handler.

Views that use Text for their content can just set Width and Height to Dim.Auto (DimAutoStyle.Text).

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