Note this PR should not be merged until after #600 is in.
I went on a rampage tonight. It all started with wanting to use more/better characters for frame and other UI elements like the round corners:
I decided I needed a character map app that would let me test which fonts had which Unicode sets in them.
As a result we have this PR
- Fixes `ScrollView` in several key ways:
- It now supports Computed layout and has constructors that don't require parameters.
- `ScrollBarViews` are now positioned using Computed layout versus error prone absoulte
- `ScrollBarViews` now correctly position themselves when one, either, or both are on/off.
- `IsVertical` is now a public property that does the expected thing when changed
- Mouse handling is better; there's still a bug where the mouse doesn't get grabbed by the `ScrollView` initially but I think this is a broader problem. I need @BDisp's help on this.
- The `Scrolling` Scenario was enhanced to demo dynamically adding/removing horizontal/vertical scrollbars (and to prove it was working right).
- I Enabled easy "infinite scroll capability" - CharMap literally lets you scroll over `int.MaxValue / 16` rows of data. Filling a `ContentView` with all of this and panning it around won't work. So I needed a way of having `Redraw` give me virtual coordinates. I did this by defining `OnDrawContent(Rect viewport)` and it's associated `event`:
```csharp
/// <summary>
/// Event invoked when the content area of the View is to be drawn.
/// </summary>
/// <remarks>
/// <para>
/// Will be invoked before any subviews added with <see cref="Add(View)"/> have been drawn.
/// </para>
/// <para>
/// Rect provides the view-relative rectangle describing the currently visible viewport into the <see cref="View"/>.
/// </para>
/// </remarks>
public event EventHandler<Rect> DrawContent;
/// <summary>
/// Enables overrides to draw infinitely scrolled content and/or a background behind added controls.
/// </summary>
/// <param name="viewport">The view-relative rectangle describing the currently visible viewport into the <see cref="View"/></param>
/// <remarks>
/// This method will be called before any subviews added with <see cref="Add(View)"/> have been drawn.
/// </remarks>
public virtual void OnDrawContent (Rect viewport)
{
DrawContent?.Invoke (this, viewport);
}
```
I originally just implemented this pattern in `ScrollView`. Then I realized I wanted the same thing out of ALL `Views`. Namely: the ability to do drawing on an event, particularly to be able to paint something in the background. So I added it to `View`.
Note, that these changes mean we are about 3 small steps away from moving the scollbars from `ScrollView` into ALL views. Which makes a lot of sense to me because I don't think we want to implement duplicative logic in, say `ListView` and `TextView` as well. Why not just do it once?
Along the way I fixed some other things:
- The `Checkbox.Toggled` event now passes state.
Here's some gifs.
Note:
- Scrollbars appear dynamically.
- Fast scrolling of huge data (using no memory).
- Static header
- Dynamic scrollbars on/off
- Note the bottom/right corner now draw correctly in all situations
