Submission: SegmentControl for Xamarin.Forms.Labs

The Klickle Development Team would like to submit to the Xamarin Forms Labs project an implementation of control that mimics the IOS UISegmentControl. The license would be the Lab's license of Apache 2.0. The source code is posted in the forums in case anyone wishes to just use this implementation.

**Usage:
**

var s = new SegmentControl();
        s.TintColor = Color.Green;
        s.AddSegment("Green");
        s.AddSegment("Yellow");
        s.AddSegment("Red");
        s.SelectedSegmentChanged += (object sender, int segmentIndex)=>{
            if (segmentIndex == 0)
                s.TintColor = Color.Green;
            else if (segmentIndex == 1)
                s.TintColor = Color.Yellow;
            else if (segmentIndex == 2)
                s.TintColor = Color.Red;
        };
        s.SelectedSegment = 1;

The source code for the control requires no platform specific renderers (at least for Android / IOS):

    /*
    Copyright 2014 Klickle LLC (www.klickle.com)

    Licensed under the Apache License, Version 2.0 (the "License");
    you may not use this file except in compliance with the License.
    You may obtain a copy of the License at

        http://www.apache.org/licenses/LICENSE-2.0

    Unless required by applicable law or agreed to in writing, software
    distributed under the License is distributed on an "AS IS" BASIS,
    WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
    See the License for the specific language governing permissions and
    limitations under the License.*/

public class SegmentControl: ContentView
{
    private StackLayout _layout;

    private Color _tintColor = Color.Black;
    public Color TintColor { get { return _tintColor; } 
        set { _tintColor = value;
            if (_layout == null)
                return;
            _layout.BackgroundColor = _tintColor;

            for (int iBtn = 0; iBtn < _layout.Children.Count; iBtn++) {
                setSelectedState (iBtn, iBtn == _selectedSegment,true);
            }
        }
    }

    public SegmentControl():base()
    {
        HorizontalOptions = LayoutOptions.FillAndExpand;
        VerticalOptions = LayoutOptions.Start;
        _layout = new StackLayout () {
            HorizontalOptions = LayoutOptions.FillAndExpand,
            Orientation = StackOrientation.Horizontal,
            Padding = new Thickness(1),
            Spacing = 1
        };
        Padding = new Thickness (0, 0);
        _selectedSegment = 0;
        Content = _layout;
        _clickedCommand = new Command(setSelectedSegment);

    }

    public void AddSegment(string segmentText)
    {
        Button b = new Button () {
            HorizontalOptions = LayoutOptions.FillAndExpand,
            BorderColor = TintColor,
            BorderRadius = 0,
            BorderWidth = 0,
            Text = segmentText,
            TextColor = TintColor,
            BackgroundColor = Color.White,
            Command = _clickedCommand,
        };
        b.CommandParameter = _layout.Children.Count;
        _layout.BackgroundColor = TintColor;
        _layout.Children.Add (b);
        setSelectedState (_layout.Children.Count - 1, _layout.Children.Count - 1 == _selectedSegment);
    }

    public event EventHandler<int> SelectedSegmentChanged;

    private Command _clickedCommand ;
    private void setSelectedSegment(object o)
    {
        int selectedIndex = (int)o;
        SelectedSegment = selectedIndex;
        if (SelectedSegmentChanged != null)
            SelectedSegmentChanged (this, selectedIndex);
    }

    public void SetSegmentText(int iSegment, string segmentText)
    {
        if (iSegment >= _layout.Children.Count || iSegment < 0)
            throw new IndexOutOfRangeException ("SetSegmentText: Attempted to change segment text for a segment doesn't exist.");

        ((Button)_layout.Children [iSegment]).Text = segmentText;
    }

    private int _selectedSegment = 0;
    public int SelectedSegment {
        get{ 
            return _selectedSegment;
        }
        set{ 
            //reset the original selected segment
            if (value == _selectedSegment)
                return;

            setSelectedState (_selectedSegment, false);
            _selectedSegment = value;
            if (value < 0 || value >= _layout.Children.Count)
                return;
            setSelectedState (_selectedSegment, true);

        }
    }

    private void setSelectedState(int indexer,bool isSelected, bool setBorderColor = false)
    {
        if (_layout.Children.Count <= indexer)
            return; //Out of bounds

        Button vw = (Button) _layout.Children [indexer];
        if (isSelected) {
            vw.BackgroundColor = TintColor;
            vw.TextColor = Color.White;
        } else {
            vw.BackgroundColor = Color.White;
            vw.TextColor = TintColor;
        }
        if (setBorderColor)
            vw.BorderColor = TintColor;

    }
}