<Window x:Class="TestOxyPlot.MainWindow"
            xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
            xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
            xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
            xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
            xmlns:oxy="http://oxyplot.org/wpf"
            xmlns:local="clr-namespace:TestOxyPlot"
            mc:Ignorable="d"
            Title="MainWindow" Height="350" Width="525">
        <Grid>
            <oxy:Plot x:Name="oxyPlot" Title="{Binding Title}" Margin="207,53,0,0">
                <oxy:Plot.Series>
                    <oxy:LineSeries ItemsSource="{Binding Points}"/>
                </oxy:Plot.Series>
            </oxy:Plot>
            <TextBox x:Name="textBox" HorizontalAlignment="Left" Height="23" Margin="44,64,0,0" TextWrapping="Wrap" VerticalAlignment="Top" Width="120" MouseLeave="textBox_MouseLeave" TextChanged="textBox_TextChanged"/>
            <TextBox x:Name="textBox1" HorizontalAlignment="Left" Height="23" Margin="44,101,0,0" TextWrapping="Wrap" VerticalAlignment="Top" Width="120" TextChanged="textBox1_TextChanged"/>
            <Button x:Name="button" Content="Button" HorizontalAlignment="Left" Margin="68,174,0,0" VerticalAlignment="Top" Width="75" Click="button_Click"/>
        </Grid>
    </Window>

using System;
    using System.Collections.Generic;
    using System.Linq;
    using System.Text;
    using System.Threading.Tasks;
    using System.Windows;
    using System.Windows.Controls;
    using System.Windows.Data;
    using System.Windows.Documents;
    using System.Windows.Input;
    using System.Windows.Media;
    using System.Windows.Media.Imaging;
    using System.Windows.Navigation;
    using System.Windows.Shapes;
    using OxyPlot;

    namespace TestOxyPlot
    {
        /// <summary>
        /// Interaktionslogik für MainWindow.xaml
        /// </summary>
        public partial class MainWindow : Window
        {
            public MainWindow()
            {
                InitializeComponent();
                this.Title = "Example 2";
                this.Points = new List<DataPoint>
                    {
                                      new DataPoint(0, 4),
                                      new DataPoint(10, 13),
                                      new DataPoint(20, 15),
                                      new DataPoint(30, 16),
                                      new DataPoint(40, 12),
                                      new DataPoint(50, 12)
                                  };


            }
            public string Title { get; private set; }

            public IList<DataPoint> Points { get; private set; }

            private void textBox_MouseLeave(object sender, MouseEventArgs e)
            {


           }

            private void textBox_TextChanged(object sender, TextChangedEventArgs e)
            {
                try
                {
                    oxyPlot.Width = Int32.Parse(textBox.Text);
                }
                catch (Exception error)
                {
                    MessageBox.Show("Message: " + error);
                }

            }

            private void button_Click(object sender, RoutedEventArgs e)
            {

            }

            private void textBox1_TextChanged(object sender, TextChangedEventArgs e)
            {
                try
                {
                    oxyPlot.Width = Int32.Parse(textBox.Text);
                }
                catch (Exception error)
                {
                    MessageBox.Show("Message: " + error);
                }
            }
        }
    }