<ScrollViewer Width="300" Height="150" BorderBrush="Brown" BorderThickness="2" VerticalScrollBarVisibility="Auto" HorizontalScrollBarVisibility="Auto">
            <TextBlock x:Name="_txtb" Background="HotPink" TextWrapping="Wrap" Foreground="Wheat"/>
        </ScrollViewer>

_txtb.Text = "1\r\n7\r\n6\r\n5dsaadsfjhduhtndsadjdhsajhscadsadsadas哈哈哈你\r\n4\r\n3\r\n2\r\n1\r\n0\r\n1\r\n2";

        public MainWindow()
　　　　　{
            InitializeComponent();

            var outer = new ScrollViewer();
            outer.Background = Brushes.Gray;
            outer.Width = 300;
            outer.Height = 100;

            var inner = new TextBlock();
            inner.Background = Brushes.Orange;
            inner.Foreground = Brushes.White;
            inner.Width = 200;

            outer.Content = inner;
            outer.MaxHeight = 80;

            inner.Text = "1\r\n7\r\n6\r\n5dsaadsfjhduhtndsadjdhsajhscadsadsadas哈哈哈你\r\n4\r\n3\r\n2\r\n1\r\n0\r\n1\r\n2";

            // 此行用于文本内容根据设定宽度，当一行过长时自动换行
            // inner.TextWrapping = TextWrapping.Wrap;

            outer.VerticalScrollBarVisibility = ScrollBarVisibility.Auto;
            outer.HorizontalScrollBarVisibility = ScrollBarVisibility.Auto;

            // 此句慎用呀，此处主要为了在界面上显示出结果
            this.Content = outer;
        }