想讓TextBox的高度自動適應內容

通過設定附加屬性attach:TextBoxAttach.AutoHeight和TextBlock.LineHeight

<TextBox VerticalContentAlignment="Top" 
    attach:TextBoxAttach.AutoHeight="True"
    AcceptsReturn="True"
    Text="{Binding Model.Content}"
    TextBlock.LineHeight="20" 
    TextWrapping="Wrap"
    VerticalScrollBarVisibility="Visible" />
 

1. 監聽AutoHeight屬性的變化，當設定為True時，如果物件是textBox，就監聽TextBox的Loaded,Unloaded,TextChanged
2. 當控制元件還沒Loaded的時候，是無法獲取實際行數的
3. 在Unloaded事件中取消所有事件的註冊
4. 控制元件高度的改變就是很簡單的事情了，獲取實際的行數和配置的行高，直接設定控制元件高度即可
5. 有一個問題：當前是在TextChanged中，每次變更都是計算設定控制元件高度，如果可以監控到行高的變化的話，應該合理一點

public class TextBoxAttach
    {
        public static bool GetAutoHeight(DependencyObject obj)
        {
            return (bool)obj.GetValue(AutoHeightProperty);
        }
        public static void SetAutoHeight(DependencyObject obj, bool value)
        {
            obj.SetValue(AutoHeightProperty, value);
        }
        public static readonly DependencyProperty AutoHeightProperty =
            DependencyProperty.RegisterAttached("AutoHeight", typeof(bool), typeof(TextBoxAttach), new PropertyMetadata(false, OnChanged));

        private static void OnChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
        {
            if (!(d is TextBox textBox))
            {
                return;
            }
            if (textBox != null)
            {
                textBox.Loaded += TextBox_Loaded;
                textBox.Unloaded += TextBox_Unloaded;
                textBox.TextChanged += TextBox_TextChanged;
            }
        }
        private static void TextBox_Unloaded(object sender, RoutedEventArgs e)
        {
            var c = sender as TextBox;
            c.Unloaded -= TextBox_Unloaded;
            c.Loaded -= TextBox_Loaded;
            c.TextChanged -= TextBox_TextChanged;
        }
        private static void TextBox_Loaded(object sender, RoutedEventArgs e)
        {
            var c = sender as TextBox;
            ReSize(c);
        }
        private static void TextBox_TextChanged(object sender, TextChangedEventArgs e)
        {
            var c = sender as TextBox;
            if (c.IsLoaded)
                ReSize(c);
        }
        private static void ReSize(TextBox textBox)
        {
            var lines = textBox.LineCount;
            var lineHeight = (double)textBox.GetValue(TextBlock.LineHeightProperty);
            double height = lineHeight * lines;
            textBox.Height = height;
        }
    }