Windows 8 键盘上推自定义处理

　　在Windows 8 应用程序中，当TextBox控件获得焦点时，输入面板会弹出，如果TextBox控件处于页面下半部分，则系统会将页面上推是的TextBox不被输入面板盖住，但是当TextBox是在FlipView控件中时，系统不会将页面上推，所以这种情况下输入框被输入面板盖住。具体原因不清楚，不知道是不是系统bug。

　　当输入面板弹出，页面上推的操作可以通过监听InputPane的Showing和Hiding事件来处理，既然当TextBox在FlipView控件时，系统没有很好的处理页面上推，那么开发者可以通过监听InputPane的事件来自己处理上推操作。

　　Windows 8 的一个实例代码Responding to the appearance of the on-screen keyboard sample中介绍了如果监听处理InputPane的相关操作，参考此实例以FlipView中的TextBox控件为例并对实例代码进行简化处理。

　　实例中的InputPaneHelper是对InputPane的事件处理的封装，直接拿来使用，InputPaneHelper代码如下：

using System;
using System.Collections.Generic;
using Windows.UI.ViewManagement;
using Windows.UI.Xaml;
using Windows.Foundation;
using Windows.UI.Xaml.Media.Animation;

namespace HuiZhang212.Keyboard
{
    public delegate void InputPaneShowingHandler(object sender, InputPaneVisibilityEventArgs e);
    public delegate void InputPaneHidingHandler(InputPane input, InputPaneVisibilityEventArgs e);
    public class InputPaneHelper
    {
        private Dictionary<UIElement, InputPaneShowingHandler> handlerMap;
        private UIElement lastFocusedElement = null;
        private InputPaneHidingHandler hidingHandlerDelegate = null;

        public InputPaneHelper()
        {
            handlerMap = new Dictionary<UIElement, InputPaneShowingHandler>();
        }

        public void SubscribeToKeyboard(bool subscribe)
        {
            InputPane input = InputPane.GetForCurrentView();
            if (subscribe)
            {
                input.Showing += ShowingHandler;
                input.Hiding += HidingHandler;
            }
            else
            {
                input.Showing -= ShowingHandler;
                input.Hiding -= HidingHandler;
            }
        }

        public void AddShowingHandler(UIElement element, InputPaneShowingHandler handler)
        {
            if (handlerMap.ContainsKey(element))
            {
                throw new System.Exception("A handler is already registered!");
            }
            else
            {
                handlerMap.Add(element, handler);
                element.GotFocus += GotFocusHandler;
                element.LostFocus += LostFocusHandler;
            }
        }

        private void GotFocusHandler(object sender, RoutedEventArgs e)
        {
            lastFocusedElement = (UIElement)sender;
        }

        private void LostFocusHandler(object sender, RoutedEventArgs e)
        {
            if (lastFocusedElement == (UIElement)sender)
            {
                lastFocusedElement = null;
            }
        }

        private void ShowingHandler(InputPane sender, InputPaneVisibilityEventArgs e)
        {
            if (lastFocusedElement != null && handlerMap.Count > 0)
            {
                handlerMap[lastFocusedElement](lastFocusedElement, e);
            }
            lastFocusedElement = null;
        }

        private void HidingHandler(InputPane sender, InputPaneVisibilityEventArgs e)
        {
            if (hidingHandlerDelegate != null)
            {
                hidingHandlerDelegate(sender, e);
            }
            lastFocusedElement = null;
        }

        public void SetHidingHandler(InputPaneHidingHandler handler)
        {
            this.hidingHandlerDelegate = handler;
        }

        public void RemoveShowingHandler(UIElement element)
        {
            handlerMap.Remove(element);
            element.GotFocus -= GotFocusHandler;
            element.LostFocus -= LostFocusHandler;
        }
    }
}

　　InputPaneHelper代码比较容易理解，简单的说就是用一个Hash表存储所有需要监听处理键盘上推事件的UIElement（一般情况下应该是TextBox控件），并且通过监听UIElement的焦点事件来判断弹出输入面板是通过那个UIElement触发的，并且通过监听InputPane的Showing和Hiding事件来对键盘上推进行处理。

　　测试页面KeyboardPage.xaml代码如下：

<Page
    x:Class="HuiZhang212.Keyboard.KeyboardPage"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    xmlns:local="using:HuiZhang212.Keyboard"
    xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
    xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
    mc:Ignorable="d">

    <!--键盘上推和隐藏动画-->
    <Page.Resources>
        <Storyboard x:Name="MoveMiddleOnShowing">
            <DoubleAnimationUsingKeyFrames Duration="0:0:0.733" Storyboard.TargetName="MiddleTranslate" Storyboard.TargetProperty="Y">
                <SplineDoubleKeyFrame x:Name="ShowingMoveSpline" KeyTime="0:0:0.733" KeySpline="0.10,0.90, 0.20,1">
                </SplineDoubleKeyFrame>
            </DoubleAnimationUsingKeyFrames>
        </Storyboard>

        <Storyboard x:Name="MoveMiddleOnHiding">
            <DoubleAnimationUsingKeyFrames Duration="0:0:0.367" Storyboard.TargetName="MiddleTranslate" Storyboard.TargetProperty="Y">
                <SplineDoubleKeyFrame KeyTime="0:0:0.367" KeySpline="0.10,0.90, 0.20,1" Value="0">
                </SplineDoubleKeyFrame>
            </DoubleAnimationUsingKeyFrames>
        </Storyboard>
    </Page.Resources>

    <Grid x:Name="LayoutRoot" Background="{StaticResource ApplicationPageBackgroundThemeBrush}">
        <Grid.RenderTransform>
            <TranslateTransform x:Name="MiddleTranslate" />
        </Grid.RenderTransform>
        <Grid Background="{StaticResource ApplicationPageBackgroundThemeBrush}">
            <FlipView Margin="100">
                <FlipViewItem Background="Yellow">
                    <TextBox  Text="自定义监听键盘上推事件" Name="textbox0"  Foreground="Black" VerticalAlignment="Bottom"  Width="300"/>
                </FlipViewItem>
                <FlipViewItem Background="Blue">
                    <TextBox  Text="系统处理键盘上推事件" Name="textbox1"  Foreground="Black" VerticalAlignment="Bottom"  Width="300"/>
                </FlipViewItem>
                <FlipViewItem Background="Green">
                    <TextBox  Text="自定义监听键盘上推事件" Name="textbox2" Foreground="Black" VerticalAlignment="Top"  Width="300"/>
                </FlipViewItem>
            </FlipView>
        </Grid>
    </Grid>
</Page>

　　MoveMiddleOnShowing和MoveMiddleOnHiding分别是定义的键盘上推和隐藏时的动画，此动画作用在Grid上，当输入面板显示和隐藏时对Grid做此两种动画偏远而达到键盘上推的效果。

　　测试代码KeyboardPage.xaml.cs如下：

using System;
using System.Collections.Generic;
using System.IO;
using System.Linq;
using Windows.Foundation;
using Windows.Foundation.Collections;
using Windows.UI.ViewManagement;
using Windows.UI.Xaml;
using Windows.UI.Xaml.Controls;
using Windows.UI.Xaml.Controls.Primitives;
using Windows.UI.Xaml.Data;
using Windows.UI.Xaml.Input;
using Windows.UI.Xaml.Media;
using Windows.UI.Xaml.Navigation;

// “空白页”项模板在 http://go.microsoft.com/fwlink/?LinkId=234238 上有介绍

namespace HuiZhang212.Keyboard
{
    /// <summary>
    /// 可用于自身或导航至 Frame 内部的空白页。
    /// 参考Responding to the appearance of the on-screen keyboard sample
    /// FlipView控件中放置的TextBox控件 不会上推
    /// </summary>
    public sealed partial class KeyboardPage : Page
    {
        public KeyboardPage()
        {
            this.InitializeComponent();

            AddInputPanelElement(textbox0);
            AddInputPanelElement(textbox2);
        }


        protected override void OnNavigatedFrom(NavigationEventArgs e)
        {
            RemoveInputPanelElement(textbox0);
            RemoveInputPanelElement(textbox2);
        }

        #region 键盘上推处理
        private double displacement = 0;
        private InputPaneHelper inputPaneHelper = new InputPaneHelper();

        public void AddInputPanelElement(FrameworkElement element)
        {
            inputPaneHelper.SubscribeToKeyboard(true);
            inputPaneHelper.AddShowingHandler(element, new InputPaneShowingHandler(CustomKeyboardHandler));
            inputPaneHelper.SetHidingHandler(new InputPaneHidingHandler(InputPaneHiding));
        }

        public void RemoveInputPanelElement(FrameworkElement element)
        {
            inputPaneHelper.SubscribeToKeyboard(false);
            inputPaneHelper.RemoveShowingHandler(element);
            inputPaneHelper.SetHidingHandler(null);
        }

        private void CustomKeyboardHandler(object sender, InputPaneVisibilityEventArgs e)
        {
            // Keep in mind that other elements could be shifting out of your control. The sticky app bar, for example
            // will move on its own. You should make sure the input element doesn't get occluded by the bar
            FrameworkElement element = sender as FrameworkElement;
            Point poppoint = element.TransformToVisual(this).TransformPoint(new Point(0, 0));
            displacement = e.OccludedRect.Y - (poppoint.Y + element.ActualHeight + 10);
            //bottomOfList = MiddleScroller.VerticalOffset + MiddleScroller.ActualHeight;


            // Be careful with this property. Once it has been set, the framework will
            // do nothing to help you keep the focused element in view.
            e.EnsuredFocusedElementInView = true;

            if (displacement > 0)
            {
                displacement = 0;
            }

            ShowingMoveSpline.Value = displacement;
            MoveMiddleOnShowing.Begin();
        }

        private void InputPaneHiding(InputPane sender, InputPaneVisibilityEventArgs e)
        {
            if (displacement != 0.0)
            {
                MoveMiddleOnShowing.Stop();

                if (displacement < 0)
                {
                    MoveMiddleOnHiding.Begin();
                }
            }
        }
        #endregion
    }
}

　　测试用例中在FlipView的三个item中分别放置一个TextBox，其中textbox0和textbox2是自定义处理键盘上推事件，而textbox1是由系统处理，通过运行程序可以发现textbox1触发弹出键盘不会使页面上推。而textbox0触发弹出键盘有自定义处理，会使页面上推。