如何防止键盘覆盖我的 UI 而不是调整它的大小？

Question

在 iOS 中，当根节点为 ScrollView 时，Xamarin.Forms 会在键盘出现时调整屏幕大小。但是当根节点不是ScrollView 时，键盘会隐藏部分 UI。你如何防止这种情况发生？

Answer 1

解决此问题的方法是使用自定义渲染器，该渲染器侦听键盘出现并在键盘出现时添加填充。

在您的 PCL 项目中，KeyboardResizingAwareContentPage.cs:

using Xamarin.Forms;

public class KeyboardResizingAwareContentPage : ContentPage {
    public bool CancelsTouchesInView = true;
}

在您的 iOS 项目中，IosKeyboardFixPageRenderer.cs:

using Foundation;
using MyProject.iOS.Renderers;
using UIKit;
using Xamarin.Forms;
using Xamarin.Forms.Platform.iOS;

[assembly: ExportRenderer(typeof(KeyboardResizingAwareContentPage), typeof(IosKeyboardFixPageRenderer))]

namespace MyProject.iOS.Renderers {
    public class IosKeyboardFixPageRenderer : PageRenderer {
        NSObject observerHideKeyboard;
        NSObject observerShowKeyboard;

        public override void ViewDidLoad()
        {
            base.ViewDidLoad();

            var cp = Element as KeyboardResizingAwareContentPage;
            if (cp != null && !cp.CancelsTouchesInView) {
                foreach (var g in View.GestureRecognizers) {
                    g.CancelsTouchesInView = false;
                }
            }
        }

        public override void ViewWillAppear(bool animated)
        {
            base.ViewWillAppear(animated);

            observerHideKeyboard = NSNotificationCenter.DefaultCenter.AddObserver(UIKeyboard.WillHideNotification, OnKeyboardNotification);
            observerShowKeyboard = NSNotificationCenter.DefaultCenter.AddObserver(UIKeyboard.WillShowNotification, OnKeyboardNotification);
        }

        public override void ViewWillDisappear(bool animated)
        {
            base.ViewWillDisappear(animated);

            NSNotificationCenter.DefaultCenter.RemoveObserver(observerHideKeyboard);
            NSNotificationCenter.DefaultCenter.RemoveObserver(observerShowKeyboard);
        }

        void OnKeyboardNotification(NSNotification notification)
        {
            if (!IsViewLoaded) return;

            var frameBegin = UIKeyboard.FrameBeginFromNotification(notification);
            var frameEnd = UIKeyboard.FrameEndFromNotification(notification);

            var page = Element as ContentPage;
            if (page != null && !(page.Content is ScrollView)) {
                var padding = page.Padding;
                page.Padding = new Thickness(padding.Left, padding.Top, padding.Right, padding.Bottom + frameBegin.Top - frameEnd.Top);
            }
        }
    }
}

Answer 2

我发现KeyboardOverlap plugin 比 Anthony 的解决方案效果更好。

我就是这样使用它的：

1. 创建自定义渲染器

public class KeyboardResizingAwareContentPage : ContentPage
{
}

1. 在 iOS 上实现自定义渲染器。这是paulpatarinski代码的重要部分：

[Preserve (AllMembers = true)]
public class KeyboardOverlapRenderer : PageRenderer
{
    NSObject _keyboardShowObserver;
    NSObject _keyboardHideObserver;
    private bool _pageWasShiftedUp;
    private double _activeViewBottom;
    private bool _isKeyboardShown;

    public static void Init ()
    {
        var now = DateTime.Now;
        Debug.WriteLine ("Keyboard Overlap plugin initialized {0}", now);
    }

    public override void ViewWillAppear (bool animated)
    {
        base.ViewWillAppear (animated);

        var page = Element as ContentPage;

        if (page != null) {
            var contentScrollView = page.Content as ScrollView;

            if (contentScrollView != null)
                return;

            RegisterForKeyboardNotifications ();
        }
    }

    public override void ViewWillDisappear (bool animated)
    {
        base.ViewWillDisappear (animated);

        UnregisterForKeyboardNotifications ();
    }

    void RegisterForKeyboardNotifications ()
    {
        if (_keyboardShowObserver == null)
            _keyboardShowObserver = NSNotificationCenter.DefaultCenter.AddObserver (UIKeyboard.WillShowNotification, OnKeyboardShow);
        if (_keyboardHideObserver == null)
            _keyboardHideObserver = NSNotificationCenter.DefaultCenter.AddObserver (UIKeyboard.WillHideNotification, OnKeyboardHide);
    }

    void UnregisterForKeyboardNotifications ()
    {
        _isKeyboardShown = false;
        if (_keyboardShowObserver != null) {
            NSNotificationCenter.DefaultCenter.RemoveObserver (_keyboardShowObserver);
            _keyboardShowObserver.Dispose ();
            _keyboardShowObserver = null;
        }

        if (_keyboardHideObserver != null) {
            NSNotificationCenter.DefaultCenter.RemoveObserver (_keyboardHideObserver);
            _keyboardHideObserver.Dispose ();
            _keyboardHideObserver = null;
        }
    }

    protected virtual void OnKeyboardShow (NSNotification notification)
    {
        if (!IsViewLoaded || _isKeyboardShown)
            return;

        _isKeyboardShown = true;
        var activeView = View.FindFirstResponder ();

        if (activeView == null)
            return;

        var keyboardFrame = UIKeyboard.FrameEndFromNotification (notification);
        var isOverlapping = activeView.IsKeyboardOverlapping (View, keyboardFrame);

        if (!isOverlapping)
            return;

        if (isOverlapping) {
            _activeViewBottom = activeView.GetViewRelativeBottom (View);
            ShiftPageUp (keyboardFrame.Height, _activeViewBottom);
        }
    }

    private void OnKeyboardHide (NSNotification notification)
    {
        if (!IsViewLoaded)
            return;

        _isKeyboardShown = false;
        var keyboardFrame = UIKeyboard.FrameEndFromNotification (notification);

        if (_pageWasShiftedUp) {
            ShiftPageDown (keyboardFrame.Height, _activeViewBottom);
        }
    }

    private void ShiftPageUp (nfloat keyboardHeight, double activeViewBottom)
    {
        var pageFrame = Element.Bounds;

        var newY = pageFrame.Y + CalculateShiftByAmount (pageFrame.Height, keyboardHeight, activeViewBottom);

        Element.LayoutTo (new Rectangle (pageFrame.X, newY,
            pageFrame.Width, pageFrame.Height));

        _pageWasShiftedUp = true;
    }

    private void ShiftPageDown (nfloat keyboardHeight, double activeViewBottom)
    {
        var pageFrame = Element.Bounds;

        var newY = pageFrame.Y - CalculateShiftByAmount (pageFrame.Height, keyboardHeight, activeViewBottom);

        Element.LayoutTo (new Rectangle (pageFrame.X, newY,
            pageFrame.Width, pageFrame.Height));

        _pageWasShiftedUp = false;
    }

    private double CalculateShiftByAmount (double pageHeight, nfloat keyboardHeight, double activeViewBottom)
    {
        return (pageHeight - activeViewBottom) - keyboardHeight;
    }
}

还有缺少的扩展：

public static class ViewExtensions
{
    /// <summary>
    /// Find the first responder in the <paramref name="view"/>'s subview hierarchy
    /// </summary>
    /// <param name="view">
    /// A <see cref="UIView"/>
    /// </param>
    /// <returns>
    /// A <see cref="UIView"/> that is the first responder or null if there is no first responder
    /// </returns>
    public static UIView FindFirstResponder (this UIView view)
    {
        if (view.IsFirstResponder) {
            return view;
        }
        foreach (UIView subView in view.Subviews) {
            var firstResponder = subView.FindFirstResponder ();
            if (firstResponder != null)
                return firstResponder;
        }
        return null;
    }

    /// <summary>
    /// Returns the new view Bottom (Y + Height) coordinates relative to the rootView
    /// </summary>
    /// <returns>The view relative bottom.</returns>
    /// <param name="view">View.</param>
    /// <param name="rootView">Root view.</param>
    public static double GetViewRelativeBottom (this UIView view, UIView rootView)
    {
        var viewRelativeCoordinates = rootView.ConvertPointFromView (view.Frame.Location, view);
        var activeViewRoundedY = Math.Round (viewRelativeCoordinates.Y, 2);

        return activeViewRoundedY + view.Frame.Height;
    }

    /// <summary>
    /// Determines if the UIView is overlapped by the keyboard
    /// </summary>
    /// <returns><c>true</c> if is keyboard overlapping the specified activeView rootView keyboardFrame; otherwise, <c>false</c>.</returns>
    /// <param name="activeView">Active view.</param>
    /// <param name="rootView">Root view.</param>
    /// <param name="keyboardFrame">Keyboard frame.</param>
    public static bool IsKeyboardOverlapping (this UIView activeView, UIView rootView, CGRect keyboardFrame)
    {
        var activeViewBottom = activeView.GetViewRelativeBottom (rootView);
        var pageHeight = rootView.Frame.Height;
        var keyboardHeight = keyboardFrame.Height;

        var isOverlapping = activeViewBottom >= (pageHeight - keyboardHeight);

        return isOverlapping;
    }
}

1. 使用自定义页面渲染器

public partial class LoginPage : KeyboardResizingAwareContentPage
{
    public LoginPage()
    {
        // your content
        // note: you have to use base.Navigation.PushAsync(), base.DisplayAlert(), ...
    }
}

<?xml version="1.0" encoding="utf-8" ?>
<renderer:KeyboardResizingAwareContentPage xmlns="http://xamarin.com/schemas/2014/forms"
     xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
     x:Class="App.Pages.LoginPage"
     xmlns:renderer="clr-namespace:App.CustomRenderers;assembly=App">
    <!-- your content -->
</renderer:KeyboardResizingAwareContentPage>

这一切归功于保罗！谢谢！

Answer 3

Xamarin Forum question 讨论它。

此外，如果您希望在 Android 中使用 Xamarin / Forms，您可以在主 Activity 中进行设置：

[Activity(WindowSoftInputMode = Android.Views.SoftInput.AdjustResize)]
public class MainActivity
    ...

Answer 4

对于Android，在MainActivityLoadApplication(new App());之后添加以下代码

App.Current.On<Xamarin.Forms.PlatformConfiguration.Android>().
UseWindowSoftInputModeAdjust(WindowSoftInputModeAdjust.Resize);