为Xamarin.Forms的导航栏增加搜索功能-C#/.NET开发

这篇文章介绍了为Xamarin.Forms的导航栏增加搜索功能的方法，文中通过示例代码介绍的非常详细。对大家的学习或工作具有一定的参考借鉴价值，需要的朋友可以参考下

在使用NavigationPage导航的时候, 我们可以给里面添加一些功能按钮, 如下所示:

    <ContentPage.ToolbarItems>
        <ToolbarItem/>
        <ToolbarItem/>
    </ContentPage.ToolbarItems>

但是如果需要给这个控件添加一些其他的控件的时候, 则无法满足我们的需求, 这个时候, 我们就需要使用页面渲染器(Page Renderer)。

真机效果演示:

实现思路:

1.添加用于搜索通知的接口 : ISearchPage
2.自定义搜索的渲染器 : SearchPageRender
3.添加Menu/Item Xml文件: mainmenu.xml
4.添加 Nuget：Plugin.CurrentActivity
5.给需要添加搜索功能的页面实现 (1)的接口
6.为自定义搜索渲染器添加支持该功能的页面
7.启动项初始化 : CrossCurrentActivity.Current.Init(this, savedInstanceState)

添加搜索通知接口

    public interface ISearchPage
    {
        void OnSearchBarTextChanged(string text);
    }

自定义渲染器

在Android项目中创建 CustomRender文件夹定义 SearchPageRender

SearchPageRender代码

     public class SearchPageRender : PageRenderer
    {
        public SearchPageRender(Context context) : base(context)
        {

        }

        protected override void OnAttachedToWindow()
        {
            base.OnAttachedToWindow();

            if (Element is ISearchPage
                && Element is Page page
                && page.Parent is NavigationPage navigationPage)
            {
                //Workaround to re-add the SearchView when navigating back to an ISearchPage, because Xamarin.Forms automatically removes it
                navigationPage.Popped += HandleNavigationPagePopped;
                navigationPage.PoppedToRoot += HandleNavigationPagePopped;
            }
        }

        //Adding the SearchBar in OnSizeChanged ensures the SearchBar is re-added after the device is rotated, because Xamarin.Forms automatically removes it
        protected override void OnSizeChanged(int w, int h, int oldw, int oldh)
        {
            base.OnSizeChanged(w, h, oldw, oldh);

            if (Element is ISearchPage && Element is Page page && page.Parent is NavigationPage navigationPage && navigationPage.CurrentPage is ISearchPage)
            {
                AddSearchToToolbar(page.Title);
            }
        }

        protected override void Dispose(bool disposing)
        {
            if (GetToolbar() is Android.Support.V7.Widget.Toolbar toolBar)
                toolBar.Menu?.RemoveItem(Resource.Menu.mainmenu);

            base.Dispose(disposing);
        }

        //Workaround to re-add the SearchView when navigating back to an ISearchPage, because Xamarin.Forms automatically removes it
        void HandleNavigationPagePopped(object sender, NavigationEventArgs e)
        {
            if (sender is NavigationPage navigationPage
                && navigationPage.CurrentPage is ISearchPage)
            {
                AddSearchToToolbar(navigationPage.CurrentPage.Title);
            }
        }

        void AddSearchToToolbar(string pageTitle)
        {
            if (GetToolbar() is Android.Support.V7.Widget.Toolbar toolBar
            && toolBar.Menu?.FindItem(Resource.Id.action_search)?.ActionView?.
            JavaCast<Android.Support.V7.Widget.SearchView>().GetType()
            != typeof(Android.Support.V7.Widget.SearchView))
            {
                toolBar.Title = pageTitle;
                toolBar.InflateMenu(Resource.Menu.mainmenu);

                if (toolBar.Menu?.FindItem(Resource.Id.action_search)?.ActionView?.
                    JavaCast<Android.Support.V7.Widget.SearchView>() is
                     Android.Support.V7.Widget.SearchView searchView)
                {
                    searchView.QueryTextChange += SearchView_QueryTextChange;
                    searchView.ImeOptions = (int)ImeAction.Search;
                    searchView.InputType = (int)InputTypes.TextVariationFilter;
                    searchView.MaxWidth = int.MaxValue;
                }
            }
        }

        private void SearchView_QueryTextChange(object sender, Android.Support.V7.Widget.SearchView.QueryTextChangeEventArgs e)
        {
            if (Element is ISearchPage searchPage)
                searchPage.OnSearchBarTextChanged(e.NewText);
        }

        private static Android.Support.V7.Widget.Toolbar GetToolbar() => (CrossCurrentActivity.Current?.Activity as MainActivity)?.FindViewById<Android.Support.V7.Widget.Toolbar>(Resource.Id.toolbar);
    }

添加Xml文件引用SearchView

创建mainmenu.xml

在Android的Resources文件夹中, 创建menu文件夹创建mainmenu.xml文件, 如下:

mainmenu.xml

    <?xml version="1.0" encoding="utf-8" ?>
<menu xmlns:android="http://schemas.android.com/apk/res/android"
      xmlns:app="http://schemas.android.com/apk/res-auto">
	<item android:id="@+id/action_search"
		  android:title="Search"
		  android:icon="@android:drawable/ic_menu_search"
		  app:showAsAction="always|collapseActionView"
		  app:actionViewClass="android.support.v7.widget.SearchView"/>
</menu>