如何在Xamarin Forms MasterDetailPage项目中加载一次detailpage

Question

我注意到每次选择masterpage菜单项时都会从头开始加载detailpage（因此每次都会调用它的构造函数）。 有没有一种方法来实现一次加载的详细信息页面，所以每次选择菜单项目的详细信息页面都显示/不显示？

感谢， Lewix

Answer 1

我解决了MasterDetailPage实现词典页面缓存：

// in constructor 
MasterPageMenuCache = new Dictionary<Type, Page>(); 

// in OnItemSelected 
if (MasterPageMenuCache.Count == 0) 
    MasterPageMenuCache.Add(typeof(FirstDefaultDetailPage), Detail); 

var item = e.SelectedItem as MasterPageItem; 
if (item != null) 
{ 
    if (MasterPageMenuCache.ContainsKey(item.TargetType)) 
    { 
     Detail = MasterPageMenuCache[item.TargetType]; 
    } 
    else 
    { 
     Detail = new NavigationPage((Page)Activator.CreateInstance(item.TargetType)); 
     MasterPageMenuCache.Add(item.TargetType, Detail); 
    } 

    masterPage.ListView.SelectedItem = null; 
    IsPresented = false; 
} 

Answer 2

是的，你可以缓存页面。

下面是一个存储页面的字典示例。

public partial class MyMasterDetailPage : MasterDetailPage 
{ 

    public MyMasterDetailPage() 
    { 
     Pages = new Dictionary<MenuType, Page>(); 
    } 

    public enum MenuType 
    { 
     Home, 
     Settings, 
     Map 
    } 
    private Dictionary<MenuType, Page> Pages { get; set; } 
    public async Task NavigateAsync(MenuType id) 
    { 
     Page newPage; 
     if (!Pages.ContainsKey(id)) // check the page is already in the dictionary 
     { 
      Page page; 
      switch (id) 
      { 
       case MenuType.Home: 
        page = new ContentPage() 
        { 
         Title = "Home", 
        }; 
        Pages.Add(id, page); 
        break; 

       case MenuType.Map: 
        page = new ContentPage() 
        { 
         Title = "Map", 
        }; 

        Pages.Add(id, page); 
        break; 

       case MenuType.Settings: 
        page = new ContentPage() 
        { 
         Title = "Settings", 
        }; 

        Pages.Add(id, page); 
        break; 
      } 
     } 

     newPage = Pages[id]; 
     if (newPage == null) 
      return; 

     Detail = newPage; // assign the page 
    } 
}