[英]How to save a page state?
在Windows Runtime应用程序中,我像这样加载数据:
private async void NavigationHelper_LoadState(object sender, LoadStateEventArgs e)
{
var userId = e.NavigationParameter as string;
List<User> followers = GetFollowers(userId);
this.DefaultViewModel["Followers"] = followers;
}
然后用户可以从ListView
选择一个项目:
private void ContentListView_ItemClick(object sender, ItemClickEventArgs e)
{
var selectedItem = e.ClickedItem as User;
if (!Frame.Navigate(typeof(FollowersPage), selectedItem.UserId))
{
throw new Exception(this.resourceLoader.GetString("NavigationFailedExceptionMessage"));
}
}
因此它向前导航到同一页面,但显示新的关注者。
问题在于,当它向后导航时,它将再次加载数据并从列表的开头显示,而不是显示最后选择的项目。
那么,如何在NavigationHelper_SaveState
保存数据List
,以及如何在NavigationHelper_LoadState
再次将数据加载到列表中的最后位置呢? 谢谢。
这是您可以开始的基本的半测试示例。 您需要对其进行修改以适合您的实际情况。 有些是从这里改编的。
void NavigationHelper_SaveState(object sender, SaveStateEventArgs e)
{
var isp = (ItemsStackPanel)listview.ItemsPanelRoot;
int firstVisibleItem = isp.FirstVisibleIndex;
e.PageState["FirstVisibleItemIndex"] = firstVisibleItem;
// This must be serializable according to the SuspensionManager
e.PageState["Followers"] = this.DefaultViewModel["Followers"];
}
void NavigationHelper_LoadState(object sender, LoadStateEventArgs e)
{
// Do we have saved state to restore?
if (e.PageState != null)
{
// Restore list view items
this.DefaultViewModel["Followers"] = (WhateverType)e.PageState["Followers"];
// Restore scroll offset
var index = (int)e.PageState["FirstVisibleItemIndex"];
var container = listview.ContainerFromIndex(index);
listview.ScrollIntoView(container);
}
else
{
// Load data for the first time
var userId = e.NavigationParameter as string;
List<User> followers = GetFollowers(userId);
this.DefaultViewModel["Followers"] = followers;
}
}
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