我的xamarin项目在listview的Android端工作。但是，IOS不能正常运行。我收到并在Web服务上列出从1到50的客户列表。但是，当列出第二50个客户时，滚动条将保持在列表顶部，并保持在不同位置。我在寻找解决方案，但没有找到。请帮助。
public partial class MusteriListesi : BasePage
{
ListView listView;
int bas;
int bit;
bool isLoading;
public string mKodu = "";
string mFirma = "";
string mSehir = "";
string mIlce = "";
string mSemt = "";
string mAdres = "";
public string mCkp = "";
public List<Musteriler> Items { get; set; }
public MusteriListesi(string kodu, string firma, string sehir, string ilce, string semt, string adres,string ckp)
{
InitializeComponent();
mKodu = kodu;mFirma = firma;mSehir = sehir;mIlce = ilce;mSemt = semt;mAdres = adres;mCkp = ckp;
if (mCkp == "P")
{
this.Title = "Aday Listesi";
}
bas = 1;
bit = 50;
if (String.IsNullOrEmpty(mSehir))
{
mSehir = "Tüm Şehirler";
}
if (String.IsNullOrEmpty(mIlce))
{
mIlce = "Tüm İlçeler";
}
if (String.IsNullOrEmpty(mSemt))
{
mSemt = "Tüm Semtler";
}
if (String.IsNullOrEmpty(mKodu))
{
mKodu = "";
}
if (String.IsNullOrEmpty(mFirma))
{
mFirma = "";
}
if (String.IsNullOrEmpty(mAdres))
{
mAdres = "";
}
listView = MyListView;
Items = new List<Musteriler>();
Mobil.webService.KartServis service = new Mobil.webService.KartServis()
{
Url = Application.Current.Properties["servisyolu"].ToString()
};
List<Mobil.webService.Musteriler> MusteriLists = new List<Mobil.webService.Musteriler>(service.MusteriListele(mCkp, bas, bit, mKodu, mFirma, mSehir, mSemt, mIlce, mAdres, Application.Current.Properties["lisans"].ToString(), Application.Current.Properties["KNO"].ToString()));
foreach (Mobil.webService.Musteriler items in MusteriLists)
{
Items.Add(new Musteriler { Kodu = items.Kodu, Firma = items.Firma, Adres = items.Adres, Telefon = items.Telefon, Sayi = items.Sayi });
}
listView.ItemsSource = Items;
}
async void Handle_ItemTapped(object sender, Xamarin.Forms.ItemTappedEventArgs e)
{
var item = (Musteriler)e.Item;
if (item == null)
{
return;
}
await Navigation.PushAsync(new MusteriDetay(item.Kodu));
((ListView)sender).SelectedItem = null;
}
protected void Handle_ItemAppearing(object sender, Xamarin.Forms.ItemVisibilityEventArgs e)
{
if(isLoading || Items.Count == 0)
{
return;
}
if (e.Item == Items[Items.Count - 1])
{
LoadItems();
}
}
public async Task LoadItems()
{
isLoading = true;
listView.ItemsSource = null;
bas = bas + 50;
bit = bit + 50;
Mobil.webService.KartServis service = new Mobil.webService.KartServis()
{
Url = Application.Current.Properties["servisyolu"].ToString()
};
List<Mobil.webService.Musteriler> MusteriLists = new List<Mobil.webService.Musteriler>(service.MusteriListele(mCkp, bas, bit, mKodu, mFirma, mSehir, mSemt, mIlce, mAdres, Application.Current.Properties["lisans"].ToString(), Application.Current.Properties["KNO"].ToString()));
if (MusteriLists.Count > 0)
{
Device.StartTimer(TimeSpan.FromSeconds(1), () =>
{
Show();
foreach (Mobil.webService.Musteriler items in MusteriLists)
{
Items.Add(new Musteriler { Kodu = items.Kodu, Firma = items.Firma, Adres = items.Adres, Telefon = items.Telefon, Sayi = items.Sayi });
}
listView.ItemsSource = Items;
listView.ScrollTo(Items[bas], ScrollToPosition.Start, false);
isLoading = false;
Hide();
return false;
});
}
else
{
isLoading = false;
}
}
答案 0 :(得分：0)
但是，当列出第二50个客户时，滚动条将保持在列表顶部，并保持在不同位置。
原因之一：下一项没有退出。在下面的代码中，应确保Items在运行下面的代码后有100个数据。
foreach (Mobil.webService.Customer items in CustomerList)
{
Items.Add(new Customer { Kodu = items.code, City = items.City });
}
原因二：运行代码时，需要更多时间来完成它，您应该添加计时器或异步任务来完成它。然后继续其余步骤。
解决方案示例：测试将本地数据添加到Items，并添加计时器以完成它。
private async Task LoadItems()
{
isLoading = true;
Title = "Loading";
//simulator delayed load
Device.StartTimer(TimeSpan.FromSeconds(2), () =>
{
for (int i = 0; i < 50; i++)
{
Items.Add(string.Format("Item {0}", Items.Count));
}
Title = "Done";
isLoading = false;
listview.ScrollTo(Items[Items.Count - 1], ScrollToPosition.Start, false);
//stop timer
return false;
});
}
-------------------------------------------------- ---------------更新---------------------------------- --------------------------
解决方案：从共享方法 LoadItems 中，问题出在以下代码中；
listView.ScrollTo(listView.SelectedItem, ScrollToPosition.MakeVisible, false);
您应该删除代码，因为导致无限循环的LoadItems方法的触发器每次在代码中都加载了+100，程序界面很快就会卡住了。
public async void LoadItems()
{
isLoading = true;
Show();
listView.ItemsSource = null;
bas = bas + 50;
bit = bit + 50;
Mobil.webService.KartServis service = new Mobil.webService.KartServis()
{
Url = Application.Current.Properties["servisyolu"].ToString()
};
List<Mobil.webService.Musteriler> MusteriLists = new List<Mobil.webService.Musteriler>(service.MusteriListele("K", bas, bit, mKodu, mFirma, mSehir, mSemt, mIlce, mAdres, Application.Current.Properties["lisans"].ToString(), Application.Current.Properties["KNO"].ToString()));
foreach (Mobil.webService.Musteriler items in MusteriLists)
{
Items.Add(new Musteriler { Kodu = items.Kodu, Firma = items.Firma, Adres = items.Adres, Telefon = items.Telefon, Sayi = items.Sayi });
}
for (int i = 0; i < Items.Count; i++)
{
Console.WriteLine(Items[i].Sayi);
}
var lastItem = Items[1];
listView.ItemsSource = Items;
isLoading = false;
listView.SelectedItem = lastItem;
//listView.ScrollTo(listView.SelectedItem, ScrollToPosition.MakeVisible, false);
Hide();
}
如果不删除，则应添加一个Timer来检查它是否在循环添加项目。下面的代码将循环添加项目，这可能不是一个好逻辑。
public async void LoadItems()
{
isLoading = true;
Show();
listView.ItemsSource = null;
bas = bas + 50;
bit = bit + 50;
Device.StartTimer(TimeSpan.FromSeconds(2), () =>
{
Mobil.webService.KartServis service = new Mobil.webService.KartServis()
{
Url = Application.Current.Properties["servisyolu"].ToString()
};
List<Mobil.webService.Musteriler> MusteriLists = new List<Mobil.webService.Musteriler>(service.MusteriListele("K", bas, bit, mKodu, mFirma, mSehir, mSemt, mIlce, mAdres, Application.Current.Properties["lisans"].ToString(), Application.Current.Properties["KNO"].ToString()));
foreach (Mobil.webService.Musteriler items in MusteriLists)
{
Items.Add(new Musteriler { Kodu = items.Kodu, Firma = items.Firma, Adres = items.Adres, Telefon = items.Telefon, Sayi = items.Sayi });
}
for (int i = 0; i < Items.Count; i++)
{
Console.WriteLine(Items[i].Sayi);
}
var lastItem = Items[1];
listView.ItemsSource = Items;
isLoading = false;
listView.SelectedItem = lastItem;
listView.ScrollTo(listView.SelectedItem, ScrollToPosition.MakeVisible, false);
Hide();
});
}
注意：如果该Api每次获得50件物品，则没有其他问题。
列表MusteriLists =新列表（service.MusteriListele（“ K”，bas，bit，mKodu，mFirma，mSehir，mSemt，mIlce，mAdres，Application.Current.Properties [“ lisans”]。ToString（），应用程序。 Current.Properties [“ KNO”]。ToString（）））;
如果不是每次都达到50，则应在 LoadItems 中设置Items = new List<Musteriler>();。然后Itmes.count将为50,100,150，等等，否则为50,150,300，等等。这将产生一个项目数量意外。