在LongListSelector中找不到WP8項目

Question

我試圖滾動到LongListSelector中的特定項目，但是當我調用llsTest.ScrollTo（m）函數時，我的longlistselector找不到它並崩潰了。

---

C＃：

public class MyItem 
{
    public string s1 {get;set;}
    public string z1 {get;set;}

}

List<MyItem> list= new List<MyItem>();
list.Add(new MyItem() { s1 = "First", z1 = "Second" });
list.Add(new MyItem() { s1 = "Third", z1 = "Fourth" });
list.Add(new MyItem() { s1 = "Fifth", z1 = "Sixth" });
list.Add(new MyItem() { s1 = "Sek8", z1 = "kj98" });
list.Add(new MyItem() { s1 = "lkdsj9", z1 = "lkdjo0" });
list.Add(new MyItem() { s1 = "jkdlhf", z1 = "98uifie" });
list.Add(new MyItem() { s1 = "Seventh11", z1 = "Eighth32" });
list.Add(new MyItem() { s1 = "Seventh45", z1 = "Eighth67" });
list.Add(new MyItem() { s1 = "Seventh86", z1 = "Eighth89" });
list.Add(new MyItem() { s1 = "Seventh6", z1 = "Eighth7" });
list.Add(new MyItem() { s1 = "Sevent4h", z1 = "Eighth8" });
list.Add(new MyItem() { s1 = "Seventh7i", z1 = "Eighthlp" });
list.Add(new MyItem() { s1 = "Seventh-09", z1 = "Eighth-0" });
list.Add(new MyItem() { s1 = "Seventh1q", z1 = "Eighthh65" });
list.Add(new MyItem() { s1 = "Second Last", z1 = "Last" });

MyItem m = new MyItem() { s1 = "Second Last", z1 = "Last" };

llsTest.ItemsSource = list;
llsTest.ScrollTo(m);  // **<========Crashes here, m cannot be found!**

---

這是XAML：

<phone:LongListSelector Name="llsTest">
    <phone:LongListSelector.ItemTemplate>
        <DataTemplate>
            <TextBlock>
                <Run Text="{Binding s1}"/><LineBreak/>
                <Run Text="{Binding z1}"/>
            </TextBlock>
        </DataTemplate>
    </phone:LongListSelector.ItemTemplate>
 </phone:LongListSelector>

Answer 1

MyItem m = new MyItem() { s1 = "Second Last", z1 = "Last" }; 現在，在此之后，行m不再添加到列表中。 因此很明顯，在嘗試滾動到不存在的項目時會拋出異常。

請注意，每次對new調用都會創建一個新對象，因此即使對象的內容相同，不同的對象也永遠不會相同。

所以對象傳入

list.Add(new MyItem() { s1 = "Second Last", z1 = "Last" }); 

與之后創建的對象不同。

MyItem m = new MyItem() { s1 = "Second Last", z1 = "Last" };

您需要在調用list.Add(m)之前先調用llsTest.ScrollTo(m);

然后，您可以通過刪除行list.Add(new MyItem() { s1 = "Second Last", z1 = "Last" });來刪除冗余元素list.Add(new MyItem() { s1 = "Second Last", z1 = "Last" });

Answer 2

而不是將新項目傳遞給ScrollTo，而是從列表數組中提供該項目。 我從代碼中看到要滾動到第15個項目。 因此，編寫如下代碼：

llsTest.ScrollTo(list[15]);