在LongListSelector中找不到WP8项目

Question

我试图滚动到LongListSelector中的特定项目，但是当我调用llsTest.ScrollTo（m）函数时，我的longlistselector找不到它并崩溃了。

---

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!**

---

这是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" }; 现在，在此之后，行m不再添加到列表中。 因此很明显，在尝试滚动到不存在的项目时会抛出异常。

请注意，每次对new调用都会创建一个新对象，因此即使对象的内容相同，不同的对象也永远不会相同。

所以对象传入

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

与之后创建的对象不同。

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

您需要在调用list.Add(m)之前先调用llsTest.ScrollTo(m);

然后，您可以通过删除行list.Add(new MyItem() { s1 = "Second Last", z1 = "Last" });来删除冗余元素list.Add(new MyItem() { s1 = "Second Last", z1 = "Last" });

Answer 2

而不是将新项目传递给ScrollTo，而是从列表数组中提供该项目。 我从代码中看到要滚动到第15个项目。 因此，编写如下代码：

llsTest.ScrollTo(list[15]);