小编iNC*_*ON_的帖子

我有一个奇怪的例外,编译器告诉我指定的强制转换是无效的,即使我正在做的非常简单.

我有一个ListView绑定到ObservableCollection.我的Listview内部是一个带网格的ViewCell.Xamarin.Forms版本2.3.2.127

<ListView ItemsSource="{Binding GiftCollection}">
      <ListView.ItemTemplate>
        <DataTemplate>
          <ViewCell>
            <ViewCell.View>
              <Grid>
          <Grid.RowDefinitions>
            <RowDefinition Height="20"/>
            <RowDefinition Height="20"/>
          </Grid.RowDefinitions>
          <Grid.ColumnDefinitions>
            <ColumnDefinition Width="*"/>
            <ColumnDefinition Width="40"/>
          </Grid.ColumnDefinitions>

          <Label Grid.Row="0" Grid.Column="0" Text="{Binding GiftName}"/>
          <Label Grid.Row="1" Grid.Column="0" Text="{Binding GiftDescription}"/>
          <Image Grid.Row="0" Grid.RowSpan="2" Grid.Column="1" Source="{Binding GiftImage}"/>
        </Grid>
        </ViewCell.View>
      </ViewCell>
        </DataTemplate>
      </ListView.ItemTemplate>
    </ListView>

模型:

 public class GiftModel {

        public string GiftName { get; set; }
        public string GiftDescription { get; set; }
        public ImageSource GiftImage { get; set; }
    }

视图模型:

public class NextRoundViewModel : BaseViewModel {

        public NextRoundViewModel(ApplicationModel …

问题

我想要实现的目标基本上可以在这里看到

因此,当用户滚动到最后我想加载更多,因为我的列表非常大,我想最大化性能.

我正在尝试按如下方式实现此目的,将主集合与数据分开,以便我可以在用户到达结尾时将ItemSource设置为新的.

到目前为止我实施了什么

 public class ViewModel : BaseViewModel {

        public ViewModel() {
            Initialize();
        }

        public List<List<Usermodel>> SplitedUserLists { get; set; }

        //Main List that im Binding to
        public List<Usermodel> ItemSourceCollection { get; set; }

        public int ChunkSize { get; set; }
        #endregion

        private async void Initialize() {

            ItemSourceCollection = await LoadList();

            // Splites the list (in this case the chunk Size is 5)
            SplitedScoreLists = ItemSourceCollection.Split(GetChunkSize()));
            ItemSourceCollection = SplitedScoreLists[0];
        }

        //Gets called from CodeBehind
        public void ListViewItemAppearing(ItemVisibilityEventArgs e) …

我正在尝试列出我的Pc的逻辑驱动器并将结果添加到矢量但我得到这个奇怪的result = ;;;.

我在这里失踪了什么？

std::vector<std::string> directory::getLogicalDrives() {
    DWORD mydrives = 100;
    char lpBuffer[100];
    DWORD drives = GetLogicalDriveStrings(mydrives, lpBuffer);

    std::vector<std::string> driveList;
    for (int i = 0; i < 100; i++) {
        std::string drive(3, '%c' + lpBuffer[0]); // Missing something?
        driveList.push_back(drive);
    }
    return driveList;
}