.net c# 限制 observablecollection 中的条目数

Question

我有一个 WPF 应用程序，其中 UI 有一个列表框。列表框绑定了 ObservableCollection。日志 class 实现 INotifyPropertyChanged。

该列表将显示应用程序的连续记录。只要应用运行。 ObservableCollection 大小不断增长。一段时间后，我得到了内存不足异常。我想在列表控件中显示最新的 1000 个条目。对此的任何建议都会有很大帮助！

XAML:

                    <DataGrid AutoGenerateColumns="False" SelectedValue="{Binding SelectedLog}" SelectionUnit="FullRow" SelectionMode="Single" Name="dataGridLogs" 
                      ItemsSource="{Binding Path=LogList}"  CanUserReorderColumns="True" CanUserResizeRows="True" CanUserDeleteRows="False"  IsReadOnly="True"
                      CanUserAddRows="False" EnableColumnVirtualization="True" EnableRowVirtualization="True" SelectionChanged="grid_SelectionChanged"> 
                <DataGrid.Columns>
                    <DataGridTextColumn Header="Time Stamp" Binding="{Binding StrTimeStamp, Mode=OneWay}" Width="Auto"/>
                    <DataGridTextColumn Header="Action" Binding="{Binding Action, Mode=OneWay}" Width="Auto"/>

            </DataGrid>

视图模型：

    public ObservableCollection<LogData> LogList
    {
        get
        {
            if (logList == null)
            {
                logList = new ObservableCollection<LogData>();
            }
            return logList;
        }
        set
        {
            logList = value;
            OnPropertyChanged("LogList");
        }
    }

型号：

     public class LogData : INotifyPropertyChanged
{
    public LogData()
    {
    }
    private String timestamp = string.Empty;
    public String StrTimestamp
    {
        get
        {
            if (timestamp == null)
                return string.Empty;
            return timestamp ;
        }
        set
        {

            timestamp = value;
        }
    }
    public string Action
    {
       get;set;
    }

}

Answer 1

如果您希望它不应该添加到集合中超过 1000 个，您可以这样做。

public ObservableCollection<LogData> LogList
{
    get
    {
        if (logList == null)
        {
            logList = new ObservableCollection<LogData>();
        }
        return logList;
    }
    set
    {
        if(LogList.Count < 1001)
        {
          logList = value;
          OnPropertyChanged("LogList");
        }
    }
}

或者您可以在添加超过 1000 个新条目时删除旧条目

public ObservableCollection<LogData> LogList
{
    get
    {
        if (logList == null)
        {
            logList = new ObservableCollection<LogData>();
        }
        return logList;
    }
    set
    {
        if(LogList.Count < 1001)
        {
          logList = value;
          OnPropertyChanged("LogList");
        }
        else 
        {
           LogList.RemoveAt(0);
           logList = value;
           OnPropertyChanged("LogList");
        }
    }
}

Answer 2

您可以创建自己的大小受限的可观察集合 class。像这样的事情应该让你开始：

public class LimitedSizeObservableCollection<T> : INotifyCollectionChanged
{        
    private ObservableCollection<T> _collection;
    private bool _ignoreChange;

    public LimitedSizeObservableCollection(int capacity)
    {
        Capacity = capacity;
        _ignoreChange = false;
        _collection = new ObservableCollection<T>();
        _collection.CollectionChanged += _collection_CollectionChanged;
    }

    public event NotifyCollectionChangedEventHandler CollectionChanged;

    public int Capacity {get;}

    public void Add(T item)
    {
        if(_collection.Count = Capacity)
        {
            _ignoreChange = true;
            _collection.RemoveAt(0);
            _ignoreChange = false;
        }
        _collection.Add(item);

    }

    private void _collection_CollectionChanged(object sender, NotifyCollectionChangedEventArgs e)
    {
        if(!_ignoreChange)
        {
            CollectionChanged?.Invoke(this, e);
        }
    }
}

当然，您可能需要公开更多的方法，但我希望这足以让您理解。

Answer 3

可以很容易地做到这一点 class:

public class LimitedSizeObservableCollection<T> : ObservableCollection<T>
{
    public int Capacity { get; }

    public LimitedSizeObservableCollection(int capacity)
    {
        Capacity = capacity;
    }

    public new void Add(T item)
    {
        if (Count >= Capacity)
        {
            this.RemoveAt(0);
        }
        base.Add(item);
    }
}

Answer 4

我找到了另一种方法来限制集合中元素的数量，而不添加破坏与父类兼容性的 "new" 方法：

public class LimitedSizeObservableCollection<T> : ObservableCollection<T>
{
    public int Capacity { get; set; } = 0;

    protected override void InsertItem(int index, T item)
    {
        if (this.Capacity > 0 && this.Count >= this.Capacity)
        {
            throw new Exception(string.Format("The maximum number of items in the list  ({0}) has been reached, unable to add further items", this.Capacity));
        }
        else
        {
            base.InsertItem(index, item);
        }
    }
}

.net c# 限制 observablecollection 中的条目数

.net c# Limit number of entries in observablecollection

c#

data-binding

observablecollection