C# collections event-handling observablecollection

如何调整 ObservableCollection 的大小？

发布于 2024-10-05 00:05:38 字数 1593 浏览 2 评论 0原文

是否可以调整可观察集合的大小或限制集合项目的最大数量？我有一个 ObservableCollection 作为视图模型中的属性（使用 MVVM 模式）。

视图绑定到集合，我尝试通过提供一个在发生 CollectionChanged 事件时执行的事件处理程序来破解解决方案。在事件处理程序中，我通过根据需要从集合顶部删除尽可能多的项目来修剪集合。

ObservableCollection<string> items = new ObservableCollection<string>();
items.CollectionChanged += new NotifyCollectionChangedEventHandler(Items_Changed);

void Items_Changed(object sender, NotifyCollectionChangedEventArgs e)
{
    if(items.Count > 10)
    {
        int trimCount = items.Count - 10;
        for(int i = 0; i < trimCount; i++)
        {
            items.Remove(items[0]);
        }
    }
}

此事件处理程序会产生 InvalidOperationException，因为它不喜欢我在 CollectionChanged 事件期间更改集合这一事实。我应该怎样做才能保持我的收藏规模适当？

解决方案： Simon Mourier 问我是否可以创建一个从 ObservableCollection 派生的新集合并覆盖 InsertItem()，这正是我为获得自动调整大小的 ObservableCollection 类型所做的事情。

public class MyCollection<T> : ObservableCollection<T>
{
    public int MaxCollectionSize { get; set; }

    public MyCollection(int maxCollectionSize = 0) : base()
    {
        MaxCollectionSize = maxCollectionsize;
    }

    protected override void InsertItem(int index, T item)
    {
        base.InsertItem(index, item);

        if(MaxCollectionSize > 0 && MaxCollectionSize < Count)
        {
            int trimCount = Count - MaxCollectionSize;
            for(int i=0; i<trimCount; i++)
            {
                RemoveAt(0);
            }
        }
    }
}

原文

Is it possible to resize an Observable Collection or perhaps restrict the max amount of collection items? I have an ObservableCollection as a property in a View Model (using the MVVM pattern).

The view binds to the collection and I've attempted to hack a solution by providing an event handler that executes when a CollectionChanged event occurs. In the event handler, I trimmed the collection by removing as many items off the top of the collection as necessary.

ObservableCollection<string> items = new ObservableCollection<string>();
items.CollectionChanged += new NotifyCollectionChangedEventHandler(Items_Changed);

void Items_Changed(object sender, NotifyCollectionChangedEventArgs e)
{
    if(items.Count > 10)
    {
        int trimCount = items.Count - 10;
        for(int i = 0; i < trimCount; i++)
        {
            items.Remove(items[0]);
        }
    }
}

This event handler yields an InvalidOperationException because it doesn't like the fact that I alter the collection during a CollectionChanged event. What should I do to keep my collection sized appropriately?

Solution:
Simon Mourier asked if I could create a new collection derived from ObservableCollection<T> and override InsertItem() and thats just what I did to have an auto-resizing ObservableCollection type.

public class MyCollection<T> : ObservableCollection<T>
{
    public int MaxCollectionSize { get; set; }

    public MyCollection(int maxCollectionSize = 0) : base()
    {
        MaxCollectionSize = maxCollectionsize;
    }

    protected override void InsertItem(int index, T item)
    {
        base.InsertItem(index, item);

        if(MaxCollectionSize > 0 && MaxCollectionSize < Count)
        {
            int trimCount = Count - MaxCollectionSize;
            for(int i=0; i<trimCount; i++)
            {
                RemoveAt(0);
            }
        }
    }
}

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莫言歌 2024-10-12 00:05:38

您可以派生 ObservableCollection 类并重写 InsertItem 方法吗？

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眼眸里的那抹悲凉 2024-10-12 00:05:38

试试这个：

public class FixedSizeObservableCollection<T> : ObservableCollection<T>
{
    private readonly int maxSize;
    public FixedSizeObservableCollection(int maxSize)
    {
        this.maxSize = maxSize;
    }

    protected override void InsertItem(int index, T item)
    {
        if (Count == maxSize)
            return; // or throw exception
        base.InsertItem(index, item);
    }
}

try this instead:

public class FixedSizeObservableCollection<T> : ObservableCollection<T>
{
    private readonly int maxSize;
    public FixedSizeObservableCollection(int maxSize)
    {
        this.maxSize = maxSize;
    }

    protected override void InsertItem(int index, T item)
    {
        if (Count == maxSize)
            return; // or throw exception
        base.InsertItem(index, item);
    }
}

回复收藏 0 原文