Question

我有一个下载列表和一个排除列表。

我想只使用for循环保留File2.zip。

然而，循环无法正常工作，同时保留File2.zip和File4.zip。

这是我想要应用于更大项目的示例代码。

在这种情况下，我不想使用download = download.Except(excluded).ToList();。

List<string> download = new List<string>();
download.Add("File1.zip");
download.Add("File2.zip");
download.Add("File3.zip");
download.Add("File4.zip");
download.Add("File5.zip");

List<string> excluded = new List<string>();
excluded.Add("File1.zip");
// keep File2.zip
excluded.Add("File3.zip");
excluded.Add("File4.zip");
excluded.Add("File5.zip");


// Remove Excluded Files from Download List
//
int count = download.Count();

for (int i = 0; i < count; i++)
{
    // index out of range check
    if (download.Count() > i )
    {
        // Remove
        if (excluded.Contains(download[i]))
        {
            download.RemoveAt(i);
            download.TrimExcess();
        }
    }
}


// Display New Download List
//
download.ForEach(x=>Console.WriteLine(x));

Answer 1

删除项目时，您希望向后循环：

//for (int i = 0; i < count; i++)
for (int i=count-1; i>=0; i--)
{
    // index out of range check
    //if (download.Count() > i ) - No longer needed.
    //{
        // Remove
        if (excluded.Contains(download[i]))
        {
            download.RemoveAt(i);
            download.TrimExcess();
        }
    //}
}

更改后，显示“File2.zip”。

Answer 2

删除时，向后循环：

：
使用HashSet<string>更有效地查找
上的项目
实现：

// Items to remove: excluded.Contains(item) is more efficient if excluded is a HashSet<T> HashSet<string> excluded = new HashSet<string>() { "File1.zip", "File3.zip", "File4.zip", "File5.zip", }; for (int i = download.Count - 1; i >= 0; --i) if (excluded.Contains(download[i])) // Shall we remove i-th item? download.RemoveAt(i); // If yes, remove it // If you want to trim the list, do not do it within the loop, // but remove all the required items and only then trim (once!) the list download.TrimExcess(); // Not necessary, but possible

编辑：在（罕见的）情况下必须循环前进（例如，如果必须按照创建顺序删除项目）循环

for (int i = 0; i < download.Count;) // please, notice, no increment here if (excluded.Contains(download[i])) // Shall we remove i-th item? download.RemoveAt(i) // If yes, remove it else i += 1; // If no, inspect the next item

使用For循环比较和删除列表项

2 个答案: