我的 using 语句应该放在哪里？以及在哪里放置 try catch？

Question

我刚刚开始使用 filestream，虽然我让代码工作了，但我真的很想让它变得漂亮:)我不知道在哪里放置 using 语句，这样我就可以跳过stream.Close()，以及如何使用 try catch 最后。这是我的代码，不是最漂亮的东西，但它有效。双文件流用于清除文件。

编辑：很抱歉发布了那个非常糟糕的代码片段脸红：P我已经发布了我的第二次尝试:)

internal static void SaveFileAsTxt()
{
    FileStream streamer = new FileStream("Shipping2.txt", FileMode.Append, FileAccess.Write, FileShare.Write);
    streamer.Close();

    FileStream f = File.Open("Shipping2.txt", FileMode.Create);  
    f.Close();

    StreamWriter writer = new StreamWriter("Shipping2.txt", true, Encoding.ASCII);

    foreach (var shipment in _shipments)
    {
        string write = (shipment.Distance + ","+ shipment.Distance).ToString();
        writer.WriteLine(write);

    };

        writer.Close();
}


//--------new code--------


internal static void SaveFileAsTxt()
{
    if (File.Exists("Shipping2.txt"))
    {
        File.Delete("Shipping2.txt");
    }

    using (StreamWriter writer = new StreamWriter("Shipping2.txt", true, Encoding.ASCII))
    { 
        foreach (var shipment in _shipments)
        {
            string write = (shipment.Duration + ","+ shipment.Distance).ToString();
                        writer.WriteLine(write);
        }
    } 
}

Answer 1

您不需要多次打开该文件 - 实际上您此时已打开它三次次。这应该没问题； File.CreateText 如果文件已经存在，则将截断该文件，否则创建它：

// Are you *sure* you want to use ASCII? UTF-8 might be a better bet...
using (TextWriter writer = File.CreateText("Shipping2.txt", Encoding.ASCII))
{
    foreach (var shipment in _shipments)
    {
        // Removed redundant ToString call, and elided local variable.
        // Consider using a format string instead:
        // writer.WriteLine("{0},{1}", shipment.Distance, shipment.Distance);
        writer.WriteLine(shipment.Distance + "," + shipment.Distance);
    }
    // Removed empty statement (trailing semi-colon)
}

现在，您说您想使用 try/catch/finally - 但为什么呢？如果无法写入文件，您是否一定要在此方法中“处理”异常，而不是让它冒泡给调用者？

Answer 2

首先，我不明白这么多流的用途，但您可以在很多地方使用 using ：

internal static void SaveFileAsTxt()
{
    using(var streamer = new FileStream("Shipping2.txt", FileMode.Append, FileAccess.Write, FileShare.Write))
    {

    }

    using(var f = File.Open("Shipping2.txt", FileMode.Create)) 
    {

    }

    using(var writer = new StreamWriter("Shipping2.txt", true, Encoding.ASCII))
    {
        foreach (var shipment in _shipments)
        {
            string write = (shipment.Distance + ","+ shipment.Distance).ToString();
            writer.WriteLine(write);

        };
    }
}

Answer 3

您可以跳过前两个 FileStreams 并仅使用 StreamWriter，它会为您创建一个文件：

// Single using
using (StreamWriter writer = new StreamWriter(
                                             "Shipping2.txt", 
                                             true, // !!!
                                             Encoding.ASCII))
{
       foreach (var shipment in _shipments)
       {
           string write = (shipment.Distance + "," + shipment.Distance)
                          .ToString();
           writer.WriteLine(write);
       }
}

MSDN：

public StreamWriter(
    string path,
    bool append,
    Encoding encoding
)

附加

类型：System.Boolean 确定是否将数据附加到
文件。如果文件存在并且append为假，则文件被覆盖。
如果文件存在并且append为true，则数据被追加到
文件。 否则，将创建一个新文件。

编辑：关于更新的问题（第二部分）

您不需要手动删除文件，只需在StreamWriter的构造函数中指定append = false，它将覆盖文件：

如果文件存在并且append为假，则文件被覆盖

Answer 4

现在，您拥有的代码相当于：

internal static void SaveFileAsTxt() {
    using (FileStream streamer = new FileStream(
         "Shipping2.txt", FileMode.Append, FileAccess.Write, FileShare.Write
    );) {}

    using(FileStream f = File.Open("Shipping2.txt", FileMode.Create)) {}

    using(StreamWriter writer =
        new StreamWriter("Shipping2.txt", true, Encoding.ASCII)) {

        foreach (var shipment in _shipments) {
            string write = (shipment.Distance + "," + shipment.Distance).ToString();
            writer.WriteLine(write);
        }
    }
}

但我不知道您为什么打开第一个文件。
关于第二个，我相信您尝试使用此方法创建文件，
但还有其他方法可以做到这一点。

Answer 5

// Single using
using (StreamWriter writer = new StreamWriter(
                                             "Shipping2.txt", 
                                             true, // !!!
                                             Encoding.ASCII))
{
       foreach (var shipment in _shipments)
       {
           string write = (shipment.Distance + "," + shipment.Distance)
                          .ToString();
           writer.WriteLine(write);
       }
}

Answer 6

为了与众不同，我将使用 LINQ :-)

File.WriteAllLines(
    "Shipping2.txt", 
    _shipments.Select(
        p => string.Format(
            "{0},{1}", 
            shipment.Distance, 
            shipment.Distance)
    ),
    Encoding.ASCII);

此版本需要 .NET 4.0。 File.WriteAllLines 将创建文件，写入所有行并关闭文件。对于 _shipments< 的每个元素，_shipments.Select(p => string.Format("{0},{1}",shipment.Distance,shipment.Distance)) 将返回/code>，包含 shipment.Distance + "," +shipment.Distance 的字符串（使用 string.Format 格式化）
`