如何更改文本文件中的值并覆盖它

本文关键字：覆盖 何更改 文本 文件 | 更新日期: 2023-09-27 18:04:01

我创建了一个*.txt文件，其中包含如下数据:

deviceid,model,availability,renterID,renterName,reneterSurname,OS
0001,iPhone_5S,false,002,John,Dowland,iOS-7.1.2
0002,GalaxyS3,false,002,Amadeus,Mozart,Android-4.3.2

在我的c#应用程序(WPF应用程序)得到这个函数来操作文件:

private void rentSaveButton_Click(object sender, RoutedEventArgs e)
    {
        StreamWriter sw = new StreamWriter(@"D:'deviceLib.txt", true);
        var currentUser = _list.Where(u => u.Id == int.Parse(userIDTextBox.Text)).FirstOrDefault();
        var currentDevice = _list2.Where(i => i.deviceId == int.Parse(deviceIDTextBox.Text)).FirstOrDefault();
        if (currentDevice != null &&  currentUser != null)
        {
            currentDevice.Availability = false;
            currentDevice.rentId = currentUser.Id;
            currentDevice.rentName = currentUser.Name;
            currentDevice.rentSurname = currentUser.Surname;
            dataGridDeviceList.Items.Refresh();
            sw.WriteLine();
            sw.Close();                
            MessageBox.Show("Rent done. Thanks!");
            tabControl.SelectedItem = mainTab;
        }
        else
        {
            MessageBox.Show("We don't have such device. Sorry :( ");
            userIDTextBox.Clear();
            deviceIDTextBox.Clear();
        }
    }

现在，问题是我通常可以在程序工作期间处理这个文件，它改变值，可以读取它等，但当我关闭应用程序(通过X按钮)什么也没有发生。

如何更改文本文件中的值并覆盖它

您没有向文件写入任何内容。

sw.WriteLine(); // you need to pass a string in to this function

在我看来，你一定是发明了一个理论，你对currentDevice所做的任何改变都应该以某种方式影响到写入sw的内容。你在这里看到的就是卡尔·波普尔(Karl Popper)过去所说的"失证":你的理论预测了可以观察到的行为;你观察;行为没有发生。第一种解释是你的理论是错误的。

事实上，这是对你所看到(没有看到)的东西的正确解释。currentDevice和sw之间绝对没有任何联系。一个也没有。这就像你在按微波炉上的按钮，试图启动你的车。如果你不换一条路，你就得走路去上班了。

currentDevice.Availability = false;
currentDevice.rentId = currentUser.Id;
currentDevice.rentName = currentUser.Name;
currentDevice.rentSurname = currentUser.Surname;
dataGridDeviceList.Items.Refresh();
sw.WriteLine();
sw.Close();

你所做的就是在一个随机对象上改变一堆属性，刷新你的数据网格，然后写一个换行符， 一个换行符，没有其他，到输出流。为什么没有参数的sw.WriteLine();会这样做?好吧，它这样做是因为这是设计师决定的。理智地不能做任何其他事情，因为你没有给它任何可以写的东西。这种行为是有记录的，如果你花十秒钟阅读文档，你就会知道。

如果你想写一个非空的行到一个文件中，使用WriteLine的许多重载中的一个，这些重载在文档中有详细的说明。如果您只想编写一行的部分，请使用Write的许多重载之一，这些重载也有文档记录。

这样的东西会很好(我猜你的字段名;如果你不知道它们是什么，也许其他人在StackOverflow上知道你的代码的那部分看起来像什么，可以帮助你):

currentDevice.Availability = false;
currentDevice.rentId = currentUser.Id;
currentDevice.rentName = currentUser.Name;
currentDevice.rentSurname = currentUser.Surname;
//  Write fields in desired order of appearance in the file. 
sw.Write(currentDevice.deviceID);
//  There are many far superior ways to write a comma to the file, 
//  and I'll hear about all of them in comments, but we're keeping 
//  it as simple as possible for the moment.  
sw.Write(",");
sw.Write(currentDevice.model);
sw.Write(",");
//  Properties you just set
sw.Write(currentDevice.Availability);
sw.Write(",");
sw.Write(currentDevice.rentID);
sw.Write(",");
sw.Write(currentDevice.rentName);
sw.Write(",");
sw.Write(currentDevice.rentSurname);
sw.Write(",");
sw.Write(currentDevice.OS);
//  NOW write a newline.
sw.WriteLine();

但那是丑陋的。我们把它卷进一个方法来隐藏它。这被称为"重构"。

public void WriteDeviceStateToStream(StreamWriter stream, WhateverTheDeviceClassIs device)
{
    //  Write fields in desired order of appearance in the file. 
    stream.Write(device.deviceID);
    //  There are many far superior ways to write a comma to the file, 
    //  and I'll hear about all of them in comments, but we're keeping 
    //  it as simple as possible for the moment.  
    stream.Write(",");
    stream.Write(device.model);
    stream.Write(",");
    //  Properties you just set
    stream.Write(device.Availability);
    stream.Write(",");
    stream.Write(device.rentID);
    stream.Write(",");
    stream.Write(device.rentName);
    stream.Write(",");
    stream.Write(device.rentSurname);
    stream.Write(",");
    stream.Write(device.OS);
    //  NOW write a newline.
    stream.WriteLine();
    //  DO NOT close the stream here. The stream belongs to the caller; make no 
    //  assumptions about what he plans to do with it next. 
}

…在事件处理程序中，调用那个方法。还要注意StreamWriter的using语句。这样就可以正确地处理它，从而关闭文件等等。这很重要。

private void rentSaveButton_Click(object sender, RoutedEventArgs e)
{
    using (StreamWriter sw = new StreamWriter(@"D:'deviceLib.txt", true))
    {
        var currentUser = _list.Where(u => u.Id == int.Parse(userIDTextBox.Text)).FirstOrDefault();
        var currentDevice = _list2.Where(i => i.deviceId == int.Parse(deviceIDTextBox.Text)).FirstOrDefault();
        if (currentDevice != null &&  currentUser != null)
        {
            currentDevice.Availability = false;
            currentDevice.rentId = currentUser.Id;
            currentDevice.rentName = currentUser.Name;
            currentDevice.rentSurname = currentUser.Surname;
            dataGridDeviceList.Items.Refresh();
            //  Call write method
            WriteDeviceStateToStream(sw, currentDevice);
            //  The user's going to get real tired of this messagebox real fast. 
            MessageBox.Show("Rent done. Thanks!");
            tabControl.SelectedItem = mainTab;
        }
        else
        {
            MessageBox.Show("We don't have such device. Sorry :( ");
            userIDTextBox.Clear();
            deviceIDTextBox.Clear();
        }
    }
}
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