尝试获取FileStream，关闭阅读器有多重要？

Question

I want to make sure to close the reader after creating a reader when there is an exception. So I want to include a finally bracket to this try and catch. But I can't close it in the finally bracket unless I have the reader declared outside above the try bracket. But if I do that I won't be catching any exceptions when creating the reader. I am not sure how critical it is to close the reader or not.

XmlSerializer xmlSr = new XmlSerializer(typeof(List<ProjectObject>));
try
{
    FileStream reader = new FileStream(mTextFilePath, FileMode.Open, FileAccess.Read, FileShare.Read);
    List<ProjectObject> addProjects = (List<ProjectObject>)xmlSr.Deserialize(reader);
    mSharedDriveLocalProjects = addProjects;
    reader.Close();
}
catch
{
    MessageBox.Show("Failed to load XML file");
}

The above is my code. Is it better to have it this way?

XmlSerializer xmlSr = new XmlSerializer(typeof(List<ProjectObject>));
FileStream reader = new FileStream(mTextFilePath, FileMode.Open, FileAccess.Read, FileShare.Read);
try
{
    List<ProjectObject> addProjects = (List<ProjectObject>)xmlSr.Deserialize(reader);
    mSharedDriveLocalProjects = addProjects;
}
catch
{
    MessageBox.Show("Failed to load XML file");
}
finally
{
    reader.Close();
}

Answer 1

The Using Statement is here to solve these dilemmas

 XmlSerializer xmlSr = new XmlSerializer(typeof(List<ProjectObject>));
 using(FileStream reader = new FileStream(mTextFilePath, FileMode.Open, FileAccess.Read, FileShare.Read))
 {
     try
     {
         List<ProjectObject> addProjects = (List<ProjectObject>)xmlSr.Deserialize(reader);
         mSharedDriveLocalProjects = addProjects;
     }
     catch
     {
         MessageBox.Show("Failed to load XML file");
     }
}

Any disposable object declared and created in a using statement is disposed at the exit of the block (the dispose method of the object is called and this method usually takes care to clean up everything, including the closure of the file)

Note that a using statement is like a try/finally, so if you want to catch the exception and show a nice error message to your user or log it somewhere, you still need to explicitly prepare a try/catch block around your code.

Answer 2

C# and .NET library provide a nice idiomatic way of doing this with using keyword:

using (var reader = new FileStream(mTextFilePath, FileMode.Open, FileAccess.Read, FileShare.Read)) {
    try {
        ...
    } catch {
        ...
    }
}

Since FileStream is IDisposable , and because its Dispose() method calls Close() , wrapping reader into using block provides a convenient method of ensuring that the stream is closed after you are done with it.