c# - 在 wp7 中重置应用程序设置

Question

我创建了一个应用程序，它最初创建一个数据库并在其中保存一些数据。现在我想在用户单击重置按钮时删除此数据库及其文件，但我收到错误消息——“这在另一个进程中使用”。我希望它在单击重置按钮时删除并重新创建数据库。有什么想法吗？

Answer 1

最常见的原因是与 Windows Phone 上的独立存储交互的线程不安全 性质。无论您如何实现数据库(在一个文件或一系列文件中)，您都在某种程度上与隔离存储进行交互。

我强烈建议您阅读并确保您理解 this overview of isolated storage在走得太远之前。

你的评论:

This is in use in another process

让我觉得您正在使用第三方库来处理您的数据库。当库本身无法访问独立存储时，将抛出此异常/错误。在不确切了解您如何实现数据库的情况下，很难准确说明您的情况。

您永远不会“重新创建 IsolatedStorage”，Isolated Storage 是一个术语，用于定义您的应用程序有权访问的磁盘空间集合。就像文件夹一样，这个磁盘空间有一个根目录，并且只包含您创建的文件。

为了避免在访问独立存储时出现线程异常，请确保使用 using C# 中的关键字如下所示:

namespace IsolatedStorageExample
{
    public class ISOAccess
    {
        // This example method will read a file inside your Isolated Storage.
        public static String ReadFile(string filename)
        {
            string fileContents = "";
            // Ideally, you should enclose this entire next section in a try/catch block since
            // if there is anything wrong with below, it will crash your app.
            // 
            // This line returns the "handle" to your Isolated Storage. The phone considers the
            // entire isolated storage folder as a single "file", which is why it can be a 
            // little bit of a confusing name.
            using(IsolatedStorageFile file = IsolatedStorageFile.GetUserStoreForAppliaction())
            {   
                // If the file does not exist, return an empty string
                if(file.Exists(filename))
                {
                    // Obtain a stream to the file
                    using(IsolatedStorageFileStream stream = File.OpenFile(filename, FileMode.Open)
                    {
                        // Open a stream reader to actually read the file.
                        using(StreamReader reader = new StreamReader(stream))
                        {
                            fileContents = reader.ReadToEnd();
                        }
                    }
                }   
            }

            return fileContents;
        }
    }
}

这应该有助于解决线程安全问题。为了更具体地帮助你想做什么，看看下面的方法(你可以把它添加到上面的类):

// BE VERY CAREFUL, running this method will delete *all* the files in isolated storage... ALL OF THEM
public static void ClearAllIsolatedStorage()
{
    // get the handle to isolated storage
    using(IsolatedStorageFile file = IsolatedStorageFile.GetUserStoreForApplication())
    {
        // Get a list of all the folders in the root directory
        Queue<String> rootFolders = new Queue<String>(file.GetDirectoryNames());

        // For each folder...
        while(0 != rootFolders.Count)
        {
            string folderName = rootFolders.Dequeue();

            // First, recursively delete all the files and folders inside the given folder.
            // This is required, because you cannot delete a non-empty directory
            DeleteFilesInFolderRecursively(file, folderName);

            // Now that all of it's contents have been deleted, you can delete the directory
            // itsself.
            file.DeleteDirectory(rootFolders.Dequeue());
        }

        // And now we delete all the files in the root directory
        Queue<String> rootFiles = new Queue<String>(file.GetFileNames());
        while(0 != rootFiles.Count)
            file.DeleteFile(rootFiles.Dequeue());
    }
}

private static void DeleteFilesInFolderRecursively(IsolatedStorageFile iso, string directory)
{
    // get the folders that are inside this folder
    Queue<string> enclosedDirectories = new Queue<string>(iso.GetDirectoryNames(directory));

    // loop through all the folders inside this folder, and recurse on all of them
    while(0 != enclosedDirectories.Count)
    {
        string nextFolderPath = Path.Combine(directory, enclosedDirectories.Dequeue());
        DeleteFilesInFolderRecursively(nextFolderPath);
    }

    // This string will allow you to see all the files in this folder.
    string fileSearch = Path.Combine(directory, "*");

    // Getting the files in this folder
    Queue<string> filesInDirectory = iso.GetFileNames(fileSearch);

    // Finally, deleting all the files in this folder
    while(0 != filesInDirectory.Count)
    {
        iso.DeleteFile(filesInDirectory.Dequeue());
    }
}

我强烈推荐的另一件事是使用描述的“多线程单例模式”实现访问 IsolatedStorage 的类 here.

希望对您有所帮助。代码是“按原样”提供的，我没有编译它，但一般概念都在那里，所以如果有什么不对劲，请阅读 MSDN 文档以查看我犯了什么错误。但我向你保证，其中大部分是从我的功能代码中复制的，因此它应该可以正常工作，只需很少的 fanagaling。