FileSystemWatcher Onchage return value

Question

I have a FileSystemEventHandler that onchange read the data from my file, now I need to return this data as I am working with a handler. now my code works but does not return anything so I do not have the updated data on my front end. this is my question : how can I return the data?

Thanks

public static string data = null;
[PermissionSet(SecurityAction.Demand, Name = "FullTrust")]
public static string Run()
{
    try
    {
        // Create a new FileSystemWatcher and set its properties.
        FileSystemWatcher watcher = new FileSystemWatcher();
        //watcher.Path = System.IO.Directory.GetCurrentDirectory();
        watcher.Path = Path.Combine(HttpRuntime.AppDomainAppPath, "view");
        /* Watch for changes in LastAccess and LastWrite times, and
           the renaming of files or directories. */
        watcher.NotifyFilter = NotifyFilters.LastWrite
           | NotifyFilters.FileName | NotifyFilters.DirectoryName;
        watcher.Filter = "info.txt";

        // Add event handlers.
        watcher.Changed += new FileSystemEventHandler(OnChanged);

        // Begin watching.
        watcher.EnableRaisingEvents = true;
    }
    catch (Exception ex)
    {
        Console.Write(ex.ToString());
    }
    return data;

}

private static void OnChanged(object source, FileSystemEventArgs e)
{
    data = FileManager.Read();
}

Do you mean you want Run() to block until OnChanged() has been raised? — CodeCaster
– CodeCaster, Commented Nov 1, 2016 at 15:42
Your run method will return with data == null long before the OnChanged event fires to set data. — ChrisF
– ChrisF, Commented Nov 1, 2016 at 15:43
If you don't need Run() to be blocked then you should not expect it to return data to update ui. You should update your ui either directly in OnChanged() or in another method that must be called in OnChanged() and that will read the data for you. — CodingNagger
– CodingNagger, Commented Nov 1, 2016 at 15:44
What kind of front-end you have?, you must have an Observer, Pub/Sub, and Data Binding — Byron
– Byron, Commented Nov 1, 2016 at 15:45
@Byron I am using angularJS a function to invoke the method using handler and return the daa — lol
– lol, Commented Nov 1, 2016 at 16:14

Daniel A. Thompson · Accepted Answer · 2016-11-01 15:44:29Z

1

FileSystemWatcher is an event-driven mechanism. You don't need to return anything from your Run() method - you need to do whatever you want to do as a result of the change in your OnChanged() event handler. Try taking a look at the API for FileSystemEventArgs.

[PermissionSet(SecurityAction.Demand, Name = "FullTrust")]
public static void Run()
{
    try
    {
        // Create a new FileSystemWatcher and set its properties.
        FileSystemWatcher watcher = new FileSystemWatcher();
        //watcher.Path = System.IO.Directory.GetCurrentDirectory();
        watcher.Path = Path.Combine(HttpRuntime.AppDomainAppPath, "view");
        /* Watch for changes in LastAccess and LastWrite times, and
           the renaming of files or directories. */
        watcher.NotifyFilter = NotifyFilters.LastWrite
           | NotifyFilters.FileName | NotifyFilters.DirectoryName;
        watcher.Filter = "info.txt";

        // Add event handlers.
        watcher.Changed += new FileSystemEventHandler(OnChanged);

        // Begin watching.
        watcher.EnableRaisingEvents = true;
    }
    catch (Exception ex)
    {
        Console.Write(ex.ToString());
    }
}


private static void OnChanged(object source, FileSystemEventArgs e)
{
    string fileText = File.ReadAllText(e.FullPath);
    // do whatever you want to do with fileText
}

answered Nov 1, 2016 at 15:44

Daniel A. Thompson

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2 Comments

lol Over a year ago

so how can I return my data , in this case handler won't be invoked

Daniel A. Thompson Over a year ago

The FileSystemWatcher will invoke OnChanged() for you when the change occurs. It's then up to you to do whatever you want to do in the handler as a result of the change. You could update your UI directly from the handler, for example.

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