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, Nov 01 '16 at 15:42
Your run method will return with data == null long before the `OnChanged` event fires to set `data`. — ChrisF, Nov 01 '16 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, Nov 01 '16 at 15:44
What kind of front-end you have?, you must have [an Observer, Pub/Sub, and Data Binding](http://stackoverflow.com/questions/15594905/difference-between-observer-pub-sub-and-data-binding) — Byron, Nov 01 '16 at 15:45
@Byron I am using angularJS a function to invoke the method using handler and return the daa — lol, Nov 01 '16 at 16:14
you are using a local varible for the `FileSystemWatcher`, so when the Run` method end the watcher will be release, it must be also static or be stored on a program lifecycle — Byron, Nov 01 '16 at 16:21

score 1 · Accepted Answer · answered Nov 01 '16 at 15:44

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
}

so how can I return my data , in this case handler won't be invoked — lol, Nov 01 '16 at 15:57
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. — Daniel A. Thompson, Nov 01 '16 at 15:59

FileSystemWatcher Onchage return value

1 Answers1