How to open and save RichEditBox (.rtf files) without using picker?

[Orion-Dev]

Hello, I am struggling to create my first UWP program in C#. I have run into a problem with reading/writing .rtf files and have not been able to work out a solution nor find one in the forums.

My program is an application for reading and writing a daily journal. The daily journal entries are displayed and edited in a RichEditBox. Next to the RichEditBox is a CalendarDatePicker.

When the CalendarDatePicker value changes, the program creates a file name based on the CalendarDatePicker date. For example, if the CalendarDatePicker's value was 7/22/2018, my program would turn that into the following file name: "2018_7_22.rtf" and then assign that to a string named fileName.

All of the above is working as desired. Here is the problem I am having:

When the value of the CalendarDatePicker changes, the program is supposed to immediately load the .rtf file (if it exists) from storage into the RichEditBox. And, when I press the SAVE button, the program is
supposed to save the RichEditBox contents to storage. Both reading and writing the file is supposed to
use the name derived from the CalendarDatePicker value rather than opening up a picker for either
opening or saving the file.

I have not been able to find any documentation about how to read and write a .rtf file for the RichEditBox without using a picker. I do not want to use a picker because I want that the given journal entry can only be read or written according to the file name that is based on the current value of the CalendarDatePicker.


Here is what I am trying to do:

String filePath = Windows.Storage.ApplicationData.Current.LocalFolder.toString;
// this returns error: "cannot convert method group 'ToString' to non-delegate type string"

String fileName = "2018_22_7.rtf"
// this is an example of a string my program would create according to the CalendarDatePicker's value.

At the end of my question is the code from the RichEditBox documentation. I want do away with the portion that uses the picker and replace the following line:
Windows.Storage.StorageFile file = await savePicker.PickSaveFileAsync();
with:
Windows.Storage.StorageFile file = filePath + fileName;

Is it possible to do this or am I forced to use a picker with the RichEditBox?
I will deeply appreciate any help I can get in solving this problem. I am
melting from frustration! Thank you!

Here is the code from the RichEditBox documentation:

private async void SaveButton_Click(object sender, RoutedEventArgs e)
{
Windows.Storage.Pickers.FileSavePicker savePicker = new Windows.Storage.Pickers.FileSavePicker();
savePicker.SuggestedStartLocation = Windows.Storage.Pickers.PickerLocationId.DocumentsLibrary;

// Dropdown of file types the user can save the file as
savePicker.FileTypeChoices.Add("Rich Text", new List<string>() { ".rtf" });

// Default file name if the user does not type one in or select a file to replace
savePicker.SuggestedFileName = "New Document";

Windows.Storage.StorageFile file = await savePicker.PickSaveFileAsync();
if (file != null)
{
// Prevent updates to the remote version of the file until we
// finish making changes and call CompleteUpdatesAsync.
Windows.Storage.CachedFileManager.DeferUpdates(file);
// write to file
Windows.Storage.Streams.IRandomAccessStream randAccStream =
await file.OpenAsync(Windows.Storage.FileAccessMode.ReadWrite);

editor.Document.SaveToStream(Windows.UI.Text.TextGetOptions.FormatRtf, randAccStream);

// Let Windows know that we're finished changing the file so the
// other app can update the remote version of the file.
Windows.Storage.Provider.FileUpdateStatus status = await Windows.Storage.CachedFileManager.CompleteUpdatesAsync(file);
if (status != Windows.Storage.Provider.FileUpdateStatus.Complete)
{
Windows.UI.Popups.MessageDialog errorBox =
new Windows.UI.Popups.MessageDialog("File " + file.Name + " couldn't be saved.");
await errorBox.ShowAsync();
}
}
}

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