c# - How do I check if one of the lines already exist in the text file? -

string filename = "";         private void opentoolstripmenuitem1_click(object sender, eventargs e)         {             openfiledialog thedialog = new openfiledialog();             thedialog.title = "open text file";             thedialog.filter = "txt files|*.txt";             thedialog.initialdirectory = @"c:\";             if (thedialog.showdialog() == dialogresult.ok)             {                 lines = file.readalllines(recentfiles);                 filename = thedialog.filename;                 (int = 0; < lines.length; i++)                 {                     recentfiles = new streamwriter(recentfiles, true);                     recentfiles.writeline(thedialog.filename);                     recentfiles.close();                     items = file                         .readlines(recentfiles)                         .select(line => new toolstripmenuitem()                         {                             text = line                         })                         .toarray();                 recentfilestoolstripmenuitem.dropdownitems.addrange(items);                 }                  textfilecontenttorichtextbox(filename);             }         } 

i'm not sure if doing loop on lines right. want when open new text file check if exists in recentfiles(recentfiles.txt) , if exist don't write again.

loop on lines , if after looping on lines , variable filename not exist write text file, , update items.

linq perfect this:

// if there not lines equal filename if (!lines.any(line => line.equals(filename))) {     // write recent files text file }