‘Null Referecnce Exception’ while setting value to Array of string one by one (2)

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C#

Dear Friends,

I should First thank you all for taking time reading and kindly answering my question. It was suggested that I should set the Array Size at the time of definition.

I understand it but the fact is, at the time of definition, I am not aware of its probable size needed. As it was pointed I have to define the ‘FileNames’
which is an Array of string outside of button1_Click event (due to some reasons). But within this event the size of it will become clear. So I don’t know it in advance.

In other words, what should I do when I need to define an array with unknown size at the time of definition so that it won’t raise such error?

In bellow my question is repeated for convenience

*************

Hello,

In a program the user may choose some files to have some operation on. In ‘OpenFileDialog’, Full path of files, both path of directory and File names could be returned. What I require is to separate File path from its following File name. To do so, I needed to set value to Array of string one by one. I used the code below but there is a error as follows:

Null Reference Exception was unhandled
Object reference not set to an instance of an object.

Could you please help me?
Thanks a lot

public Form1()
        {
            InitializeComponent();
        }
 
 string[] FilePathNames;
        string[] FileNames; // I need to define here, instead of defining inside 'button1_Click' method 

        private void button1_Click(object sender, EventArgs e)
        {
 
           ... 
 

            if (myOpenFileDialog.ShowDialog() == DialogResult.OK)
            {
                 FilePathNames = myOpenFileDialog.FileNames;
                //FilePathNames, includes Full path of files, both path of                                directory and File names
                                            
                int counter = 0;
 
                // in loop below, i want to detach File path from its following File name
                foreach (string fname in FilePathNames)  
                {
                    int idx = fname.LastIndexOf('\\');
                    FileNames[counter] = fname.Substring(idx + 1); // Here, Error Ocuurs!!!
                    counter += 1;
                }
            }
 
        }