How to clear data readed by scanner from textbox to recieve another one?

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C#5.0

.NET4.5

barcode

Problem

When read qr using barcode scanner for more than one it append the same textbox4 .

i need to clear data after every scanning done .

Details

I using usb scanner reader qr code with type metro logic working as keyboard

and using USB

i read data in textbox4 key down success

but problem if i read data for new qr code

it append in same text box

so that what i do to clear the data recieved before and prevent append to old

my code

private void textBox4_KeyDown(object sender, KeyEventArgs e)
        {

                string[] lines = textBox4.Text.Split(new string[] { Environment.NewLine }, StringSplitOptions.None);

            if (lines.Length > 4)
            {
                textBox1.Text = lines[1].Substring(lines[1].IndexOf(":") + 1);
                textBox2.Text = lines[2].Substring(lines[2].IndexOf(":") + 1);
                textBox3.Text = lines[3].Substring(lines[3].IndexOf(":") + 1);
                textBox5.Text = lines[4].Substring(lines[4].IndexOf(":") + 1);
            }

textbox4 read data from reader device then split them to textboxes

What I have tried:

How to clear data readed by scanner from textbox to recieve another one?