Multiline textbox printing last item only

Question

I’m using TextBoxt Multiline to "issue" the report in the system itself. Ta printing, however, appears the following message: "System.Windows.Forms.Textbox" and then the data.

public Formulário()
{
    InitializeComponent();
}

private void button1_Click(object sender, EventArgs e)
{
    using (StreamReader ler = new StreamReader(@"escrevesaida.txt"))
    {
        string leitor;

        while ((leitor = ler.ReadLine()) != null)
        {
            textBox1.AppendText($"{leitor}{Environment.NewLine}");
        }
    }
}

Answer 1

The problem is that in Text of textBox, for each line it reads you are assigning the value, replacing the value it had previously.

textBox1.Text = leitor;

The correct one would be to concatenate, that is, to join the results of each line. As follows:

textBox1.Text += leitor;

Answer 2

If the goal is to separate line by line, the best way will be:

string leitor;

while ((leitor = ler.ReadLine()) != null)
{
    textBox1.AppendText($"{leitor}{Environment.NewLine}");
}

Placing the following code before the while:

leitor = ler.ReadLine();
textBox1.Text = leitor;

I was "picking up" the first line and only then the rest. You can put everything into the cycle.

---

In relation to the text System.Windows.Forms.TextBox, Text: 123, really, as @Thiagomagalhães said, it seems to originate in textBox1.Text += textBox1; or something like that. Unless it already comes from the file...