winform获得焦点和失去焦点的问题

    this.textBox1.Validating += new System.ComponentModel.CancelEventHandler(this.textBox1_Validating);
    private void textBox1_Validating(object sender, CancelEventArgs e)
        {
            if (string.IsNullOrEmpty(textBox1.Text))
            {
                e.Cancel = true;
            }
        }

this.textBox1.Leave += new System.EventHandler(this.textBox1_Leave);
        private void textBox1_Leave(object sender, EventArgs e)
        {
            if (button1.Focused)
                return;
            if (textBox1.Text == "")
                textBox1.Focus();
        }

this.textBox1.Leave += new System.EventHandler(this.textBox1_Leave);

        private void textBox1_Leave(object sender, EventArgs e)
        {
            if (textBox1.Text == "")
                textBox1.Focus();
        }