如何点击按钮执行两个函数？

C# code

public bool IsPositiveDouble(TextBox textBox)        {            if(Regex.IsMatch(textBox1.Text,"^[1-9]\\d*$") && Regex.IsMatch(textBox2.Text,"^[1-9]\\d*$")&&Regex.IsMatch(textBox3.Text,"^[1-9]\\d*$"))            {                textBox1.BackColor = Color.Green;                textBox2.BackColor = Color.Green;                textBox3.BackColor = Color.Green;                return true;            }            else            {                textBox1.BackColor = Color.Red;                textBox2.BackColor = Color.Red;                textBox3.BackColor = Color.Red;                MessageBox.Show("Error!");                return false;            }        }        public bool Volume(TextBox textBox)        {            double a = Convert.ToDouble(textBox1.Text.Trim());            double b = Convert.ToDouble(textBox2.Text.Trim());            double c = Convert.ToDouble(textBox3.Text.Trim());            textBox4.Text = (a * b * c).ToString();            return true;        }        private void button1_Click(object sender, EventArgs e)        {                    }

我想实现点击button1之后先执行IsPositiveDouble判断输入的数字，如果是的话就执行Volume，不是的话就提示一个MessageBox。请问这个应该怎么写？

[解决办法]

C# code

if (IsPositiveDouble(this.textBox1))    Volume(this.TextBox1);else    MessageBox.Show("...");
[解决办法]
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引用:
C# code
if (IsPositiveDouble(this.textBox1))
Volume(this.TextBox1);
else
MessageBox.Show("...");


对了。谢谢！
请教一下为什么是textbox1而不是textbox4？