private void ButtonNumber_Click(object sender, RoutedEventArgs e)

{

    Button btn = (Button)sender;

    string number = btn.Content.ToString();

    string keyword = txtKeyword.Text;

    //已经存在点"."

    if (keyword.Contains(".") && number.Equals("."))

    {

        txtKeyword.Focus();

        return;

    }

    //当前焦点位置

    int start = txtKeyword.SelectionStart;

    //焦点后面添加内容

    if (Common.Utils.isNumber(number) || number.Equals("."))

    {

        txtKeyword.Text = keyword.Insert(start, number);

        txtKeyword.SelectionStart = (start + number.Length);

    }

    else

    {

        //删除焦点前面的内容

        if (start > 0)

        {

            txtKeyword.Text = txtKeyword.Text.Remove(start - 1, 1);

            txtKeyword.SelectionStart = start - 1;

        }

    }

    txtKeyword.Focus();

}