//this.textBox2.Lines是string[]
 this.textBox2.Lines = new String[3]{"abc","cde","fgh"};

------解决方案--------------------

C# code
public string[] Lines
{
    get
    {
        string text = this.Text;
        ArrayList arrayList = new ArrayList();
        int j;
        for (int i = 0; i < text.Length; i = j)
        {
            for (j = i; j < text.Length; j++)
            {
                char c = text[j];
                if (c == '\r' || c == '\n')
                {
                    break;
                }
            }
            string value = text.Substring(i, j - i);
            arrayList.Add(value);
            if (j < text.Length && text[j] == '\r')
            {
                j++;
            }
            if (j < text.Length && text[j] == '\n')
            {
                j++;
            }
        }
        if (text.Length > 0 && (text[text.Length - 1] == '\r' || text[text.Length - 1] == '\n'))
        {
            arrayList.Add("");
        }
        return (string[])arrayList.ToArray(typeof(string));
    }
    set
    {
        if (value != null && value.Length > 0)
        {
            StringBuilder stringBuilder = new StringBuilder(value[0]);
            for (int i = 1; i < value.Length; i++)
            {
                stringBuilder.Append("\r\n");
                stringBuilder.Append(value[i]);
            }
            this.Text = stringBuilder.ToString();
            return;
        }
        this.Text = "";
    }
}