c# 判斷字串是否為空值IsNullOrEmpty

若有一個字串為空值，例如： string a=""; string b=null; string c=string.Empty; 所以要判斷a、b、c是否為空值,可以使用IsNullOrEmpty來判斷，所以上面三個字串，其結果皆為true。 string.IsNullOrEmpty(a) = true； string.IsNullOrEmpty(b) = true； string.IsNullOrEmpty(c) = true；

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<%@ Page Language="C#" AutoEventWireup="true" CodeFile="Default.aspx.cs" Inherits="_Default" %>



    


    

    

      

               
                
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.cs頁面

using System;
using System.Data;
using System.Configuration;
using System.Web;
using System.Web.Security;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Web.UI.WebControls.WebParts;
using System.Web.UI.HtmlControls;
public partial class _Default : System.Web.UI.Page
{
    CommonClass CC = new CommonClass();
    protected void Page_Load(object sender, EventArgs e)
    {
        if (!IsPostBack)
        {
            string id = Request["id"].ToString();
            bindNext(Convert.ToInt32(id));
        }
    }
    private void bindNext(int id)
    {
        int lastid = id - 1;
        int nextid = id + 1;
        this.ViewState["NextDetails"] = nextid.ToString();
        this.ViewState["lastid"] = lastid.ToString();
        this.ViewState["nextid"] = nextid.ToString();
        if (lastid > 0)
        {
            string sql = "select * from news where id=" + lastid + "";
            DataSet ds = CC.GetDataSet(sql, "dttit");
            DataRow[] row = ds.Tables["dttit"].Select();
            foreach (DataRow rs in row)
            {
                this.lbName.Text = rs["title"].ToString();
                this.lkLast.Text = rs["title"].ToString();
                this.ViewState["lastDetails"] = rs["content"].ToString();
            }

        }
        else
        {
            this.lkLast.Text = "已經是第一篇";
        }
        string sql1 = "select * from news where id=" + nextid + "";
        DataSet ds1 = CC.GetDataSet(sql1, "dttit");
        DataRow[] row1 = ds1.Tables["dttit"].Select();
        foreach (DataRow rs1 in row1)
        {
            this.lbName.Text = rs1["title"].ToString();
            this.lkNext.Text = rs1["title"].ToString();
            this.ViewState["nextDetails"] = rs1["content"].ToString();
        }

    }
    protected void lkLast_Click(object sender, EventArgs e)
    {
        this.LbDetails.Text = this.ViewState["lastDetails"].ToString();
        int id = Convert.ToInt32(this.ViewState["lastid"].ToString());
        bindNext(id);
    }
    protected void lkNext_Click(object sender, EventArgs e)
    {
        this.LbDetails.Text = this.ViewState["nextDetails"].ToString();
        int id = Convert.ToInt32(this.ViewState["nextid"].ToString());
        bindNext(id);
    }
}