Question

得到这个错误，已经做了一些研究，但我无法修复它，如果有人可以帮助我：

错误：

WindowsFormsApplication2.exe中出现未处理的“System.NullReferenceException”类型异常

附加信息：对象引用未定义为对象的实例。

它发生在con.Open();

上

我的代码：

    using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows.Forms;
using System.Data.Sql;
using System.Data.SqlClient;

namespace WindowsFormsApplication2
    {
            public partial class Form1 : Form
            {
                SqlConnection con;
                SqlDataAdapter adap;
                DataSet ds;

    public Form1()
    {
        InitializeComponent();
    }

    private void button1_Click(object sender, EventArgs e)
    {
        AdicionarFornecedor add = new AdicionarFornecedor();
        add.ShowDialog();
    }

    private void button3_Click(object sender, EventArgs e)
    {
        }

    private void Form1_Load(object sender, EventArgs e)
    {
        try
        {
            SqlConnection con;
            SqlDataAdapter adap;
            DataSet ds;
            con = new SqlConnection();
            con.ConnectionString = (@"Data Source=(LocalDB)\v11.0;AttachDbFilename=C:\Users\Duarte\Documents\Visual Studio 2013\Projects\WindowsFormsApplication2\WindowsFormsApplication2\PAPPloran.mdf;Integrated Security=True;Connect Timeout=30");
            con.Open();
            adap = new SqlDataAdapter("select * from Pagamentos", con);
            ds = new System.Data.DataSet();
            adap.Fill(ds, "P");
            dataGridView1.DataSource = ds.Tables[0];
        }
        catch(Exception ex)
        {
            MessageBox.Show("Erro\n" + ex.Message, "Error",MessageBoxButtons.OK,MessageBoxIcon.Error);

        }


        }

    private void button4_Click(object sender, EventArgs e)
    {
            AdicionarPagamento add2 = new AdicionarPagamento();
            add2.ShowDialog();
    }

    private void button6_Click(object sender, EventArgs e)
    {
            VerFornecedores add = new VerFornecedores();
            add.ShowDialog();
    }

    private void button5_Click(object sender, EventArgs e)
{
        foreach (DataGridViewRow item in this.dataGridView1.SelectedRows)
         {
             dataGridView1.Rows.RemoveAt(item.Index);
         }
}

    private void search()
    {

    con.Open();
        SqlCommand cmd = con.CreateCommand();
        cmd.CommandType = CommandType.Text;
        cmd.CommandText = "select * from Pagamentos where name like ('" + textBox1.Text + "%')";
        cmd.ExecuteNonQuery();
        DataTable dt = new DataTable();
        SqlDataAdapter da = new SqlDataAdapter(cmd);
        da.Fill(dt);
        dataGridView1.DataSource = dt;

        con.Close();
    }
    private void textBox1_TextChanged (object sender, EventArgs e)
    {
        search();


    }

    private void button2_Click(object sender, EventArgs e)
    {

    }
    }
    }

我想在写一封信后立即进行实时搜索，程序显示以该字母开头的数据。

Answer 1

您正在为Form1_Load中的连接对象创建新引用。在Form_Load方法中尝试这个：

    try
    {

        SqlDataAdapter adap;
        DataSet ds;
        this.con = new SqlConnection();
        this.con.ConnectionString = (@"Data Source=(LocalDB)\v11.0;AttachDbFilename=C:\Users\Duarte\Documents\Visual Studio 2013\Projects\WindowsFormsApplication2\WindowsFormsApplication2\PAPPloran.mdf;Integrated Security=True;Connect Timeout=30");
        this.con.Open();
        adap = new SqlDataAdapter("select * from Pagamentos", con);
        ds = new System.Data.DataSet();
        adap.Fill(ds, "P");
        dataGridView1.DataSource = ds.Tables[0];
    }
    catch(Exception ex)
    {
        MessageBox.Show("Erro\n" + ex.Message, "Error",MessageBoxButtons.OK,MessageBoxIcon.Error);

    }

或在搜索方法中创建一个新实例。

Visual C＃ - 错误：WindowsFormsApplication2.exe中出现'System.NullReferenceException'

1 个答案: