Question

当用户名或密码文本框为空时，我试图显示一个消息框但是当我运行项目时，显示的唯一文本框是“JOptionPane.showMessageDialog（null，”您的用户名或密码不正确“）;”请帮忙，谢谢！

private void jButton1ActionPerformed(ActionEvent evt) {                                         
  String user=txtUsername.getText();
  char[] pass=txtPassword.getPassword();

  if(user == null) {
    JOptionPane.showMessageDialog(null,"Username Field is empty"); 
  } else if(pass==null) {
    JOptionPane.showMessageDialog(null,"Password Field is empty");     
  } else {
    String sql="select * from account where username=? and password=?";

    try{
      pst=conn.prepareStatement(sql);
      pst.setString(1,txtUsername.getText());
      pst.setString(2,txtPassword.getText());

      rs=pst.executeQuery();

      if (rs.next()) {
        GridlockMain a=new GridlockMain();
        a.setVisible(true);
      } else {
        JOptionPane.showMessageDialog(null,"Your Username or Password is incorrect"); 
        txtUsername.setText(null);
        txtPassword.setText(null);
      }
    } catch (SQLException e) {
      JOptionPane.showMessageDialog(null,e); 
    }
  }
}

Answer 1

如果您将其保留为空，则

JTextField.getText()不会返回null。尝试在isEmpty条件下使用if方法检查值。

  String user=txtUsername.getText();// It return empty String "" 
                                    // even no data is entered.

  if(user.isEmpty){
     JOptionPane.showMessageDialog(null,"Username Field is empty"); 
  }
  ......

Answer 2

试试这个..

if(!user.length() > 0){
  JOptionPane.showMessageDialog(null,"Username Field is empty"); 
  }
else if(!pass.length > 0){
  JOptionPane.showMessageDialog(null,"Password Field is empty");     
}

Answer 3

它返回一个空字符串“”比较

StringUtils.isEmpty(txtUsername.getText())

Answer 4

我还在文本验证过程中遇到了困难。我找到了一种非常简单的测试方法。在这里，我只是不允许他们进入，或者按下按钮，而不是使用JOptionPane向用户显示消息。这是我的代码：

//Validate whether user Has input some information:
                if(UserNameTA.getText() == null || UserNameTA.getText().trim().isEmpty()) 
                {
                    btnEnter.setEnabled(false);
                }
                else
                {
                    //Make a new JFrame for login
                    new ProfileHome().setVisible(true);
                    frame.dispose();
                }
                btnEnter.setEnabled(true);

我希望这至少可以指导您取得成功。

Answer 5

String user = txtUsername.getText();
String pw = txtPassword.getText();      

if(user.isEmpty() || (pw.isEmpty()))

{       
    JOptionPane.showMessageDialog(null, "Your Username or Password is incorrect" );
}
    else
{
   //proceed to query

Answer 6

public void save(object sender, EventArgs e)
{
    string s = Session["num"].ToString();
    int num = Int32.Parse(s);
    DataTable t = (DataTable)Session["table"];
    DataRow row1 = t.NewRow();
    for(int i=0;i<num;i++){
        TextBox tt = (TextBox)(form.FindControl("txtser" + i.ToString()));
        string str= tt.Text + " ";
    }
    t.Rows.Add(row1);
    Session["table"] = t;
    GridView1.EditIndex = -1;
    GridView1.DataSource = t;
    GridView1.DataBind();
}

检查空文本框

6 个答案: