小编Tan*_*ner的帖子

当我尝试安装mysql2 gem时,它失败并没有明显的错误.有谁知道如何解决这个问题,所以mysql2安装？

$ sudo gem install mysql2
Building native extensions.  This could take a while...
ERROR:  Error installing mysql2:
    ERROR: Failed to build gem native extension.

/System/Library/Frameworks/Ruby.framework/Versions/1.8/usr/bin/ruby extconf.rb
checking for rb_thread_blocking_region()... no
checking for mysql_query() in -lmysqlclient... no
checking for main() in -lm... yes
checking for mysql_query() in -lmysqlclient... no
checking for main() in -lz... yes
checking for mysql_query() in -lmysqlclient... no
checking for main() in -lsocket... no
checking for mysql_query() in -lmysqlclient... no
checking for main() in -lnsl... no …

Ruby新手在这里试图弄清楚如何使用宝石,到目前为止,体验并不是那么好.

通过gem安装mysql2之后我尝试在一个简单的文件中使用它.

require 'mysql2'

#client = Mysql2::Client.new(:host => "localhost", :username => "username")

虽然当我运行这个时,我得到:

Parse.rb:1:in `require': no such file to load -- mysql2 (LoadError)
 from Parse.rb:1

然而我的宝石列表包含mysql2:

Tanner-Smiths-MacBook-Pro:Humans_vs_Zombies_Parse tanner$ gem list

*** LOCAL GEMS ***

abstract (1.0.0)
actionmailer (3.0.1, 2.3.5, 1.3.6)
actionpack (3.0.1, 2.3.5, 1.13.6)
actionwebservice (1.2.6)
activemodel (3.0.1)
activerecord (3.0.1, 2.3.5, 1.15.6)
activeresource (3.0.1, 2.3.5)
activesupport (3.0.1, 2.3.5, 1.4.4)
acts_as_ferret (0.4.3)
arel (2.0.2)
builder (2.1.2)
capistrano (2.5.19, 2.5.2)
cgi_multipart_eof_fix (2.5.0)
daemons (1.1.0, 1.0.10)
dnssd (1.4, 0.6.0)
erubis (2.6.6)
fastthread (1.0.7, …

我有一个通过JPanel中的GridLayout布局的对象数组.我需要能够在数组中的索引中重新创建对象,并使用GridLayout更新来反映这一点.到目前为止,我无法找到"刷新"或重绘GridLayout.是否可以在不创建整个GridLayout或JPanel的情况下刷新GridLayout？假设我无权访问JFrame.

import javax.swing.*;
import java.awt.*;

public class Test
{
    public static void main(String args[])
    {
        JFrame frame = new JFrame();
        JPanel panel = new JPanel();

        panel.setLayout(new GridLayout(5,5));

        JLabel[][] labels = new JLabel[5][5];
        for (int i = 0; i < 5; i++)
        {
            for (int j = 0; j < 5; j++)
            {
                labels[j][i] = new JLabel("("+j+", "+i+")");
                panel.add(labels[j][i]);
            }
        }

        labels[0][0] = new JLabel("Hello World");

        //Without doing it this way (cause my objects can't do this)
        //labels[0][0].setText("Hello World!");

        frame.add(panel);

        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); …