Ruby with Java swing 表示计数为零

Question

你好，我是 javax.swing 的新手，我想问问你们为什么我会收到这个错误（我会在我的代码后面加上确切的错误）。我已经尝试了我能找到的一切。谢谢你们，我很抱歉，如果这是一个简单的修复，我现在真的很糟糕ruby
testGui.rb

# javaSwingHello.rb  
require 'java' # Line 2  
JFrame = javax.swing.JFrame  
JLabel = javax.swing.JLabel  
JPanel = javax.swing.JPanel
JButton = javax.swing.JButton
BorderFactory = javax.swing.BorderFactory
BorderLayout = java.awt.BorderLayout
GridLayout = java.awt.GridLayout
count = 1
frame  = JFrame.new  
panel  = JPanel.new
button = JButton.new "Click me" 
button.addActionListener self
label = JLabel.new "Number of clicks: 0"
panel.setBorder BorderFactory.createEmptyBorder(70, 70, 20, 70)
panel.setLayout GridLayout.new(0, 1)
panel.add button
panel.add label
frame.add panel, BorderLayout::CENTER
frame.setDefaultCloseOperation(JFrame::EXIT_ON_CLOSE)
frame.setTitle "TEST GUI"
frame.pack
frame.setVisible true 
def actionPerformed(event)
    count += 1
    texttoset = "Number of clicks " + count
    label.setText(texttoset)
end

错误（当我按下按钮时出现此错误）

Exception in thread "AWT-EventQueue-0" org.jruby.exceptions.NoMethodError: (NoMethodError) undefined method `+' for nil:NilClass
        at testGui.actionPerformed(testGui.rb:26)

Answer 1

更多 Ruby 问题 - 局部变量不会被复制到新范围：

def actionPerformed(event)
    count += 1
    texttoset = "Number of clicks " + count
    label.setText(texttoset)
end

count 是方法的局部变量（最初是 nil），因此失败。

如果你只是想测试一下，你可以使用全局变量来解决这个问题：

$count = 1

def actionPerformed(event)
    $count += 1
    texttoset = "Number of clicks " + count
    label.setText(texttoset)
end

据说不要使用全局变量，而是设置一个适当的对象来封装状态和 'implement' actionPerformed 接口。

Answer 2

你没有说，你将如何使用 actionPerformed，但一种可能是将方法设为 lambda:

count = 1
$ActionPerformed = -> (event) do
    count += 1
    texttoset = "Number of clicks " + count
    label.setText(texttoset)
end

您必须将其调用为

$ActionPerformed.call(myEvent)

Ruby with Java swing 表示计数为零

Ruby with Java swing is saying that count is nil

ruby

swing

jruby