如何在for循环中使用每个按钮的lamda表达式制作按钮? [英] How can I make buttons in a for loop with a lamda expression for each?

问题描述

我正在尝试用javafx制作子手游戏.因此，很自然，我没有使用26个单独的按钮，而是尝试使用for循环来创建每个按钮.我将它们放入一个名为Alphabet的ArrayList中，并将其添加到flowPane中.我遇到的麻烦是，当我尝试将每个按钮的操作设置为带有字母参数的函数时，该功能会检查字母是否已使用或是否在单词中.

I'm trying to make a hangman game in javafx. So naturally, instead of making 26 individual buttons, I am trying to use a for loop to create each button. I am putting them into an ArrayList called alphabet and adding them to a flowPane. The trouble I am running into is when I try to set the action of each button to go to a function with the parameter of it's letter that checks to see if the letter has been used or if it is in the word.

所有实例:

ArrayList<Button> alphabet = new ArrayList<Button>();
FlowPane keyboard = new FlowPane();

letterGuess函数(当前为空)

letterGuess function (currently empty)

public void letterGuess(char letter) {

}

launch()函数中的代码:

The code in my launch() function:

char letter;
for(int i=0 ; i<26 ; i++) {
    letter = (char) (i+65);
    alphabet.add(new Button("" + letter));
    keyboard.getChildren().add(alphabet.get(i));
    alphabet.get(i).setOnAction(e -> letterGuess(letter));
}

我希望代码能够正确运行，并成功将每个按钮的字母传递给letterGuess().我得到的错误是字母 Alphabet.get(i).setOnAction(e-> letterGuess(字母));该错误表明:在包围范围内定义的局部变量字母必须是最终的或实际上是最终的

I expect the code to run through without an error and successfully pass letter to letterGuess() for each button. The error I get is at letter in alphabet.get(i).setOnAction(e -> letterGuess(letter)); The error says: Local variable letter defined in an enclosing scope must be final or effectively final

推荐答案

问题是您在循环外声明了letter，因此试图在循环内更改其值.这意味着lambda不能使用它，因为它不是最终版本或有效"最终版本.

The issue is that you're declaring letter outside the loop and thus trying to change it's value inside the loop. This means the lambda can't use it since it isn't a final or "effectively" final.

您可以通过在循环中将char声明为新来解决此问题.

You can solve this by declaring the char as new within the loop.

这是您编写循环的另一种方法，它将很好地工作:

Here is another way you could write the loop which will work fine:

    for (int i = 0; i < 26; i++) {
        char letter = (char) (i + 65);
        Button button = new Button(String.valueOf(letter));
        button.setOnAction(event -> letterGuess(letter));
        alphabet.add(button);
    }

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您还可以在循环内将letter声明为final，但是在这种情况下没有必要.因为letter在循环中只分配了一次值，所以有效 final并且兰巴知道它.

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You could also declare letter as final within the loop, but it is not necessary in this case. Because letter is only assigned a value once in the loop, it is effectively final and the lamba knows it.

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