如何修复此错误：＆＃34;尝试从对象[1]＆＃34;中插入nil对象

Question

我正在制作一个SKAction序列，我在序列中放了两个其他SKActions，它给了我这个错误：

Terminating app due to uncaught exception
'NSInvalidArgumentException', reason: '*** -[__NSPlaceholderArray
initWithObjects:count:]: attempt to insert nil object from

对象[1]“

当我设置异常断点时，它指向这一行：

  

SKAction * sequence = [SKAction序列：@ [moveUp，moveDown]];

以下是整个方法代码：

-(void) animateLetters{

    moveUp = [SKAction moveByX:0 y:15 duration:2];
    moveUp = [SKAction moveByX:0 y:-15 duration:2];

    SKAction *sequence = [SKAction sequence:@[moveUp, moveDown]];

    SKAction *runForever = [SKAction repeatActionForever:sequence];
    [letter1 runAction:runForever];
}

Answer 1

您要分配moveUp两次，moveDown永远不会。在这种情况下，使用局部变量可能更有意义 -

-(void) animateLetters{

    SKAction *moveUp = [SKAction moveByX:0 y:15 duration:2];
    SKAction *moveDown = [SKAction moveByX:0 y:-15 duration:2];

    SKAction *sequence = [SKAction sequence:@[moveUp, moveDown]];

    SKAction *runForever = [SKAction repeatActionForever:sequence];
    [letter1 runAction:runForever];
}