开关语句的错误呈现新视角
我试图将下面的代码切换到switch语句（您可以忽略注释）：
之前
if (self.players == 1) {
OnePlayerViewController *onePlayerViewController = [self.storyboard instantiateViewControllerWithIdentifier:@"OnePlayerViewController"];
/*onePlayerViewController.dictionary = self.words;
onePlayerViewController.wordsText = self.wordsText;*/
onePlayerViewController.modalTransitionStyle = UIModalTransitionStyleCrossDissolve;
[self presentViewController:onePlayerViewController animated:YES completion:nil];
} else if (self.players == 2) {
TwoPlayersViewController *twoPlayersViewController = [self.storyboard instantiateViewControllerWithIdentifier:@"TwoPlayersViewController"];
/*twoPlayersViewController.dictionary = self.words;
twoPlayersViewController.wordsText = self.wordsText;*/
twoPlayersViewController.modalTransitionStyle = UIModalTransitionStyleCrossDissolve;
[self presentViewController:twoPlayersViewController animated:YES completion:nil];
} else if (self.players == 3) {
ThreePlayersViewController *threePlayersViewController = [self.storyboard instantiateViewControllerWithIdentifier:@"ThreePlayersViewController"];
/*threePlayersViewController.dictionary = self.words;
threePlayersViewController.wordsText = self.wordsText;*/
threePlayersViewController.modalTransitionStyle = UIModalTransitionStyleCrossDissolve;
[self presentViewController:threePlayersViewController animated:YES completion:nil];
} else {
FourPlayersViewController *fourPlayersViewController = [self.storyboard instantiateViewControllerWithIdentifier:@"FourPlayersViewController"];
/*fourPlayersViewController.dictionary = self.words;
fourPlayersViewController.wordsText = self.wordsText;*/
fourPlayersViewController.modalTransitionStyle = UIModalTransitionStyleCrossDissolve;
[self presentViewController:fourPlayersViewController animated:YES completion:nil];
}
后
switch (self.players) {
case 1:
OnePlayerViewController *onePlayerViewController = [self.storyboard instantiateViewControllerWithIdentifier:@"OnePlayerViewController"];
/*onePlayerViewController.dictionary = self.words;
onePlayerViewController.wordsText = self.wordsText;*/
onePlayerViewController.modalTransitionStyle = UIModalTransitionStyleCrossDissolve;
[self presentViewController:onePlayerViewController animated:YES completion:nil];
break;
case 2:
TwoPlayersViewController *twoPlayersViewController = [self.storyboard instantiateViewControllerWithIdentifier:@"TwoPlayersViewController"];
/*twoPlayersViewController.dictionary = self.words;
twoPlayersViewController.wordsText = self.wordsText;*/
twoPlayersViewController.modalTransitionStyle = UIModalTransitionStyleCrossDissolve;
break;
case 3:
ThreePlayersViewController *threePlayersViewController = [self.storyboard instantiateViewControllerWithIdentifier:@"ThreePlayersViewController"];
/*threePlayersViewController.dictionary = self.words;
threePlayersViewController.wordsText = self.wordsText;*/
threePlayersViewController.modalTransitionStyle = UIModalTransitionStyleCrossDissolve;
[self presentViewController:threePlayersViewController animated:YES completion:nil];
break;
case 4:
FourPlayersViewController *fourPlayersViewController = [self.storyboard instantiateViewControllerWithIdentifier:@"FourPlayersViewController"];
/*fourPlayersViewController.dictionary = self.words;
fourPlayersViewController.wordsText = self.wordsText;*/
fourPlayersViewController.modalTransitionStyle = UIModalTransitionStyleCrossDissolve;
[self presentViewController:fourPlayersViewController animated:YES completion:nil];
break;
}
然而 ， if ， else if和else代码完美工作，但switch语句在运行编译器时会产生很多错误。 最大的一个就是在实例化视图控制器的行上给出的“预期表达式”。 我猜测它正在期待一个“表达”的case blah:并且由于某种奇怪的原因，该行不足以作为“表达式”。 因为它似乎没有注册该行，并给视图控制器一个标识符，它会产生更多的错误，主要包括“使用未声明的标识符'blahPlayerViewController';你的意思是'BlahViewController'？”。 为什么会发生？ 我能做些什么来解决这个问题？
关于“ switch ”语句的一个不幸的事情是，你不能在其中声明变量。
你需要在你的switch语句之上和之外声明你的变量。
就像是：
OnePlayerViewController *onePlayerViewController;
TwoPlayersViewController *twoPlayersViewController;
switch (self.players) {
case 1:
onePlayerViewController = [self.storyboard instantiateViewControllerWithIdentifier:@"OnePlayerViewController"];
onePlayerViewController.dictionary = self.words;
onePlayerViewController.wordsText = self.wordsText;
onePlayerViewController.modalTransitionStyle = UIModalTransitionStyleCrossDissolve;
[self presentViewController:onePlayerViewController animated:YES completion:nil];
break;
case 2:
twoPlayersViewController = [self.storyboard instantiateViewControllerWithIdentifier:@"TwoPlayersViewController"];
twoPlayersViewController.dictionary = self.words;
twoPlayersViewController.wordsText = self.wordsText;
twoPlayersViewController.modalTransitionStyle = UIModalTransitionStyleCrossDissolve;
break;