窥视 iOS 9 个应用程序崩溃

Question

我正在尝试在支持 iOS 9 的应用程序中执行 Peek 和 Pop。有问题的视图有一个 UITableView，所以我的代码中有：

- (UIViewController *)previewingContext:(id<UIViewControllerPreviewing>)previewingContext viewControllerForLocation:(CGPoint)location {

    // check if we're not already displaying a preview controller
    if ([self.presentedViewController isKindOfClass:[WebViewController class]]) {
        return nil;
    }

    // shallow press: return the preview controller here (peek)
        self.webViewController = [[[WebViewController alloc] initWithNibName:@"WebViewController" bundle:[NSBundle mainBundle]] autorelease];




    return self.webViewController;
}
- (void)previewingContext:(id<UIViewControllerPreviewing>)previewingContext commitViewController:(UIViewController *)viewControllerToCommit {

    // deep press: bring up the commit view controller (pop)
    self.webViewController = [[[WebViewController alloc] initWithNibName:@"WebViewController" bundle:[NSBundle mainBundle]] autorelease];


    [self showViewController:self.webViewController sender:self];
}

WebViewController是我已经设置的ViewController选择tableview的行时显示内容。我得到的错误是：

Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: '*** -[__NSCFConstantString stringByAppendingString:]: nil argument'
*** First throw call stack:
(0x182160f5c 0x19764bf80 0x182160ea4 0x182fb8868 0x1001307a4 0x1876cf9ac 0x1876cf720 0x187a025f8 0x187960844 0x18796cde4 0x1876a91e4 0x182117c30 0x1821159d4 0x182115e04 0x182044dc0 0x18d4e0088 0x18771ef60 0x10014ca68 0x197e6a8b8)
libc++abi.dylib: terminating with uncaught exception of type NSException

Answer 1

您的日志准确说明了您的代码有什么问题：

-[__NSCFConstantString stringByAppendingString:]: nil argument'

您正在执行 stringByAppendingString 传递的值为 nil

此外，如果您使用的是 ARC，则不再使用 autorelease（现在是默认设置）

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