Question

自从升级到XCode 5 / iOS 7后，我在调用一个应该呈现Redlaser SDK barcodepickercontroller的函数时遇到以下错误：

由于未捕获的异常'NSInvalidArgumentException'而终止应用程序，原因：'应用程序尝试在目标上显示nil模态视图控制器。 * 第一次抛出调用堆栈：

（

0   CoreFoundation                      0x02ef25e4 __exceptionPreprocess + 180

1   libobjc.A.dylib                     0x028dd8b6 objc_exception_throw + 44

2   UIKit                               0x006e817a -[UIViewControllerpresentViewController:withTransition:completion:] + 4879

3   UIKit                               0x006e8caf -[UIViewController presentViewController:animated:completion:] + 130
4   UIKit                               0x006e8cef -[UIViewController presentModalViewController:animated:] + 56
5   Extinguishers                       0x0000b703 -[LoginViewController scanPressed] + 1299

这是导致它的方法：

-(IBAction) scanPressed
{   
if (overlayController.parentPicker == nil)
{
    BarcodePickerController * picker = [[BarcodePickerController alloc] init];

    [picker setOverlay:overlayController]; 
    [picker setDelegate:self];

    // Initialize with portrait mode as default
    picker.orientation = UIImageOrientationUp;

    // The active scanning region size is set in OverlayController.m
}

// Update barcode on/off settings
[overlayController.parentPicker setScanUPCE:YES];
[overlayController.parentPicker setScanEAN8:YES];
[overlayController.parentPicker setScanEAN13:YES];
//[overlayController.parentPicker setScanSTICKY:YES];
//[overlayController.parentPicker setScanQRCODE:YES];
[overlayController.parentPicker setScanCODE128:YES];
[overlayController.parentPicker setScanCODE39:YES];
[overlayController.parentPicker setScanITF:YES];

// Data matrix decoding does not work very well so it is disabled for now
[overlayController.parentPicker setScanDATAMATRIX:NO];

// hide the status bar
[[UIApplication sharedApplication] setStatusBarHidden:YES];

// Show the scanner overlay - THIS LINE CAUSES THE CRASH
    [self presentModalViewController:overlayController.parentPicker animated:TRUE];

}

我也尝试升级到最新版本的Redlaser SDK，错误仍然相同。在切换到iOS 7作为基本SDK之前，我没有遇到此问题。

Answer 1

我唯一能想到的是picker（父母）可能超出范围并被取消分配。在错误线之前进行测试以检查父级是否仍然存在：if(overlayController.parentPicker == nil) NSLog(@"Parent is nil");

如果确实是nil（就像您原来的错误所说的那样），请尝试在之前声明picker 第一个if声明。

BarcodePickerController *picker; if(overlayController.parentPicker == nil) { picker = [[BarcodePickerController alloc] init]; //...

孩子可能只有weak指向父母的指针，因此您可能需要将父级声明为@property或在viewController之前不会取消分配的地方从堆栈中弹出。

Redlaser SDK和nil模态视图控制器

1 个答案: