当我分配 init NSMetaDataQuery 时，我的 applicationDidFinishLaunching 崩溃......请帮忙

Question

我正在更新我的应用程序以使用 iCloud，并希望我的 iOS 部署目标保持为 3.2。我有条件地屏蔽任何 iOS 5 调用，以防止任何后台版本崩溃。我的 applicationDidFinishLaunching 看起来像...

- (void)applicationDidFinishLaunching:(UIApplication *)application { 

NSLog(@"Launching Began...");
navigationController = [[UINavigationController alloc] init];
navigationController.navigationBar.barStyle = UIBarStyleBlack;
[window addSubview:navigationController.view];
[window makeKeyAndVisible];


//  Getting the documentsPath.
NSArray *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);
NSString *documentsPath = [paths objectAtIndex:0];


//  Setting up the mainCarList

//unarchive the saved carlist 
NSString *archivePathFilename = [documentsPath stringByAppendingString:@"/carlist.archive"];    
self.mainCarList = nil;
self.mainCarList = [[NSKeyedUnarchiver unarchiveObjectWithFile:archivePathFilename] retain];

//if OS version => 5.0 then 
NSString *reqSysVer = @"5.0";
NSString *currSysVer = [[UIDevice currentDevice] systemVersion];
if ([currSysVer compare:reqSysVer options:NSNumericSearch] != NSOrderedAscending) {
    NSLog(@"in ApplicationDidFinishLaunching iOS version > 5.0");
    [[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(carListDocumentStateChanged) name:@"UIDocumentStateChangedNotification" object:Nil];


    NSString *carListDocumentURLString = [documentsPath stringByAppendingString:@"/mainCarListDocument.CLD"];
    self.mainCarListDocumentURL = [NSURL fileURLWithPath:carListDocumentURLString]; //sets the local save location only in this property


    Class cls = NSClassFromString (@"NSMetadataQuery");
    if (cls) {
        NSMetadataQuery *query;
        query = [[NSMetadataQuery alloc] init];  // <------- This crashes when running v4.3 iPhone sim.
     /*
        NSMetadataQuery *query = [[NSMetadataQuery alloc] init];

        [self setDocumentMetaDataQuery:query];
        [query setSearchScopes:[NSArray arrayWithObject:NSMetadataQueryUbiquitousDataScope]];
        [query setPredicate:[NSPredicate predicateWithFormat:@"%K == %@", NSMetadataItemFSNameKey, @"mainCarListDocument.CLD"]];
        [[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(queryDidFinishGathering) name:NSMetadataQueryDidFinishGatheringNotification object:Nil];

        BOOL didStart = NO;
        didStart = [query startQuery];

        if (didStart) {
            NSLog(@"documentMetaDataQuery started");
        }
        else {
            NSLog(@"error starting documentMetaDataQuery");
        }
   */
        [query release];

    }


...

我认为编译时发生了一些事情，因为“启动开始”日志没有发布。条件块工作正常。如果我注释掉查询的 alloc init，则仅当 iOS 5 正在运行时该块才会运行。有什么想法吗？

Answer 1

替换以下代码：

NSMetadataQuery *query;
query = [[NSMetadataQuery alloc] init];

通过此代码：

id query;
query = [[cls alloc] init];

Answer 2

您必须使用 cls 而不是 NSMetadataQuery。