莫问天涯路几重,轻衫侧帽且从容。这篇文章主要讲述[AppDelegate managedObjectContext]:发送到实例的无法识别的选择器相关的知识,希望能为你提供帮助。
我正在按照教程学习核心数据存储和检索。下面是我的表视图代码。
#import "DeviceViewController.h"
#import <
CoreData/CoreData.h>
@interface DeviceViewController ()
@property(strong) NSMutableArray *devices;
@end@implementation DeviceViewController- (NSManagedObjectContext *)managedObjectContext
{
NSManagedObjectContext *context = nil;
id delegate = [[UIApplication sharedApplication] delegate];
if ([delegate performSelector:@selector(managedObjectContext)]) {
context = [delegate managedObjectContext];
}
return context;
}
- (void)viewDidAppear:(BOOL)animated {
[super viewDidAppear:animated];
//Fetch the devices from persistent data store
NSManagedObjectContext *managedObjectContext = [self managedObjectContext];
NSFetchRequest *fetchRequest = [[NSFetchRequest alloc] initWithEntityName:@"Device"];
self.devices = [[managedObjectContext executeFetchRequest:fetchRequest error:nil] mutableCopy];
[self.tableView reloadData];
}- (void)didReceiveMemoryWarning {
[super didReceiveMemoryWarning];
// Dispose of any resources that can be recreated.
}#pragma mark - Table view data source-(NSInteger)numberOfSectionsIntableView: (UITableView *)tableView{
return 1;
}-(NSInteger)tableView:(UITableView *) tableView numberOfRowsInSection:(NSInteger) section{
return self.devices.count;
}-(UITableViewCell *) tableView:(UITableView *)tableView cellForRowAtindexPath:(NSIndexPath *)indexPath{
static NSString *cellIndentifier = @"cell";
UITableViewCell *cell = [tableView dequeueReusableCellWithIdentifier:cellIndentifier forIndexPath:indexPath];
//Configure the cell
NSManagedObject *device = [self.devices objectAtIndex:indexPath.row];
[cell.textLabel setText:[NSString stringWithFormat:@" %@ %@ ",[device valueForKey:@"name"],[device valueForKey:@"version"]]];
[cell.detailTextLabel setText:[device valueForKey:@"company"]];
return cell;
}
我在创建项目时检查了核心数据的复选框,但是我收到以下错误。
Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: '-[AppDelegate managedObjectContext]: unrecognized selector sent to instance 0x60800003c200'
*** First throw call stack:
(
0CoreFoundation0x0000000107ab8d4b __exceptionPreprocess + 171
1libobjc.A.dylib0x00000001070f921e objc_exception_throw + 48
2CoreFoundation0x0000000107b28f04 -[NSObject(NSObject) doesNotRecognizeSelector:] + 132
3CoreFoundation0x0000000107a3e005 ___forwarding___ + 1013
4CoreFoundation0x0000000107a3db88 _CF_forwarding_prep_0 + 120
5MyStore0x0000000106b1ff80 -[DeviceViewController managedObjectContext] + 128
6MyStore0x0000000106b20058 -[DeviceViewController viewDidAppear:] + 88
7UIKit0x0000000108084a6c -[UIViewController _setViewAppearState:isAnimating:] + 945
8UIKit0x00000001080b98d7 -[UINavigationController viewDidAppear:] + 207
9UIKit0x0000000108084a6c -[UIViewController _setViewAppearState:isAnimating:] + 945
10UIKit0x00000001080877da __64-[UIViewController viewDidMoveToWindow:shouldAppearOrDisappear:]_block_invoke + 42
11UIKit0x0000000108085ac4 -[UIViewController _executeAfterAppearanceBlock] + 86
12UIKit0x0000000107ee977c _runAfterCACommitDeferredBlocks + 653
13UIKit0x0000000107ed6273 _cleanUpAfterCAFlushAndRunDeferredBlocks + 566
14UIKit0x0000000107ef9757 __84-[UIApplication _handleApplicationActivationWithScene:transitionContext:completion:]_block_invoke_2 + 194
15CoreFoundation0x0000000107a5d6ac __CFRUNLOOP_IS_CALLING_OUT_TO_A_BLOCK__ + 12
16CoreFoundation0x0000000107a426f4 __CFRunLoopDoBlocks + 356
17CoreFoundation0x0000000107a41e65 __CFRunLoopRun + 901
18CoreFoundation0x0000000107a41884 CFRunLoopRunSpecific + 420
19GraphicsServices0x000000010b952a6f GSEventRunModal + 161
20UIKit0x0000000107edcc68 UIApplicationMain + 159
21MyStore0x0000000106b2132f main + 111
22libdyld.dylib0x000000010a9ae68d start + 1
23???0x0000000000000001 0x0 + 1
)
libc++abi.dylib: terminating with uncaught exception of type NSException
我不熟悉在目标c中使用核心数据。我已经搜索了堆栈和互联网,但无法找到解决方案。
编辑:我的AppDelegate.m如下
#import "AppDelegate.h"
#import <
CoreData/CoreData.h>
@interface AppDelegate ()@end@implementation AppDelegate- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions {
return YES;
}
#pragma mark - Core Data stack@synthesize persistentContainer = _persistentContainer;
- (NSPersistentContainer *)persistentContainer {
// The persistent container for the application. This implementation creates and returns a container, having loaded the store for the application to it.
@synchronized (self) {
if (_persistentContainer == nil) {
_persistentContainer = [[NSPersistentContainer alloc] initWithName:@"MyStore"];
[_persistentContainer loadPersistentStoresWithCompletionHandler:^(NSPersistentStoreDescription *storeDescription, NSError *error) {
if (error != nil) {
NSLog(@"Unresolved error %@, %@", error, error.userInfo);
abort();
}
}];
}
}return _persistentContainer;
}#pragma mark - Core Data Saving support- (void)saveContext {
NSManagedObjectContext *context = self.persistentContainer.viewContext;
NSError *error = nil;
if ([context hasChanges] &
&
![context save:&
error]) {
NSLog(@"Unresolved error %@, %@", error, error.userInfo);
abort();
}
}@end
正如我所说,我正在关注这个教程,并且AppDelegate类没有任何变化。
答案您的代码有两个问题。 1)您正在使用
performSelector
(执行操作)而不是respondsToSelector
(测试是否允许操作)。 2)appDelete有一个方法persistentContainer
而不是managedObjectContext
。更换
if ([delegate performSelector:@selector(managedObjectContext)]) {
context = [delegate managedObjectContext];
}
【[AppDelegate managedObjectContext](发送到实例的无法识别的选择器)】同
if ([delegate respondsToSelector:@selector(persistentContainer)]) {
context = delegate.persistentContainer.viewContext;
}
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