ios - NSUndoManager removeAllActionsWithTarget 崩溃

Question

我有一些简短的 iOS Objective-C 示例代码(从一个较大的项目中简化而来)导致 NSUndoManager 崩溃，我无法解释。

即，当一个对象仅由 NSUndoManager 持有时 deallocs(因为它超出了撤消级别)，并且根据 docs调用 removeAllActionsWithTarget:self，我得到一个 EXC_BAD_ACCESS。

// SimpleViewController.m
@interface ViewController ()
@property (nonatomic, strong) NSUndoManager *undoManager;
@end

@implementation ViewController

@synthesize undoManager;

// called from a simple button
- (IBAction)doItTapped:(id)sender
{
    CoolObject *object = [CoolObject new];
    object.undoManager = self.undoManager;
    // according to docs, object will be retained by NSUndoManager here
    // but target will not (which should be okay)
    [self.undoManager registerUndoWithTarget:self selector:@selector(notCool:) object:object];
}

- (void)viewDidLoad
{
    [super viewDidLoad];

    self.undoManager = [NSUndoManager new];
    self.undoManager.levelsOfUndo = 3;
}

和

// CoolObject.m
@implementation CoolObject

- (void)dealloc
{
    [self.undoManager removeAllActionsWithTarget:self];
}

@end

在第 4 次点击按钮 (levelsOfUndo + 1) 后，它崩溃了。如果我将 NSUndoManager 与 GCUndoManager 交换，没有崩溃。在 iOS 10.2 sim 和设备中测试。

感谢任何想法!

Answer 1

您可能会遇到此错误，因为 self.undoManager 在您使用它的那一刻没有保留。当对象已经被释放并且您尝试访问它时，您将得到错误的访问异常。

试着改变你的代码:

CoolObject *object = [CoolObject new];

为此:

@interface ViewController (){
CoolObject *object;
}
@property (nonatomic, strong) NSUndoManager *undoManager;
@end
@implementation ViewController
- (IBAction)doItTapped:(id)sender
{
    object = [CoolObject new];
    object.undoManager = self.undoManager;
    // according to docs, object will be retained by NSUndoManager here
    // but target will not (which should be okay)
    [self.undoManager registerUndoWithTarget:self selector:@selector(notCool:) object:object];
}
@end

希望这会有所帮助。