Question

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我目前正在学习Objective-C和书Cocoa Programming For Mac OS X，它在第10章介绍了归档.I（AFAIK）确实完成了作者希望我做的事情，但是在打开文件并因此取消归档时应用程序崩溃了：

array = [NSKeyedUnarchiver unarchiveObjectWithData:data];

它说GDB received signal: EXC_BAD_ACCESS。我只是在访问超出界限的数组插槽时遇到过这种情况，我相信我我没有这样做。我最好的猜测是，Cocoa场景背后的东西出了问题，间接由我引起。这可能是什么？
正如我所说，我目前正在学习Objective-C（但我知道Java），所以不要指望我知道每一个模糊的语言特征。

文件打开方法（MyDocument.m）：

- (BOOL)readFromData:(NSData *)data ofType:(NSString *)typeName error:(NSError **)outError {
    NSMutableArray *array = nil;
    NSLog(@"data is %@", data);

    @try {
        array = [NSKeyedUnarchiver unarchiveObjectWithData:data]; // line of the EXC_BAD_ACCESS
    }
    @catch (NSException * e) {
        if (outError) {
            NSDictionary *d = [NSDictionary dictionaryWithObject:@"The data is corrupted." forKey:NSLocalizedFailureReasonErrorKey];
            *outError = [NSError errorWithDomain:NSOSStatusErrorDomain code:unimpErr userInfo:d];
        }
        return NO;
    }
    [self setEmployees:array];
    return YES;
}

文件保存方法（仍为MyDocument.m）：

- (NSData *)dataOfType:(NSString *)typeName error:(NSError **)outError {
    [[tv window] endEditingFor:nil]; // tv is my IBOutlet to an NSTableView

    return [NSKeyedArchiver archivedDataWithRootObject:employees];
}

这是堆栈跟踪（Thanks，H2CO3）：

(gdb) bt
#0  0x00007fff858da104 in objc_msgSend_vtable13 ()
#1  0x00007fff858dcff5 in objc_getProperty ()
#2  0x00000001000022cf in -[Person name] (self=0x1001d4480, _cmd=0x7fff89d1a790) at /Users/mauritsfriedrichkoelmans/Desktop/RaiseMan1/Person.m:14
#3  0x00007fff86e79674 in -[NSObject(NSKeyValueCoding) valueForKey:] ()
#4  0x00007fff86e7cfb8 in -[NSObject(NSKeyValueCoding) valueForKeyPath:] ()
#5  0x00007fff897e10df in -[NSBinder valueForBinding:atIndex:resolveMarkersToPlaceholders:] ()
#6  0x00007fff89682aa2 in -[NSValueBinder _adjustObject:mode:observedController:observedKeyPath:context:editableState:adjustState:] ()
#7  0x00007fff897e0e75 in -[NSValueBinder updateTableColumnDataCell:forDisplayAtIndex:] ()
#8  0x00007fff897e0d83 in -[NSTextValueBinder updateTableColumnDataCell:forDisplayAtIndex:] ()
#9  0x00007fff897e0d30 in -[_NSBindingAdaptor tableColumn:willDisplayCell:row:] ()
#10 0x00007fff896cab00 in -[NSTableView preparedCellAtColumn:row:] ()
#11 0x00007fff896ca306 in -[NSTableView _dirtyVisibleCellsForKeyStateChange] ()
#12 0x00007fff896c9e96 in -[NSTableView _windowChangedKeyState] ()
#13 0x00007fff88ba0d3e in CFArrayApplyFunction ()
#14 0x00007fff89611478 in -[NSView _windowChangedKeyState] ()
#15 0x00007fff88ba0d3e in CFArrayApplyFunction ()
#16 0x00007fff89611478 in -[NSView _windowChangedKeyState] ()
#17 0x00007fff88ba0d3e in CFArrayApplyFunction ()
#18 0x00007fff89611478 in -[NSView _windowChangedKeyState] ()
#19 0x00007fff88ba0d3e in CFArrayApplyFunction ()
#20 0x00007fff89611478 in -[NSView _windowChangedKeyState] ()
#21 0x00007fff896c991f in -[NSFrameView _windowChangedKeyState] ()
#22 0x00007fff89611171 in -[NSWindow _setFrameNeedsDisplay:] ()
#23 0x00007fff8960f1d8 in -[NSWindow _makeKeyRegardlessOfVisibility] ()
#24 0x00007fff8960f13e in -[NSWindow makeKeyAndOrderFront:] ()
#25 0x00007fff89814401 in -[NSWindowController showWindow:] ()
#26 0x00007fff897e5c5c in -[NSDocument showWindows] ()
#27 0x00007fff899539c1 in -[NSDocumentController openDocumentWithContentsOfURL:display:error:] ()
#28 0x00007fff89953072 in -[NSDocumentController _openDocumentsWithContentsOfURLs:display:presentErrors:] ()
#29 0x00007fff8976eeda in -[NSApplication sendAction:to:from:] ()
#30 0x00007fff8979346a in -[NSMenuItem _corePerformAction] ()
#31 0x00007fff897931d4 in -[NSCarbonMenuImpl performActionWithHighlightingForItemAtIndex:] ()
#32 0x00007fff89778e45 in -[NSMenu performKeyEquivalent:] ()
#33 0x00007fff89777bed in -[NSApplication _handleKeyEquivalent:] ()
#34 0x00007fff896486b9 in -[NSApplication sendEvent:] ()
#35 0x00007fff895df6de in -[NSApplication run] ()
#36 0x00007fff895d83b0 in NSApplicationMain ()
#37 0x0000000100001e9b in main (argc=1, argv=0x7fff5fbff660) at /Users/mauritsfriedrichkoelmans/Desktop/RaiseMan1/main.m:13
(gdb)

数据对象不 nil，NSLog()编辑它。

Answer 1

我自己解决了！

在本书中，Person类的initWithCoder:方法（我尝试取消归档的数组填充了该类的实例）如下所示：

- (id)initWithCoder:(NSCoder *)coder {
    [super init];
    name = [coder decodeObjectForKey:@"name"];
    expectedRaise = [coder decodeFloatForKey:@"expectedRaise"];
    return self;
}

但必须是：

- (id)initWithCoder:(NSCoder *)coder {
    [super init];
    self.name = [coder decodeObjectForKey:@"name"];
    self.expectedRaise = [coder decodeFloatForKey:@"expectedRaise"];
    return self;
}

Answer 2

我的经验告诉我，您的data对象是nil

Answer 3

确保您的保存成功：

if (![NSKeyedArchiver archiveRootObject:myDictionary toFile:path])
{
    // saving failed for some reason
    return;
}

在尝试取消归档之前，请确保该文件存在：

if ([[NSFileManager defaultManager] fileExistsAtPath:path])
{
    // file does not exist at path (deleted?)
    return;
}

[NSKeyedUnarchiver unarchiveObjectWithData：]上的EXC_BAD_ACCESS;

3 个答案: