NSMutableArray addObject 使 iPhone 应用程序崩溃答案

【问题标题】：NSMutableArray addObject crashes iPhone appNSMutableArray addObject 使 iPhone 应用程序崩溃
【发布时间】：2009-05-26 20:39:19
【问题描述】：

我有一个 XMLParser 类。只要我不删除将节点添加到 NSMutableArray 的行的注释，它就可以正常工作：

[nodes addObject:self.currentNode];

如果我这样做了，应用程序就会崩溃 - 在调试日志中不会留下任何痕迹。这怎么可能？

XMLParser.m：

#import "XMLParser.h"
#import "MyViewController.h"
#import "Node.h"


@implementation XMLParser
@synthesize currentNode, currentProperty, currentAddress, nodes;


- (NSMutableArray *)parseNodeData:(NSString *)url {
    NSURL *urlObj = [[NSURL alloc] initWithString:url];
    NSXMLParser *parser = [[NSXMLParser alloc] initWithContentsOfURL:urlObj];

    self.nodes = [[NSMutableArray alloc] init];

    [parser setDelegate:self];
    [parser setShouldProcessNamespaces:NO];
    [parser setShouldReportNamespacePrefixes:NO];
    [parser setShouldResolveExternalEntities:NO];
    [parser parse];
    NSLog(@"Proceeded from parser.");

    NSLog(@"Returning %@ rows", [nodes count]);
    //[parser release];
    return self.nodes;
}

- (void)parser:(NSXMLParser *)parser foundCharacters:(NSString *)string
{
    if (self.currentProperty) {
        [currentProperty appendString:string];
    }
}

- (void)parser:(NSXMLParser *)parser didStartElement:(NSString *)elementName namespaceURI:(NSString *)namespaceURI qualifiedName:(NSString *)qName attributes:(NSDictionary *)attributeDict {
    if (qName) {
        elementName = qName;
    }

    NSLog(@"<%@>", elementName);

    if(self.currentNode)
    {
        if ([elementName isEqualToString:@"id"] || [elementName isEqualToString:@"name"])
        {
            self.currentProperty = [NSMutableString string];
        }
    } else {
        // We are outside of everything, so we need a
        // Check for deeper nested node
        if ([elementName isEqualToString:@"node"]) {
            self.currentNode = [[Node alloc] init];
            NSLog(@"Initialized new node...");
        }
    }
}

- (void)parser:(NSXMLParser *)parser didEndElement:(NSString *)elementName namespaceURI:(NSString *)namespaceURI qualifiedName:(NSString *)qName
{
    if(self.currentNode)
    {
        if ([elementName isEqualToString:@"id"]) {
            NSLog(@"Tried setting node id: %@", self.currentProperty);
            self.currentNode.nodeId = self.currentProperty;

        } else if ([elementName isEqualToString:@"name"]) {
            NSLog(@"Tried setting node name: %@", self.currentProperty);
            self.currentNode.name = self.currentProperty;
        } else if ([elementName isEqualToString:@"node"]) {
            NSLog(@"Adding node to array");
            //[nodes addObject:self.currentNode];
            self.currentNode = nil;
        }
    }

    NSLog(@"</%@>", elementName);

    self.currentProperty = nil;
}

- (void) dealloc {
    [currentNode release];
    [currentAddress release];
    [currentProperty release];
    [super dealloc];
}


@end

XMLParser.h：

#import <UIKit/UIKit.h>
#import "Address.h"
#import "Node.h"

@class XMLAppDelegate;

@interface XMLParser : NSObject {
    NSMutableString *currentProperty;
    Address *currentAddress;
    Node *currentNode;
    NSMutableArray *nodes;

}

@property (nonatomic, retain) NSMutableString *currentProperty;
@property (nonatomic, retain) Address *currentAddress;
@property (nonatomic, retain) Node *currentNode;
@property (nonatomic, retain) NSMutableArray *nodes;

- (NSMutableArray *)parseNodeData:(NSString *)data;

@end

编辑：调试日志的输出

[Session started at 2009-05-26 23:31:26 +0200.]
2009-05-26 23:31:28.352 HelloWorld[6914:20b] <response>
2009-05-26 23:31:28.353 HelloWorld[6914:20b] <nodesearchresult>
2009-05-26 23:31:28.354 HelloWorld[6914:20b] <resultsreturned>
2009-05-26 23:31:28.354 HelloWorld[6914:20b] </resultsreturned>
2009-05-26 23:31:28.354 HelloWorld[6914:20b] <resultsfound>
2009-05-26 23:31:28.354 HelloWorld[6914:20b] </resultsfound>
2009-05-26 23:31:28.355 HelloWorld[6914:20b] <nodes>
2009-05-26 23:31:28.355 HelloWorld[6914:20b] <node>
2009-05-26 23:31:28.356 HelloWorld[6914:20b] Initialized new node...
2009-05-26 23:31:28.356 HelloWorld[6914:20b] <id>
2009-05-26 23:31:28.356 HelloWorld[6914:20b] Tried setting node id: 614
2009-05-26 23:31:28.356 HelloWorld[6914:20b] </id>
2009-05-26 23:31:28.357 HelloWorld[6914:20b] <name>
2009-05-26 23:31:28.357 HelloWorld[6914:20b] Tried setting node name: Roberts coffee
2009-05-26 23:31:28.357 HelloWorld[6914:20b] </name>
2009-05-26 23:31:28.358 HelloWorld[6914:20b] <address>
2009-05-26 23:31:28.358 HelloWorld[6914:20b] <street>
2009-05-26 23:31:28.358 HelloWorld[6914:20b] </street>
2009-05-26 23:31:28.358 HelloWorld[6914:20b] <zipcode>
2009-05-26 23:31:28.359 HelloWorld[6914:20b] </zipcode>
2009-05-26 23:31:28.359 HelloWorld[6914:20b] </address>
2009-05-26 23:31:28.359 HelloWorld[6914:20b] <position>
2009-05-26 23:31:28.359 HelloWorld[6914:20b] <latitude>
2009-05-26 23:31:28.360 HelloWorld[6914:20b] </latitude>
2009-05-26 23:31:28.360 HelloWorld[6914:20b] <longitude>
2009-05-26 23:31:28.360 HelloWorld[6914:20b] </longitude>
2009-05-26 23:31:28.361 HelloWorld[6914:20b] </position>
2009-05-26 23:31:28.361 HelloWorld[6914:20b] <phone>
2009-05-26 23:31:28.361 HelloWorld[6914:20b] </phone>
2009-05-26 23:31:28.363 HelloWorld[6914:20b] <nodetypes>
2009-05-26 23:31:28.363 HelloWorld[6914:20b] <nodetype>
2009-05-26 23:31:28.363 HelloWorld[6914:20b] </nodetype>
2009-05-26 23:31:28.364 HelloWorld[6914:20b] </nodetypes>
2009-05-26 23:31:28.364 HelloWorld[6914:20b] <rating>
2009-05-26 23:31:28.364 HelloWorld[6914:20b] <score>
2009-05-26 23:31:28.365 HelloWorld[6914:20b] </score>
2009-05-26 23:31:28.365 HelloWorld[6914:20b] <votes>
2009-05-26 23:31:28.366 HelloWorld[6914:20b] </votes>
2009-05-26 23:31:28.366 HelloWorld[6914:20b] </rating>
2009-05-26 23:31:28.366 HelloWorld[6914:20b] <teaser>
2009-05-26 23:31:28.367 HelloWorld[6914:20b] </teaser>
2009-05-26 23:31:28.367 HelloWorld[6914:20b] Adding node to array
2009-05-26 23:31:28.367 HelloWorld[6914:20b] </node>
2009-05-26 23:31:28.367 HelloWorld[6914:20b] <node>
2009-05-26 23:31:28.368 HelloWorld[6914:20b] Initialized new node...
2009-05-26 23:31:28.368 HelloWorld[6914:20b] <id>
2009-05-26 23:31:28.368 HelloWorld[6914:20b] Tried setting node id: 326
2009-05-26 23:31:28.368 HelloWorld[6914:20b] </id>
2009-05-26 23:31:28.369 HelloWorld[6914:20b] <name>
2009-05-26 23:31:28.369 HelloWorld[6914:20b] Tried setting node name: Sort kaffe & vinyl
2009-05-26 23:31:28.369 HelloWorld[6914:20b] </name>
2009-05-26 23:31:28.369 HelloWorld[6914:20b] <address>
2009-05-26 23:31:28.370 HelloWorld[6914:20b] <street>
2009-05-26 23:31:28.370 HelloWorld[6914:20b] </street>
2009-05-26 23:31:28.371 HelloWorld[6914:20b] <zipcode>
2009-05-26 23:31:28.371 HelloWorld[6914:20b] </zipcode>
2009-05-26 23:31:28.372 HelloWorld[6914:20b] </address>
2009-05-26 23:31:28.372 HelloWorld[6914:20b] <position>
2009-05-26 23:31:28.372 HelloWorld[6914:20b] <latitude>
2009-05-26 23:31:28.373 HelloWorld[6914:20b] </latitude>
2009-05-26 23:31:28.373 HelloWorld[6914:20b] <longitude>
2009-05-26 23:31:28.373 HelloWorld[6914:20b] </longitude>
2009-05-26 23:31:28.374 HelloWorld[6914:20b] </position>
2009-05-26 23:31:28.374 HelloWorld[6914:20b] <phone>
2009-05-26 23:31:28.375 HelloWorld[6914:20b] </phone>
2009-05-26 23:31:28.375 HelloWorld[6914:20b] <nodetypes>
2009-05-26 23:31:28.375 HelloWorld[6914:20b] <nodetype>
2009-05-26 23:31:28.375 HelloWorld[6914:20b] </nodetype>
2009-05-26 23:31:28.376 HelloWorld[6914:20b] <nodetype>
2009-05-26 23:31:28.376 HelloWorld[6914:20b] </nodetype>
2009-05-26 23:31:28.376 HelloWorld[6914:20b] </nodetypes>
2009-05-26 23:31:28.376 HelloWorld[6914:20b] <rating>
2009-05-26 23:31:28.377 HelloWorld[6914:20b] <score>
2009-05-26 23:31:28.377 HelloWorld[6914:20b] </score>
2009-05-26 23:31:28.377 HelloWorld[6914:20b] <votes>
2009-05-26 23:31:28.377 HelloWorld[6914:20b] </votes>
2009-05-26 23:31:28.378 HelloWorld[6914:20b] </rating>
2009-05-26 23:31:28.378 HelloWorld[6914:20b] <teaser>
2009-05-26 23:31:28.379 HelloWorld[6914:20b] </teaser>
2009-05-26 23:31:28.379 HelloWorld[6914:20b] Adding node to array
2009-05-26 23:31:28.379 HelloWorld[6914:20b] </node>
2009-05-26 23:31:28.380 HelloWorld[6914:20b] </nodes>
2009-05-26 23:31:28.380 HelloWorld[6914:20b] </nodesearchresult>
2009-05-26 23:31:28.381 HelloWorld[6914:20b] </response>
2009-05-26 23:31:28.381 HelloWorld[6914:20b] Proceeded from parser.

[Session started at 2009-05-26 23:31:28 +0200.]
Loading program into debugger…
GNU gdb 6.3.50-20050815 (Apple version gdb-962) (Sat Jul 26 08:14:40 UTC 2008)
Copyright 2004 Free Software Foundation, Inc.
GDB is free software, covered by the GNU General Public License, and you are
welcome to change it and/or distribute copies of it under certain conditions.
Type "show copying" to see the conditions.
There is absolutely no warranty for GDB.  Type "show warranty" for details.
This GDB was configured as "i386-apple-darwin".warning: Unable to read symbols for "/System/Library/Frameworks/UIKit.framework/UIKit" (file not found).
warning: Unable to read symbols from "UIKit" (not yet mapped into memory).
warning: Unable to read symbols for "/System/Library/Frameworks/CoreLocation.framework/Versions/A/CoreLocation" (file not found).
warning: Unable to read symbols from "CoreLocation" (not yet mapped into memory).
warning: Unable to read symbols for "/System/Library/Frameworks/CoreGraphics.framework/CoreGraphics" (file not found).
warning: Unable to read symbols from "CoreGraphics" (not yet mapped into memory).
Program loaded.
sharedlibrary apply-load-rules all
Attaching to program: `/Users/philipdahlstrm/Library/Application Support/iPhone Simulator/User/Applications/6BD1CC99-F133-4B97-A041-1D210851B6C6/HelloWorld.app/HelloWorld', process 6914.
(gdb)

【问题讨论】：

调试日志中没有任何痕迹？因此，您甚至没有在控制台中看到“将节点添加到数组”，也没有在程序崩溃时看到堆栈跟踪？尝试清理您的项目并从“运行”菜单中选择“调试”。
另外，我建议在导致崩溃的注释行之前使用 NSLogging self.nodes 和 self.currentNode，以确保它们是有效的对象指针。
不确定这与问题有什么关系，但您的代码正在泄漏Node 对象。当您使用 alloc 创建它并将其分配给属性 currentNode 时，它的保留计数会增加（您在 2 上）。稍后，当您将它添加到数组中时，它会再次递增，计数为 3，并且您永远不会释放该对象，而是将引用设置为 nil。
您的代码也泄漏了 NSMutableArray（同样，您将保留对象分配给保留属性）。您是否尝试过在 objc_exception_throw() 上设置符号断点？我认为您将不得不向我们展示 Node.h。

标签： iphone objective-c cocoa-touch

【解决方案1】：

您的错误在最终的 NSLog 中：

NSLog(@"Returning %@ rows", [nodes count]);

%@ 接受一个指向对象的指针。 [nodes count] 返回一个无符号整数，然后您可以将其作为指针取消引用。如果nodes为空也没关系，因为然后-count返回0，也就是nil，这样解引用是安全的。您应该在这里使用%d 而不是%@。

调试器堆栈应该向您显示发生这种情况的确切位置。我通过查看日志的最后一行并查看之后立即发生的事情找到了它。

顺便说一句，您在这里泄漏了大量内存。如果您在分配给保留访问器（如self.nodes =...）中使用Three Magic Words 之一，则需要autorelease。

self.currentNode = [[Node alloc] init];

应该是：

self.currentNode = [[[Node alloc] init] autorelease];

而且您应该始终使用访问器访问 ivars。永远不要以你的方式直接访问节点（除了它们的访问器和dealloc）。

【讨论】：