问题
EDIT - added .h file
I'm having difficulty trying to find the cause of a double free error.
Steps taken to solve
1) Used the Zombies tool. Zombies reports that tid is being double freed
2) Set a breakpoint on malloc_error_break. This identifitied the following code segment as faulty:
- (void)viewWillDisappear:(BOOL)animated
{
[super viewWillDisappear:animated];
[connection release];
[ldestination release];
[ldeparts_from release];
[ltime release];
[lcs_id release]; /// It breaks here
[carsharexml release];
}
3) I looked through the code to see where I had [lcs_id release] before - I found nothing.
4) In a desperate attempt to solve it I commented out [lcs_id release]. This stopped the
double free error messages but when I ran it through leaks it said that this was causing memory leaks.
What am I doing wrong?
Thanks very much.
Below is a complete copy of the code:
#import <UIKit/UIKit.h>
#import "MyManager.h"
@interface ListOfCarShares : UITableViewController <NSXMLParserDelegate>
{
NSURLConnection *connection;
NSMutableData *carsharexml;
NSMutableArray *ldestination;
NSMutableArray *ldeparts_from;
NSMutableArray *lcs_id;
NSMutableArray *ltime;
NSMutableString *currentElement;
NSMutableString *tdest;
NSMutableString *tfrom;
NSMutableString *ttime;
NSMutableString *tid;
}
-(void)fetchcarshares;
@property (nonatomic, assign) IBOutlet UITableViewCell *maincell;
@end
//
// ListOfCarShares.m
// Warwick_Culture
//
// Created by Me on 26/10/2011.
// Copyright 2011 __MyCompanyName__. All rights reserved.
//
#import "ListOfCarShares.h"
@implementation ListOfCarShares
@synthesize maincell;
- (id)initWithStyle:(UITableViewStyle)style
{
self = [super initWithStyle:style];
if (self) {
// Custom initialization
}
return self;
}
- (void)parser:(NSXMLParser *)parser
didStartElement:(NSString *)elementName
namespaceURI:(NSString *)namespaceURI
qualifiedName:(NSString *)qualifiedName
attributes:(NSDictionary *)attributeDict
{
currentElement = [[elementName copy] autorelease];
if ([elementName isEqualToString:@"destination"])
{
//NSLog(@"found current conditions tag it reads %@",currentElement);
tdest = [[NSMutableString alloc] init];
}
if ([elementName isEqualToString:@"departs_from"])
{
tfrom = [[NSMutableString alloc] init];
}
if ([elementName isEqualToString:@"time"])
{
ttime = [[NSMutableString alloc] init];
}
if ([elementName isEqualToString:@"cs_id"])
{
tid = [[NSMutableString alloc] init];
}
}
- (void)parser:(NSXMLParser *)parser foundCharacters:(NSString *)string
{
if ([currentElement isEqualToString:@"destination"])
{
[tdest appendString:string];
}
if ([currentElement isEqualToString:@"departs_from"])
{
[tfrom appendString:string];
}
if ([currentElement isEqualToString:@"time"])
{
[ttime appendString:string];
}
if ([currentElement isEqualToString:@"cs_id"])
{
[tid appendString:string];
}
}
- (void)parser:(NSXMLParser *)parser didEndElement:(NSString *)elementName
namespaceURI:(NSString *)namespaceURI qualifiedName:(NSString *)qName
{
if ([currentElement isEqualToString:@"destination"])
{
[ldestination addObject:tdest];
[tdest release];
}
if ([currentElement isEqualToString:@"departs_from"])
{
[ldeparts_from addObject:tfrom];
[tfrom release];
}
if ([currentElement isEqualToString:@"time"])
{
[ltime addObject:ttime];
[ttime release];
}
if ([currentElement isEqualToString:@"cs_id"])
{
[lcs_id addObject:tid];
[tid release];
}
}
- (void)didReceiveMemoryWarning
{
[super didReceiveMemoryWarning];
}
#pragma mark - View lifecycle
- (void)viewDidLoad
{
[super viewDidLoad];
// Uncomment the following line to preserve selection between presentations.
// self.clearsSelectionOnViewWillAppear = NO;
// Uncomment the following line to display an Edit button in the navigation bar for this view controller.
// self.navigationItem.rightBarButtonItem = self.editButtonItem;
}
- (void)viewDidUnload
{
[super viewDidUnload];
}
- (void)viewWillAppear:(BOOL)animated
{
[super viewWillAppear:animated];
ldestination = [[NSMutableArray alloc] init];
ldeparts_from = [[NSMutableArray alloc] init];
ltime = [[NSMutableArray alloc] init];
lcs_id = [[NSMutableArray alloc] init];
carsharexml = [[NSMutableData alloc] init];
[self fetchcarshares];
}
- (void)viewDidAppear:(BOOL)animated
{
[super viewDidAppear:animated];
}
- (void)viewWillDisappear:(BOOL)animated
{
[super viewWillDisappear:animated];
[connection release];
[ldestination release];
[ldeparts_from release];
[ltime release];
[lcs_id release]; ///
[carsharexml release];
}
- (void)viewDidDisappear:(BOOL)animated
{
[super viewDidDisappear:animated];
}
- (BOOL)shouldAutorotateToInterfaceOrientation:(UIInterfaceOrientation)interfaceOrientation
{
// Return YES for supported orientations
return (interfaceOrientation == UIInterfaceOrientationPortrait);
}
#pragma mark - Table view data source
- (NSInteger)numberOfSectionsInTableView:(UITableView *)tableView
{
// Return the number of sections.
return 1;
}
- (NSInteger)tableView:(UITableView *)tableView numberOfRowsInSection:(NSInteger)section
{
// Return the number of rows in the section.
return [ltime count];
}
- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath
{
//static NSString *CellIdentifier = @"Cell";
UITableViewCell *cell = [tableView dequeueReusableCellWithIdentifier:nil];
if (cell == nil)
{
[[NSBundle mainBundle] loadNibNamed:@"carsharecell" owner:self options:nil];
}
// Configure the cell...
cell=maincell;
UILabel *from;
UILabel *dest;
UILabel *time;
from = (UILabel *)[cell viewWithTag:4];
dest = (UILabel *)[cell viewWithTag:5];
time = (UILabel *)[cell viewWithTag:6];
from.text=[ldeparts_from objectAtIndex:indexPath.row];
dest.text=[ldestination objectAtIndex:indexPath.row];
time.text=[ltime objectAtIndex:indexPath.row];
return cell;
}
/*
// Override to support conditional editing of the table view.
- (BOOL)tableView:(UITableView *)tableView canEditRowAtIndexPath:(NSIndexPath *)indexPath
{
// Return NO if you do not want the specified item to be editable.
return YES;
}
*/
/*
// Override to support editing the table view.
- (void)tableView:(UITableView *)tableView commitEditingStyle:(UITableViewCellEditingStyle)editingStyle forRowAtIndexPath:(NSIndexPath *)indexPath
{
if (editingStyle == UITableViewCellEditingStyleDelete) {
// Delete the row from the data source
[tableView deleteRowsAtIndexPaths:[NSArray arrayWithObject:indexPath] withRowAnimation:UITableViewRowAnimationFade];
}
else if (editingStyle == UITableViewCellEditingStyleInsert) {
// Create a new instance of the appropriate class, insert it into the array, and add a new row to the table view
}
}
*/
/*
// Override to support rearranging the table view.
- (void)tableView:(UITableView *)tableView moveRowAtIndexPath:(NSIndexPath *)fromIndexPath toIndexPath:(NSIndexPath *)toIndexPath
{
}
*/
/*
// Override to support conditional rearranging of the table view.
- (BOOL)tableView:(UITableView *)tableView canMoveRowAtIndexPath:(NSIndexPath *)indexPath
{
// Return NO if you do not want the item to be re-orderable.
return YES;
}
*/
-(void)fetchcarshares
{
MyManager *sharedManager = [MyManager sharedManager];
NSString *urlString = [NSString stringWithFormat:@"http://url/get.php?username=%@&password=%@",sharedManager.user,sharedManager.passw];
NSURL *url = [NSURL URLWithString:urlString];
NSURLRequest *req = [NSURLRequest requestWithURL:url];
connection = [[NSURLConnection alloc] initWithRequest:req delegate:self startImmediately:YES];
}
-(void) connection:(NSURLConnection *)conn didReceiveData:(NSData *)data
{
[carsharexml appendData:data];
}
-(void) connectionDidFinishLoading:(NSURLConnection *)conn
{
NSString *xmlcheck = [[NSString alloc] initWithData:carsharexml encoding:NSUTF8StringEncoding];
NSLog(@"%@",xmlcheck);
[xmlcheck release];
NSXMLParser *parser = [[NSXMLParser alloc] initWithData: carsharexml];
[parser setDelegate:self];
[parser parse];
[parser release];
[[self tableView] reloadData];
}
-(CGFloat)tableView:(UITableView *)tableView heightForRowAtIndexPath:(NSIndexPath *)indexPath
{
return 102;
}
#pragma mark - Table view delegate
- (void)tableView:(UITableView *)tableView didSelectRowAtIndexPath:(NSIndexPath *)indexPath
{
}
-(void)dealloc
{
[super dealloc];
}
@end
回答1:
Try this....
- (void)viewWillAppear:(BOOL)animated
{
[super viewWillAppear:animated];
ldestination = [[[NSMutableArray alloc] init]retain];
ldeparts_from = [[[NSMutableArray alloc] init]retain];
ltime = [[[NSMutableArray alloc] init]retain];
lcs_id = [[[NSMutableArray alloc] init]retain];
carsharexml = [[[NSMutableData alloc] init]retain];
[self fetchcarshares];
}
回答2:
if lcs_id property not define as retain you need to replace the line
lcs_id = [[NSMutableArray alloc] init];
to
lcs_id = [[[NSMutableArray alloc] init] retain];
or another work around would be in
- (void)viewWillDisappear:(BOOL)animated
{
if(lcs_id)
{
[lcs_id release];
lcd_id = nil;
}
}
回答3:
For the Crashing issue, please check below point 1. Please make sure you haven't use [autorelease] for object lcs_id 2. Most important, if you have use same variable in other pages in application, you have received above error.
please try
[this.lcs_id release] Your error will resolved.
来源：https://stackoverflow.com/questions/8191714/confusing-double-free-error-message-memory-leak-in-iphone-app