Question

我是Objective-c编程语言的新手，我注意到内存管理中有一种奇怪的行为。使用iOS 5 ARC默认启用但是对象过早发布，也许有人可以给我一些建议。

情况就是这样：

我有一个Dao对象，它使用Core Data PersistenceStore从SQLite数据库中检索数据。这个Dao实现了一个方法“getAllAuthors”

在viewWillAppear方法的viewController中我加载了这个数据并加载了数据但是当我填充tableView时，对象是（null）。

我发布了一些代码：

@synthesize authors;
@synthesize authorsTable;
@synthesize dao;

- (void)didReceiveMemoryWarning {
    [super didReceiveMemoryWarning];
}

#pragma mark - View lifecycle

- (void)viewDidLoad {
    [super viewDidLoad];
    NSLog(@"author in viewDidLoad: %@", [[authors objectAtIndex:0] name]);
}

- (void)viewDidUnload {
    [super viewDidUnload];
}

- (void)viewWillAppear:(BOOL)animated {
    [super viewWillAppear:animated];
    dao = [[CrossoverDao alloc] init];
    authors = [NSArray arrayWithArray:[dao getAllAuthors]];
    [authorsTable reloadData];
    NSLog(@"author in viewWillAppear: %@", [[authors objectAtIndex:0] name]);
}

- (void)viewDidAppear:(BOOL)animated {
    [super viewDidAppear:animated];
    [authorsTable reloadData];
}

- (void)viewWillDisappear:(BOOL)animated {
    [super viewWillDisappear:animated];
    NSLog(@"author in viewWillDisappear: %@", [[authors objectAtIndex:0] name]);
}

- (void)viewDidDisappear:(BOOL)animated {
    [super viewDidDisappear:animated];
    NSLog(@"author in viewDidDisappear: %@", [[authors objectAtIndex:0] name]);
}

- (BOOL)shouldAutorotateToInterfaceOrientation:    (UIInterfaceOrientation)interfaceOrientation {
    return YES;
}

#pragma mark -
#pragma mark UITableViewDataSource datasource

- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath     *)indexPath {
    NSLog(@"[AuthorsViewController::cellForRowAtIndexPath] Constructing row at indexPath: %d",     indexPath.row);
    static NSString *CellIdentifier = @"Cell";
    UITableViewCell *cell = [tableView 
                             dequeueReusableCellWithIdentifier:CellIdentifier];
    if (cell == nil) {
        if(indexPath.section == 0)
            cell = [[UITableViewCell alloc]     initWithStyle:UITableViewCellStyleValue2 reuseIdentifier:CellIdentifier];
        else
            cell = [[UITableViewCell alloc]     initWithStyle:UITableViewCellStyleValue1 reuseIdentifier:CellIdentifier];
    }
    cell.textLabel.text = [[authors objectAtIndex:indexPath.row] name];
    cell.detailTextLabel.text = [[authors objectAtIndex:indexPath.row] bio];
    cell.selectionStyle = UITableViewCellSelectionStyleNone;
    return cell;
}

- (NSInteger)numberOfSectionsInTableView:(UITableView *)tableView {
    return 1;
}

- (NSInteger)tableView:(UITableView *)tv numberOfRowsInSection:(NSInteger)section {
    NSLog(@"author in numberOfRowsInSection: %@", [[authors objectAtIndex:0] name]);
    return [authors count];
}

在cellForRowAtIndexPath中，作者为null。任何线索？

提前致谢

Answer 1

dao = [[CrossoverDao alloc] init];
authors = [NSArray arrayWithArray:[dao getAllAuthors]];
[authorsTable reloadData];
NSLog(@"author in viewWillAppear: %@", [[authors objectAtIndex:0] name]);

这应该在控制器的viewDidLoad或loadView方法中完成。在viewWillAppear中，您通常只是请求UI更新。

Answer 2

您应该确保使用合成访问器设置属性，以便ARC知道如果它们很强大就要保留它们（这里它只是在viewWillAppear方法的末尾插入了版本）。变化

dao = [[CrossoverDao alloc] init];
authors = [NSArray arrayWithArray:[dao getAllAuthors]];

到

self.dao = [[CrossoverDao alloc] init];
self.authors = [NSArray arrayWithArray:[dao getAllAuthors]];

Answer 3

我没有使用ios5 ARC，但也许您可以尝试保留viewWillAppear并在viewWillDisappear中发布？

[authors retain];

对象iOS 5 ARC发布太快了

3 个答案: