iPhone：核心数据：NSManagedObjects 和 UITableView 崩溃
这个 fetch 方法工作完美，NSLog 打印出数据库的内容...（NSArray 中的 fetchedObjects）：
NSError *error2;
fetchedObjects = [moc executeFetchRequest:fetchRequest error:&error2];
if (!fetchedObjects) {
NSLog(@"Error %@",[error2 localizedDescription]);
}
for (NSManagedObject *info in fetchedObjects) {
NSLog(@"Name: %@", [info valueForKey:@"Name"]);
NSLog(@"Description: %@", [info valueForKey:@"Description"]);
NSLog(@"Ingredients: %@", [info valueForKey:@"Ingredients"]);
..但是当我尝试填充 tableView 时（我已经构建了很多表，并且感觉我很好地理解了如何他们工作），程序崩溃并显示“EXE_BAD_ACCESS at int retVal = UIApplicationMain(argc, argv, nil, nil);”。就是这样，没有其他错误消息。
为了尝试调试，我将这个简单的 NSLog 放入“cellForRowAtIndexPath”方法中，但它在 NSLog(@"fetchedObjects count in tableview %i",[fetchedObjects count]) 处崩溃。
据我所知，我还没有发布该数组。
UITableViewCell *cell = [tableView dequeueReusableCellWithIdentifier:CellIdentifier];
if (cell == nil) {
cell = [[[UITableViewCell alloc] initWithStyle:UITableViewCellStyleDefault reuseIdentifier:CellIdentifier] autorelease];
}
// Configure the cell.
NSLog(@"fetchedObjects count in tableview %i",[fetchedObjects count]);
NSManagedObject *info3 = [fetchedObjects objectAtIndex:indexPath.row];
NSLog(@"Name: %@", [info3 valueForKey:@"Name"]);
cell.textLabel.text = [info3 valueForKey:@"Name"];
This fetch method work perfectly and the NSLog prints out the contents of the database...(fetchedObjects in an NSArray):
NSError *error2;
fetchedObjects = [moc executeFetchRequest:fetchRequest error:&error2];
if (!fetchedObjects) {
NSLog(@"Error %@",[error2 localizedDescription]);
}
for (NSManagedObject *info in fetchedObjects) {
NSLog(@"Name: %@", [info valueForKey:@"Name"]);
NSLog(@"Description: %@", [info valueForKey:@"Description"]);
NSLog(@"Ingredients: %@", [info valueForKey:@"Ingredients"]);
.. but when I try to populate a tableView (I have built many tables and feel i have a good understanding of how they work), the program crashes with a "EXE_BAD_ACCESS at int retVal = UIApplicationMain(argc, argv, nil, nil);." That is it, no other error messages.
To try and debug, I put this simple NSLog in the "cellForRowAtIndexPath" method, but it crashes at NSLog(@"fetchedObjects count in tableview %i",[fetchedObjects count]).
I haven't released the array as far as I can tell.
UITableViewCell *cell = [tableView dequeueReusableCellWithIdentifier:CellIdentifier];
if (cell == nil) {
cell = [[[UITableViewCell alloc] initWithStyle:UITableViewCellStyleDefault reuseIdentifier:CellIdentifier] autorelease];
}
// Configure the cell.
NSLog(@"fetchedObjects count in tableview %i",[fetchedObjects count]);
NSManagedObject *info3 = [fetchedObjects objectAtIndex:indexPath.row];
NSLog(@"Name: %@", [info3 valueForKey:@"Name"]);
cell.textLabel.text = [info3 valueForKey:@"Name"];
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看起来您的 fetchedObjects 实例变量由于自动释放池刷新而被释放。
NSManagedObjectContext的-executeFetchRequest:error:方法返回一个 autoreleasedNSArray实例，您没有获得其所有权，因此，当执行到达 -tableView:cellForRowAtIndexPath: 方法时，自动释放池已被刷新，并且该对象被释放，现在您有一个悬空指针。啊，经典。当然，解决方案是通过将
-executeFetchRequest:error:发送到您的来将。-retain消息发送到返回的NSArrayNSManagedObjectContext不要忘记在
-dealloc方法中向其发送-release消息。Looks like your
fetchedObjectsinstance variable is being deallocated because of an autorelease pool flush.NSManagedObjectContext's-executeFetchRequest:error:method returns an autoreleasedNSArrayinstance, which you aren't obtaining ownership of, therefore by the time execution reaches the-tableView:cellForRowAtIndexPath:method, the autorelease pool has been flushed, and that object is deallocated, and you now have a dangling pointer. Ah, classic.The solution, of course, is to send the
-retainmessage to the returnedNSArrayfrom sending-executeFetchRequest:error:to yourNSManagedObjectContext.Don't forget to send the
-releasemessage to it in your-deallocmethod.问题似乎出在这一行
NSManagedObject *info3 = [fetchedObjects objectAtIndex:indexPath.row];
尝试使用
NSManagedObject *info3 = [fetchedObjects objectAtIndex:0];
因为您的 UiTableViewCell 计数和 fetchedObjects 计数在整个过程中应该相等。
如果不匹配，则会出现索引错误。
The problem seems to be on this line
NSManagedObject *info3 = [fetchedObjects objectAtIndex:indexPath.row];
Try to use
NSManagedObject *info3 = [fetchedObjects objectAtIndex:0];
Because your UiTableViewCell count and fetchedObjects count should be equal at whole process.
If it doesn't match then it will give you index error.