Iphone 在UITableViewController中取消分配目标C类实例属性

在iPhone应用程序中，我有一个类实例，该类实例定义为全局类，并在UITableViewController的ViewDidLoad中初始化

当它到达cellForRowAtIndexPath时，实例属性被解除分配，并显示在调试器中

正在从数据库加载属性

Foo.h

NSString *prop1;

@property(nonatomic, retain)NSString *prop1;
-(void)shouldLoadProperties;

Foo *foo;

NSString *_prop1;

@property(nonatomic, retain)NSString *prop1;
-(void)shouldLoadProperties;

Foo.m

@synthesize prop1;

-(void)shouldLoadProperties {
    <FMDatabase stuff here>

    FMResultSet *rs = [self executeQuery:sql];
    prop1 = [rs stringForColumn:@"col1"];  //loads db value "Test" into prop1
}

-(void)viewDidLoad {
   foo = [[[Foo alloc] init] retain];
   [foo shouldLoadProperties];

   //Breakpoint here shows that foo.prop1 is set to "Test"

}

- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath {

   //foo is is still allocated, but foo.prop1 has been 
   //deallocated;  shows as <freed object>  

  NSLog(@"Prop 1 is %@", foo.prop1);  //throws exception


}

@synthesize prop1 = _prop1;

TestTableViewController.m

@synthesize prop1;

-(void)shouldLoadProperties {
    <FMDatabase stuff here>

    FMResultSet *rs = [self executeQuery:sql];
    prop1 = [rs stringForColumn:@"col1"];  //loads db value "Test" into prop1
}

-(void)viewDidLoad {
   foo = [[[Foo alloc] init] retain];
   [foo shouldLoadProperties];

   //Breakpoint here shows that foo.prop1 is set to "Test"

}

- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath {

   //foo is is still allocated, but foo.prop1 has been 
   //deallocated;  shows as <freed object>  

  NSLog(@"Prop 1 is %@", foo.prop1);  //throws exception


}

@synthesize prop1 = _prop1;

---

这是正确的还是我遗漏了什么？

这里的问题是，您没有将

prop1

用作属性，而是用作类中的变量。你可以也应该给这些不同的名字。通常在变量名的开头加下划线：

foo.h

NSString *prop1;

@property(nonatomic, retain)NSString *prop1;
-(void)shouldLoadProperties;

Foo *foo;

NSString *_prop1;

@property(nonatomic, retain)NSString *prop1;
-(void)shouldLoadProperties;

foo.m

@synthesize prop1;

-(void)shouldLoadProperties {
    <FMDatabase stuff here>

    FMResultSet *rs = [self executeQuery:sql];
    prop1 = [rs stringForColumn:@"col1"];  //loads db value "Test" into prop1
}

-(void)viewDidLoad {
   foo = [[[Foo alloc] init] retain];
   [foo shouldLoadProperties];

   //Breakpoint here shows that foo.prop1 is set to "Test"

}

- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath {

   //foo is is still allocated, but foo.prop1 has been 
   //deallocated;  shows as <freed object>  

  NSLog(@"Prop 1 is %@", foo.prop1);  //throws exception


}

@synthesize prop1 = _prop1;

现在，要实际使用属性，请使用getter和setter。这将保留您的价值，并在适当时释放它

[self setProp1:[rs stringForColumn:@"col1"]];  //loads db value "Test" into prop1

及

都是有效的，并且彼此相等

_prop1 = [rs stringForColumn:@"col1"];  //loads db value "Test" into prop1

将导致撞车和其他不良行为

---

您的更新将防止崩溃，但如果您多次这样做，将泄漏内存。

这里的问题是您没有将

prop1

用作属性，而是将其用作类中的变量。你可以也应该给这些不同的名字。通常在变量名的开头加下划线：

foo.h

NSString *prop1;

@property(nonatomic, retain)NSString *prop1;
-(void)shouldLoadProperties;

Foo *foo;

NSString *_prop1;

@property(nonatomic, retain)NSString *prop1;
-(void)shouldLoadProperties;

foo.m

@synthesize prop1;

-(void)shouldLoadProperties {
    <FMDatabase stuff here>

    FMResultSet *rs = [self executeQuery:sql];
    prop1 = [rs stringForColumn:@"col1"];  //loads db value "Test" into prop1
}

-(void)viewDidLoad {
   foo = [[[Foo alloc] init] retain];
   [foo shouldLoadProperties];

   //Breakpoint here shows that foo.prop1 is set to "Test"

}

- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath {

   //foo is is still allocated, but foo.prop1 has been 
   //deallocated;  shows as <freed object>  

  NSLog(@"Prop 1 is %@", foo.prop1);  //throws exception


}

@synthesize prop1 = _prop1;

现在，要实际使用属性，请使用getter和setter。这将保留您的价值，并在适当时释放它

[self setProp1:[rs stringForColumn:@"col1"]];  //loads db value "Test" into prop1

及

都是有效的，并且彼此相等

_prop1 = [rs stringForColumn:@"col1"];  //loads db value "Test" into prop1

将导致撞车和其他不良行为

---

您的更新将防止崩溃，但如果您多次更新，将导致内存泄漏。

非常好。谢谢你的回复！杰出的谢谢你的回复！