Dealloc方法的使用
今天我们来学习一下Dealloc方法的使用。Dealloc方法的作用是，当对象的引用计数为0时，系统会自动调用dealloc方法来回收内存。它的一般写法有两种：
1. 调用父类的dealloc方法：
```objective-c
-(void)dealloc{
[super dealloc];
}
```
2. 调用父类的dealloc方法并释放子类拥有的对象实例：
```objective-c
-(void)dealloc{
NSLog(@"laptop dead");
[_cpu release];
[super dealloc];
}
```
接下来我们来了解一下为什么需要调用父类的dealloc方法以及调用的顺序。
(一)为什么需要调用父类的dealloc方法？
子类的对象实例有时是继承自父类的。因此，我们需要调用父类的dealloc方法来释放父类拥有的这些对象。
(二)调用的顺序
一般来说，调用的顺序是先释放子类的对象实例，然后再释放父类所拥有的实例。这一点与调用初始化方法正好相反。下面我们使用一个例子来演示一下：
1. 父类Vehicle.h
```objective-c
#import
@interface Vehicle : NSObject {
@private
NSString *_name;
}
-(id)initWithName:(NSString *)name;
@end
```
2. 父类Vehicle.m
```objective-c
#import "Vehicle.h"
@implementation Vehicle
-(id)initWithName:(NSString *)name{
self=[super init];
if(self){
_name=[name copy];
}
return self;
}
-(void)dealloc{
NSLog(@"vehicle dead");
[_name release];
[super dealloc];
}
@end
```
3. 子类Car.h
```objective-c
#import
#import "Vehicle.h"
@class Engine;
@interface Car : Vehicle {
Engine *_engine;
}
-(void)setEngine:(Engine *)engine;
@end
```
:子类Car.m
```objective-c
#import "Car.h"
@implementation Car {
Engine *_engine;
}
- (void)setEngine:(Engine *)engine {
if (_engine != engine) {
[_engine release];
_engine = [engine retain];
}
}
- (Engine *)engine {
return _engine;
}
- (void)dealloc {
NSLog(@"Car dead");
[_engine release];
[super dealloc];
}
@end
```
5:测试main.m代码
```objective-c
#import
#import "Engine.h"
#import "Car.h"
int main(int argc, const char *argv[]) {
@autoreleasepool {
NSString *name = [[NSString alloc] initWithFormat:@"audi"];
Car *car = [[Car alloc] initWithName:name];
[name release];
Engine *v6 = [[Engine alloc] init];
[car setEngine:v6];
[v6 release];
//do something
[car release];
}
return 0;
}
```
