1. Attribute modifiers need to pay attention to the place

In arc, properties outside the basic variables are preferred for weak references.weakTo avoid the appearance of wild pointers,weakCan be automatically set to when the pointed object is deallocnil(The attribute value will be cleared).

Used in arcassignModificationdelegateIs very dangerous, inassignProperty values ​​are not cleared when the decorated property is destroyed. If you use this timeself.delegateWill cause a programcrash。

Strong reference in arc to try to usestrongOf course herestrongwithretainThe role is the same, but in order to maintain code consistency, it is recommended to use here.strong。

2. How to access instance variables inside an object

@interface Person : NSObject
@property (nonatomic, copy) NSString *name;

There are two access methods: 1. Access by property, ie setter getter method. 2. Direct access method.

Access to properties when setting instance variables, ieself. name. Because of direct access to instance variables_name, does not call the setter method, it also bypasses the 'memory management semantics' defined for the property (ie the modifiers copy, strong, weak... does not work). Direct access also does not trigger the 'key-value observation KVO' notification. If the property uses lazy loading, use direct access_nameIt is also invalid.

3. Declare constants

NSString *const kNotificationName = @"failNotificationName Name";

If the constant is not global, add static before it. Otherwise a duplicate symbol error may occur.
If you need to declare a global constant, you need to include it in the .h file.

FOUNDATION_EXPORT NSString * const kNotificationName;
or
extern NSString * const kNotificationName;

Similarly we can use macros to declare variables and define preprocessor directives. There are several disadvantages to using preprocessing directives: 1. The defined constants have no type information and can only be replaced. 2. When the macro is modified elsewhere, it will cause the constant to change. (For example, other developers define macros with the same name in the project, the compiler will not report an error) and using type constants can solve these two problems.

4. Switching the environment in the program

In the development process, it is often necessary to switch environments. Such as test environment, development environment, and production environment. We can return the url by constructing a category of NSString.

#import "NSString+URL.h"
static NSString * const kBaseURL = @"http://220.175.104.19:8080";

@implementation NSString (URL)
+ (NSString *)RequestUrlWithString:(NSString *)url
{
    return [NSString stringWithFormat:@"%@%@",kBaseURL, url];
}
@end

Instructions:

NSString *url = [NSString RequestUrlWithString:@"xxx/xxxx"];

5. Notification additions and removals

See a colleague using this method to add notifications and remove notifications

-(void)viewWillAppear:(BOOL)animated{
    
    [[NSNotificationCenter defaultCenter ] addObserver:self selector:@selector(keyboardWillShow:) name:UIKeyboardWillShowNotification object:nil] ;
    
    [[NSNotificationCenter defaultCenter ] addObserver:self selector:@selector(keyboardWillHidden:) name:UIKeyboardWillHideNotification object:nil] ;
    
}
-(void)viewWillDisappear:(BOOL)animated{
    
    [[NSNotificationCenter defaultCenter ] removeObserver:self name:UIKeyboardWillHideNotification object:nil ] ;
    [[NSNotificationCenter defaultCenter ] removeObserver:self name:UIKeyboardWillShowNotification object:nil ];
    
}

becausewillAppearwithDisappearThe order of appearance is not necessarily one-to-one. So it is possible to cause multiple additions and remove notifications multiple times. The view controller cannot receive notifications when the view is not showing, causing some operations not to proceed.
is recommended inviewDidLoadAdd a notification. indeallocRemove notifications. Of course, this method can be used when notifying the root view controller to display the operation, avoiding all the loaded controllers responding to the notification.

6. Use lazy loading

inviewDidLoadAfter that, the initialization process must generate the corresponding control or data, regardless of whether these controls or data are immediately useful, which will take up a relatively large memory space. We can solve the above problem by rewriting the getter method of the property.

@property (nonatomic, strong) NSMutableArray *dataSource;

- (NSMutableArray *)dataSource {
    if (!_dataSource) {
        self.dataSource = [NSMutableArray array];
    }
    return _dataSource;
}

7.delegate needs to verify the incoming parameters

Especially when encapsulating your own UI controls, when we use the proxy method of the system UI control, we will find that the proxy method will always pass the control object as a parameter. In this method, you can access the properties of the object.

- (void)textViewDidEndEditing:(YYTextView *)textView {
    self.navigationItem.rightBarButtonItem = nil;
}

If your delegate method is only used as a delegate callback for a textView, there is no problem with this type of writing. But if you want to extend your interface, it is likely that another textView will appear in the future interface, then you have to distinguish between the two textViews who are calling this proxy method. At this point, if you have not added the incoming parameter judgment before, then you need to find the name of the previous textView variable, and transfer the previous logic to an if branch before processing the newly added textView logic. Your thoughts are likely to be interrupted. To make matters worse, it is very likely that your little friend is doing this. So it is a good habit to add parameter validation before the extension.

- (void)textViewDidEndEditing:(YYTextView *)textView {
    if (textView == self.textView) {
        self.navigationItem.rightBarButtonItem = nil;
    }
}