IOS開發基礎知識--片段28，ios基礎知識--28

IOS開發基礎知識--片段28，ios基礎知識--28

1：通用的weakify和strongify

/*** 強弱引用轉換，用於解決代碼塊（block）與強引用self之間的循環參考問題* 調用方式: `@weakify_self`實現弱引用轉換，`@strongify_self`實現強引用轉換** 樣本：* @weakify_self* [obj block:^{* @strongify_self* self.property = something;* }];*/#ifndef    weakify_self#if __has_feature(objc_arc)#define weakify_self autoreleasepool{} __weak __typeof__(self) weakSelf = self;#else#define weakify_self autoreleasepool{} __block __typeof__(self) blockSelf = self;#endif#endif#ifndef    strongify_self#if __has_feature(objc_arc)#define strongify_self try{} @finally{} __typeof__(weakSelf) self = weakSelf;#else#define strongify_self try{} @finally{} __typeof__(blockSelf) self = blockSelf;#endif#endif/*** 強弱引用轉換，用於解決代碼塊（block）與強引用對象之間的循環參考問題* 調用方式: `@weakify(object)`實現弱引用轉換，`@strongify(object)`實現強引用轉換** 樣本：* @weakify(object)* [obj block:^{* @strongify(object)* strong_object = something;* }];*/#ifndef    weakify#if __has_feature(objc_arc)#define weakify(object) autoreleasepool{} __weak __typeof__(object) weak##_##object = object;#else#define weakify(object) autoreleasepool{} __block __typeof__(object) block##_##object = object;#endif#endif#ifndef    strongify#if __has_feature(objc_arc)#define strongify(object) try{} @finally{} __typeof__(object) strong##_##object = weak##_##object;#else#define strongify(object) try{} @finally{} __typeof__(object) strong##_##object = block##_##object;#endif#endif

 運用（這兩個宏一定成對出現，先weak再strong）：

@weakify(self); // 定義了一個__weak的self_weak_變數 [RACObserve(self, name) subscribeNext:^(NSString *name) {     @strongify(self); // 局域定義了一個__strong的self指標指向self_weak     self.outputLabel.text = name; }]; 

 

2：objc runtime 動態增加屬性

說明：給類擴充增加了一個新屬性。通常下類擴充只允許添加方法。必須要先引入 objc/runtime.h，主要是下面兩個方法：

賦值：OBJC_EXPORT void objc_setAssociatedObject(id object, const void *key, id value, objc_AssociationPolicy policy)獲得值：OBJC_EXPORT id objc_getAssociatedObject(id object, const void *key)

執行個體（引用）：

UILabel+Associate.h#import <UIKit/UIKit.h>@interface UILabel (Associate)- (void) setFlashColor:(UIColor *) flashColor;- (UIColor *) getFlashColor;@endUILabel+Associate.m#import "UILabel+Associate.h"#import <objc/runtime.h>@implementation UILabel (Associate)static char flashColorKey;- (void) setFlashColor:(UIColor *) flashColor{    objc_setAssociatedObject(self, &flashColorKey, flashColor, OBJC_ASSOCIATION_RETAIN_NONATOMIC);}- (UIColor *) getFlashColor{   return objc_getAssociatedObject(self, &flashColorKey);}@end

調用代碼：

    UILabel *lab = [[UILabel alloc] init];    [lab setFlashColor:[UIColor redColor]];    NSLog(@"%@", [lab getFlashColor]);

 

3:navigationController popToViewController跳轉到上上層

        NSUInteger index=self.navigationController.viewControllers.count-3;        [self.navigationController popToViewController:[self.navigationController.viewControllers objectAtIndex:index] animated:YES];

如果動畫是翻轉頁面，有可能是因為當前頁面有鍵盤，可以先把鍵盤迴收後，動作就變成正常的回退動畫效果