编程技巧 - 1

来源：互联网发布：卓智网络锐捷编辑：程序博客网时间：2024/05/16 08:35

1.销毁变量技巧.

学习XMPP的时候学到的一个很优雅的销毁和置nil方法：

- (void)setupStream;//对应着初始化stream- (void)teardownStream;//对应着销毁stream- (void)teardownStream//将相关的变量销毁，看见了没，remove   deactivate   dieconnect    = nil{[xmppStreamremoveDelegate:self];[xmppRosterremoveDelegate:self];[xmppReconnect        deactivate];[xmppRoster           deactivate];[xmppvCardTempModule  deactivate];[xmppvCardAvatarModuledeactivate];[xmppCapabilities     deactivate];[xmppStreamdisconnect];xmppStream =nil;xmppReconnect =nil;    xmppRoster =nil;xmppRosterStorage =nil;xmppvCardStorage =nil;    xmppvCardTempModule =nil;xmppvCardAvatarModule =nil;xmppCapabilities =nil;xmppCapabilitiesStorage =nil;}- (void)applicationWillTerminate:(UIApplication *)application//应用被关闭的时候也销毁，所以销毁的情况也要注意！{    DDLogVerbose(@"%@: %@",THIS_FILE, THIS_METHOD);    [selfteardownStream];}- (void)dealloc//最常见的啦{[selfteardownStream];}

同样的：

- (void)cleanup{    [[NSNotificationCenter defaultCenter] removeObserver:self];    [self.containerView removeFromSuperview];    [[[[UIApplication sharedApplication] delegate] window] makeKeyWindow];    [self.window removeFromSuperview];    self.contentViewController = nil;    self.window = nil;}- (void)dealloc{    [self cleanup];}

总结：不用的变量都要销毁，那内存才可以得以轻松，这是个好习惯，而怎么封装和编码得更漂亮，就得看个人的功底啦！

2.颜色的定义.

#define KCColor(r,g,b) [UIColor colorWithHue:r/255.0 saturation:g/255.0 brightness:b/255.0 alpha:1]#define kStatusTableViewCellBackgroundColor KCColor(251,251,251)

总结：要用的时候直接调，又方便又好看

3.iOS的API也存在嵌套.

sizeToFit的作用就不详说了，查看文档：

- (CGSize)sizeThatFits:(CGSize)size;     // return 'best' size to fit given size. does not actually resize view. Default is return existing view size- (void)sizeToFit;                       // calls sizeThatFits: with current view bounds and changes bounds size.

注意到 calls sizeThatFits : 这个方法意思是用当前的视图bounds调用方法sizeThatFits去改变bounds的大小，且用当前的视图bounds大小为参数，说明适度的嵌套又好看又方便！

4.字典的取value非常简单

dictionayVariable[keyValue] 就是等于： [dictionaryVariable objectForKey:keyValue]

iOS6以后提供的装箱拆箱：

NSNumber:

原始写法：

NSNumber *value1;value1 = [NSNumber numberWithInt:12345];value1 = [NSNumber numberWithFloat:123.45f];value1 = [NSNumber numberWithDouble:123.45];value1 = [NSNumber numberWithBool:YES];

便捷写法：

NSNumber *value2;value2 = @12345;value2 = @123.45f;value2 = @123.45;value2 = @YES;

例子：

NSNumber *piOverSixteen1 = [NSNumber numberWithDouble: ( M_PI / 16 )];NSString *path1 = [NSString stringWithUTF8String: getenv("PATH")];

可以写成：

NSNumber *piOverSixteen2 = @( M_PI / 16 );NSString *path2= @( getenv("PATH") );

NSArray:

NSArray *array;array = @[]; //空数组array = @[ a ]; //一个对象的数组array = @[ a, b, c ]; //多个对象的数组//编译器在处理时：array = @[ a, b, c ];//编译器生成的代码：id objects[] = { a, b, c };NSUInteger count = sizeof(objects)/ sizeof(id);array = [NSArray arrayWithObjects:objects count:count];

这里小心的是上面这样写的话编译器无法帮你直面地检查是否有nil值的存在而通过编译

NSDictionary:

NSDictionary *dict;dict = @{}; //空字典dict = @{@"key1":@"value1" }; //包含一个键值对的字典dict = @{ @"key1" : @"value1", @"key2" : @"value", @"key3" : @"value3" }; //包含多个键值对的字典

可以很明显地看到区别就是数组用的是[ ]，而字典用的是 { }。

上面讲得都是不可变的，那可变的呢，记得深浅复制吧？由可变到不可变和不可变到可变都是改变指针的复制，所以：

//采用上述写法构建的容器都是不可变的，如果需要生成可变容器，可以传递-mutableCopy消息。例如NSMutableArray *mutablePlanets = [@[@"Mercury", @"Venus", @"Earth",@"Mars", @"Jupiter", @"Saturn",@"Uranus", @"Neptune"] mutableCopy];NSMutableDictionary *dic=[@{ @"key1" : @"value1", @"key2" : @"value", @"key3" : @"value3" } mutableCopy];

生成可变容器，传递xxx消息多好的专业名词！

5.工具函数如何封装得漂亮

封装前：冗杂！

    constraint = [NSLayoutConstraint constraintWithItem:newView                                                attribute:NSLayoutAttributeLeading                                                relatedBy:NSLayoutRelationEqual                                                   toItem:self.view                                                attribute:NSLayoutAttributeLeading                                               multiplier:1.0f                                                 constant:20];      [self.view addConstraint:constraint];            constraint = [NSLayoutConstraint constraintWithItem:newView                                                attribute:NSLayoutAttributeTrailing                                                relatedBy:NSLayoutRelationEqual                                                   toItem:self.view                                                attribute:NSLayoutAttributeTrailing                                               multiplier:1.0f                                                 constant:-20];      [self.view addConstraint:constraint];            constraint = [NSLayoutConstraint constraintWithItem:newView                                                attribute:NSLayoutAttributeTop                                                relatedBy:NSLayoutRelationEqual                                                   toItem:self.view                                                attribute:NSLayoutAttributeTop                                               multiplier:1.0f                                                 constant:20];      [self.view addConstraint:constraint];            constraint = [NSLayoutConstraint constraintWithItem:newView                                                attribute:NSLayoutAttributeBottom                                                relatedBy:NSLayoutRelationEqual                                                   toItem:self.view                                                attribute:NSLayoutAttributeBottom                                               multiplier:1.0f                                                 constant:-20];      [self.view addConstraint:constraint];

好的封装方式：

- (void)setEdge:(UIView*)superview view:(UIView*)view attr:(NSLayoutAttribute)attr constant:(CGFloat)constant{    [superview addConstraint:[NSLayoutConstraint constraintWithItem:view attribute:attr relatedBy:NSLayoutRelationEqual toItem:superview attribute:attr multiplier:1.0 constant:constant]];}

还有这样的：

- (NSMutableArray*)portraitConstraints:(UIView*)greenView yellowView:(UIView*)yellowView blueView:(UIView*)blueView{    NSMutableArray* constraintArray = [NSMutableArray array];        [constraintArray addObjectsFromArray:[NSLayoutConstraint constraintsWithVisualFormat:@"H:|-20-[greenView]-20-[yellowView(==greenView)]-20-|" options:0 metrics:nil views:NSDictionaryOfVariableBindings(greenView, yellowView)]];        [constraintArray addObjectsFromArray:[NSLayoutConstraint constraintsWithVisualFormat:@"V:|-20-[greenView]-20-[blueView(==greenView)]-20-|" options:0 metrics:nil views:NSDictionaryOfVariableBindings(greenView, blueView)]];        [constraintArray addObjectsFromArray:[NSLayoutConstraint constraintsWithVisualFormat:@"V:|-20-[yellowView]-20-[blueView(==yellowView)]-20-|" options:0 metrics:nil views:NSDictionaryOfVariableBindings(yellowView, blueView)]];        [constraintArray addObjectsFromArray:[NSLayoutConstraint constraintsWithVisualFormat:@"H:|-20-[blueView]-20|" options:0 metrics:nil views:NSDictionaryOfVariableBindings(blueView)]];        return constraintArray;}

好的封装在于：

1.重复的可以用一个来表示：上面的attr

2.约定俗成或者规定的可以直接在函数体里面设置好：上面的的NSLayoutRelationEqual multiplier: 1.0

3.可以语意化：例如上面的superView在语义上是优先级高的所以先作为变量，即时在API上并不是首个变量

有待补充...

6.适当使用宏

上面提到的有颜色方法的定义宏，还有很多字符串等等的操作都可以定义成宏，并写在一个.h文件中

定义：

/** @brief 判断NSString是否为空 */#define isStringEmpty(str)  ((str) == nil || [(str) isKindOfClass:[NSNull class]] || [(str) isEqual:@""])

使用：

if (money == 0 && isStringEmpty(serverId) && isStringEmpty(outId) && !dic &&([dic count] == 0) ){//do something.}

比白白写一个 if 判断语句强多了吧！我经常说的要提高代码的质量，就是如此嘛。

7.“时机”的控制

- (void)willRotateToInterfaceOrientation:(UIInterfaceOrientation)toInterfaceOrientation duration:(NSTimeInterval)duration{    NSLog(@"UIViewController will rotate to Orientation: %d", toInterfaceOrientation);}- (void)didRotateFromInterfaceOrientation:(UIInterfaceOrientation)fromInterfaceOrientation{    NSLog(@"did rotated to new Orientation, view Information %@", self.view);}

will did 这种“时机”性的方法，要细细品味，为什么要如此做

待续：

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