iOS开发基础知识--碎片46

 iOS开发基础知识--碎片46

1:带中文的URL处理

// http://static.tripbe.com/videofiles/视频/我的自拍视频.mp4
NSString *path  = (__bridge_transfer NSString *)CFURLCreateStringByReplacingPercentEscapesUsingEncoding(NULL,(__bridge CFStringRef)model.mp4_url, CFSTR(""),CFStringConvertNSStringEncodingToEncoding(NSUTF8StringEncoding));

2:取WebView高度

- (void)webViewDidFinishLoad:(UIWebView *)webView  {  
    CGFloat height = [[webView stringByEvaluatingJavaScriptFromString:@"document.body.offsetHeight"] floatValue];  
    CGRect frame = webView.frame;  
    webView.frame = CGRectMake(frame.origin.x, frame.origin.y, frame.size.width, height);  
}  

另外一种方式利用KVO实例：

-(void)viewDidLoad{

    // KVO,作为一个观察者,只要属性"contentSize"发生变化,回调方法里面就会通知
    [_webView.scrollView addObserver:self forKeyPath:@"contentSize" options:NSKeyValueObservingOptionNew context:NULL];
}

//  回调方法
- (void)observeValueForKeyPath:(NSString *)keyPath ofObject:(id)object change:(NSDictionary *)change context:(void *)context
{
    if(object == _webView.scrollView && [keyPath isEqualToString:@"contentSize"])
    {
        //  得到最大的Y坐标
        CGSize size = _webView.scrollView.contentSize;

        if (size.height > 568.0) {

            // 遮挡广告
            _hideBottomImage = [[UIImageView alloc] initWithFrame:CGRectMake(0, size.height-67, ScreenWidth, 67)];
            _hideBottomImage.image = [UIImage imageNamed:@"banner"];
            [_webView.scrollView addSubview:_hideBottomImage];
        }
    }
    else
    {
        //  调用父类的方法
        [super observeValueForKeyPath:keyPath ofObject:object change:change context:context];
    }
}

- (void)dealloc{//---->在ARC环境下也能调用dealloc方法,只是不需要写[super dealloc]

    // 移除KVO,否则会引起资源泄露
    [_webView.scrollView removeObserver:self forKeyPath:@"contentSize"];
}

3:UIView的部分圆角问题

UIView *view2 = [[UIView alloc] initWithFrame:CGRectMake(120, 10, 80, 80)];
view2.backgroundColor = [UIColor redColor];
[self.view addSubview:view2];
 
UIBezierPath *maskPath = [UIBezierPath bezierPathWithRoundedRect:view2.bounds byRoundingCorners:UIRectCornerBottomLeft | UIRectCornerBottomRight cornerRadii:CGSizeMake(10, 10)];
CAShapeLayer *maskLayer = [[CAShapeLayer alloc] init];
maskLayer.frame = view2.bounds;
maskLayer.path = maskPath.CGPath;
view2.layer.mask = maskLayer;
//其中，byRoundingCorners:UIRectCornerBottomLeft |UIRectCornerBottomRight
//指定了需要成为圆角的角。该参数是UIRectCorner类型的，可选的值有：
* UIRectCornerTopLeft
* UIRectCornerTopRight
* UIRectCornerBottomLeft
* UIRectCornerBottomRight
* UIRectCornerAllCorners

4：强制App直接退出

- (void)exitApplication {
    AppDelegate *app = [UIApplication sharedApplication].delegate;
    UIWindow *window = app.window;
    [UIView animateWithDuration:1.0f animations:^{
        window.alpha = 0;
    } completion:^(BOOL finished) {
        exit(0);
    }];
}

5：修改占位符颜色和大小

textField.placeholder = @"请输入用户名";  
[textField setValue:[UIColor redColor] forKeyPath:@"_placeholderLabel.textColor"];  
[textField setValue:[UIFont boldSystemFontOfSize:16] forKeyPath:@"_placeholderLabel.font"];

6：取消系统的返回手势

self.navigationController.interactivePopGestureRecognizer.enabled = NO;

7：改WebView字体/颜色

UIWebView设置字体大小，颜色，字体： UIWebView无法通过自身的属性设置字体的一些属性，只能通过html代码进行设置 在webView加载完毕后：

- (void)webViewDidFinishLoad:(UIWebView *)webView {  
    NSString *str = @"document.getElementsByTagName(‘body‘)[0].style.webkitTextSizeAdjust= ‘60%‘";  
    [webView stringByEvaluatingJavaScriptFromString:str];
}

或者加入以下代码

NSString *jsString = [[NSString alloc] initWithFormat:@"document.body.style.fontSize=%f;document.body.style.color=%@",fontSize,fontColor];  
[webView stringByEvaluatingJavaScriptFromString:jsString];

8：WebView图片自适应屏幕

- (void)webViewDidFinishLoad:(UIWebView *)webView {
  NSString *js = @"function imgAutoFit() {      var imgs = document.getElementsByTagName(‘img‘);      for (var i = 0; i < imgs.length; ++i) {        var img = imgs[i];           img.style.maxWidth = %f;        }   }";
  js = [NSString stringWithFormat:js, [UIScreen mainScreen].bounds.size.width - 20];

  [webView stringByEvaluatingJavaScriptFromString:js];
  [webView stringByEvaluatingJavaScriptFromString:@"imgAutoFit()"];
}

9：BOOL / bool / Boolean / NSCFBoolean的区别

10：nil / Nil / NULL / NSNull区别

a、nil：一般赋值给空对象；

b、NULL：一般赋值给nil之外的其他空值。如SEL等；

　　举个栗子（好重啊~）：

　　　　[NSApp beginSheet:sheet
             　　 modalForWindow:mainWindow

　　modalDelegate:nil //pointing to an object

　　didEndSelector:NULL //pointing to a non object/class

　　contextInfo:NULL]; //pointing to a non object/class

c、NSNULL：NSNull只有一个方法：+ (NSNull *) null;

　　[NSNull null]用来在NSArray和NSDictionary中加入非nil（表示列表结束）的空值.

NSMutableDictionary *mutableDictionary = [NSMutableDictionary dictionary];
mutableDictionary[@"someKey"] = [NSNull null]; // Sets value of NSNull singleton for `someKey`
NSLog(@"Keys: %@", [mutableDictionary allKeys]); // @[@"someKey"]

d、当向nil发送消息时，返回NO，不会有异常，程序将继续执行下去；

　　而向NSNull的对象发送消息时会收到异常。

11:子类中实现 -isEqual: 和 hash

@interface Person
@property NSString *name;
@property NSDate *birthday;

- (BOOL)isEqualToPerson:(Person *)person;
@end

@implementation Person

- (BOOL)isEqualToPerson:(Person *)person {
  if (!person) {
    return NO;
  }

  BOOL haveEqualNames = (!self.name && !person.name) || [self.name isEqualToString:person.name];
  BOOL haveEqualBirthdays = (!self.birthday && !person.birthday) || [self.birthday isEqualToDate:person.birthday];

  return haveEqualNames && haveEqualBirthdays;
}

#pragma mark - NSObject

- (BOOL)isEqual:(id)object {
  if (self == object) {
    return YES;
  }

  if (![object isKindOfClass:[Person class]]) {
    return NO;
  }

  return [self isEqualToPerson:(Person *)object];
}

- (NSUInteger)hash {
  return [self.name hash] ^ [self.birthday hash];
}