IOS開發基礎知識--碎片46

1:帶中文的URL處理

// http://static.tripbe.com/videofiles/視頻/我的自拍視頻.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);  
}  

3:UIView的部分圓角問題

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
//指定了需要成為圓角的角。該參數是UIRectCorner類型的，可選的值有：
* UIRectCornerTopLeft
* UIRectCornerTopRight
* UIRectCornerBottomLeft
* UIRectCornerBottomRight
* UIRectCornerAllCorners

4：強制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：修改占位符顏色和大小

textField.placeholder = @"請輸入用戶名";  
[textField setValue:[UIColor redColor] forKeyPath:@"_placeholderLabel.textColor"];  
[textField setValue:[UIFont boldSystemFontOfSize:16] forKeyPath:@"_placeholderLabel.font"];

6：取消系統的返回手勢

self.navigationController.interactivePopGestureRecognizer.enabled = NO;

7：改WebView字體/顏色

UIWebView設置字體大小，顏色，字體： UIWebView無法通過自身的屬性設置字體的一些屬性，只能通過html代碼進行設置 在webView載入完畢後：

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

或者加入以下代碼

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

8：WebView圖片自適應屏幕

- (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的區別

10：nil / Nil / NULL / NSNull區別

a、nil：一般賦值給空對象；

b、NULL：一般賦值給nil之外的其他空值。如SEL等；

　　舉個慄子（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只有一個方法：+ (NSNull *) null;

　　[NSNull null]用來在NSArray和NSDictionary中加入非nil（表示列表結束）的空值.

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

d、當向nil發送消息時，返回NO，不會有異常，程式將繼續執行下去；

　　而向NSNull的對象發送消息時會收到異常。