GCD的簡單應用--非同步載入圖片
在這裡，簡單介紹下GCD的應用。
1.程式設計場景 ：
在iPhone上做一個下載圖片的功能，很簡單，就是在螢幕上放置一個按鈕，點選該按鈕，顯示一個轉動的圓圈，表示正在下載，下載完成後，將圖片顯示出來。
2.主要程式碼如下：
#import "ViewController.h"
@interface ViewController ()
@property (nonatomic,strong) UIActivityIndicatorView *indicator; // 指示檢視
@property (nonatomic,strong) UIImageView *imgV; // 顯示圖片
@property (nonatomic,strong) UIButton *btn; // 點選按鈕
@end
@implementation ViewController
- (void)viewDidLoad {
[superviewDidLoad];
// Do any additional setup after loading the view, typically from a nib.
[self.viewaddSubview:self.btn];
}
-(UIActivityIndicatorView
if (_indicator == nil) {
_indicator = [[UIActivityIndicatorViewalloc] initWithActivityIndicatorStyle:UIActivityIndicatorViewStyleWhite];
_indicator.frame = CGRectMake(0, 0, [UIScreenmainScreen].bounds.size.width, [UIScreenmainScreen].bounds.size.width);
_indicator.backgroundColor = [
}
[self.viewaddSubview:_indicator];
return_indicator;
}
-(UIImageView *)imgV {
if (_imgV == nil) {
_imgV = [[UIImageViewalloc] initWithFrame:CGRectMake(0, 230, [UIScreenmainScreen].bounds.size.width, [UIScreenmainScreen].bounds.size.width)];
_imgV.backgroundColor = [UIColorblueColor];
}
[self.viewaddSubview:_imgV];
return_imgV;
}
-(UIButton *)btn {
if (_btn == nil) {
_btn = [UIButtonbuttonWithType:UIButtonTypeCustom];
_btn.frame = CGRectMake(10, 50, 200, 50);
_btn.backgroundColor = [UIColorredColor];
[_btnsetTitle:@"點選載入圖片"forState:UIControlStateNormal];
[_btnaddTarget:selfaction:@selector(loadImage) forControlEvents:UIControlEventTouchUpInside];
}
return_btn;
}
/** 載入圖片 */
-(void)loadImage {
self.indicator.hidden = NO;
[self.indicatorstartAnimating];
[self.imgVaddSubview:self.indicator];
// 開啟一個執行緒進行資料請求
dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
NSURL *url1 = [NSURLURLWithString:@"http://pic.qiantucdn.com/58pic/18/32/08/32658PICPUs_1024.png"];
NSError *error;
NSData *data = [NSDatadataWithContentsOfURL:url1];
if (data != nil) {
// 在主執行緒中完成UI操作
dispatch_async(dispatch_get_main_queue(), ^{
[self.indicatorstopAnimating];
self.indicator.hidden = YES;
UIImage *image = [UIImageimageWithData:data];
self.imgV.image = image;
});
}else {
NSLog(@"error whin download:%@",error);
}
});
}
- (void)didReceiveMemoryWarning {
[superdidReceiveMemoryWarning];
// Dispose of any resources that can be recreated.
}
@end