渐进渲染大图对加载大图特别重要，地图都是局部加载，放大移动时候一部分一部分的渐进的加载，一般在对大图进行网络请求时候，可以获得一部分数据就加载一部分数据。
用本地图片和定时器来模拟网络加载图片。
@interfaceViewController(){
NSMutableData* _data;
NSData* _allData;
NSUInteger length;
UIImageView* _imageView;
NSTimer* timer;
NSInteger le;
}
@end
@implementation ViewController
-(void)viewDidload{
[super viewDidload];
_data = [NSMutableData alloc]init];
NSString *path =[[NSBundlemainBundle]pathForResource:@"Portrait-ns@2x"ofType:@"png"];
_allData = [NSDatadataWithContentsOfFile:path];
length = _allData.length;
le = length/10;
timer = [NSTimer scheduledTimerWithTimeInterval:1target:self selector:@selector(updateImage) userInfo:nil repeats:YES];
_imageView = [[UIImageViewalloc]initWithFrame:self.view.frame];
[self.view addSubview:_imageView];
}
}
-(void)updateImage{
staticintindex =0;
if(index==10) {
return;
}
NSUInteger l;
if(index==9) {
l=length-le*9;
}else{
l= le;
}
Byte by[l];
[_allData getBytes:by range:NSMakeRange(index*le, l)];//得到新增字节然后渲染图片。
[_data appendBytes:by length:l];
CGImageSourceRefmyImageSource =CGImageSourceCreateWithData((CFDataRef)_data,NULL);
CGImageRefmyImage =CGImageSourceCreateImageAtIndex(myImageSource,0,NULL);
CFRelease(myImageSource);
_imageView.image = [UIImageimageWithCGImage:myImage];
// image.image = [UIImage imageNamed:@"image.ico"];
index++;
}
