項目中有加載網絡圖片的需求，加一個加載的進度條會提高用戶體驗，網絡不好的時候會清晰的看到圖片加載的進度，比讓用戶看著滿屏幕空白好。下面是我們項目自己封裝的圓形進度條，分享給大家。

其實實現原理很簡單，只是根據圖片加載的進度來繪制一個圓。

先來看.h文件，需要一個進度的屬性和進度條展示位置的方法：

 

@property (nonatomic, assign) CGFloat progress;

+(HMProgressView *)showHMProgressView:(UIView *)parentView :(CGFloat)viewHeight;

再看.m文件中的實現：

 

 

+(HMProgressView *)showHMProgressView:(UIView *)parentView :(CGFloat)viewHeight{
    HMProgressView *progressView=(HMProgressView *)[parentView viewWithTag:999];
    if (!progressView) {
        progressView=[[HMProgressView alloc] initWithFrame:CGRectMake(0, 0, 50, 50)];
        progressView.tag=999;
        progressView.center=parentView.center;
        progressView.y=viewHeight+kScreenWidth/2-25;
        progressView.backgroundColor=[UIColor clearColor];
        [parentView addSubview:progressView];
    }
    return progressView;
    
}

- (void)setProgress:(CGFloat)progress
{
    _progress = progress;
    
    // 重新繪制
    // 在view上做一個重繪的標記，當下次屏幕刷新的時候，就會調用drawRect.
    [self setNeedsDisplay];
    if (_progress==1) {//加載完成時移除
        [self removeFromSuperview];
    }

}


// Only override drawRect: if you perform custom drawing.
// An empty implementation adversely affects performance during animation.
// 當視圖顯示的時候會調用 默認只會調用一次
- (void)drawRect:(CGRect)rect
{
    // Drawing code
    
    // 1.獲取上下文
    CGContextRef ctx = UIGraphicsGetCurrentContext();
    
    // 2.拼接路徑
    CGPoint center = CGPointMake(25, 25);
    CGFloat radius = 25 - 2;
    CGFloat startA = -M_PI_2;
    CGFloat endA = -M_PI_2 + _progress * M_PI * 2;
    UIBezierPath *path = [UIBezierPath bezierPathWithArcCenter:center radius:radius startAngle:startA endAngle:endA clockwise:YES];
    CGContextSetLineCap(ctx, kCGLineCapRound);

    CGContextSetLineWidth(ctx, 4);
    // 3.把路徑添加到上下文
    [[UIColor lightGrayColor] set];
    CGContextAddPath(ctx, path.CGPath);
    
    // 4.把上下文渲染到視圖
    CGContextStrokePath(ctx);
    
}

使用也很簡單，項目中設置圖片用的是第三方框架SDWebImage，在加載圖片的方法中設置一下進度：

 

 

        ImgProgressView *progressView=[ImgProgressView showImgProgressView:self.contentView :layoutFrame.photoRect.origin.y];
        [self.orgPhoto setImageWithURL:[NSURL URLWithString:photoUrl] placeholderImage:nil options:SDWebImageProgressiveDownload progress:^(NSInteger receivedSize, NSInteger expectedSize)
         {
             if (expectedSize!=-1) {
                 [progressView setProgress:(CGFloat)receivedSize/expectedSize];
             }
         }
            completed:^(UIImage *image, NSError *error, SDImageCacheType cacheType)
         {

         }];