Question

在我的应用中，用户可以下载大文件（1GB +）。我有自己的进度视图来指示下载进度。我正在使用AFNetworking这样的

[operation setDownloadProgressBlock:^(NSUInteger bytesRead, long long totalBytesRead, long long totalBytesExpectedToRead){
                [[UIApplication sharedApplication] setIdleTimerDisabled:NO];
                double progress = (double)(size + totalBytesRead) / (size + totalBytesExpectedToRead);
                [[NSNotificationCenter defaultCenter] postNotificationName:ETBDownloadManagerProgressNotification object:component userInfo:@{ ETBDownloadProgressKey : [NSNumber numberWithDouble:progress], ETBDownloadExpectedSizeKey : [NSNumber numberWithDouble:(size + totalBytesExpectedToRead)*1.0/1024.0/1024.0] }];
        }];

我在下载文件时遇到性能问题。同时，只能下载一个文件。 Time Profiler显示我更新UI并经常调用drawRect:。所以这是我的进度视图setProgress：

- (void)setProgress:(double)progress
{
    _progress = progress;
    if (_progress > 1)
        _progress = 1;
    self.textLabel.text = [NSString stringWithFormat:@"%.f%%", 100*self.progress];
    [self setNeedsDisplay];
}

进度视图drawRect：

- (void)drawRect:(CGRect)rect
{
    UIBezierPath* bezierPath = [UIBezierPath bezierPath];
    [bezierPath addArcWithCenter:CGPointMake(rect.size.width/2, rect.size.height/2)
                          radius:rect.size.width/2 - kLineWidth/2 - kPadding
                      startAngle:0
                        endAngle:2*M_PI
                       clockwise:YES];

    bezierPath.lineWidth = kLineWidth;
    [[UIColor colorWithRed:1 green:1 blue:1 alpha:.3] setStroke];
    [bezierPath stroke];

    bezierPath = [UIBezierPath bezierPath];
    [bezierPath addArcWithCenter:CGPointMake(rect.size.width/2, rect.size.height/2)
                          radius:(rect.size.width/2 - kLineWidth - kPadding)/2
                      startAngle:startAngle
                        endAngle:(endAngle - startAngle) * self.progress + startAngle
                       clockwise:YES];

    bezierPath.lineWidth = rect.size.width/2 - kLineWidth - kPadding;
    [[UIColor colorWithRed:1 green:1 blue:1 alpha:.3] setStroke];
    [bezierPath stroke];
}

问题是如何避免滞后？我发现的唯一方法是减少用于更新UI的postNotification个数。但是怎么样？我尝试在if (i++%3 == 0)内使用setDownloadProgressBlock之类的条件，但它很难看:) 我还尝试将self.textLabel.text = ...替换为drawRect:，但这没有任何意义。也许可以设置下载包的大小？

Answer 1

i ++％3 == 0可能很丑，但不是很糟糕，我会做的更像是

// outside of the loop
[[UIApplication sharedApplication] setIdleTimerDisabled:NO];

__block double progressTmp = 0;
[operation setDownloadProgressBlock:^(NSUInteger bytesRead, long long totalBytesRead, long  long totalBytesExpectedToRead){
    double progress = (double)(size + totalBytesRead) / (size + totalBytesExpectedToRead);

    // if there was a significant change in progress ratio
    if ((progress - progressTmp) > 0.05) { 
        [[NSNotificationCenter defaultCenter] postNotificationName:ETBDownloadManagerProgressNotification object:component userInfo:@{ ETBDownloadProgressKey : [NSNumber numberWithDouble:progress], ETBDownloadExpectedSizeKey : [NSNumber numberWithDouble:(size + totalBytesExpectedToRead)*1.0/1024.0/1024.0] }];
        progressTmp = progress;
    }
}];

0.05可能必须更改为更符合您需求的内容。

AFNetworking +进度视图+性能

1 个答案: