iphone - 代码花费的时间比预期的要长

Question

我的代码花费的时间比预期的要长。如何减少加载时间？以前不需要花这么多时间。我没有更改代码，但速度变慢了。我的代码流程如下:

for (i =1 ; i< [productList count]; i++) {
    UIImage *image;
    products *productItem = [productList objectAtIndex:i-1];
    if(![productItem.productItemPhoto isEqualToString:@""]){
        NSString *productItemPhoto = productItem.productItemPhoto;          
        NSData* data = [NSData dataWithContentsOfFile:productItemPhoto];
        image = [[UIImage alloc] initWithData:data];
    }
    else{
        if(numberOfProductsPerRow == 1)
            image = [UIImage imageNamed:@"no-image-2.png"];
        else
            image = [UIImage imageNamed:@"no-image-1.png"];
    }
    UIImageView *bg1;
    if(numberOfProductsPerRow == 1)
        bg1 = [[UIImageView alloc] initWithImage:[UIImage imageNamed:@"image-box-s7.png"]];
    else            
        bg1 = [[UIImageView alloc] initWithImage:[UIImage imageNamed:@"image-box-s4.png"]];
        bg1.frame = CGRectMake(x, y,width, height);
        [productScrollView addSubview:bg1];

        UIButton *pro1 = [[UIButton alloc] initWithFrame:CGRectMake(x+spacingX, y+spacingY-15, btnWidth, btnHeight)];

    [pro1 setImage:image forState:UIControlStateNormal];

        [pro1 setTag:i];
        [pro1 addTarget:self action:@selector(selectProduct:) forControlEvents:UIControlEventTouchUpInside];
        [productScrollView addSubview:pro1 ];

        UILabel *lblProductModel = [[UILabel alloc] initWithFrame:CGRectMake(0, height - 40, width, 30)];
        lblProductModel.backgroundColor = [UIColor clearColor];
        lblProductModel.textAlignment = UITextAlignmentCenter;
        lblProductModel.textColor = [UIColor colorWithRed:1.0 green:0.8 blue:0.0 alpha:1];
        NSString *price;

        if([userSettings.priceToShow isEqualToString:@"WholesalePrice"])
            price = [NSString stringWithFormat:@"%@%.0f",productItem.productCurrencySymbol, productItem.productWholesalePrice];
        else if([userSettings.priceToShow isEqualToString:@"RetailsalePrice"])
            price = [NSString stringWithFormat:@"%@%.0f",productItem.productCurrencySymbol, productItem.productRetailSalesValue];
        else
            price = @"";
        lblProductModel.tag = [productList count] + i;
        lblProductModel.text = [NSString stringWithFormat:@"%@ %@", productItem.productModelCode,  price];
        [bg1 addSubview:lblProductModel];
        x = x + width + 10;
        if(i%numberOfProductsPerRow == 0){
            x = 20;
            y=y+height+10;
        }
        [pro1 release];
        [image release];
        [bg1 release];
        [lblProductModel release];

}
if((i-1)%numberOfProductsPerRow!=0)
    scrollViewParent.contentSize = CGSizeMake(0, y+height+spacingY);
else    
    scrollViewParent.contentSize = CGSizeMake(0, y + spacingY);
productScrollView.contentSize = scrollViewParent.contentSize;
[scrollViewParent addSubview:productScrollView];
}

productList 中有大约 380 条记录。我认为它不应该花费这么多时间。

Answer 1

鉴于该代码中使用 UI* API 的 futzing 数量，该代码必须在主线程上运行。您正在主线程上加载大量图像，相对而言，图像加载是一个非常缓慢且昂贵的操作。

首先，你真的需要在开始时加载所有 380 图像吗？当它增长到 500 或 1,500 或 15,000 时会发生什么？我敢打赌您的应用程序会在 380 到 15,000 之间的某处耗尽内存....

您的代码应该只加载它需要的图像，然后在该循​​环之外执行此操作。任何在主线程上运行的东西都会在运行期间阻塞用户交互；保持这些时间段尽可能短(或者，理想情况下，根本不通过将计算移动到后台队列/线程)是理想的。