需求：

从后台请求数据，一共多少条不固定。每次最多可以请求10条（请求时传递本次请求的数据启始位置，本次请求的数据个数），每次请求会返回（数据总数，本次返回的数据启始位置，本次返回的数据个数）。我现在想请求所有数据。有什么好的解决思路吗？

我的方法：

每次请求10条数据，请求成功后继续请求下10条。直到请求完所有数据。

数据请求成功后通过block回调通知，所以使用了block递归。用动画写了一个模仿的代码，如下：

#import "ViewController.h"
typedef  void (^myBlock)(int );
@interface ViewController ()
//测试用的视图，用闪烁此视图模仿请求。
@property (strong, nonatomic) IBOutlet UIView *testView;
@end
@implementation ViewController
//一个按钮，点击开始模仿请求
- (IBAction)blockTest:(id)sender
{
    //假如请求10次
    [self blockRecursion:0];
}
//模仿请求，n－请求数据开始位置
- (void)blockRecursion:(NSInteger)n
{
    __weak myBlock __block block = ^(int bn)
    {
        NSLog(@"%d", bn);
        //大于10次就退出
        if(bn < 10)
        {
            //请求，成功后回调自己(block)
            [self getData:block num:++bn];
        }
    };
    block(0);
}
//模仿一次网络请求，成功后通过block回调
- (void)getData:(myBlock)block num:(NSInteger)bn
{
    self.testView.alpha = 1;
    [UIView animateWithDuration:0.5 delay:0 options:UIViewAnimationOptionCurveEaseInOut animations:^{
        self.testView.alpha = 0;
    } completion:^(BOOL finished) {
        block(bn);
    }];
}
@end

问题：

[self getData:block num:++bn]; 这一行有一个警告：Capturing 'block' strongly in this block is likely to lead to a retain cycle

怎么消除？（是因为Blocks 会自动 retain，所以才报retain cycle吧？加__weak？）

如果我在定义block时：myBlock __weak __block block = ^(int bn)... 警告会消失，但是getData回调时候程序会崩溃。（是因为异步请求所以block被释放了吗？）

求指点。

解决方案

(http://stackoverflow.com/questions/19853878/objective-c-uiview-animate-block-recursion)

The problem with your code is that there is no strong reference to the block object. block is a weak reference. So after the statement where the block object is created, the block object can potentially be deallocated, which will set the __weak variable block to nil. Invoking a block with a nil block pointer crashes.

When you remove the __weak, you create a retain cycle -- the block retains a strong reference to itself.

What you need is two variables, one strong and one weak. The block captures the weak one. The one the block captures needs to be __block to reflect the assignment after the block was created.

myBlock blockStrong;
__block __weak myBlock blockWeak;
blockWeak = blockStrong = ^(int bn)
{
    NSLog(@"%d", bn);
    if(bn < 10)
    {
        [self getData:blockWeak num:++bn];
    }
};