决绝Capturing 'demo' strongly in this block is likely to lead to a retain cycle

- (IBAction)onTest:(id)sender
{
    BlockDemo *demo = [[BlockDemo alloc]init];

    __weak typeof(BlockDemo) *weakDemo = demo;

    [demo setExecuteFinished:^{
        if (weakDemo.resultCode == 200) {
            NSLog(@"call back ok.");
        }
    }];
    [demo executeTest];
}