有一个UITextField，每次输入到第七次时，就会崩溃。而且没有什么信息在XCode中显示。我在iPad中运行：
App[12345] has active assertions beyond permitted time:
{(
<BKProcessAssertion: 0x1f5bf200> identifier: Suspending process: App[12345] permittedBackgroundDuration: 10.000000 reason: suspend owner pid:26 preventSuspend preventThrottleDownCPU preventThrottleDownUI
)}
将有关UITextField 的代码贴出来看看