弹跳UITableView会导致崩溃

Question

我正在开发一款使用RSS的iPhone应用程序。 当我滚动UITableView时，如果我将它反弹到底部太多，我的应用程序崩溃了，我得到了__TERMINATING_DUE_TO_UNCAUGHT_EXCEPTION__。

这是我的代码： http://pages.stern.nyu.edu/~abc329/SS/

这是我得到的错误：

warning: Unable to read symbols for 
 "/System/Library/Frameworks/UIKit.framework/UIKit" (file not found).

warning: Unable to read symbols from 
 "UIKit" (not yet mapped into memory).

warning: Unable to read symbols for 
  "/System/Library/Frameworks/CoreGraphics.framework/CoreGraphics" (file not found).

warning: Unable to read symbols from 
  "CoreGraphics" (not yet mapped into memory).
Program loaded.
sharedlibrary apply-load-rules all

Attaching to program: `/Users/abc329/Library/Application Support/
                      iPhone Simulator/User/Applications/
                      D1B397C8-9464-4979-9F12-4302A502680E/
                      street-spotted.app/street-spotted', process 18528.

(gdb)