webview滚动时back退出应用crash,该如何处理

webview滚动时back退出应用crash,急!
webview加载完某一个网页时,然后快速滚动时按back键finish这个应用,结果就crash了。
怎么回事啊。 必须要快速的操作才会crash。如果设断点,是不会crash的。如果慢慢滚动网页,退出应用也不会crash。静止时退出更不会crash了。。。求大神指点啊!!小女多谢多谢!!!

退出时代码如下:

  _View.stopLoading();
  _View.destroy();
  this.finish();
在log里,只能看到空指钟了,但是在程序里没有对应的行数。

如下:

05-24 13:22:02.888: E/AndroidRuntime(21937): FATAL EXCEPTION: main
05-24 13:22:02.888: E/AndroidRuntime(21937): java.lang.NullPointerException
05-24 13:22:02.888: E/AndroidRuntime(21937): at android.webkit.WebView.sendOurVisibleRect(WebView.java:2429)
05-24 13:22:02.888: E/AndroidRuntime(21937): at android.webkit.WebView.onScrollChanged(WebView.java:4995)
05-24 13:22:02.888: E/AndroidRuntime(21937): at android.view.View.scrollTo(View.java:5017)
05-24 13:22:02.888: E/AndroidRuntime(21937): at android.webkit.WebView.onOverScrolled(WebView.java:2648)
05-24 13:22:02.888: E/AndroidRuntime(21937): at android.view.View.overScrollBy(View.java:8882)
05-24 13:22:02.888: E/AndroidRuntime(21937): at android.webkit.WebView.computeScroll(WebView.java:3049)
05-24 13:22:02.888: E/AndroidRuntime(21937): at android.view.ViewGroup.drawChild(ViewGroup.java:1562)
05-24 13:22:02.888: E/AndroidRuntime(21937): at android.view.ViewGroup.dispatchDraw(ViewGroup.java:1373)
05-24 13:22:02.888: E/AndroidRuntime(21937): at android.view.ViewGroup.drawChild(ViewGroup.java:1644)
05-24 13:22:02.888: E/AndroidRuntime(21937): at android.view.ViewGroup.dispatchDraw(ViewGroup.java:1373)
05-24 13:22:02.888: E/AndroidRuntime(21937): at android.view.View.draw(View.java:6884)
05-24 13:22:02.888: E/AndroidRuntime(21937): at android.widget.FrameLayout.draw(FrameLayout.java:357)
05-24 13:22:02.888: E/AndroidRuntime(21937): at android.view.ViewGroup.drawChild(ViewGroup.java:1646)
05-24 13:22:02.888: E/AndroidRuntime(21937): at android.view.ViewGroup.dispatchDraw(ViewGroup.java:1373)
05-24 13:22:02.888: E/AndroidRuntime(21937): at android.view.View.draw(View.java:6884)
05-24 13:22:02.888: E/AndroidRuntime(21937): at android.widget.FrameLayout.draw(FrameLayout.java:357)
05-24 13:22:02.888: E/AndroidRuntime(21937): at com.android.internal.policy.impl.PhoneWindow$DecorView.draw(PhoneWindow.java:1912)
05-24 13:22:02.888: E/AndroidRuntime(21937): at android.view.ViewRoot.draw(ViewRoot.java:1524)
05-24 13:22:02.888: E/AndroidRuntime(21937): at android.view.ViewRoot.performTraversals(ViewRoot.java:1260)
05-24 13:22:02.888: E/AndroidRuntime(21937): at android.view.ViewRoot.handleMessage(ViewRoot.java:1861)
05-24 13:22:02.888: E/AndroidRuntime(21937): at android.os.Handler.dispatchMessage(Handler.java:99)
05-24 13:22:02.888: E/AndroidRuntime(21937): at android.os.Looper.loop(Looper.java:130)
05-24 13:22:02.888: E/AndroidRuntime(21937): at android.app.ActivityThread.main(ActivityThread.java:3765)
05-24 13:22:02.888: E/AndroidRuntime(21937): at java.lang.reflect.Method.invokeNative(Native Method)
05-24 13:22:02.888: E/AndroidRuntime(21937): at java.lang.reflect.Method.invoke(Method.java:507)
05-24 13:22:02.888: E/AndroidRuntime(21937): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:894)
05-24 13:22:02.888: E/AndroidRuntime(21937): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:652)
05-24 13:22:02.888: E/AndroidRuntime(21937): at dalvik.system.NativeStart.main(Native Method)


------解决方案--------------------
系统的bug,可以提给google
------解决方案--------------------
你在webview里面onScrollChanged中判断webView是否为空,不为空再继续,把onScrollChanged里面的代码发上来看看。