这是我第一次使用Android Studio，但我之前使用过Eclipse和Xamarin。但是当我打开main_activity.xml时，没有“可视”，也没有选择的选项。我也得到了致命错误：
这是错误：
null
java.lang.AssertionError
at org.jetbrains.android.actions.AndroidRunSdkToolAction.actionPerformed(AndroidRunSdkToolAction.java:40)
at com.intellij.ui.popup.PopupFactoryImpl$ActionPopupStep$1.run(PopupFactoryImpl.java:733)
at com.intellij.ui.popup.AbstractPopup$18.run(AbstractPopup.java:1258)
at com.intellij.openapi.wm.impl.FocusManagerImpl.flushRequest(FocusManagerImpl.java:641)
at com.intellij.openapi.wm.impl.FocusManagerImpl.flushNow(FocusManagerImpl.java:622)
at com.intellij.openapi.wm.impl.FocusManagerImpl.flushIdleRequests(FocusManagerImpl.java:592)
at com.intellij.openapi.wm.impl.FocusManagerImpl.access$200(FocusManagerImpl.java:59)
at com.intellij.openapi.wm.impl.FocusManagerImpl$IdleRunnable.runEdt(FocusManagerImpl.java:107)
at com.intellij.openapi.util.EdtRunnable$1.run(EdtRunnable.java:28)
at java.awt.event.InvocationEvent.dispatch(InvocationEvent.java:251)
at java.awt.EventQueue.dispatchEventImpl(EventQueue.java:733)
at java.awt.EventQueue.access$200(EventQueue.java:103)
at java.awt.EventQueue$3.run(EventQueue.java:694)
at java.awt.EventQueue$3.run(EventQueue.java:692)
at java.security.AccessController.doPrivileged(Native Method)
at java.security.ProtectionDomain$1.doIntersectionPrivilege(ProtectionDomain.java:76)
at java.awt.EventQueue.dispatchEvent(EventQueue.java:703)
at com.intellij.ide.IdeEventQueue.defaultDispatchEvent(IdeEventQueue.java:697)
at com.intellij.ide.IdeEventQueue._dispatchEvent(IdeEventQueue.java:524)
at com.intellij.ide.IdeEventQueue.dispatchEvent(IdeEventQueue.java:335)
at java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:242)
at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:161)
at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:150)
at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:146)
at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:138)
at java.awt.EventDispatchThread.run(EventDispatchThread.java:91)
很抱歉很久，我不知道这意味着什么。我尝试删除并重新安装sdk，虽然没有用。