activity_main.xml: java.lang.NullPointerException[通俗易懂]

1、错误描写叙述

eclipse.buildId=4.4.0.I20140606-1215
java.version=1.7.0_67
java.vendor=Oracle Corporation
BootLoader constants: OS=win32, ARCH=x86_64, WS=win32, NL=zh_CN
Framework arguments:  -product org.eclipse.epp.package.jee.product
Command-line arguments:  -os win32 -ws win32 -arch x86_64 -product org.eclipse.epp.package.jee.product

com.android.ide.eclipse.adt
Error
Fri Jun 05 23:50:22 CST 2015
activity_main.xml: java.lang.NullPointerException

java.lang.NullPointerException
	at android.support.v7.internal.widget.ActionBarOverlayLayout.getDecorToolbar(ActionBarOverlayLayout.java:599)
	at android.support.v7.internal.widget.ActionBarOverlayLayout.pullChildren(ActionBarOverlayLayout.java:588)
	at android.support.v7.internal.widget.ActionBarOverlayLayout.onMeasure(ActionBarOverlayLayout.java:359)
	at android.view.View.measure(View.java:17547)
	at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5535)
	at android.widget.LinearLayout.measureChildBeforeLayout(LinearLayout.java:1436)
	at android.widget.LinearLayout.measureVertical(LinearLayout.java:722)
	at android.widget.LinearLayout.onMeasure(LinearLayout.java:613)
	at android.view.View.measure(View.java:17547)
	at android.widget.LinearLayout.measureVertical(LinearLayout.java:875)
	at android.widget.LinearLayout.onMeasure(LinearLayout.java:613)
	at android.view.View.measure(View.java:17547)
	at com.android.layoutlib.bridge.impl.RenderSessionImpl.measureView(RenderSessionImpl.java:640)
	at com.android.layoutlib.bridge.impl.RenderSessionImpl.render(RenderSessionImpl.java:540)
	at com.android.layoutlib.bridge.Bridge.createSession(Bridge.java:323)
	at com.android.ide.common.rendering.LayoutLibrary.createSession(LayoutLibrary.java:349)
	at com.android.ide.eclipse.adt.internal.editors.layout.gle2.RenderService.createRenderSession(RenderService.java:519)
	at com.android.ide.eclipse.adt.internal.editors.layout.gle2.GraphicalEditorPart.renderWithBridge(GraphicalEditorPart.java:1584)
	at com.android.ide.eclipse.adt.internal.editors.layout.gle2.GraphicalEditorPart.recomputeLayout(GraphicalEditorPart.java:1309)
	at com.android.ide.eclipse.adt.internal.editors.layout.gle2.GraphicalEditorPart.activated(GraphicalEditorPart.java:1066)
	at com.android.ide.eclipse.adt.internal.editors.layout.LayoutEditorDelegate.delegatePageChange(LayoutEditorDelegate.java:686)
	at com.android.ide.eclipse.adt.internal.editors.common.CommonXmlEditor.pageChange(CommonXmlEditor.java:360)
	at org.eclipse.ui.part.MultiPageEditorPart.setActivePage(MultiPageEditorPart.java:1101)
	at org.eclipse.ui.forms.editor.FormEditor.setActivePage(FormEditor.java:607)
	at com.android.ide.eclipse.adt.internal.editors.AndroidXmlEditor.selectDefaultPage(AndroidXmlEditor.java:450)
	at com.android.ide.eclipse.adt.internal.editors.AndroidXmlEditor.addPages(AndroidXmlEditor.java:311)
	at com.android.ide.eclipse.adt.internal.editors.common.CommonXmlEditor.addPages(CommonXmlEditor.java:285)
	at org.eclipse.ui.forms.editor.FormEditor.createPages(FormEditor.java:138)
	at org.eclipse.ui.part.MultiPageEditorPart.createPartControl(MultiPageEditorPart.java:362)
	at org.eclipse.ui.internal.e4.compatibility.CompatibilityPart.createPartControl(CompatibilityPart.java:140)
	at org.eclipse.ui.internal.e4.compatibility.CompatibilityEditor.createPartControl(CompatibilityEditor.java:99)
	at org.eclipse.ui.internal.e4.compatibility.CompatibilityPart.create(CompatibilityPart.java:321)
	at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
	at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57)
	at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
	at java.lang.reflect.Method.invoke(Method.java:606)
	at org.eclipse.e4.core.internal.di.MethodRequestor.execute(MethodRequestor.java:55)
	at org.eclipse.e4.core.internal.di.InjectorImpl.processAnnotated(InjectorImpl.java:888)
	at org.eclipse.e4.core.internal.di.InjectorImpl.processAnnotated(InjectorImpl.java:869)
	at org.eclipse.e4.core.internal.di.InjectorImpl.inject(InjectorImpl.java:120)
	at org.eclipse.e4.core.internal.di.InjectorImpl.internalMake(InjectorImpl.java:337)
	at org.eclipse.e4.core.internal.di.InjectorImpl.make(InjectorImpl.java:258)
	at org.eclipse.e4.core.contexts.ContextInjectionFactory.make(ContextInjectionFactory.java:162)
	at org.eclipse.e4.ui.internal.workbench.ReflectionContributionFactory.createFromBundle(ReflectionContributionFactory.java:104)
	at org.eclipse.e4.ui.internal.workbench.ReflectionContributionFactory.doCreate(ReflectionContributionFactory.java:73)
	at org.eclipse.e4.ui.internal.workbench.ReflectionContributionFactory.create(ReflectionContributionFactory.java:55)
	at org.eclipse.e4.ui.workbench.renderers.swt.ContributedPartRenderer.createWidget(ContributedPartRenderer.java:127)
	at org.eclipse.e4.ui.internal.workbench.swt.PartRenderingEngine.createWidget(PartRenderingEngine.java:983)
	at org.eclipse.e4.ui.internal.workbench.swt.PartRenderingEngine.safeCreateGui(PartRenderingEngine.java:662)
	at org.eclipse.e4.ui.internal.workbench.swt.PartRenderingEngine.safeCreateGui(PartRenderingEngine.java:766)
	at org.eclipse.e4.ui.internal.workbench.swt.PartRenderingEngine.access$2(PartRenderingEngine.java:737)
	at org.eclipse.e4.ui.internal.workbench.swt.PartRenderingEngine$7.run(PartRenderingEngine.java:731)
	at org.eclipse.core.runtime.SafeRunner.run(SafeRunner.java:42)
	at org.eclipse.e4.ui.internal.workbench.swt.PartRenderingEngine.createGui(PartRenderingEngine.java:715)
	at org.eclipse.e4.ui.workbench.renderers.swt.StackRenderer.showTab(StackRenderer.java:1251)
	at org.eclipse.e4.ui.workbench.renderers.swt.LazyStackRenderer$1.handleEvent(LazyStackRenderer.java:66)
	at org.eclipse.e4.ui.services.internal.events.UIEventHandler$1.run(UIEventHandler.java:40)
	at org.eclipse.swt.widgets.Synchronizer.syncExec(Synchronizer.java:187)
	at org.eclipse.ui.internal.UISynchronizer.syncExec(UISynchronizer.java:156)
	at org.eclipse.swt.widgets.Display.syncExec(Display.java:4734)
	at org.eclipse.e4.ui.internal.workbench.swt.E4Application$1.syncExec(E4Application.java:218)
	at org.eclipse.e4.ui.services.internal.events.UIEventHandler.handleEvent(UIEventHandler.java:36)
	at org.eclipse.equinox.internal.event.EventHandlerWrapper.handleEvent(EventHandlerWrapper.java:197)
	at org.eclipse.equinox.internal.event.EventHandlerTracker.dispatchEvent(EventHandlerTracker.java:197)
	at org.eclipse.equinox.internal.event.EventHandlerTracker.dispatchEvent(EventHandlerTracker.java:1)
	at org.eclipse.osgi.framework.eventmgr.EventManager.dispatchEvent(EventManager.java:230)
	at org.eclipse.osgi.framework.eventmgr.ListenerQueue.dispatchEventSynchronous(ListenerQueue.java:148)
	at org.eclipse.equinox.internal.event.EventAdminImpl.dispatchEvent(EventAdminImpl.java:135)
	at org.eclipse.equinox.internal.event.EventAdminImpl.sendEvent(EventAdminImpl.java:78)
	at org.eclipse.equinox.internal.event.EventComponent.sendEvent(EventComponent.java:39)
	at org.eclipse.e4.ui.services.internal.events.EventBroker.send(EventBroker.java:81)
	at org.eclipse.e4.ui.internal.workbench.UIEventPublisher.notifyChanged(UIEventPublisher.java:59)
	at org.eclipse.emf.common.notify.impl.BasicNotifierImpl.eNotify(BasicNotifierImpl.java:374)
	at org.eclipse.e4.ui.model.application.ui.impl.ElementContainerImpl.setSelectedElement(ElementContainerImpl.java:171)
	at org.eclipse.e4.ui.internal.workbench.ModelServiceImpl.showElementInWindow(ModelServiceImpl.java:488)
	at org.eclipse.e4.ui.internal.workbench.ModelServiceImpl.bringToTop(ModelServiceImpl.java:454)
	at org.eclipse.e4.ui.internal.workbench.PartServiceImpl.delegateBringToTop(PartServiceImpl.java:692)
	at org.eclipse.e4.ui.internal.workbench.PartServiceImpl.bringToTop(PartServiceImpl.java:385)
	at org.eclipse.e4.ui.internal.workbench.PartServiceImpl.showPart(PartServiceImpl.java:1126)
	at org.eclipse.ui.internal.WorkbenchPage.busyOpenEditor(WorkbenchPage.java:3182)
	at org.eclipse.ui.internal.WorkbenchPage.access$23(WorkbenchPage.java:3104)
	at org.eclipse.ui.internal.WorkbenchPage$9.run(WorkbenchPage.java:3086)
	at org.eclipse.swt.custom.BusyIndicator.showWhile(BusyIndicator.java:70)
	at org.eclipse.ui.internal.WorkbenchPage.openEditor(WorkbenchPage.java:3081)
	at org.eclipse.ui.internal.WorkbenchPage.openEditor(WorkbenchPage.java:3045)
	at org.eclipse.ui.internal.WorkbenchPage.openEditor(WorkbenchPage.java:3035)
	at org.eclipse.ui.ide.IDE.openEditor(IDE.java:541)
	at org.eclipse.ui.ide.IDE.openEditor(IDE.java:500)
	at org.eclipse.jdt.internal.ui.javaeditor.EditorUtility.openInEditor(EditorUtility.java:360)
	at org.eclipse.jdt.internal.ui.javaeditor.EditorUtility.openInEditor(EditorUtility.java:167)
	at org.eclipse.jdt.ui.actions.OpenAction.run(OpenAction.java:268)
	at org.eclipse.jdt.ui.actions.OpenAction.run(OpenAction.java:233)
	at org.eclipse.jdt.ui.actions.SelectionDispatchAction.dispatchRun(SelectionDispatchAction.java:275)
	at org.eclipse.jdt.ui.actions.SelectionDispatchAction.run(SelectionDispatchAction.java:251)
	at org.eclipse.jdt.internal.ui.packageview.PackageExplorerActionGroup.handleOpen(PackageExplorerActionGroup.java:376)
	at org.eclipse.jdt.internal.ui.packageview.PackageExplorerPart$4.open(PackageExplorerPart.java:538)
	at org.eclipse.ui.OpenAndLinkWithEditorHelper$InternalListener.open(OpenAndLinkWithEditorHelper.java:48)
	at org.eclipse.jface.viewers.StructuredViewer$2.run(StructuredViewer.java:853)
	at org.eclipse.core.runtime.SafeRunner.run(SafeRunner.java:42)
	at org.eclipse.ui.internal.JFaceUtil$1.run(JFaceUtil.java:50)
	at org.eclipse.jface.util.SafeRunnable.run(SafeRunnable.java:178)
	at org.eclipse.jface.viewers.StructuredViewer.fireOpen(StructuredViewer.java:850)
	at org.eclipse.jface.viewers.StructuredViewer.handleOpen(StructuredViewer.java:1142)
	at org.eclipse.jface.viewers.StructuredViewer$6.handleOpen(StructuredViewer.java:1249)
	at org.eclipse.jface.util.OpenStrategy.fireOpenEvent(OpenStrategy.java:278)
	at org.eclipse.jface.util.OpenStrategy.access$2(OpenStrategy.java:272)
	at org.eclipse.jface.util.OpenStrategy$1.handleEvent(OpenStrategy.java:313)
	at org.eclipse.swt.widgets.EventTable.sendEvent(EventTable.java:84)
	at org.eclipse.swt.widgets.Display.sendEvent(Display.java:4353)
	at org.eclipse.swt.widgets.Widget.sendEvent(Widget.java:1061)
	at org.eclipse.swt.widgets.Display.runDeferredEvents(Display.java:4172)
	at org.eclipse.swt.widgets.Display.readAndDispatch(Display.java:3761)
	at org.eclipse.e4.ui.internal.workbench.swt.PartRenderingEngine$9.run(PartRenderingEngine.java:1151)
	at org.eclipse.core.databinding.observable.Realm.runWithDefault(Realm.java:332)
	at org.eclipse.e4.ui.internal.workbench.swt.PartRenderingEngine.run(PartRenderingEngine.java:1032)
	at org.eclipse.e4.ui.internal.workbench.E4Workbench.createAndRunUI(E4Workbench.java:148)
	at org.eclipse.ui.internal.Workbench$5.run(Workbench.java:636)
	at org.eclipse.core.databinding.observable.Realm.runWithDefault(Realm.java:332)
	at org.eclipse.ui.internal.Workbench.createAndRunWorkbench(Workbench.java:579)
	at org.eclipse.ui.PlatformUI.createAndRunWorkbench(PlatformUI.java:150)
	at org.eclipse.ui.internal.ide.application.IDEApplication.start(IDEApplication.java:135)
	at org.eclipse.equinox.internal.app.EclipseAppHandle.run(EclipseAppHandle.java:196)
	at org.eclipse.core.runtime.internal.adaptor.EclipseAppLauncher.runApplication(EclipseAppLauncher.java:134)
	at org.eclipse.core.runtime.internal.adaptor.EclipseAppLauncher.start(EclipseAppLauncher.java:104)
	at org.eclipse.core.runtime.adaptor.EclipseStarter.run(EclipseStarter.java:382)
	at org.eclipse.core.runtime.adaptor.EclipseStarter.run(EclipseStarter.java:236)
	at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
	at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57)
	at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
	at java.lang.reflect.Method.invoke(Method.java:606)
	at org.eclipse.equinox.launcher.Main.invokeFramework(Main.java:648)
	at org.eclipse.equinox.launcher.Main.basicRun(Main.java:603)
	at org.eclipse.equinox.launcher.Main.run(Main.java:1465)

2、错误原因

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:paddingBottom="@dimen/activity_vertical_margin"
    android:paddingLeft="@dimen/activity_horizontal_margin"
    android:paddingRight="@dimen/activity_horizontal_margin"
    android:paddingTop="@dimen/activity_vertical_margin"
    tools:context="com.example.helloworld.MainActivity" >

    <TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="@string/hello_world" />
    
    <CheckBox
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"/>

</RelativeLayout>

3、解决的方法