ViewPagerIndicator无法实例化CirclePageIndicator

Question

我将ViewPageIndicator添加到现有项目中。我在下面的链接中做了所有的事情。

https://www.youtube.com/watch?v=yTaIQ0LMLy0

当我将CirclePageIndicator添加到布局中时，我收到此错误。

异常堆栈跟踪：

java.lang.NullPointerException
    at com.android.layoutlib.bridge.android.BridgeContext.obtainStyledAttributes(BridgeContext.java:568)
    at android.view.View.<init>(View.java:3283)
    at com.viewpagerindicator.CirclePageIndicator.<init>(CirclePageIndicator.java:76)
    at com.viewpagerindicator.CirclePageIndicator.<init>(CirclePageIndicator.java:72)
    at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
    at sun.reflect.NativeConstructorAccessorImpl.newInstance(Unknown Source)
    at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(Unknown Source)
    at java.lang.reflect.Constructor.newInstance(Unknown Source)
    at com.android.ide.eclipse.adt.internal.editors.layout.ProjectCallback.instantiateClass(ProjectCallback.java:422)
    at com.android.ide.eclipse.adt.internal.editors.layout.ProjectCallback.loadView(ProjectCallback.java:179)
    at android.view.BridgeInflater.loadCustomView(BridgeInflater.java:207)
    at android.view.BridgeInflater.createViewFromTag(BridgeInflater.java:135)
    at android.view.LayoutInflater.rInflate_Original(LayoutInflater.java:746)
    at android.view.LayoutInflater_Delegate.rInflate(LayoutInflater_Delegate.java:64)
    at android.view.LayoutInflater.rInflate(LayoutInflater.java:718)
    at android.view.LayoutInflater.rInflate_Original(LayoutInflater.java:749)
    at android.view.LayoutInflater_Delegate.rInflate(LayoutInflater_Delegate.java:64)
    at android.view.LayoutInflater.rInflate(LayoutInflater.java:718)
    at android.view.LayoutInflater.inflate(LayoutInflater.java:489)
    at android.view.LayoutInflater.inflate(LayoutInflater.java:372)
    at com.android.layoutlib.bridge.impl.RenderSessionImpl.inflate(RenderSessionImpl.java:385)
    at com.android.layoutlib.bridge.Bridge.createSession(Bridge.java:332)
    at com.android.ide.common.rendering.LayoutLibrary.createSession(LayoutLibrary.java:325)
    at com.android.ide.eclipse.adt.internal.editors.layout.gle2.RenderService.createRenderSession(RenderService.java:440)
    at com.android.ide.eclipse.adt.internal.editors.layout.gle2.GraphicalEditorPart.renderWithBridge(GraphicalEditorPart.java:1545)
    at com.android.ide.eclipse.adt.internal.editors.layout.gle2.GraphicalEditorPart.recomputeLayout(GraphicalEditorPart.java:1302)
    at com.android.ide.eclipse.adt.internal.editors.layout.LayoutEditorDelegate.recomputeLayout(LayoutEditorDelegate.java:410)
    at com.android.ide.eclipse.adt.internal.editors.layout.gle2.SelectionManager.setSelection(SelectionManager.java:285)
    at com.android.ide.eclipse.adt.internal.editors.layout.gle2.LayoutCanvasViewer.setSelection(LayoutCanvasViewer.java:120)
    at org.eclipse.jface.viewers.Viewer.setSelection(Viewer.java:394)
    at com.android.ide.eclipse.adt.internal.editors.layout.gle2.GraphicalEditorPart.selectionChanged(GraphicalEditorPart.java:611)
    at org.eclipse.ui.internal.e4.compatibility.SelectionService.notifyListeners(SelectionService.java:154)
    at org.eclipse.ui.internal.e4.compatibility.SelectionService.updateSelection(SelectionService.java:119)
    at org.eclipse.ui.internal.WorkbenchPage$E4PartListener.partActivated(WorkbenchPage.java:170)
    at org.eclipse.e4.ui.internal.workbench.PartServiceImpl$2.run(PartServiceImpl.java:193)
    at org.eclipse.core.runtime.SafeRunner.run(SafeRunner.java:42)
    at org.eclipse.e4.ui.internal.workbench.PartServiceImpl.firePartActivated(PartServiceImpl.java:191)
    at org.eclipse.e4.ui.internal.workbench.PartServiceImpl.activate(PartServiceImpl.java:596)
    at org.eclipse.e4.ui.internal.workbench.PartServiceImpl.activate(PartServiceImpl.java:549)
    at org.eclipse.e4.ui.internal.workbench.swt.AbstractPartRenderer.activate(AbstractPartRenderer.java:105)
    at org.eclipse.e4.ui.workbench.renderers.swt.ContributedPartRenderer$1.handleEvent(ContributedPartRenderer.java:61)
    at org.eclipse.swt.widgets.EventTable.sendEvent(EventTable.java:84)
    at org.eclipse.swt.widgets.Widget.sendEvent(Widget.java:1053)
    at org.eclipse.swt.widgets.Widget.sendEvent(Widget.java:1077)
    at org.eclipse.swt.widgets.Widget.sendEvent(Widget.java:1058)
    at org.eclipse.swt.widgets.Shell.setActiveControl(Shell.java:1447)
    at org.eclipse.swt.widgets.Shell.WM_MOUSEACTIVATE(Shell.java:2328)
    at org.eclipse.swt.widgets.Control.windowProc(Control.java:4572)
    at org.eclipse.swt.widgets.Canvas.windowProc(Canvas.java:341)
    at org.eclipse.swt.widgets.Decorations.windowProc(Decorations.java:1627)
    at org.eclipse.swt.widgets.Shell.windowProc(Shell.java:2069)
    at org.eclipse.swt.widgets.Display.windowProc(Display.java:4989)
    at org.eclipse.swt.internal.win32.OS.DefWindowProcW(Native Method)
    at org.eclipse.swt.internal.win32.OS.DefWindowProc(OS.java:2541)
    at org.eclipse.swt.widgets.Scrollable.callWindowProc(Scrollable.java:80)
    at org.eclipse.swt.widgets.Control.windowProc(Control.java:4623)
    at org.eclipse.swt.widgets.Display.windowProc(Display.java:4989)
    at org.eclipse.swt.internal.win32.OS.DefWindowProcW(Native Method)
    at org.eclipse.swt.internal.win32.OS.DefWindowProc(OS.java:2541)
    at org.eclipse.swt.widgets.Scrollable.callWindowProc(Scrollable.java:80)
    at org.eclipse.swt.widgets.Control.windowProc(Control.java:4623)
    at org.eclipse.swt.widgets.Display.windowProc(Display.java:4989)
    at org.eclipse.swt.internal.win32.OS.DefWindowProcW(Native Method)
    at org.eclipse.swt.internal.win32.OS.DefWindowProc(OS.java:2541)
    at org.eclipse.swt.widgets.Scrollable.callWindowProc(Scrollable.java:80)
    at org.eclipse.swt.widgets.Control.windowProc(Control.java:4623)
    at org.eclipse.swt.widgets.Display.windowProc(Display.java:4989)
    at org.eclipse.swt.internal.win32.OS.DefWindowProcW(Native Method)
    at org.eclipse.swt.internal.win32.OS.DefWindowProc(OS.java:2541)
    at org.eclipse.swt.widgets.Scrollable.callWindowProc(Scrollable.java:80)
    at org.eclipse.swt.widgets.Control.windowProc(Control.java:4623)
    at org.eclipse.swt.widgets.Display.windowProc(Display.java:4989)
    at org.eclipse.swt.internal.win32.OS.DefWindowProcW(Native Method)
    at org.eclipse.swt.internal.win32.OS.DefWindowProc(OS.java:2541)
    at org.eclipse.swt.widgets.Scrollable.callWindowProc(Scrollable.java:80)
    at org.eclipse.swt.widgets.Control.windowProc(Control.java:4623)
    at org.eclipse.swt.widgets.Display.windowProc(Display.java:4989)
    at org.eclipse.swt.internal.win32.OS.DefWindowProcW(Native Method)
    at org.eclipse.swt.internal.win32.OS.DefWindowProc(OS.java:2541)
    at org.eclipse.swt.widgets.Scrollable.callWindowProc(Scrollable.java:80)
    at org.eclipse.swt.widgets.Control.windowProc(Control.java:4623)
    at org.eclipse.swt.widgets.Display.windowProc(Display.java:4989)
    at org.eclipse.swt.internal.win32.OS.DefWindowProcW(Native Method)
    at org.eclipse.swt.internal.win32.OS.DefWindowProc(OS.java:2541)
    at org.eclipse.swt.widgets.Scrollable.callWindowProc(Scrollable.java:80)
    at org.eclipse.swt.widgets.Control.windowProc(Control.java:4623)
    at org.eclipse.swt.widgets.Display.windowProc(Display.java:4989)
    at org.eclipse.swt.internal.win32.OS.DefWindowProcW(Native Method)
    at org.eclipse.swt.internal.win32.OS.DefWindowProc(OS.java:2541)
    at org.eclipse.swt.widgets.Scrollable.callWindowProc(Scrollable.java:80)
    at org.eclipse.swt.widgets.Control.windowProc(Control.java:4623)
    at org.eclipse.swt.widgets.Display.windowProc(Display.java:4989)
    at org.eclipse.swt.internal.win32.OS.DefWindowProcW(Native Method)
    at org.eclipse.swt.internal.win32.OS.DefWindowProc(OS.java:2541)
    at org.eclipse.swt.widgets.Scrollable.callWindowProc(Scrollable.java:80)
    at org.eclipse.swt.widgets.Control.windowProc(Control.java:4623)
    at org.eclipse.swt.widgets.Display.windowProc(Display.java:4989)
    at org.eclipse.swt.internal.win32.OS.DefWindowProcW(Native Method)
    at org.eclipse.swt.internal.win32.OS.DefWindowProc(OS.java:2541)
    at org.eclipse.swt.widgets.Scrollable.callWindowProc(Scrollable.java:80)
    at org.eclipse.swt.widgets.Control.windowProc(Control.java:4623)
    at org.eclipse.swt.widgets.Display.windowProc(Display.java:4989)
    at org.eclipse.swt.internal.win32.OS.DefWindowProcW(Native Method)
    at org.eclipse.swt.internal.win32.OS.DefWindowProc(OS.java:2541)
    at org.eclipse.swt.widgets.Scrollable.callWindowProc(Scrollable.java:80)
    at org.eclipse.swt.widgets.Control.windowProc(Control.java:4623)
    at org.eclipse.swt.widgets.Display.windowProc(Display.java:4989)
    at org.eclipse.swt.internal.win32.OS.DefWindowProcW(Native Method)
    at org.eclipse.swt.internal.win32.OS.DefWindowProc(OS.java:2541)
    at org.eclipse.swt.widgets.Scrollable.callWindowProc(Scrollable.java:80)
    at org.eclipse.swt.widgets.Control.windowProc(Control.java:4623)
    at org.eclipse.swt.widgets.Display.windowProc(Display.java:4989)
    at org.eclipse.swt.internal.win32.OS.DefWindowProcW(Native Method)
    at org.eclipse.swt.internal.win32.OS.DefWindowProc(OS.java:2541)
    at org.eclipse.swt.widgets.Tree.callWindowProc(Tree.java:1442)
    at org.eclipse.swt.widgets.Tree.windowProc(Tree.java:5878)
    at org.eclipse.swt.widgets.Display.windowProc(Display.java:4989)
    at org.eclipse.swt.internal.win32.OS.CallWindowProcW(Native Method)
    at org.eclipse.swt.internal.win32.OS.CallWindowProc(OS.java:2440)
    at org.eclipse.swt.widgets.Tree.callWindowProc(Tree.java:1534)
    at org.eclipse.swt.widgets.Control.windowProc(Control.java:4623)
    at org.eclipse.swt.widgets.Tree.windowProc(Tree.java:5977)
    at org.eclipse.swt.widgets.Display.windowProc(Display.java:4989)
    at org.eclipse.swt.internal.win32.OS.PeekMessageW(Native Method)
    at org.eclipse.swt.internal.win32.OS.PeekMessage(OS.java:3129)
    at org.eclipse.swt.widgets.Display.readAndDispatch(Display.java:3753)
    at org.eclipse.e4.ui.internal.workbench.swt.PartRenderingEngine$9.run(PartRenderingEngine.java:1053)
    at org.eclipse.core.databinding.observable.Realm.runWithDefault(Realm.java:332)
    at org.eclipse.e4.ui.internal.workbench.swt.PartRenderingEngine.run(PartRenderingEngine.java:942)
    at org.eclipse.e4.ui.internal.workbench.E4Workbench.createAndRunUI(E4Workbench.java:86)
    at org.eclipse.ui.internal.Workbench$5.run(Workbench.java:588)
    at org.eclipse.core.databinding.observable.Realm.runWithDefault(Realm.java:332)
    at org.eclipse.ui.internal.Workbench.createAndRunWorkbench(Workbench.java:543)
    at org.eclipse.ui.PlatformUI.createAndRunWorkbench(PlatformUI.java:149)
    at org.eclipse.ui.internal.ide.application.IDEApplication.start(IDEApplication.java:124)
    at org.eclipse.equinox.internal.app.EclipseAppHandle.run(EclipseAppHandle.java:196)
    at org.eclipse.core.runtime.internal.adaptor.EclipseAppLauncher.runApplication(EclipseAppLauncher.java:110)
    at org.eclipse.core.runtime.internal.adaptor.EclipseAppLauncher.start(EclipseAppLauncher.java:79)
    at org.eclipse.core.runtime.adaptor.EclipseStarter.run(EclipseStarter.java:353)
    at org.eclipse.core.runtime.adaptor.EclipseStarter.run(EclipseStarter.java:180)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
    at java.lang.reflect.Method.invoke(Unknown Source)
    at org.eclipse.equinox.launcher.Main.invokeFramework(Main.java:629)
    at org.eclipse.equinox.launcher.Main.basicRun(Main.java:584)
    at org.eclipse.equinox.launcher.Main.run(Main.java:1438)
    at org.eclipse.equinox.launcher.Main.main(Main.java:1414)

这是我的布局xml。

 <LinearLayout
    android:layout_width="fill_parent"
    android:layout_height="match_parent"
    android:layout_below="@id/linearLayout1"
    android:orientation="vertical" >

    <android.support.v4.view.ViewPager
      android:id="@+id/view_pager"
      android:layout_width="match_parent"
      android:layout_height="match_parent" />

    <com.viewpagerindicator.CirclePageIndicator
        android:id="@+id/indicator"
        android:padding="10dip"
        android:layout_height="wrap_content"
        android:layout_width="fill_parent"
        />

</LinearLayout>

在代码端（onCreate方法）之后，我添加了代码。

    CirclePageIndicator titleIndicator = (CirclePageIndicator)findViewById(R.id.indicator);
    titleIndicator.setViewPager(viewPager);

当我启动应用程序时，指示器未显示。可能是什么问题？

Answer 1

因为您设置了ViewPager以占据整个屏幕。你应该像下面那样制作你的xml。

<LinearLayout
android:layout_width="fill_parent"
android:layout_height="match_parent"
android:layout_below="@id/linearLayout1"
android:orientation="vertical" >

<android.support.v4.view.ViewPager
  android:id="@+id/view_pager"
  android:layout_width="match_parent"
  android:layout_height="0dp"
  android:layout_weight="1" />

<com.viewpagerindicator.CirclePageIndicator
    android:id="@+id/indicator"
    android:padding="10dip"
    android:layout_height="wrap_content"
    android:layout_width="fill_parent"
    />

</LinearLayout>