我是 java、eclipse 和 android 开发的新手，所以尽管我已经多次检查过拼写等基本内容，但我可能会遗漏一些简单的内容。
由于公共Android SDK中没有数字选择器控件（例如日期选择器中使用的控件），因此一般常识 http://groups.google.com/group/android-developers/browse_thread/thread/65da9820998fddc9就是“克隆并拥有”Android源代码中存在的控件。
为了尝试做到这一点，我已将 NumberPicker 的代码复制到我的项目及其依赖项 NumberPickerButton 中。我还复制了支持资源。
我遇到的问题是，当我尝试将 NumberPicker 包含在布局中时，Eclipse 中布局的渲染版本不起作用。
<com.spencerandbrown.PatientTracker1.NumberPicker
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:id="@+id/spanEnd2" />
添加该标记会导致 XML 文件的布局视图仅显示以下错误。
ClassCastException: com.spencerandbrown.PatientTracker1.NumberPickerButton cannot be cast to com.spencerandbrown.PatientTracker1.NumberPickerButton
我已经尝试过完全限定名称和非限定名称，但没有区别。
奇怪的是，该控件在运行时可以工作，只是不会在 Eclipse 中呈现。
这个问题有解决办法吗？我只是做错了什么吗？
如果有必要，我可以从我的项目中添加更多代码来澄清。
如果我引用内部 Android 小部件，它在 Eclipse 布局视图中工作正常，但以这种方式交互很笨拙，并且将来可能会崩溃。
<com.android.internal.widget.NumberPicker
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:id="@+id/spanStart"/>
这是 Eclipse 的堆栈跟踪。
java.lang.ClassCastException: com.spencerandbrown.PatientTracker1.NumberPickerButton cannot be cast to com.spencerandbrown.PatientTracker1.NumberPickerButton
at com.spencerandbrown.PatientTracker1.NumberPicker.<init>(NumberPicker.java:110)
at com.spencerandbrown.PatientTracker1.NumberPicker.<init>(NumberPicker.java:98)
at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
at sun.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:57)
at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:45)
at java.lang.reflect.Constructor.newInstance(Constructor.java:532)
at com.android.ide.eclipse.adt.internal.editors.layout.ProjectCallback.instantiateClass(Unknown Source)
at com.android.ide.eclipse.adt.internal.editors.layout.ProjectCallback.loadView(Unknown Source)
at android.view.BridgeInflater.loadCustomView(BridgeInflater.java:198)
at android.view.BridgeInflater.createViewFromTag(BridgeInflater.java:126)
at android.view.LayoutInflater.rInflate(LayoutInflater.java:617)
at android.view.LayoutInflater.rInflate(LayoutInflater.java:620)
at android.view.LayoutInflater.rInflate(LayoutInflater.java:620)
at android.view.LayoutInflater.inflate(LayoutInflater.java:407)
at android.view.LayoutInflater.inflate(LayoutInflater.java:296)
at com.android.layoutlib.bridge.Bridge.computeLayout(Bridge.java:377)
at com.android.ide.eclipse.adt.internal.editors.layout.GraphicalLayoutEditor.computeLayout(Unknown Source)
at com.android.ide.eclipse.adt.internal.editors.layout.GraphicalLayoutEditor.recomputeLayout(Unknown Source)
at com.android.ide.eclipse.adt.internal.editors.layout.GraphicalLayoutEditor.activated(Unknown Source)
at com.android.ide.eclipse.adt.internal.editors.layout.LayoutEditor.pageChange(Unknown Source)
at org.eclipse.ui.part.MultiPageEditorPart$2.widgetSelected(MultiPageEditorPart.java:291)
at org.eclipse.swt.widgets.TypedListener.handleEvent(TypedListener.java:228)
at org.eclipse.swt.widgets.EventTable.sendEvent(EventTable.java:84)
at org.eclipse.swt.widgets.Widget.sendEvent(Widget.java:1176)
at org.eclipse.swt.widgets.Widget.sendEvent(Widget.java:1200)
at org.eclipse.swt.widgets.Widget.sendEvent(Widget.java:1185)
at org.eclipse.swt.widgets.Widget.notifyListeners(Widget.java:1025)
at org.eclipse.swt.custom.CTabFolder.setSelection(CTabFolder.java:3256)
at org.eclipse.swt.custom.CTabFolder.onMouse(CTabFolder.java:2045)
at org.eclipse.swt.custom.CTabFolder$1.handleEvent(CTabFolder.java:323)
at org.eclipse.swt.widgets.EventTable.sendEvent(EventTable.java:84)
at org.eclipse.swt.widgets.Widget.sendEvent(Widget.java:1176)
at org.eclipse.swt.widgets.Display.runDeferredEvents(Display.java:3493)
at org.eclipse.swt.widgets.Display.readAndDispatch(Display.java:3112)
at org.eclipse.ui.internal.Workbench.runEventLoop(Workbench.java:2405)
at org.eclipse.ui.internal.Workbench.runUI(Workbench.java:2369)
at org.eclipse.ui.internal.Workbench.access$4(Workbench.java:2221)
at org.eclipse.ui.internal.Workbench$5.run(Workbench.java:500)
at org.eclipse.core.databinding.observable.Realm.runWithDefault(Realm.java:332)
at org.eclipse.ui.internal.Workbench.createAndRunWorkbench(Workbench.java:493)
at org.eclipse.ui.PlatformUI.createAndRunWorkbench(PlatformUI.java:149)
at org.eclipse.ui.internal.ide.application.IDEApplication.start(IDEApplication.java:113)
at org.eclipse.equinox.internal.app.EclipseAppHandle.run(EclipseAppHandle.java:194)
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:368)
at org.eclipse.core.runtime.adaptor.EclipseStarter.run(EclipseStarter.java:179)
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:616)
at org.eclipse.equinox.launcher.Main.invokeFramework(Main.java:559)
at org.eclipse.equinox.launcher.Main.basicRun(Main.java:514)
at org.eclipse.equinox.launcher.Main.run(Main.java:1311)
