问题
I am new to java, eclipse, and android development, so I may be missing something simple although I have checked basic stuff like spelling several times.
Because there is no number picker control (such as that used in the date picker) in the public Android SDK, the conventional wisdom is to "clone and own" the control that exists in the Android source.
In an attempt to do that, I have copied the code for NumberPicker into my project and its dependency, NumberPickerButton. I have also copied the supporting resources.
The problem I am having is that when I try to include the NumberPicker in a layout, the rendered version of the layout within Eclipse does not work.
<com.spencerandbrown.PatientTracker1.NumberPicker
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:id="@+id/spanEnd2" />
Adding that tag causes the Layout view of the XML file to only show the following error.
ClassCastException: com.spencerandbrown.PatientTracker1.NumberPickerButton cannot be cast to com.spencerandbrown.PatientTracker1.NumberPickerButton
I have tried both the fully qualified name and the unqualified name and it makes no difference.
The strange thing is that the control works at run time, it just will not render in Eclipse.
Is there a solution for this issue? Am I just doing something wrong?
If necessary, I can include more code from my project to clarify.
If I reference the internal Android widget, it works fine in the Eclipse layout view, but it is clumsy to interact with that way and it might break in the future.
<com.android.internal.widget.NumberPicker
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:id="@+id/spanStart"/>
Here is the stack trace from Eclipse.
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)
回答1:
Workaround: I have found that if I catch and ignore the ClassCastException, and obviously then don't try to do anything with the View I was trying to find, there are no further problems and I can use the layout editor again: the editor will quite happily load, initialise and draw the problematic view, you just can't cast to its class.
try {
picker = (NumberPicker) findViewById(R.id.myPicker);
picker.blargh();
// everything else involving picker
} catch (ClassCastException issue6894) {} // ignore
回答2:
If this is similar to the bug at http://code.google.com/p/android/issues/detail?id=6894 (ie the custom view loads another custom view), then the problem is likely due to the custom class loader that loads the custom view classes.
you can use View.isInEditMode (only returns true when your code is running inside eclipse) if you want to properly differentiate between running inside Eclipse or inside Android.
来源：https://stackoverflow.com/questions/2078475/eclipse-classcastexception-when-trying-to-expand-xml-layout-for-android