运行代码时出现堆栈跟踪错误。
MainActivity.java：
package com.example.android.effectivenavigation;
import android.app.ActionBar;
import android.app.FragmentTransaction;
import android.content.Intent;
import android.os.Bundle;
import android.support.v4.app.Fragment;
import android.support.v4.app.FragmentActivity;
import android.support.v4.app.FragmentManager;
import android.support.v4.app.FragmentPagerAdapter;
import android.support.v4.view.ViewPager;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.TextView;
public class MainActivity extends FragmentActivity implements ActionBar.TabListener {
/**
* The {@link android.support.v4.view.PagerAdapter} that will provide fragments for each of the
* three primary sections of the app. We use a {@link android.support.v4.app.FragmentPagerAdapter}
* derivative, which will keep every loaded fragment in memory. If this becomes too memory
* intensive, it may be best to switch to a {@link android.support.v4.app.FragmentStatePagerAdapter}.
*/
AppSectionsPagerAdapter mAppSectionsPagerAdapter;
/**
* The {@link ViewPager} that will display the three primary sections of the app, one at a
* time.
*/
ViewPager mViewPager;
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
// Create the adapter that will return a fragment for each of the three primary sections
// of the app.
mAppSectionsPagerAdapter = new AppSectionsPagerAdapter(getSupportFragmentManager());
// Set up the action bar.
final ActionBar actionBar = getActionBar();
// Specify that the Home/Up button should not be enabled, since there is no hierarchical
// parent.
actionBar.setHomeButtonEnabled(false);
// Specify that we will be displaying tabs in the action bar.
actionBar.setNavigationMode(ActionBar.NAVIGATION_MODE_TABS);
// Set up the ViewPager, attaching the adapter and setting up a listener for when the
// user swipes between sections.
mViewPager = (ViewPager) findViewById(R.id.pager);
mViewPager.setAdapter(mAppSectionsPagerAdapter);
mViewPager.setOnPageChangeListener(new ViewPager.SimpleOnPageChangeListener() {
@Override
public void onPageSelected(int position) {
// When swiping between different app sections, select the corresponding tab.
// We can also use ActionBar.Tab#select() to do this if we have a reference to the
// Tab.
actionBar.setSelectedNavigationItem(position);
}
});
// For each of the sections in the app, add a tab to the action bar.
for (int i = 0; i < mAppSectionsPagerAdapter.getCount(); i++) {
// Create a tab with text corresponding to the page title defined by the adapter.
// Also specify this Activity object, which implements the TabListener interface, as the
// listener for when this tab is selected.
actionBar.addTab(
actionBar.newTab()
.setText(mAppSectionsPagerAdapter.getPageTitle(i))
.setTabListener(this));
}
}
@Override
public void onTabUnselected(ActionBar.Tab tab, FragmentTransaction fragmentTransaction) {
}
@Override
public void onTabSelected(ActionBar.Tab tab, FragmentTransaction fragmentTransaction) {
// When the given tab is selected, switch to the corresponding page in the ViewPager.
mViewPager.setCurrentItem(tab.getPosition());
}
@Override
public void onTabReselected(ActionBar.Tab tab, FragmentTransaction fragmentTransaction) {
}
/**
* A {@link FragmentPagerAdapter} that returns a fragment corresponding to one of the primary
* sections of the app.
*/
public static class AppSectionsPagerAdapter extends FragmentPagerAdapter {
public AppSectionsPagerAdapter(FragmentManager fm) {
super(fm);
}
@Override
public Fragment getItem(int i) {
switch (i) {
case 0:
// The first section of the app is the most interesting -- it offers
// a launchpad into the other demonstrations in this example application.
return new LaunchpadSectionFragment();
default:
// The other sections of the app are dummy placeholders.
Fragment fragment = new DummySectionFragment();
Bundle args = new Bundle();
args.putInt(DummySectionFragment.ARG_SECTION_NUMBER, i + 1);
fragment.setArguments(args);
return fragment;
}
}
@Override
public int getCount() {
return 3;
}
@Override
public CharSequence getPageTitle(int position) {
return "Section " + (position + 1);
}
}
/**
* A fragment that launches other parts of the demo application.
*/
public static class LaunchpadSectionFragment extends Fragment {
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
View rootView = inflater.inflate(R.layout.fragment_section_launchpad, container, false);
// Demonstration of a collection-browsing activity.
rootView.findViewById(R.id.demo_collection_button)
.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View view) {
Intent intent = new Intent(getActivity(), CollectionDemoActivity.class);
startActivity(intent);
}
});
// Demonstration of navigating to external activities.
rootView.findViewById(R.id.demo_external_activity)
.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View view) {
// Create an intent that asks the user to pick a photo, but using
// FLAG_ACTIVITY_CLEAR_WHEN_TASK_RESET, ensures that relaunching
// the application from the device home screen does not return
// to the external activity.
Intent externalActivityIntent = new Intent(Intent.ACTION_PICK);
externalActivityIntent.setType("image/*");
externalActivityIntent.addFlags(
Intent.FLAG_ACTIVITY_CLEAR_WHEN_TASK_RESET);
startActivity(externalActivityIntent);
}
});
return rootView;
}
}
/**
* A dummy fragment representing a section of the app, but that simply displays dummy text.
*/
public static class DummySectionFragment extends Fragment {
public static final String ARG_SECTION_NUMBER = "section_number";
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
View rootView = inflater.inflate(R.layout.fragment_section_dummy, container, false);
Bundle args = getArguments();
((TextView) rootView.findViewById(android.R.id.text1)).setText(
getString(R.string.dummy_section_text, args.getInt(ARG_SECTION_NUMBER)));
return rootView;
}
}
}
CollectionDemoActivity.java：
package com.example.android.effectivenavigation;
import android.app.ActionBar;
import android.content.Intent;
import android.os.Bundle;
import android.support.v4.app.Fragment;
import android.support.v4.app.FragmentActivity;
import android.support.v4.app.FragmentManager;
import android.support.v4.app.FragmentStatePagerAdapter;
import android.support.v4.app.NavUtils;
import android.support.v4.app.TaskStackBuilder;
import android.support.v4.view.ViewPager;
import android.view.LayoutInflater;
import android.view.MenuItem;
import android.view.View;
import android.view.ViewGroup;
import android.widget.TextView;
public class CollectionDemoActivity extends FragmentActivity {
/**
* The {@link android.support.v4.view.PagerAdapter} that will provide fragments representing
* each object in a collection. We use a {@link android.support.v4.app.FragmentStatePagerAdapter}
* derivative, which will destroy and re-create fragments as needed, saving and restoring their
* state in the process. This is important to conserve memory and is a best practice when
* allowing navigation between objects in a potentially large collection.
*/
DemoCollectionPagerAdapter mDemoCollectionPagerAdapter;
/**
* The {@link android.support.v4.view.ViewPager} that will display the object collection.
*/
ViewPager mViewPager;
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_collection_demo);
// Create an adapter that when requested, will return a fragment representing an object in
// the collection.
//
// ViewPager and its adapters use support library fragments, so we must use
// getSupportFragmentManager.
mDemoCollectionPagerAdapter = new DemoCollectionPagerAdapter(getSupportFragmentManager());
// Set up action bar.
final ActionBar actionBar = getActionBar();
// Specify that the Home button should show an "Up" caret, indicating that touching the
// button will take the user one step up in the application's hierarchy.
actionBar.setDisplayHomeAsUpEnabled(true);
// Set up the ViewPager, attaching the adapter.
mViewPager = (ViewPager) findViewById(R.id.pager);
mViewPager.setAdapter(mDemoCollectionPagerAdapter);
}
@Override
public boolean onOptionsItemSelected(MenuItem item) {
switch (item.getItemId()) {
case android.R.id.home:
// This is called when the Home (Up) button is pressed in the action bar.
// Create a simple intent that starts the hierarchical parent activity and
// use NavUtils in the Support Package to ensure proper handling of Up.
Intent upIntent = new Intent(this, MainActivity.class);
if (NavUtils.shouldUpRecreateTask(this, upIntent)) {
// This activity is not part of the application's task, so create a new task
// with a synthesized back stack.
TaskStackBuilder.from(this)
// If there are ancestor activities, they should be added here.
.addNextIntent(upIntent)
.startActivities();
finish();
} else {
// This activity is part of the application's task, so simply
// navigate up to the hierarchical parent activity.
NavUtils.navigateUpTo(this, upIntent);
}
return true;
}
return super.onOptionsItemSelected(item);
}
/**
* A {@link android.support.v4.app.FragmentStatePagerAdapter} that returns a fragment
* representing an object in the collection.
*/
public static class DemoCollectionPagerAdapter extends FragmentStatePagerAdapter {
public DemoCollectionPagerAdapter(FragmentManager fm) {
super(fm);
}
@Override
public Fragment getItem(int i) {
Fragment fragment = new DemoObjectFragment();
Bundle args = new Bundle();
args.putInt(DemoObjectFragment.ARG_OBJECT, i + 1); // Our object is just an integer :-P
fragment.setArguments(args);
return fragment;
}
@Override
public int getCount() {
// For this contrived example, we have a 100-object collection.
return 100;
}
@Override
public CharSequence getPageTitle(int position) {
return "OBJECT " + (position + 1);
}
}
/**
* A dummy fragment representing a section of the app, but that simply displays dummy text.
*/
public static class DemoObjectFragment extends Fragment {
public static final String ARG_OBJECT = "object";
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
View rootView = inflater.inflate(R.layout.fragment_collection_object, container, false);
Bundle args = getArguments();
((TextView) rootView.findViewById(android.R.id.text1)).setText(
Integer.toString(args.getInt(ARG_OBJECT)));
return rootView;
}
}
}
Stacktrace错误：
E/AndroidRuntime(1365): Process: com.example.android.effectivenavigation, PID: 1365
E/AndroidRuntime(1365): java.lang.RuntimeException: Unable to instantiate activity ComponentInfo{com.example.android.effectivenavigation/com.example.android.effectivenavigation.MainActivity}: java.lang.ClassNotFoundException: Didn't find class "com.example.android.effectivenavigation.MainActivity" on path: DexPathList[[zip file "/data/app/com.example.android.effectivenavigation-2.apk"],nativeLibraryDirectories=[/data/app-lib/com.example.android.effectivenavigation-2, /system/lib]]
E/AndroidRuntime(1365): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2121)
E/AndroidRuntime(1365): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2245)
E/AndroidRuntime(1365): at android.app.ActivityThread.access$800(ActivityThread.java:135)
E/AndroidRuntime(1365): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1196)
E/AndroidRuntime(1365): at android.os.Handler.dispatchMessage(Handler.java:102)
E/AndroidRuntime(1365): at android.os.Looper.loop(Looper.java:136)
E/AndroidRuntime(1365): at android.app.ActivityThread.main(ActivityThread.java:5017)
E/AndroidRuntime(1365): at java.lang.reflect.Method.invokeNative(Native Method)
E/AndroidRuntime(1365): at java.lang.reflect.Method.invoke(Method.java:515)
E/AndroidRuntime(1365): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:779)
E/AndroidRuntime(1365): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:595)
E/AndroidRuntime(1365): at dalvik.system.NativeStart.main(Native Method)
E/AndroidRuntime(1365): Caused by: java.lang.ClassNotFoundException: Didn't find class "com.example.android.effectivenavigation.MainActivity" on path: DexPathList[[zip file "/data/app/com.example.android.effectivenavigation-2.apk"],nativeLibraryDirectories=[/data/app-lib/com.example.android.effectivenavigation-2, /system/lib]]
E/AndroidRuntime(1365): at dalvik.system.BaseDexClassLoader.findClass(BaseDexClassLoader.java:56)
E/AndroidRuntime(1365): at java.lang.ClassLoader.loadClass(ClassLoader.java:497)
E/AndroidRuntime(1365): at java.lang.ClassLoader.loadClass(ClassLoader.java:457)
E/AndroidRuntime(1365): at android.app.Instrumentation.newActivity(Instrumentation.java:1061)
E/AndroidRuntime(1365): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2112)
E/AndroidRuntime(1365): ... 11 more
答案 0 :(得分：2)
我遇到了这个问题并浪费了大量时间尝试手动添加支持库到java构建路径。但是，对我来说真正有用的是使用android工具选项添加支持库。我是这样做的：
右键单击Eclipse中的项目文件夹＆gt; Android工具＆gt;支持库
看起来，Eclipse为我找到了正确的库并将其添加到构建路径中。
答案 1 :(得分：1)
我遇到了同样的问题。 我使用了这个解决方案（谢谢你＆＃39; swap_1712＆＃39;）：
Project Folder -> Android Tools -> Add Support Library...
答案 2 :(得分：0)
在Eclipse菜单中：
项目 - ＆gt;清理以重建de app