错误：java.lang.NoClassDefFoundError

Question

抱歉，这是一个重复性的问题，但是我还没有找到答案。 为了在我的Android应用程序中创建FileChooser，我使用了this 。 所以我在Properties-> Java Build路径中添加了2个jar文件（其中一个是android-support-v4.jar ，另一个是手工库（ afilechooser ）），但是当运行时，我遇到这些错误onResume()方法。

1-libs是否有问题？

2-您的解决方案是什么？

3- FileChooserActivity是否有问题？

该类是：

public class FileChooserActivity extends FragmentActivity implements
        OnBackStackChangedListener {

    public static final String PATH = "path";
    public static final String EXTERNAL_BASE_PATH = Environment.getExternalStorageDirectory().getAbsolutePath();

    private FragmentManager mFragmentManager;
    private BroadcastReceiver mStorageListener = new BroadcastReceiver() {
        @Override
        public void onReceive(Context context, Intent intent) {
            Toast.makeText(context, R.string.storage_removed, Toast.LENGTH_LONG).show();
            finishWithResult(null);
        }
    };

    private String mPath;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);

        setContentView(R.layout.chooser);

        mFragmentManager = getSupportFragmentManager();
        mFragmentManager.addOnBackStackChangedListener(this);

        if (savedInstanceState == null) {
            mPath = EXTERNAL_BASE_PATH;
            addFragment(mPath);
        } else {
            mPath = savedInstanceState.getString(PATH);
        }

        setTitle(mPath);
    }

    @Override
    protected void onPause() {
        super.onPause();
        unregisterStorageListener();
    }

    @Override
    protected void onResume() {
        super.onResume();
        registerStorageListener();
    }

    @Override
    protected void onSaveInstanceState(Bundle outState) {
        super.onSaveInstanceState(outState);

        outState.putString(PATH, mPath);
    }

    @Override
    public void onBackStackChanged() {
        mPath = EXTERNAL_BASE_PATH;

        int count = mFragmentManager.getBackStackEntryCount();
        if (count > 0) {
            BackStackEntry fragment = mFragmentManager
                    .getBackStackEntryAt(count - 1);
            mPath = fragment.getName();
        }

        setTitle(mPath);
    }

    /**
     * Add the initial Fragment with given path.
     * 
     * @param path The absolute path of the file (directory) to display.
     */
    private void addFragment(String path) {
        FileListFragment explorerFragment = FileListFragment.newInstance(mPath);
        mFragmentManager.beginTransaction()
                .add(R.id.explorer_fragment, explorerFragment).commit();
    }

    /**
     * "Replace" the existing Fragment with a new one using given path.
     * We're really adding a Fragment to the back stack.
     * 
     * @param path The absolute path of the file (directory) to display.
     */
    private void replaceFragment(String path) {
        FileListFragment explorerFragment = FileListFragment.newInstance(path);
        mFragmentManager.beginTransaction()
                .replace(R.id.explorer_fragment, explorerFragment)
                .setTransition(FragmentTransaction.TRANSIT_FRAGMENT_OPEN)
                .addToBackStack(path).commit();
    }

    /**
     * Finish this Activity with a result code and URI of the selected file.
     * 
     * @param file The file selected.
     */
    private void finishWithResult(File file) {
        if (file != null) {
            Uri uri = Uri.fromFile(file);
            setResult(RESULT_OK, new Intent().setData(uri));
            finish();
        } else {
            setResult(RESULT_CANCELED); 
            finish();
        }
    }

    /**
     * Called when the user selects a File
     * 
     * @param file The file that was selected
     */
    protected void onFileSelected(File file) {
        if (file != null) {
            mPath = file.getAbsolutePath();

            if (file.isDirectory()) {
                replaceFragment(mPath);
            } else {
                finishWithResult(file); 
            }
        } else {
            Toast.makeText(FileChooserActivity.this, R.string.error_selecting_file, Toast.LENGTH_SHORT).show();
        }
    }

    /**
     * Register the external storage BroadcastReceiver.
     */
    private void registerStorageListener() {
        IntentFilter filter = new IntentFilter();
        filter.addAction(Intent.ACTION_MEDIA_REMOVED);
        registerReceiver(mStorageListener, filter);
    }

    /**
     * Unregister the external storage BroadcastReceiver.
     */
    private void unregisterStorageListener() {
        unregisterReceiver(mStorageListener);
    }
}

错误是：

06-04 04:30:57.547: E/AndroidRuntime(605): FATAL EXCEPTION: main
06-04 04:30:57.547: E/AndroidRuntime(605): java.lang.NoClassDefFoundError: com.ipaulpro.afilechooser.R$layout
06-04 04:30:57.547: E/AndroidRuntime(605):  at com.ipaulpro.afilechooser.FileChooserActivity.onCreate(FileChooserActivity.java:65)
06-04 04:30:57.547: E/AndroidRuntime(605):  at android.app.Activity.performCreate(Activity.java:5104)
06-04 04:30:57.547: E/AndroidRuntime(605):  at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1080)
06-04 04:30:57.547: E/AndroidRuntime(605):  at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2144)

。 。 。

Answer 1

在Eclipse中：

1. 右键点击您的项目
2. 选择属性-> Java构建路径->订单和导出
3. 检查Android私有库 ，然后单击确定按钮。

Answer 2

您应该将该库作为现有的Android项目导入到Eclipse工作区中。 签入定义为库的属性。

然后，您必须将其导入项目中。 这是在Properties => Android => Add（在库部分）中完成的。 选择库，然后它应该可以工作

Answer 3

请替换android-support-v4.jar文件。 并将ActivityNot Found异常。

    Intent target = FileUtils.createGetContentIntent();
    Intent intent = Intent.createChooser(
            target, getString(R.string.chooser_title));
    try {
        startActivityForResult(intent, REQUEST_CODE);
    } catch (ActivityNotFoundException e) {

    }