当使用另一个android项目作为库时，为什么不获取NoSuchFiledException？

我有一个可以自己运行的android项目。我想创建另一个android项目，扩展前一个项目。但是当库项目试图创建使用findViewById（R.id.something）的组件时，它抛出NoSuchFieldException

以下是库项目的代码：

/*
 * Copyright 2012 The Android Open Source Project
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

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.Menu;
import android.view.View;
import android.view.ViewGroup;
import android.view.Window;
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}.
     */
    protected AppSectionsPagerAdapter mAppSectionsPagerAdapter;

    /**
     * The {@link ViewPager} that will display the three primary sections of the app, one at a
     * time.
     */
    protected ViewPager mViewPager;

    public void onCreate(Bundle savedInstanceState) {
//      this.requestWindowFeature(Window.FEATURE_NO_TITLE);
        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);
        actionBar.setDisplayShowHomeEnabled(false);
        actionBar.setDisplayUseLogoEnabled(false);
        actionBar.setDisplayShowTitleEnabled(false);

        closeOptionsMenu();

        // 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) {
    }

    @Override
    public boolean onCreateOptionsMenu(Menu menu) { //this method is used for adding menu items to the Activity
        // Inflate the menu; this adds items to the action bar if it is present.
        getMenuInflater().inflate(R.menu.main, menu);
        return true;
    }

    protected void setViewPager(ViewPager viewPager) {
        this.mViewPager = viewPager;
    }

    /**
     * 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;
        }
    }
}

此时会出现NoSuchFieldException：

mViewPager = (ViewPager) findViewById(R.id.pager);


java.lang.NoSuchFieldError: com.example.android.effectivenavigation.R$id.pager

我相信在库项目中使用findviewbyd（）创建组件时也会发生同样的情况。 有解决办法吗？我希望通过将所有的建设工作委托给图书馆项目，使子项目尽可能轻

以下是库项目声明ViewPager的方式：

<android.support.v4.view.ViewPager xmlns:android="http://schemas.android.com/apk/res/android"
    android:id="@+id/pager"
    android:layout_width="match_parent"
    android:layout_height="match_parent" />

但是ViewPager是声明的，并且它本身工作得很好，而不是作为库项目。
请确保您创建了id为“pager”的小部件，并且确保mViewPager没有指向null。
库和子项目具有相同的布局名称：activity\u main。
重命名其中一个可以解决问题

增加了这个问题。另外，库项目本身工作正常。我也有同样的问题…我想补充一点，重命名名称时要小心，因为它会重构所有项目，甚至是主活动的布局名称。
<android.support.v4.view.ViewPager xmlns:android="http://schemas.android.com/apk/res/android"
    android:id="@+id/pager"
    android:layout_width="match_parent"
    android:layout_height="match_parent" />