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Why getting a NoSuchFiledException when using another Android project as a library?

I have an Android project that can work on its own. I want to create another Android project that extends the previous project. But it throws a NoSuchFieldException when the library project tries to create some kind of component that uses findViewById (R.id.something).

Here is the code for the library project:

/* * 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; } } }

And a project expanding it:

 import com.example.android.effectivenavigation.MainActivity; import com.example.android.effectivenavigation.R; import android.os.Bundle; import android.app.ActionBar; import android.app.Activity; import android.app.FragmentTransaction; import android.support.v4.view.ViewPager; import android.view.Menu; public class MainActivity2 extends MainActivity { @Override public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); // setContentView(R.layout.activity_main); } }

and here comes NoSuchFieldException:

 mViewPager = (ViewPager) findViewById(R.id.pager); java.lang.NoSuchFieldError: com.example.android.effectivenavigation.R$id.pager

I believe the same thing happens when creating components using findViewById () in the library project. Any solution? I want the child’s project to be as easy as possible by delegating all projects to the library project.

So the library project announces the ViewPager:

 <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" />

Quote from developer.android.com: Thrown when VM notices that a program is trying to reference a class or object, a field that does not exist . But ViewPager is declared and works fine on its own, not as a library project.

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2 answers

The library and child project have the same layout name: activity_main. Renaming any of them solves the problem.

Android, NoSuchFieldError when starting the second action

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Please make sure that you create a widget with the identifier "pager", and also make sure that mViewPager does not point to zero.

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Source: https://habr.com/ru/post/1498102/

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