java - setAdapter 导致应用程序崩溃

Question

当我在 fragment 类中的代码底部调用 setAdapter 方法时，它导致我的应用程序在启动前崩溃。但是，当我将其注释掉时，该应用程序运行良好(显然没有适配器)。

package com.example.android.navigationdrawerexample;

import android.app.Activity;
import android.app.Fragment;
import android.app.FragmentManager;
import android.content.res.Configuration;
import android.os.Bundle;
import android.support.v4.app.ActionBarDrawerToggle;
import android.support.v4.view.GravityCompat;
import android.support.v4.widget.DrawerLayout;
import android.view.LayoutInflater;
import android.view.Menu;
import android.view.MenuInflater;
import android.view.MenuItem;
import android.view.View;
import android.view.ViewGroup;
import android.widget.AdapterView;
import android.widget.ArrayAdapter;
import android.widget.AutoCompleteTextView;
import android.widget.ListView;

public class MainActivity extends Activity {
private DrawerLayout mDrawerLayout;
private ListView mDrawerList;
private ActionBarDrawerToggle mDrawerToggle;

private CharSequence mDrawerTitle;
private CharSequence mTitle;
private String[] mNavigationTitles;


@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);

    mTitle = mDrawerTitle = getTitle();
    mNavigationTitles = getResources().getStringArray(R.array.navigaton_array);
    mDrawerLayout = (DrawerLayout) findViewById(R.id.drawer_layout);
    mDrawerList = (ListView) findViewById(R.id.left_drawer);

    // set a custom shadow that overlays the main content when the drawer opens
    mDrawerLayout.setDrawerShadow(R.drawable.drawer_shadow, GravityCompat.START);
    // set up the drawer's list view with items and click listener
    mDrawerList.setAdapter(new ArrayAdapter<String>(this,
            R.layout.drawer_list_item, mNavigationTitles));
    mDrawerList.setOnItemClickListener(new DrawerItemClickListener());

    // enable ActionBar app icon to behave as action to toggle nav drawer
    getActionBar().setDisplayHomeAsUpEnabled(true);
    getActionBar().setHomeButtonEnabled(true);

    // ActionBarDrawerToggle ties together the the proper interactions
    // between the sliding drawer and the action bar app icon
    mDrawerToggle = new ActionBarDrawerToggle(
            this,                  /* host Activity */
            mDrawerLayout,         /* DrawerLayout object */
            R.drawable.ic_drawer,  /* nav drawer image to replace 'Up' caret */
            R.string.drawer_open,  /* "open drawer" description for accessibility */
            R.string.drawer_close  /* "close drawer" description for accessibility */
            ) {
        public void onDrawerClosed(View view) {
            getActionBar().setTitle(mTitle);
            invalidateOptionsMenu(); // creates call to onPrepareOptionsMenu()
        }

        public void onDrawerOpened(View drawerView) {
            getActionBar().setTitle(mDrawerTitle);
            invalidateOptionsMenu(); // creates call to onPrepareOptionsMenu()
        }
    };
    mDrawerLayout.setDrawerListener(mDrawerToggle);

    if (savedInstanceState == null) {
        selectItem(0);
    }
}

@Override
public boolean onCreateOptionsMenu(Menu menu) {
    MenuInflater inflater = getMenuInflater();
    inflater.inflate(R.menu.main, menu);
    return super.onCreateOptionsMenu(menu);
}

@Override
public boolean onOptionsItemSelected(MenuItem item) {
     // The action bar home/up action should open or close the drawer.
     // ActionBarDrawerToggle will take care of this.
    if (mDrawerToggle.onOptionsItemSelected(item)) {
        return true;
    }
    // Handle action buttons
    switch(item.getItemId()) {

    default:
        return super.onOptionsItemSelected(item);
    }
}

/* The click listner for ListView in the navigation drawer */
private class DrawerItemClickListener implements ListView.OnItemClickListener {
    @Override
    public void onItemClick(AdapterView<?> parent, View view, int position, long id) {
        selectItem(position);
    }
}

private void selectItem(int position) {
    // update the main content by replacing fragments
    Fragment fragment = new NavigationFragment();
    Bundle args = new Bundle();
    args.putInt(NavigationFragment.ARG_NAVIGATION_POSITION, position);
    fragment.setArguments(args);

    FragmentManager fragmentManager = getFragmentManager();
    fragmentManager.beginTransaction().replace(R.id.content_frame, fragment).commit();

    // update selected item and title, then close the drawer
    mDrawerList.setItemChecked(position, true);
    setTitle(mNavigationTitles[position]);
    mDrawerLayout.closeDrawer(mDrawerList);
}

@Override
public void setTitle(CharSequence title) {
    mTitle = title;
    getActionBar().setTitle(mTitle);
}
/**
 * When using the ActionBarDrawerToggle, you must call it during
 * onPostCreate() and onConfigurationChanged()...
 */

@Override
protected void onPostCreate(Bundle savedInstanceState) {
    super.onPostCreate(savedInstanceState);
    // Sync the toggle state after onRestoreInstanceState has occurred.
    mDrawerToggle.syncState();
}

@Override
public void onConfigurationChanged(Configuration newConfig) {
    super.onConfigurationChanged(newConfig);
    // Pass any configuration change to the drawer toggls
    mDrawerToggle.onConfigurationChanged(newConfig);
}
/**
 * Fragment that appears in the "content_frame", shows a planet
 */
public static class NavigationFragment extends Fragment {
    public static final String ARG_NAVIGATION_POSITION = "navgation_position";

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
            Bundle savedInstanceState) {
        View rootView = inflater.inflate(R.layout.fragment_navigation, container, false);
        int i = getArguments().getInt(ARG_NAVIGATION_POSITION);
        String navigation = getResources().getStringArray(R.array.navigaton_array)[i];

       AutoCompleteTextView countriesAutoComplete = (AutoCompleteTextView) getActivity().findViewById(R.id.countries_autoComplete);
       String[] countriesListFullName = getResources().getStringArray(R.array.countryNames);
       ArrayAdapter<String> adapter = new ArrayAdapter<String>(countriesAutoComplete.getContext(), android.R.layout.simple_dropdown_item_1line, countriesListFullName);
       countriesAutoComplete.setAdapter(adapter);
       countriesAutoComplete.setThreshold(1);
       //int imageId = getResources().getIdentifier()(navigation.toLowerCase(Locale.getDefault()),
       //                "drawable", getActivity().getPackageName());
       // ((ImageView) rootView.findViewById(R.id.image)).setImageResource(imageId);
        getActivity().setTitle(navigation);
        return rootView;
    }
}

Answer 1

改变

AutoCompleteTextView countriesAutoComplete = (AutoCompleteTextView) getActivity().findViewById(R.id.countries_autoComplete);

到

AutoCompleteTextView countriesAutoComplete = (AutoCompleteTextView) rootView.findViewById(R.id.countries_autoComplete); // use rootView.findViewById

findViewById 在当前展开的布局中查找 View 。所以你需要使用膨胀的 View 对象来初始化你的 AutoCompleteTextView