onTouchListener 上的 Java NullPointerException

Question

我在 Android 上构建第一个应用程序时遇到了一些困难。我已经按照 Google 的教程制作了一个带有抽屉的应用程序，它可以工作，但是当我想放置图片以外的其他内容时，它会使我的应用程序崩溃。

我的布局在我的 AVD 设备上正确显示，但是当我放置 onTouchListener 时，我得到一个 Java NullPointerException。我怀疑这是因为我没有使用好的布局，但我不明白为什么。有什么想法吗？
多谢 !

它在“b1.setOnTouchListener(touchListenerBouton);”上崩溃

public class MainActivity extends Activity implements View.OnTouchListener{
private DrawerLayout mDrawerLayout;
private ListView mDrawerList;
private ActionBarDrawerToggle mDrawerToggle;

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

Button b1 = null;
TextView Text = null;
EditText PhraseUser = null;
TextView TxtResultat = null;

private OnTouchListener touchListenerBouton = new View.OnTouchListener() 
    {
    @Override
    public boolean onTouch(View v, MotionEvent event) 
    {
        TxtResultat.setText("TEST")
        return true;
    }
    };

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

    mTitle = mDrawerTitle = getTitle();
    mPlanetTitles = getResources().getStringArray(R.array.planets_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, mPlanetTitles));
    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);
    }
    b1 = (Button) findViewById(R.id.button1);
    b1.setOnTouchListener(touchListenerBouton);
}

@Override
public boolean onTouch(View v, MotionEvent event) {
  /* Réagir au toucher */
  return true;
}

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

/* Called whenever we call invalidateOptionsMenu() */
@Override
public boolean onPrepareOptionsMenu(Menu menu) {
    // If the nav drawer is open, hide action items related to the content view
    boolean drawerOpen = mDrawerLayout.isDrawerOpen(mDrawerList);
    menu.findItem(R.id.action_websearch).setVisible(!drawerOpen);
    return super.onPrepareOptionsMenu(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()) {
    case R.id.action_websearch:
        // create intent to perform web search for this planet
        Intent intent = new Intent(Intent.ACTION_WEB_SEARCH);
        intent.putExtra(SearchManager.QUERY, getActionBar().getTitle());
        // catch event that there's no activity to handle intent
        if (intent.resolveActivity(getPackageManager()) != null) {
            startActivity(intent);
        } else {
            Toast.makeText(this, R.string.app_not_available, Toast.LENGTH_LONG).show();
        }
        return true;
    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
    System.out.println(position);
    Fragment fragment = new PlanetFragment();
    Bundle args = new Bundle();
    args.putInt(PlanetFragment.ARG_PLANET_NUMBER, 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(mPlanetTitles[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 PlanetFragment extends Fragment {
    public static final String ARG_PLANET_NUMBER = "planet_number";

    public PlanetFragment() {
        // Empty constructor required for fragment subclasses
    }



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

        int imageId = getResources().getIdentifier(planet.toLowerCase(Locale.getDefault()),
                        "drawable", getActivity().getPackageName());
     //   ((ImageView) rootView.findViewById(R.id.image)).setImageResource(imageId);
        getActivity().setTitle(planet);

        return rootView;
    }
}
}

Answer 1

在onCreate()中添加此行:

TxtResultat = (textView) findViewById(R.id.**your textview's id**);

您刚刚创建了类 TextView 的引用，但没有为其分配内存，这就是您收到 NullPointerException 错误的原因