滑动菜单Android不起作用

Question

我创建了添加了滑动菜单的项目。 我的代码未显示任何错误，但应用程序未在Android Studio中运行。 我无法解决问题，需要帮助来解决此问题。

MainActivity.java

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

// nav drawer title
private CharSequence mDrawerTitle;

// used to store app title
private CharSequence mTitle;

// slide menu items
private String[] navMenuTitles;
private TypedArray navMenuIcons;

private ArrayList<NavDrawerItem> navDrawerItems;
private NavDrawerListAdapter adapter;

@Override
protected void onCreate(Bundle savedInstanceState) {

    mDrawerList.setOnItemClickListener(new SlideMenuClickListener());
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);

    mTitle = mDrawerTitle = getTitle();

    // load slide menu items
    navMenuTitles = getResources().getStringArray(R.array.nav_drawer_items);

    // nav drawer icons from resources
    navMenuIcons = getResources()
            .obtainTypedArray(R.array.nav_drawer_icons);

    mDrawerLayout = (DrawerLayout) findViewById(R.id.drawer_layout);
    mDrawerList = (ListView) findViewById(R.id.list_slidermenu);

    navDrawerItems = new ArrayList<NavDrawerItem>();

    // adding nav drawer items to array
    // Home
    navDrawerItems.add(new NavDrawerItem(navMenuTitles[0], navMenuIcons.getResourceId(0, -1)));
    // Find People
    navDrawerItems.add(new NavDrawerItem(navMenuTitles[1], navMenuIcons.getResourceId(1, -1)));
    // Photos
    navDrawerItems.add(new NavDrawerItem(navMenuTitles[2], navMenuIcons.getResourceId(2, -1)));
    // Communities, Will add a counter here
    navDrawerItems.add(new NavDrawerItem(navMenuTitles[3], navMenuIcons.getResourceId(3, -1)));


    // Recycle the typed array
    navMenuIcons.recycle();

    // setting the nav drawer list adapter
    adapter = new NavDrawerListAdapter(getApplicationContext(),
            navDrawerItems);
    mDrawerList.setAdapter(adapter);

    // enabling action bar app icon and behaving it as toggle button
    getActionBar().setDisplayHomeAsUpEnabled(true);
    getActionBar().setHomeButtonEnabled(true);

    mDrawerToggle = new ActionBarDrawerToggle(this, mDrawerLayout,
            R.string.app_name, // nav drawer open - description for accessibility
            R.string.app_name // nav drawer close - description for accessibility
    ) {
        public void onDrawerClosed(View view) {
            getActionBar().setTitle(mTitle);
            // calling onPrepareOptionsMenu() to show action bar icons
            invalidateOptionsMenu();
        }

        public void onDrawerOpened(View drawerView) {
            getActionBar().setTitle(mDrawerTitle);
            // calling onPrepareOptionsMenu() to hide action bar icons
            invalidateOptionsMenu();
        }
    };
    mDrawerLayout.setDrawerListener(mDrawerToggle);

    if (savedInstanceState == null) {
        // on first time display view for first nav item
        displayView(0);
    }
}

private void displayView(int i) {
}

@Override
public boolean onCreateOptionsMenu(Menu menu) {
    getMenuInflater().inflate(R.menu.menu_main, menu);
    return true;
}

@Override
public boolean onOptionsItemSelected(MenuItem item) {
    // toggle nav drawer on selecting action bar app icon/title
    if (mDrawerToggle.onOptionsItemSelected(item)) {
        return true;
    }
    // Handle action bar actions click
    switch (item.getItemId()) {
        case R.id.action_settings:
            return true;
        default:
            return super.onOptionsItemSelected(item);
    }
}

/***
 * Called when invalidateOptionsMenu() is triggered
 */
@Override
public boolean onPrepareOptionsMenu(Menu menu) {
    // if nav drawer is opened, hide the action items
    boolean drawerOpen = mDrawerLayout.isDrawerOpen(mDrawerList);
    menu.findItem(R.id.action_settings).setVisible(!drawerOpen);
    return super.onPrepareOptionsMenu(menu);
}

@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);
}

private class SlideMenuClickListener implements android.widget.AdapterView.OnItemClickListener {
    @Override
    public void onItemClick(AdapterView<?> parent, View view, int position,
                            long id) {
        // display view for selected nav drawer item
        displayView(position);

    }
    private void displayView(int position) {
        // update the main content by replacing fragments
        Fragment fragment = null;
        switch (position) {
            case 0:
                fragment = new FragmentDoctor();
                break;
            case 1:
                fragment = new FragmentHospital();
                break;
            case 2:
                fragment = new FragmentPharmacy();
                break;
            case 3:
                fragment = new FragmentClinic();
                break;
            default:
                break;
        }

        if (fragment != null) {
            FragmentManager fragmentManager = getFragmentManager();
            fragmentManager.beginTransaction()
                    .replace(R.id.frame_container, fragment).commit();

            // update selected item and title, then close the drawer
            mDrawerList.setItemChecked(position, true);
            mDrawerList.setSelection(position);
            setTitle(navMenuTitles[position]);
            mDrawerLayout.closeDrawer(mDrawerList);
        } else {
            // error in creating fragment
            Log.e("MainActivity", "Error in creating fragment");
        }
    }
}
}

logcat的

E/AndroidRuntime﹕ FATAL EXCEPTION: main
Process: com.example.jathniel.menu, PID: 25237
java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.jathniel.menu/com.example.jathniel.menu.MainActivity}: java.lang.NullPointerException
        at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2195)
        at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2245)
        at android.app.ActivityThread.access$800(ActivityThread.java:135)
        at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1196)
        at android.os.Handler.dispatchMessage(Handler.java:102)
        at android.os.Looper.loop(Looper.java:136)
        at android.app.ActivityThread.main(ActivityThread.java:5021)
        at java.lang.reflect.Method.invokeNative(Native Method)
        at java.lang.reflect.Method.invoke(Method.java:515)
        at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:827)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:643)
        at dalvik.system.NativeStart.main(Native Method)
 Caused by: java.lang.NullPointerException
        at com.example.jathniel.menu.MainActivity.onCreate(MainActivity.java:82)
        at android.app.Activity.performCreate(Activity.java:5231)
        at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1090)
        at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2159)

Answer 1

请检查您的代码。 您试图在将listview初始化之前将侦听器置于listview

这是错误的：

@Override
protected void onCreate(Bundle savedInstanceState) {

    mDrawerList.setOnItemClickListener(new SlideMenuClickListener()); //very wrong
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);

您应该先初始化listview并像这样给oncliclistener

 mDrawerList = (ListView) findViewById(R.id.list_slidermenu);
 mDrawerList.setOnItemClickListener(new SlideMenuClickListener());