我正在尝试将搜索图标添加到工具栏，按下该图标将打开搜索栏。

但是我试过的各种方法都不行，没有图标出现。 现在我收到此错误，但找不到解决方案:

java.lang.NullPointerException: Attempt to invoke virtual method 'void android.support.v7.widget.SearchView.setOnQueryTextListener(android.support.v7.widget.SearchView$OnQueryTextListener)' on a null object reference
    at pl.michalz.hideonscrollexample.activity.partthree.PartThreeActivity.onCreateOptionsMenu(PartThreeActivity.java:62)

这是我的主要 Activity :

public class PartThreeActivity extends AppCompatActivity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        setTheme(R.style.AppThemeBlue);
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_part_three);

        initToolbar();
        initViewPagerAndTabs();
    }

    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        // Inflate the menu; this adds items to the action bar if it is present.
        getMenuInflater().inflate(R.menu.menu_main, menu);

        MenuItem seachItem = menu.findItem(R.id.action_search);
        SearchView searchView = (SearchView)
                MenuItemCompat.getActionView(seachItem);

        searchView.setOnQueryTextListener(
            new SearchView.OnQueryTextListener(){

            @Override
            public boolean onQueryTextSubmit(String query) {
                Log.d("myApp", "onQueryTextSubmit ");
                return false;
            }

            @Override
            public boolean onQueryTextChange(String newText) {
                Log.d("myApp", "onQueryTextChange ");
                return false;
            }
        });

        return true;
    }

    private void initToolbar() {
        Toolbar mToolbar = (Toolbar) findViewById(R.id.toolbar);
        setSupportActionBar(mToolbar);
        setTitle(getString(R.string.app_name));
        mToolbar.setTitleTextColor(getResources().getColor(android.R.color.white));
    }

    private void initViewPagerAndTabs() {
        ViewPager viewPager = (ViewPager) findViewById(R.id.viewPager);
        PagerAdapter pagerAdapter = new PagerAdapter(getSupportFragmentManager());
        pagerAdapter.addFragment(PartThreeFragment.createInstance(), getString(R.string.tab_1));
        pagerAdapter.addFragment(BlankFragment.createInstance("F word"), getString(R.string.tab_2));
        viewPager.setAdapter(pagerAdapter);
        TabLayout tabLayout = (TabLayout) findViewById(R.id.tabLayout);
        tabLayout.setupWithViewPager(viewPager);
    }

    static class PagerAdapter extends FragmentPagerAdapter {

        private final List<Fragment> fragmentList = new ArrayList<>();
        private final List<String> fragmentTitleList = new ArrayList<>();

        public PagerAdapter(FragmentManager fragmentManager) {
            super(fragmentManager);
        }

        public void addFragment(Fragment fragment, String title) {
            fragmentList.add(fragment);
            fragmentTitleList.add(title);
        }

        @Override
        public Fragment getItem(int position) {
            return fragmentList.get(position);
        }

        @Override
        public int getCount() {
            return fragmentList.size();
        }
        @Override
        public CharSequence getPageTitle(int position) {
            return fragmentTitleList.get(position);
        }
    }


    //kai paskaudzia toolbaro iconas
    @Override
    public boolean onOptionsItemSelected(MenuItem item) {
        switch (item.getItemId()) {
            case R.id.action_settings:
                // User chose the "Settings" item, show the app settings UI...
                return true;

            case R.id.action_search:
                // User chose the "Favorite" action, mark the current item
                // as a favorite...
                return true;

            default:
                // If we got here, the user's action was not recognized.
                // Invoke the superclass to handle it.
                return super.onOptionsItemSelected(item);

        }
    }

}

主 Activity.xml

<android.support.design.widget.CoordinatorLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    android:id="@+id/coordinatorLayout"
    android:layout_width="match_parent"
    android:layout_height="match_parent">

    <android.support.design.widget.AppBarLayout
        android:id="@+id/appBarLayout"
        android:layout_width="match_parent"
        android:layout_height="wrap_content">

        <android.support.v7.widget.Toolbar
            android:id="@+id/toolbar"
            android:layout_width="match_parent"
            android:layout_height="?attr/actionBarSize"
            android:background="?attr/colorPrimary"
            app:layout_scrollFlags="scroll|enterAlways|snap" />

        <android.support.design.widget.TabLayout
            android:id="@+id/tabLayout"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            app:tabIndicatorColor="@android:color/white"
            app:tabIndicatorHeight="6dp"
            app:tabSelectedTextColor="@android:color/white"
            app:tabTextColor="@android:color/white" />
    </android.support.design.widget.AppBarLayout>

    <android.support.v4.view.ViewPager
        android:id="@+id/viewPager"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        app:layout_behavior="@string/appbar_scrolling_view_behavior" />


</android.support.design.widget.CoordinatorLayout>

还有searchable.xml

<searchable xmlns:android="http://schemas.android.com/apk/res/android"
    android:hint="@string/hint"
    android:label="@string/app_name" />

和res/menu/menu_main.xml，将ic_search自己添加到drawable

<menu xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/tools">

    <item
        android:id="@+id/action_search"
        android:icon="@drawable/ic_search"
        android:title="@string/action_search"
        app:actionViewClass="android.support.v7.widget.SearchView"
        app:showAsAction="ifRoom|collapseActionView" />


    <!-- Settings, should always be in the overflow -->
    <item
        android:id="@+id/action_settings"
        android:title="@string/action_settings"
        app:showAsAction="never" />

</menu>

有人可以帮忙吗？

最佳答案

我通过将 menu_main.xml 中的命名空间从 app 更改为我自己的 myapp 来修复错误，并通过按“Alt+Enter”自动修复".

res/menu/menu_main.xml

<menu xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/tools"
    //----------- it created automaticly --------------
    xmlns:myapp="http://schemas.android.com/apk/res-auto">

    <item
        android:id="@+id/action_search"
        android:icon="@drawable/ic_search"
        android:title="@string/action_search"
        //-------------- H E R E --------------------
        myapp:showAsAction="always|collapseActionView"
        myapp:actionViewClass="android.support.v7.widget.SearchView" />

    <!-- Settings, should always be in the overflow -->
    <item
        android:id="@+id/action_settings"
        android:title="@string/action_settings"
        app:showAsAction="never" />

</menu>

主要 Activity

@Override
public boolean onCreateOptionsMenu(Menu menu) {
    // Inflate the menu; this adds items to the action bar if it is present.
    getMenuInflater().inflate(R.menu.menu_main, menu);

    Log.w("myApp", "onCreateOptionsMenu -started- ");

    SearchManager searchManager = (SearchManager) getSystemService(Context.SEARCH_SERVICE);
    MenuItem menuItem = menu.findItem(R.id.action_search);
    SearchView searchView = (SearchView) MenuItemCompat.getActionView(menuItem);

    searchView.setSearchableInfo( searchManager.getSearchableInfo(getComponentName()));
    searchView.setQueryHint(getResources().getString(R.string.hint));

    searchView.setOnQueryTextListener(
        new SearchView.OnQueryTextListener(){
            @Override
            public boolean onQueryTextSubmit(String query) {
            Log.w("myApp", "onQueryTextSubmit ");
                return false;
            }

            @Override
            public boolean onQueryTextChange(String newText) {
                Log.w("myApp", "onQueryTextChange ");
                return false;
            }
    });

    return true;
}

关于android - 为什么 setOnQueryTextListener() 会出现 "on a null object reference"错误？，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/35664384/