java - 哪里可以在 Fragment 中创建 Android Spinner？

Question

我的问题很简单:如何在 Fragments 中使用(填充)Spinners？或者更好地说，我下面的代码有什么问题？像我一样添加 Spinner 非常简单，但是在尝试了所有不同的方法之后，没有任何效果。 FragmentPagerAdapter 与 Spinner 有什么关系？如果我从其他地方声明的方法添加 Spinner，spinner 填充没有问题(例如，如果从 spinner 填充 按钮)。

提前致谢

public class MainActivity extends FragmentActivity {

/**
 * The {@link android.support.v4.view.PagerAdapter} that will provide
 * fragments for each of the sections. 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}.
 */
SectionsPagerAdapter mSectionsPagerAdapter;
public List<String> fragments = new Vector<String>();

/**
 * The {@link ViewPager} that will host the section contents.
 */
ViewPager mViewPager;
private MySQLite database;

@Override
protected void onCreate(Bundle savedInstanceState) {
    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.
    mSectionsPagerAdapter = new SectionsPagerAdapter(
            getSupportFragmentManager());

    // Set up the ViewPager with the sections adapter.
    mViewPager = (ViewPager) findViewById(R.id.pager); // pager
    mViewPager.setAdapter(mSectionsPagerAdapter);

    // We initialise the database
    database = new MySQLite(this);

    Spinner spin = (Spinner)findViewById(R.id.spinner1);
    List<String> toSpin = new ArrayList<String>();
    toSpin.add("ONE");
    toSpin.add("TWO");
    toSpin.add("THREE");
    ArrayAdapter<String> adapter = new ArrayAdapter<String>(this,android.R.layout.simple_spinner_item,toSpin);
    spin.setAdapter(adapter);
}

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

/**
 * A {@link FragmentPagerAdapter} that returns a fragment corresponding to
 * one of the sections/tabs/pages.
 */

public class SectionsPagerAdapter extends FragmentPagerAdapter {

    public SectionsPagerAdapter(FragmentManager fm) {
        super(fm);
        fragments.add(ConnectionFragment.class.getName());
        fragments.add(DataFragment.class.getName());

    }

    @Override
    public Fragment getItem(int position) {
        // we need to instantiate the list of fragments
        return Fragment.instantiate(getBaseContext(),
                fragments.get(position));

    }

    @Override
    public int getCount() {
        // Show 3 total pages.
        return 2;
    }

    @Override
    public CharSequence getPageTitle(int position) {
        Locale l = Locale.getDefault();
        switch (position) {
        case 0:
            return getString(R.string.title_section1).toUpperCase(l);
        case 1:
            return getString(R.string.title_section2).toUpperCase(l);
        }
        return null;
    }
}

/**
 * A dummy fragment representing a section of the app, but that simply
 * displays dummy text.
 */
public static class ConnectionFragment extends Fragment {
    /**
     * The fragment argument representing the section number for this
     * fragment.
     */
    public static final String ARG_SECTION_NUMBER = "section_number";

    public ConnectionFragment() {
    }

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
            Bundle savedInstanceState) {
        View connectionView = inflater.inflate(
                R.layout.fragment_main_dummy, container, false);
        return connectionView;
    }
}

public static class DataFragment extends Fragment {

    public DataFragment() {
    }

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
            Bundle savedInstanceState) {
        View dataView = inflater.inflate(R.layout.fragment_linear,
                container, false);
        return dataView;
    }
}

日志:

11-16 18:26:13.092: E/AndroidRuntime(16442): FATAL EXCEPTION: main
11-16 18:26:13.092: E/AndroidRuntime(16442): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.iwallet/com.example.iwallet.MainActivity}: java.lang.NullPointerException
11-16 18:26:13.092: E/AndroidRuntime(16442):    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2071)
11-16 18:26:13.092: E/AndroidRuntime(16442):    at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2096)
11-16 18:26:13.092: E/AndroidRuntime(16442):    at android.app.ActivityThread.access$600(ActivityThread.java:138)
11-16 18:26:13.092: E/AndroidRuntime(16442):    at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1207)
11-16 18:26:13.092: E/AndroidRuntime(16442):    at android.os.Handler.dispatchMessage(Handler.java:99)
11-16 18:26:13.092: E/AndroidRuntime(16442):    at android.os.Looper.loop(Looper.java:213)
11-16 18:26:13.092: E/AndroidRuntime(16442):    at android.app.ActivityThread.main(ActivityThread.java:4787)
11-16 18:26:13.092: E/AndroidRuntime(16442):    at java.lang.reflect.Method.invokeNative(Native Method)
11-16 18:26:13.092: E/AndroidRuntime(16442):    at java.lang.reflect.Method.invoke(Method.java:511)
11-16 18:26:13.092: E/AndroidRuntime(16442):    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:789)
11-16 18:26:13.092: E/AndroidRuntime(16442):    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:556)
11-16 18:26:13.092: E/AndroidRuntime(16442):    at dalvik.system.NativeStart.main(Native Method)
11-16 18:26:13.092: E/AndroidRuntime(16442): Caused by: java.lang.NullPointerException
11-16 18:26:13.092: E/AndroidRuntime(16442):    at com.example.iwallet.MainActivity.onCreate(MainActivity.java:65)
11-16 18:26:13.092: E/AndroidRuntime(16442):    at android.app.Activity.performCreate(Activity.java:5008)
11-16 18:26:13.092: E/AndroidRuntime(16442):    at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1079)
11-16 18:26:13.092: E/AndroidRuntime(16442):    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2035)
11-16 18:26:13.092: E/AndroidRuntime(16442):    ... 11 more

Answer 1

如果你想在你的 Fragment 中制作你的 Spinner，也许你必须在 onCreatedView() 中声明这些 Fragment。不在 FragmentActivity 的 onCreate() 中。

你可以这样做:Error populating spinner in a fragment