Question

下面找到我的所有代码和xml。我的问题是，微调器（在代码spinner1中）由于某些原因我无法确定是空的，除了应用程序无法运行之外我没有得到任何错误。任何帮助将不胜感激！

activity_main.xml中：

<android.support.v4.view.ViewPager xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:id="@+id/pager"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:background="@color/black"
    tools:context=".MainActivity" />

MainActivity.java：

package com.example.passwordplayground;

import java.util.Locale;

import com.example.MyApplication.EncryptionSpinner;
import com.example.MyApplication.MyApplication;

import android.app.ActionBar;
import android.app.Activity;
import android.app.FragmentTransaction;
import android.content.Context;
import android.os.Bundle;
import android.support.v4.app.Fragment;
import android.support.v4.app.FragmentActivity;
import android.support.v4.app.FragmentManager;
import android.support.v4.app.FragmentPagerAdapter;
import android.support.v4.app.NavUtils;
import android.support.v4.view.ViewPager;
import android.view.Gravity;
import android.view.LayoutInflater;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.view.ViewGroup;
import android.widget.AdapterView;
import android.widget.AdapterView.OnItemSelectedListener;
import android.widget.ArrayAdapter;
import android.widget.Button;
import android.widget.Spinner;
import android.widget.TextView;
import android.widget.Toast;

public class MainActivity extends FragmentActivity implements
        ActionBar.TabListener {

    /**
     * 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;

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

    @Override
    protected void onCreate(Bundle savedInstanceState) {

        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        // Set up the action bar.
        final ActionBar actionBar = getActionBar();
        actionBar.setNavigationMode(ActionBar.NAVIGATION_MODE_TABS);
        Spinner spinner1 = (Spinner) findViewById(R.id.encryptionSpin);
        if (spinner1 == null)
            System.out.println("Spinner1 is null");
        else
            System.out.println("Funcion is null");
        spinner1.setOnItemSelectedListener(new EncryptionSpinner());

        // 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);
        mViewPager.setAdapter(mSectionsPagerAdapter);

        // When swiping between different sections, select the corresponding
        // tab. We can also use ActionBar.Tab#select() to do this if we have
        // a reference to the Tab.
        mViewPager
                .setOnPageChangeListener(new ViewPager.SimpleOnPageChangeListener() {
                    @Override
                    public void onPageSelected(int position) {
                        actionBar.setSelectedNavigationItem(position);
                    }
                });

        // For each of the sections in the app, add a tab to the action bar.
        for (int i = 0; i < mSectionsPagerAdapter.getCount(); i++) {
            // Create a tab with text corresponding to the page title defined by
            // the adapter. Also specify this Activity object, which implements
            // the TabListener interface, as the callback (listener) for when
            // this tab is selected.
            actionBar.addTab(actionBar.newTab()
                    .setText(mSectionsPagerAdapter.getPageTitle(i))
                    .setTabListener(this));
        }
    }

    @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;
    }

    @Override
    public void onTabSelected(ActionBar.Tab tab,
            FragmentTransaction fragmentTransaction) {
        // When the given tab is selected, switch to the corresponding page in
        // the ViewPager.
        mViewPager.setCurrentItem(tab.getPosition());
    }

    @Override
    public void onTabUnselected(ActionBar.Tab tab,
            FragmentTransaction fragmentTransaction) {
    }

    @Override
    public void onTabReselected(ActionBar.Tab tab,
            FragmentTransaction fragmentTransaction) {
    }

    /**
     * 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);
        }

        @Override
        public Fragment getItem(int position) {
            // getItem is called to instantiate the fragment for the given page.
            // Return a DummySectionFragment (defined as a static inner class
            // below) with the page number as its lone argument.
            Fragment fragment = new DummySectionFragment();
            Bundle args = new Bundle();
            args.putInt(DummySectionFragment.ARG_SECTION_NUMBER, position + 1);
            fragment.setArguments(args);
            return fragment;
        }

        @Override
        public int getCount() {
            // Show 4 total pages.
            return 4;
        }

        @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);
            case 2:
                return getString(R.string.title_section3).toUpperCase(l);
            case 3:
                return ("Practicality").toUpperCase();
            }
            return null;
        }
    }

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

        public DummySectionFragment() {
        }
        @Override
        public View onCreateView(LayoutInflater inflater, ViewGroup container,
                Bundle savedInstanceState) {
            View rootView = null;
            if (getArguments().getInt(ARG_SECTION_NUMBER)==1) {
                rootView = inflater.inflate(R.layout.encryption,container, false);
            }
            else if (getArguments().getInt(ARG_SECTION_NUMBER)==2) {
                rootView = inflater.inflate(R.layout.fragment_main_dummy,
                        container, false);
                TextView dummyTextView = (TextView) rootView
                        .findViewById(R.id.section_label);
                dummyTextView.setText("I'm second!");
            }
            else if (getArguments().getInt(ARG_SECTION_NUMBER)==3) {
                //dummyTextView.setText("I'm third");
            }
            else if (getArguments().getInt(ARG_SECTION_NUMBER)==4) {
                //dummyTextView.setText("I'm fourth and last!");
            }
            return rootView;
        }
    }

}

encryption.xml：

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    xmlns:android1="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:paddingBottom="@dimen/activity_vertical_margin"
    android:paddingLeft="@dimen/activity_horizontal_margin"
    android:paddingRight="@dimen/activity_horizontal_margin"
    android:paddingTop="@dimen/activity_vertical_margin"
    tools:context=".MainActivity$Encryption" >

    <Spinner
        android1:id="@+id/encryptionSpin"
        android1:layout_width="fill_parent"
        android1:layout_height="wrap_content"
        android1:layout_alignParentTop="true"
        android1:layout_centerHorizontal="true"
        android1:layout_marginTop="14dp"
        android1:background="@color/orange"
        android1:entries="@array/cryptArray" />

</RelativeLayout>

EncryptionSpinner.java：

package com.example.MyApplication;

import android.view.View;
import android.widget.AdapterView;
import android.widget.Toast;
import android.widget.AdapterView.OnItemSelectedListener;

public class EncryptionSpinner implements OnItemSelectedListener {

    public void onItemSelected(AdapterView<?> parent, View view, int pos, long id) {
        // An item was selected. You can retrieve the selected item using
        // parent.getItemAtPosition(pos)
        Toast toast = Toast.makeText(MyApplication.getAppContext(), parent.getItemAtPosition(pos).toString(), Toast.LENGTH_LONG);
        toast.show();
        System.out.println(parent.getItemAtPosition(pos).toString());
    }

    public void onNothingSelected(AdapterView<?> parent) {
        // Another interface callback
    }
}

Logcat错误：

04-09 01:16:28.637: I/System.out(1440): Spinner1 is null
04-09 01:16:28.657: D/AndroidRuntime(1440): Shutting down VM
04-09 01:16:28.657: W/dalvikvm(1440): threadid=1: thread exiting with uncaught exception (group=0x414c4700)
04-09 01:16:28.692: E/AndroidRuntime(1440): FATAL EXCEPTION: main
04-09 01:16:28.692: E/AndroidRuntime(1440): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.passwordplayground/com.example.passwordplayground.MainActivity}: java.lang.NullPointerException
04-09 01:16:28.692: E/AndroidRuntime(1440):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2211)
04-09 01:16:28.692: E/AndroidRuntime(1440):     at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2261)
04-09 01:16:28.692: E/AndroidRuntime(1440):     at android.app.ActivityThread.access$600(ActivityThread.java:141)
04-09 01:16:28.692: E/AndroidRuntime(1440):     at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1256)
04-09 01:16:28.692: E/AndroidRuntime(1440):     at android.os.Handler.dispatchMessage(Handler.java:99)
04-09 01:16:28.692: E/AndroidRuntime(1440):     at android.os.Looper.loop(Looper.java:137)
04-09 01:16:28.692: E/AndroidRuntime(1440):     at android.app.ActivityThread.main(ActivityThread.java:5103)
04-09 01:16:28.692: E/AndroidRuntime(1440):     at java.lang.reflect.Method.invokeNative(Native Method)
04-09 01:16:28.692: E/AndroidRuntime(1440):     at java.lang.reflect.Method.invoke(Method.java:525)
04-09 01:16:28.692: E/AndroidRuntime(1440):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:737)
04-09 01:16:28.692: E/AndroidRuntime(1440):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:553)
04-09 01:16:28.692: E/AndroidRuntime(1440):     at dalvik.system.NativeStart.main(Native Method)
04-09 01:16:28.692: E/AndroidRuntime(1440): Caused by: java.lang.NullPointerException
04-09 01:16:28.692: E/AndroidRuntime(1440):     at com.example.passwordplayground.MainActivity.onCreate(MainActivity.java:65)
04-09 01:16:28.692: E/AndroidRuntime(1440):     at android.app.Activity.performCreate(Activity.java:5133)
04-09 01:16:28.692: E/AndroidRuntime(1440):     at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1087)
04-09 01:16:28.692: E/AndroidRuntime(1440):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2175)
04-09 01:16:28.692: E/AndroidRuntime(1440):     ... 11 more

Layouts'Gui： layouta_main vs encryption

Answer 1

如果你想从activity_main使用微调器，那么你必须把它放在那个文件中，因为它现在不是它们的，而是在encryption.xml文件中。

make activity_main.xml如下所示：

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    xmlns:android1="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:paddingBottom="@dimen/activity_vertical_margin"
    android:paddingLeft="@dimen/activity_horizontal_margin"
    android:paddingRight="@dimen/activity_horizontal_margin"
    android:paddingTop="@dimen/activity_vertical_margin"
    tools:context=".MainActivity$Encryption" >

<android.support.v4.view.ViewPager 

    android:id="@+id/pager"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:background="@color/black"
    tools:context=".MainActivity" />

    <Spinner
        android1:id="@+id/encryptionSpin"
        android1:layout_width="fill_parent"
        android1:layout_height="wrap_content"
        android1:layout_alignParentTop="true"
        android1:layout_centerHorizontal="true"
        android1:layout_marginTop="14dp"
        android1:background="@color/orange"
        android1:entries="@array/cryptArray" />

</RelativeLayout>

Answer 2

您在活动中夸大了布局activity_main，并且您正在尝试访问Spinner布局中不属于的activity_main。

在这一点上你会收到错误。由于Spinner不在您的activity_main布局中。

因此，必须在Spinner DummySectionFragment方法中初始化您的onCreateView，如下所示：

 public static class DummySectionFragment extends Fragment {

    public static final String ARG_SECTION_NUMBER = "section_number";

    public DummySectionFragment() {
    }
    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
            Bundle savedInstanceState) {
        View rootView = null;
        if (getArguments().getInt(ARG_SECTION_NUMBER)==1) {
            rootView = inflater.inflate(R.layout.encryption,container, false);
              Spinner spinner1 = (Spinner)rootView.findViewById(R.id.encryptionSpin);
        }

Answer 3

你看到有空指针异常。表示您无法控制正在使用的组件。这可能是由于两个原因造成的 1.两个组件具有相同的ID。 2.错误定义的布局。

在您的情况下，您正在使用布局

R.layout.activity_main

，而您的布局名称是

R.layout.encryption

更改布局名称，您就可以开始了。

Answer 4

如果您将内容视图设置为xml中的任何一个，则将ViewPager置于activity_mail布局中，将Spinner置于encryption.xml中。所以任何一个人都会认定另一个人不会被认同。它会抛出空指针异常。

具有ViewPager的R.layout.activity_main

R.layout.encryption有Spinner

如果你设置setcontentView(R.layout.activity_main)，那么findViewById(R.id.encryptionSpin);行将抛出空指针。

如果你设置setcontentView(R.layout.encryption)，那么mViewPager = (ViewPager) findViewById(R.id.pager);行将抛出空指针。

Android spinner onselecteditem微调器是null？

4 个答案: