0

我使用导航类型 Tabs + Viewpager 在 Android Studio 中创建了一个简单的 android 项目。代码编译并运行正常。但是在我包含 android 注释之后，我得到了 viewPager 对象的空指针异常。

代码如下：

MainActivity.java;

package com.example.tabnanot;

import java.util.Locale;

import android.support.v7.app.ActionBarActivity;
import android.support.v7.app.ActionBar;
import android.support.v4.app.Fragment;
import android.support.v4.app.FragmentManager;
import android.support.v4.app.FragmentTransaction;
import android.support.v4.app.FragmentPagerAdapter;
import android.os.Bundle;
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.TextView;
import com.googlecode.androidannotations.annotations.EActivity;


@EActivity(R.layout.activity_main)
public class MainActivity extends ActionBarActivity implements ActionBar.TabListener {

    /**
     * The {@link android.support.v4.view.PagerAdapter} that will provide
     * fragments for each of the sections. We use a
     * {@link 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 = getSupportActionBar();
        actionBar.setNavigationMode(ActionBar.NAVIGATION_MODE_TABS);

        // Create the adapter that will return a fragment for each of the three
        // primary sections of the activity.
        mSectionsPagerAdapter = new SectionsPagerAdapter(getSupportFragmentManager());

        // Set up the ViewPager with the sections adapter.
        mViewPager = (ViewPager) findViewById(R.id.pager);
        mViewPager.setAdapter(mSectionsPagerAdapter);       // This is where the null pointer occurs

        // 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 boolean onOptionsItemSelected(MenuItem item) {
        // Handle action bar item clicks here. The action bar will
        // automatically handle clicks on the Home/Up button, so long
        // as you specify a parent activity in AndroidManifest.xml.
        switch (item.getItemId()) {
            case R.id.action_settings:
                return true;
        }
        return super.onOptionsItemSelected(item);
    }

    @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 PlaceholderFragment (defined as a static inner class below).
            return PlaceholderFragment.newInstance(position + 1);
        }

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

        @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);
            }
            return null;
        }
    }

    /**
     * A placeholder fragment containing a simple view.
     */
    public static class PlaceholderFragment extends Fragment {
        /**
         * The fragment argument representing the section number for this
         * fragment.
         */
        private static final String ARG_SECTION_NUMBER = "section_number";

        /**
         * Returns a new instance of this fragment for the given section
         * number.
         */
        public static PlaceholderFragment newInstance(int sectionNumber) {
            PlaceholderFragment fragment = new PlaceholderFragment();
            Bundle args = new Bundle();
            args.putInt(ARG_SECTION_NUMBER, sectionNumber);
            fragment.setArguments(args);
            return fragment;
        }

        public PlaceholderFragment() {
        }

        @Override
        public View onCreateView(LayoutInflater inflater, ViewGroup container,
                Bundle savedInstanceState) {
            View rootView = inflater.inflate(R.layout.fragment_main, container, false);
            TextView textView = (TextView) rootView.findViewById(R.id.section_label);
            textView.setText(Integer.toString(getArguments().getInt(ARG_SECTION_NUMBER)));
            return rootView;
        }
    }

}

活动主.xml；

<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"
    tools:context=".MainActivity" />

片段主.xml；

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

    <TextView
        android:id="@+id/section_label"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content" />

</RelativeLayout>

这是我的 build.gradle 文件；

buildscript {
    repositories {
        mavenCentral()
    }
    dependencies {
        classpath 'com.android.tools.build:gradle:0.6.+'
    }
}
apply plugin: 'android'

repositories {
    mavenCentral()
}

ext.daggerVersion = '1.0.0';
ext.androidAnnotationsVersion = '2.7.1';

configurations {
    apt
}

dependencies {

    apt "com.googlecode.androidannotations:androidannotations:${androidAnnotationsVersion}"
    compile "com.googlecode.androidannotations:androidannotations-api:${androidAnnotationsVersion}"
    apt "com.squareup.dagger:dagger-compiler:${daggerVersion}"
    compile "com.squareup.dagger:dagger:${daggerVersion}"
}

android {
    compileSdkVersion 18
    buildToolsVersion "18.1.1"

    defaultConfig {
        minSdkVersion 12
        targetSdkVersion 18
    }
}

dependencies {
    compile 'com.android.support:appcompat-v7:+'
}

android.applicationVariants.all { variant ->
    aptOutput = file("${project.buildDir}/source/apt_generated/${variant.dirName}")
    println "****************************"
    println "variant: ${variant.name}"
    println "manifest:  ${variant.processResources.manifestFile}"
    println "aptOutput:  ${aptOutput}"
    println "****************************"

    variant.javaCompile.doFirst {
        println "*** compile doFirst ${variant.name}"
        aptOutput.mkdirs()
        variant.javaCompile.options.compilerArgs += [
                '-processorpath', configurations.apt.getAsPath(),
                '-AandroidManifestFile=' + variant.processResources.manifestFile,
                '-s', aptOutput
        ]
    }
}

这是清单文件；

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
package="com.example.tabnanot"
android:versionCode="1"
android:versionName="1.0" >

<uses-sdk
    android:minSdkVersion="12"
    android:targetSdkVersion="18" />

<uses-feature
    android:name="android.hardware.camera"
    android:required="false" />

<uses-permission android:name="android.permission.CAMERA" />
<uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE" />
<uses-permission android:name="android.permission.ACCESS_FINE_LOCATION" />
<uses-permission android:name="android.permission.INTERNET" />
<uses-permission android:name="android.permission.ACCESS_NETWORK_STATE" />

<application
    android:allowBackup="true"
    android:icon="@drawable/ic_launcher"
    android:label="@string/app_name"
    android:theme="@style/AppTheme" >
    <activity
        android:name="MainActivity_"
        android:label="@string/app_name" >
        <intent-filter>
            <action android:name="android.intent.action.MAIN" />

            <category android:name="android.intent.category.LAUNCHER" />
        </intent-filter>
    </activity>
</application>

</manifest>

这是来自 log cat 的错误日志

10-29 13:28:17.229      628-628/com.android.exchange E/ActivityThread﹕ Service com.android.exchange.ExchangeService has leaked ServiceConnection com.android.emailcommon.service.ServiceProxy$ProxyConnection@40d1e2f8 that was originally bound here
    android.app.ServiceConnectionLeaked: Service com.android.exchange.ExchangeService has leaked ServiceConnection com.android.emailcommon.service.ServiceProxy$ProxyConnection@40d1e2f8 that was originally bound here
            at android.app.LoadedApk$ServiceDispatcher.<init>(LoadedApk.java:969)
            at android.app.LoadedApk.getServiceDispatcher(LoadedApk.java:863)
            at android.app.ContextImpl.bindService(ContextImpl.java:1418)
            at android.app.ContextImpl.bindService(ContextImpl.java:1407)
            at android.content.ContextWrapper.bindService(ContextWrapper.java:473)
            at com.android.emailcommon.service.ServiceProxy.setTask(ServiceProxy.java:157)
            at com.android.emailcommon.service.ServiceProxy.setTask(ServiceProxy.java:145)
            at com.android.emailcommon.service.AccountServiceProxy.getDeviceId(AccountServiceProxy.java:116)
            at com.android.exchange.ExchangeService.getDeviceId(ExchangeService.java:1249)
            at com.android.exchange.ExchangeService$7.run(ExchangeService.java:1856)
            at com.android.emailcommon.utility.Utility$2.doInBackground(Utility.java:551)
            at com.android.emailcommon.utility.Utility$2.doInBackground(Utility.java:549)
            at android.os.AsyncTask$2.call(AsyncTask.java:287)
            at java.util.concurrent.FutureTask.run(FutureTask.java:234)
            at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1080)
            at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:573)
            at java.lang.Thread.run(Thread.java:856)
10-29 13:28:17.279      628-628/com.android.exchange E/StrictMode﹕ null
    android.app.ServiceConnectionLeaked: Service com.android.exchange.ExchangeService has leaked ServiceConnection com.android.emailcommon.service.ServiceProxy$ProxyConnection@40d1e2f8 that was originally bound here
            at android.app.LoadedApk$ServiceDispatcher.<init>(LoadedApk.java:969)
            at android.app.LoadedApk.getServiceDispatcher(LoadedApk.java:863)
            at android.app.ContextImpl.bindService(ContextImpl.java:1418)
            at android.app.ContextImpl.bindService(ContextImpl.java:1407)
            at android.content.ContextWrapper.bindService(ContextWrapper.java:473)
            at com.android.emailcommon.service.ServiceProxy.setTask(ServiceProxy.java:157)
            at com.android.emailcommon.service.ServiceProxy.setTask(ServiceProxy.java:145)
            at com.android.emailcommon.service.AccountServiceProxy.getDeviceId(AccountServiceProxy.java:116)
            at com.android.exchange.ExchangeService.getDeviceId(ExchangeService.java:1249)
            at com.android.exchange.ExchangeService$7.run(ExchangeService.java:1856)
            at com.android.emailcommon.utility.Utility$2.doInBackground(Utility.java:551)
            at com.android.emailcommon.utility.Utility$2.doInBackground(Utility.java:549)
            at android.os.AsyncTask$2.call(AsyncTask.java:287)
            at java.util.concurrent.FutureTask.run(FutureTask.java:234)
            at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1080)
            at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:573)
            at java.lang.Thread.run(Thread.java:856)
10-29 13:28:17.319      628-628/com.android.exchange E/ActivityThread﹕ Service com.android.exchange.ExchangeService has leaked ServiceConnection com.android.emailcommon.service.ServiceProxy$ProxyConnection@40d37b28 that was originally bound here
    android.app.ServiceConnectionLeaked: Service com.android.exchange.ExchangeService has leaked ServiceConnection com.android.emailcommon.service.ServiceProxy$ProxyConnection@40d37b28 that was originally bound here
            at android.app.LoadedApk$ServiceDispatcher.<init>(LoadedApk.java:969)
            at android.app.LoadedApk.getServiceDispatcher(LoadedApk.java:863)
            at android.app.ContextImpl.bindService(ContextImpl.java:1418)
            at android.app.ContextImpl.bindService(ContextImpl.java:1407)
            at android.content.ContextWrapper.bindService(ContextWrapper.java:473)
            at com.android.emailcommon.service.ServiceProxy.setTask(ServiceProxy.java:157)
            at com.android.emailcommon.service.ServiceProxy.setTask(ServiceProxy.java:145)
            at com.android.emailcommon.service.ServiceProxy.test(ServiceProxy.java:191)
            at com.android.exchange.ExchangeService$7.run(ExchangeService.java:1850)
            at com.android.emailcommon.utility.Utility$2.doInBackground(Utility.java:551)
            at com.android.emailcommon.utility.Utility$2.doInBackground(Utility.java:549)
            at android.os.AsyncTask$2.call(AsyncTask.java:287)
            at java.util.concurrent.FutureTask.run(FutureTask.java:234)
            at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1080)
            at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:573)
            at java.lang.Thread.run(Thread.java:856)
10-29 13:28:17.379      628-628/com.android.exchange E/StrictMode﹕ null
    android.app.ServiceConnectionLeaked: Service com.android.exchange.ExchangeService has leaked ServiceConnection com.android.emailcommon.service.ServiceProxy$ProxyConnection@40d37b28 that was originally bound here
            at android.app.LoadedApk$ServiceDispatcher.<init>(LoadedApk.java:969)
            at android.app.LoadedApk.getServiceDispatcher(LoadedApk.java:863)
            at android.app.ContextImpl.bindService(ContextImpl.java:1418)
            at android.app.ContextImpl.bindService(ContextImpl.java:1407)
            at android.content.ContextWrapper.bindService(ContextWrapper.java:473)
            at com.android.emailcommon.service.ServiceProxy.setTask(ServiceProxy.java:157)
            at com.android.emailcommon.service.ServiceProxy.setTask(ServiceProxy.java:145)
            at com.android.emailcommon.service.ServiceProxy.test(ServiceProxy.java:191)
            at com.android.exchange.ExchangeService$7.run(ExchangeService.java:1850)
            at com.android.emailcommon.utility.Utility$2.doInBackground(Utility.java:551)
            at com.android.emailcommon.utility.Utility$2.doInBackground(Utility.java:549)
            at android.os.AsyncTask$2.call(AsyncTask.java:287)
            at java.util.concurrent.FutureTask.run(FutureTask.java:234)
            at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1080)
            at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:573)
            at java.lang.Thread.run(Thread.java:856)
10-29 13:28:34.880        37-81/? E/SurfaceFlinger﹕ ro.sf.lcd_density must be defined as a build property
10-29 13:28:35.170    1641-1641/? E/Trace﹕ error opening trace file: No such file or directory (2)
10-29 13:28:35.999    1641-1641/com.example.tabnanot E/AndroidRuntime﹕ FATAL EXCEPTION: main
    java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.tabnanot/com.example.tabnanot.MainActivity_}: java.lang.NullPointerException
            at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2180)
            at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2230)
            at android.app.ActivityThread.access$600(ActivityThread.java:141)
            at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1234)
            at android.os.Handler.dispatchMessage(Handler.java:99)
            at android.os.Looper.loop(Looper.java:137)
            at android.app.ActivityThread.main(ActivityThread.java:5041)
            at java.lang.reflect.Method.invokeNative(Native Method)
            at java.lang.reflect.Method.invoke(Method.java:511)
            at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:793)
            at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:560)
            at dalvik.system.NativeStart.main(Native Method)
     Caused by: java.lang.NullPointerException
            at com.example.tabnanot.MainActivity.onCreate(MainActivity.java:56)
            at com.example.tabnanot.MainActivity_.onCreate(MainActivity_.java:26)
            at android.app.Activity.performCreate(Activity.java:5104)
            at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1080)
            at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2144)
            at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2230)
            at android.app.ActivityThread.access$600(ActivityThread.java:141)
            at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1234)
            at android.os.Handler.dispatchMessage(Handler.java:99)
            at android.os.Looper.loop(Looper.java:137)
            at android.app.ActivityThread.main(ActivityThread.java:5041)
            at java.lang.reflect.Method.invokeNative(Native Method)
            at java.lang.reflect.Method.invoke(Method.java:511)
            at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:793)
            at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:560)
            at dalvik.system.NativeStart.main(Native Method)
10-29 13:28:36.619        37-37/? E/SurfaceFlinger﹕ ro.sf.lcd_density must be defined as a build property
10-29 13:28:36.710       37-421/? E/SurfaceFlinger﹕ ro.sf.lcd_density must be defined as a build property

我尝试调试并意识到视图寻呼机对象为空。我不知道这是什么原因造成的。我将 android 注释 jar 添加到 libs 文件夹并将生成的源标记为源根。

注意：我可以使用注释成功地正常项目（即那些导航类型为无的项目），但对于选项卡的事情它失败了任何帮助将不胜感激。谢谢大家。

编辑:: 当我查看生成的 MainActivity_.java 时，我看到了这一行

setContentView(layout.activity_main);

我认为应该是

setContentView(R.layout.activity_main);

我不确定

4

2 回答 2

3

如果在类声明中添加布局，则不应在 onCreate 中引用视图。相反，您应该使用@ViewById 注入视图，并使用@AfterViews 在单独的方法中使用它们。更多关于这里：

https://github.com/excilys/androidannotations/wiki/Injecting-Views

于 2013-11-11T11:09:21.300 回答
0

是的，完全同意上面的答案，有两种使用视图的方法

1.）如果你使用...... @EActivity(R.layout.activity_main)你必须使用@AfterViews ...和

2.）如果你想使用@Override protected void onCreate(Bundle savedInstanceState)..你必须使用setContentView(R.layout.activity_main);

-以上是为了正确使用代码而应始终一起使用的组合

_谢谢！~！

于 2015-11-05T04:42:32.163 回答