我正在使用我从网站material design sliding tabs借来的Android Sliding标签应用程序。我已经成功实现了代码，但是从一个选项卡滑动到另一个选项卡时出现错误。基本上发生的情况是，当我滑动到第二个选项卡时，选项卡按预期切换但是一旦我释放屏幕，应用程序就会关闭。我检查了logcat，这是显示的错误：
31431-31431/com.skibzy.skibzydesigns E/MessageQueue-JNI? java.lang.NullPointerException
at com.skibzy.skibzydesigns.SlidingTabLayout$InternalViewPagerListener.onPageSelected(SlidingTabLayout.java:264)
at android.support.v4.view.ViewPager.dispatchOnPageSelected(ViewPager.java:1786)
at android.support.v4.view.ViewPager.scrollToItem(ViewPager.java:568)
at android.support.v4.view.ViewPager.setCurrentItemInternal(ViewPager.java:552)
at android.support.v4.view.ViewPager.onTouchEvent(ViewPager.java:2101)
at android.view.View.dispatchTouchEvent(View.java:7315)
at android.view.ViewGroup.dispatchTransformedTouchEvent(ViewGroup.java:2253)
at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:1950)
at android.view.ViewGroup.dispatchTransformedTouchEvent(ViewGroup.java:2259)
at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:1964)
at android.view.ViewGroup.dispatchTransformedTouchEvent(ViewGroup.java:2259)
at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:1964)
at android.view.ViewGroup.dispatchTransformedTouchEvent(ViewGroup.java:2259)
at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:1964)
at android.view.ViewGroup.dispatchTransformedTouchEvent(ViewGroup.java:2259)
at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:1964)
at android.view.ViewGroup.dispatchTransformedTouchEvent(ViewGroup.java:2259)
at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:1964)
at android.view.ViewGroup.dispatchTransformedTouchEvent(ViewGroup.java:2259)
at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:1964)
at android.view.ViewGroup.dispatchTransformedTouchEvent(ViewGroup.java:2259)
at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:1964)
at android.view.ViewGroup.dispatchTransformedTouchEvent(ViewGroup.java:2259)
at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:1964)
at com.android.internal.policy.impl.PhoneWindow$DecorView.superDispatchTouchEvent(PhoneWindow.java:1971)
at com.android.internal.policy.impl.PhoneWindow.superDispatchTouchEvent(PhoneWindow.java:1421)
at android.app.Activity.dispatchTouchEvent(Activity.java:2428)
at android.support.v7.internal.view.WindowCallbackWrapper.dispatchTouchEvent(WindowCallbackWrapper.java:59)
at com.android.internal.policy.impl.PhoneWindow$DecorView.dispatchTouchEvent(PhoneWindow.java:1919)
at android.view.View.dispatchPointerEvent(View.java:7506)
at android.view.ViewRootImpl.deliverPointerEvent(ViewRootImpl.java:3654)
at android.view.ViewRootImpl.deliverInputEvent(ViewRootImpl.java:3579)
at android.view.ViewRootImpl.doProcessInputEvents(ViewRootImpl.java:4849)
at android.view.ViewRootImpl.enqueueInputEvent(ViewRootImpl.java:4809)
at android.view.ViewRootImpl$WindowInputEventReceiver.onInputEvent(ViewRootImpl.java:4965)
at android.view.InputEventReceiver.dispatchInputEvent(InputEventReceiver.java:179)
at android.os.MessageQueue.nativePollOnce(Native Method)
at android.os.MessageQueue.next(MessageQueue.java:128)
at android.os.Looper.loop(Looper.java:151)
at android.app.ActivityThread.main(ActivityThread.java:5370)
at java.lang.reflect.Method.invokeNative(Native Method)
at java.lang.reflect.Method.invoke(Method.java:525)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:833)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:600)
at dalvik.system.NativeStart.main(Native Method)
我的代码如下： activity.java
package com.skibzy.skibzydesigns;
import android.app.AlertDialog;
import android.content.ActivityNotFoundException;
import android.content.Context;
import android.content.DialogInterface;
import android.content.Intent;
import android.net.Uri;
import android.os.Bundle;
import android.support.v4.view.ViewPager;
import android.support.v7.app.ActionBarActivity;
import android.support.v7.widget.Toolbar;
import android.util.Log;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.widget.ImageButton;
import android.widget.Toast;
public class MessageActivity extends ActionBarActivity {
private Toolbar toolbar;
ViewPager pager;
ViewPagerAdapter adapter;
SlidingTabLayout tabs;
CharSequence Titles[]={"Inbox","Draft"};
int Numboftabs =2;
final Context context = this;
private ImageButton btnCall;
private ImageButton btnMessage;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_message);
toolbar = (Toolbar) findViewById(R.id.toolbar);
setSupportActionBar(toolbar);
// Creating The ViewPagerAdapter and Passing Fragment Manager, Titles fot the Tabs and Number Of Tabs.
adapter = new ViewPagerAdapter(getSupportFragmentManager(),Titles,Numboftabs);
// Assigning ViewPager View and setting the adapter
pager = (ViewPager) findViewById(R.id.pager);
pager.setAdapter(adapter);
// Assiging the Sliding Tab Layout View
tabs = (SlidingTabLayout) findViewById(R.id.tabs);
tabs.setDistributeEvenly(true); // To make the Tabs Fixed set this true, This makes the tabs Space Evenly in Available width
// Setting Custom Color for the Scroll bar indicator of the Tab View
tabs.setCustomTabColorizer(new SlidingTabLayout.TabColorizer() {
@Override
public int getIndicatorColor(int position) {
return getResources().getColor(R.color.tabsScrollColor);
}
});
// Setting the ViewPager For the SlidingTabsLayout
tabs.setViewPager(pager);
}
layout.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"
tools:context="com.skibzy.skibzydesigns.MessageActivity">
<include
android:id="@+id/toolbar"
layout="@layout/toolbar" />
<RelativeLayout
android:id="@+id/body"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
android:layout_above="@+id/appFooter"
android:layout_below="@+id/toolbar">
<LinearLayout
android:layout_width="fill_parent"
android:layout_height="match_parent"
android:orientation="vertical">
<com.skibzy.skibzydesigns.SlidingTabLayout
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:id="@+id/tabs"
android:elevation="2dp"
android:background="@color/ColorPrimary"/>
<android.support.v4.view.ViewPager
android:layout_width="match_parent"
android:layout_height="match_parent"
android:layout_weight="1"
android:id="@+id/pager"
style="@style/appBody"/>
</LinearLayout>
</RelativeLayout>
<View
android:layout_width="fill_parent"
android:layout_height="1dp"
android:background="@color/divider"
android:layout_above="@+id/appFooter"/>
<RelativeLayout
android:id="@+id/appFooter"
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:layout_alignParentBottom="true"
android:padding="10dp">
<ImageButton
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:id="@+id/callButton"
android:background="#ffeeeeee"
android:src="@drawable/phone"
android:layout_alignParentLeft="true"
style="@style/footerImageButton"/>
<ImageButton
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:id="@+id/msgButton"
android:src="@drawable/sms"
android:background="#ffeeeeee"
android:layout_centerHorizontal="true"/>
<ImageButton
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:id="@+id/mapButton"
android:src="@drawable/maps"
android:background="#ffeeeeee"
android:layout_alignParentRight="true"/>
</RelativeLayout>
</RelativeLayout>
ViewPagerAdapter.java
package com.skibzy.skibzydesigns;
import android.support.v4.app.Fragment;
import android.support.v4.app.FragmentManager;
import android.support.v4.app.FragmentStatePagerAdapter;
public class ViewPagerAdapter extends FragmentStatePagerAdapter {
CharSequence Titles[];
int NumbOfTabs;
public ViewPagerAdapter(FragmentManager fm,CharSequence mTitles[], int mNumbOfTabsumb) {
super(fm);
this.Titles = mTitles;
this.NumbOfTabs = mNumbOfTabsumb;
}
//This method return the fragment for the every position in the View Pager
@Override
public Fragment getItem(int position) {
if(position == 0) // if the position is 0 we are returning the First tab
{
inboxTab tab1 = new inboxTab();
return tab1;
}
else // As we are having 2 tabs if the position is now 0 it must be 1 so we are returning second tab
{
draftTab tab2 = new draftTab();
return tab2;
}
}
// This method return the titles for the Tabs in the Tab Strip
@Override
public CharSequence getPageTitle(int position) {
return Titles[position];
}
// This method return the Number of tabs for the tabs Strip
@Override
public int getCount() {
return NumbOfTabs;
}
}
我真的很感谢你的帮助。