我知道NullPointerException有很多线程,我也知道这是由某个地方的空值引起的,但我是Android开发中的新手(以及Java),我试图运行第一次使用Tabs示例,所以我不太实际。
例如:https://github.com/codepath/android_guides/wiki/Google-Play-Style-Tabs-using-TabLayout
当我启动应用程序时,它会崩溃并返回以下错误:
9892-9892/com.mycompany.myfirstapp E/AndroidRuntime﹕ FATAL EXCEPTION: main
java.lang.RuntimeException: Unable to start activity ComponentInfo{com.mycompany.myfirstapp/com.mycompany.myfirstapp.TabActivity}: 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.mycompany.myfirstapp.TabActivity.onCreate(TabActivity.java:20)
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)
这是 /res/layout/activity_tab_test.xml
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical">
<android.support.design.widget.TabLayout
android:id="@+id/sliding_tabs"
android:layout_width="match_parent"
android:layout_height="wrap_content"
app:tabMode="scrollable" />
<android.support.v4.view.ViewPager
android:id="@+id/viewpager"
android:layout_width="match_parent"
android:layout_height="0px"
android:layout_weight="1"
android:background="@android:color/white" />
</LinearLayout>
这是 /res/layout/fragment_page.xml
<?xml version="1.0" encoding="utf-8"?>
<TextView xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:gravity="center" />
PageFragment.java
package com.mycompany.myfirstapp;
import android.support.v4.app.Fragment;
import android.os.Bundle;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.TextView;
public class PageFragment extends Fragment {
public static final String ARG_PAGE = "ARG_PAGE";
private int mPage;
public static PageFragment newInstance(int page) {
Bundle args = new Bundle();
args.putInt(ARG_PAGE, page);
PageFragment fragment = new PageFragment();
fragment.setArguments(args);
return fragment;
}
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
mPage = getArguments().getInt(ARG_PAGE);
}
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
View view = inflater.inflate(R.layout.fragment_page, container, false);
TextView textView = (TextView) view;
textView.setText("Fragment #" + mPage);
return view;
}
}
SampleFragmentPagerAdapter.java
package com.mycompany.myfirstapp;
import android.support.v4.app.Fragment;
import android.support.v4.app.FragmentManager;
import android.content.Context;
import android.support.v4.app.FragmentPagerAdapter;
public class SampleFragmentPagerAdapter extends FragmentPagerAdapter {
final int PAGE_COUNT = 3;
private String tabTitles[] = new String[] { "Tab1", "Tab2", "Tab3" };
private Context context;
public SampleFragmentPagerAdapter(FragmentManager fm, Context context) {
super(fm);
this.context = context;
}
@Override
public int getCount() {
return PAGE_COUNT;
}
@Override
public Fragment getItem(int position) {
return PageFragment.newInstance(position + 1);
}
@Override
public CharSequence getPageTitle(int position) {
// Generate title based on item position
return tabTitles[position];
}
}
TabActivity.java (示例的MainActivity)
package com.mycompany.myfirstapp;
import android.os.Bundle;
import android.support.design.widget.TabLayout;
import android.support.v4.app.FragmentActivity;
import android.support.v4.view.ViewPager;
public class TabActivity extends FragmentActivity {
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.fragment_page);
// Get the ViewPager and set it's PagerAdapter so that it can display items
ViewPager viewPager = (ViewPager) findViewById(R.id.viewpager);
viewPager.setAdapter(new SampleFragmentPagerAdapter(getSupportFragmentManager(),
TabActivity.this));
// Give the TabLayout the ViewPager
TabLayout tabLayout = (TabLayout) findViewById(R.id.sliding_tabs);
tabLayout.setupWithViewPager(viewPager);
}
}
哪里可以是空值?
答案 0 :(得分:6)
根据您发布的内容,您的ViewPager属于activity_tab_test.xml
,而不属于fragment_page.xml
,TextView
仅包含一个 setContentView(R.layout.fragment_page);
。改变
setContentView(R.layout.activity_tab_test);
与
var div = '<div class="row" id="flightsummary"><div class="col-md-6"><div class="summary"><p> Transportation Start Time =' + data[i]["TRANSPORT_START_TIME"]
+ '</p><p> Reporting Start Time =' + data[i]["REPORTING_START_TIME"] +
'</p><p> Chocks Off Time =' + data[i]["CHOCKS_OFF_TIME"]
+ '</p><p> Chocks On Time =' + data[i]["CHOCKS_ON_TIME"]
+ '</p><p>+Duty End Time =' + data[i]["DUTY_END_TIME"]
+ '</p><p> Flight Time =' + data[i]["FLIGHT_TIME"]
+ '</p><p> Flight Duty Period =' + data[i]["FLIGHT_DUTY_PERIOD"]
+ '</p></p></div></div><div class="col-md-6"><div class="summary summary-right"><p> Rest Period Start Time ='
+ data[i]["REST_PERIOD_START_TIME"]
+ '</p><p> Minimum Rest Hours ='
+ data[i]["MINIMUM_REST_HOURS"]
+ '</p><p> Next Transportation Start Time <span class="calendar"></span> ='
+ data[i]["NEXT_TRNS_START_TIME"]
+ '</p><p> Next Reporting Time <span class="calendar"></span> ='
+ data[i]["NEXT_REPORTING_TIME"]
+ '</p><p> Next Earliest Take Off <span class="calendar"></span> ='
+ data[i]["NEXT_EARLIEST_TAKE_OFF"] + '</p><p> Last Landing Time <span class="calendar"></span> ='
+ data[i]["LAST_LANDING_TIME"]; +'</p></div></div></div>;';