i am using Android Studio and i am trying to make an TabHost with ViewPager based on this tutorial
https://www.youtube.com/watch?v=GxEi_I3tv2k
but i am having a problem and i cannot determine it.
the main_activity.xml code:
<?xml version="1.0" encoding="utf-8"?>
<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: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="com.subhi.navtabs.MainActivity">
<TabHost
android:layout_width="match_parent"
android:layout_height="match_parent"
android:id="@+id/tabHost"
>
<LinearLayout
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical">
<HorizontalScrollView
android:layout_width="match_parent"
android:id="@+id/h_Scroll_View"
android:layout_height="wrap_content">
<TabWidget
android:id="@android:id/tabs"
android:fillViewport="true"
android:scrollbars="none"
android:layout_width="match_parent"
android:layout_height="wrap_content"></TabWidget>
</HorizontalScrollView>
<FrameLayout
android:id="@android:id/tabcontent"
android:layout_width="match_parent"
android:layout_height="match_parent">
<android.support.v4.view.ViewPager
android:layout_width="match_parent"
android:id="@+id/viewpager"
android:layout_height="match_parent"></android.support.v4.view.ViewPager>
</FrameLayout>
</LinearLayout>
</TabHost>
</RelativeLayout>
and this is mainactivity class :
package com.subhi.navtabs;
import android.content.Context;
import android.os.Bundle;
import android.support.v4.app.Fragment;
import android.support.v4.view.ViewPager;
import android.support.v7.app.AppCompatActivity;
import android.view.View;
import android.widget.HorizontalScrollView;
import android.widget.TabHost;
import java.util.ArrayList;
import java.util.List;
public class MainActivity extends AppCompatActivity implements ViewPager.OnPageChangeListener, TabHost.OnTabChangeListener {
ViewPager viewPager;
TabHost tabHost;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
initViewPager();
initTabHost();
}
private void initTabHost() {
tabHost = (TabHost) findViewById(android.R.id.tabhost);
tabHost.setup();
String[] tabanames = {"Tab1", "Tab2", "Tab3", "Tab4", "Tab5", "Tab6"};
for (int i = 0; i < tabanames.length; i++) {
TabHost.TabSpec tabSpec;
tabSpec = tabHost.newTabSpec(tabanames[i]);
tabSpec.setIndicator(tabanames[i]);
tabSpec.setContent(new FakeContent(getApplicationContext()));
tabHost.addTab(tabSpec);
}
tabHost.setOnTabChangedListener(this);
}
@Override
public void onPageScrolled(int position, float positionOffset, int positionOffsetPixels) {
}
@Override
public void onPageSelected(int selecteditem) {
tabHost.setCurrentTab(selecteditem);
}
@Override
public void onPageScrollStateChanged(int state) {
}
@Override
public void onTabChanged(String tabId) {
int selecteditem = tabHost.getCurrentTab();
viewPager.setCurrentItem(selecteditem);
HorizontalScrollView horizontalScrollView = (HorizontalScrollView) findViewById(R.id.h_Scroll_View);
View tabView = tabHost.getCurrentTabView();
int scrollpos = tabView.getLeft()
- (horizontalScrollView.getWidth() - tabView.getWidth()) / 2;
horizontalScrollView.smoothScrollBy(scrollpos, 0);
}
public class FakeContent implements TabHost.TabContentFactory {
Context context;
public FakeContent(Context context) {
this.context = context;
}
@Override
public View createTabContent(String tag) {
View fakeview = new View(context);
fakeview.setMinimumHeight(0);
fakeview.setMinimumHeight(0);
return fakeview;
}
}
private void initViewPager() {
viewPager = (ViewPager) findViewById(R.id.viewpager);
List<Fragment> listfragment = new ArrayList<Fragment>();
listfragment.add(new Fragment1());
listfragment.add(new Fragment2());
listfragment.add(new Fragment3());
listfragment.add(new Fragment1());
listfragment.add(new Fragment2());
listfragment.add(new Fragment3());
MyFragmentPagerAdapter myFragmentPagerAdapter = new MyFragmentPagerAdapter(getSupportFragmentManager(), listfragment);
viewPager.setAdapter(myFragmentPagerAdapter);
viewPager.setOnPageChangeListener(this);
}
}
and this is a code of one the fragments:
package com.subhi.navtabs;
import android.os.Bundle;
import android.support.annotation.Nullable;
import android.support.v4.app.Fragment;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
/**
* Created by subhi on 2/9/2016.
*/
public class Fragment1 extends Fragment {
@Nullable
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
View v=inflater.inflate(R.layout.fragment1_layout,container,false);
return v;
}
}
And this is the log cat :
02-09 08:35:36.925 2501-2501/? E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.subhi.navtabs, PID: 2501
java.lang.RuntimeException: Unable to start activity ComponentInfo{com.subhi.navtabs/com.subhi.navtabs.MainActivity}: java.lang.NullPointerException
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2195)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2245)
at android.app.ActivityThread.access$800(ActivityThread.java:135)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1196)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:136)
at android.app.ActivityThread.main(ActivityThread.java:5017)
at java.lang.reflect.Method.invokeNative(Native Method)
at java.lang.reflect.Method.invoke(Method.java:515)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:779)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:595)
at dalvik.system.NativeStart.main(Native Method)
Caused by: java.lang.NullPointerException
at com.subhi.navtabs.MainActivity.initTabHost(MainActivity.java:37)
at com.subhi.navtabs.MainActivity.onCreate(MainActivity.java:28)
at android.app.Activity.performCreate(Activity.java:5231)
at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1087)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2159)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2245)
at android.app.ActivityThread.access$800(ActivityThread.java:135)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1196)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:136)
at android.app.ActivityThread.main(ActivityThread.java:5017)
at java.lang.reflect.Method.invokeNative(Native Method)
at java.lang.reflect.Method.invoke(Method.java:515)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:779)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:595)
at dalvik.system.NativeStart.main(Native Method)
02-09 08:35:36.925 1268-1438/? W/ActivityManager: Force finishing activity com.subhi.navtabs/.MainActivity
02-09 08:35:37.145 1268-1438/? D/dalvikvm: GC_FOR_ALLOC freed 1812K, 26% free 12136K/16264K, paused 10ms, total 10ms
02-09 08:35:37.665 1268-1283/? W/ActivityManager: Activity pause timeout for ActivityRecord{b1549268 u0 com.subhi.navtabs/.MainActivity t6 f}
02-09 08:35:37.735 1402-1402/? W/EGL_emulation: eglSurfaceAttrib not implemented
i don't know where is the problem, if anyone can help me?!
tabHost (with uppercase "H") is different than tabhost.
Your TabHost id is "@+id/tabHost" and you're using android.R.id.tabhost in findViewById() method.
This is why findViewById() return a null object.
To solve this, just change:
From java code,
tabHost = (TabHost) findViewById(android.R.id.tabhost);
to tabHost = (TabHost) findViewById(R.id.tabhost);
From xml, android:id="@+id/tabHost" to android:id="@android:id/tabhost"