Android Studio Can't resolve fragmentActivity and ViewPager imports

Question

I follow the tutorial of developing swipe-able tabs. When I import:

import android.support.v4.app.FragmentActivity;
import android.support.v4.view.ViewPager;

Android Studio shows me cannot resolve the symbol "ViewPager" and "FragmentActivity". How to solve this? thanks.

Below is the entire code of my project.

import android.app.ActionBar;
import android.app.ActionBar.Tab;
import android.app.FragmentTransaction;
import android.os.Bundle;
import android.support.v4.app.FragmentActivity;
import android.support.v4.view.ViewPager;

public class MainActivity extends FragmentActivity implements
    ActionBar.TabListener {

private ViewPager viewPager;
private TabsPagerAdapter mAdapter;
private ActionBar actionBar;
// Tab titles
private String[] tabs = { "Top Rated", "Games", "Movies" };

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);

    // Initilization
    viewPager = (ViewPager) findViewById(R.id.pager);
    actionBar = getActionBar();
    mAdapter = new TabsPagerAdapter(getSupportFragmentManager());

    viewPager.setAdapter(mAdapter);
    actionBar.setHomeButtonEnabled(false);
    actionBar.setNavigationMode(ActionBar.NAVIGATION_MODE_TABS);

    // Adding Tabs
    for (String tab_name : tabs) {
        actionBar.addTab(actionBar.newTab().setText(tab_name)
                .setTabListener(this));
    }

    /**
     * on swiping the viewpager make respective tab selected
     * */
    viewPager.setOnPageChangeListener(new ViewPager.OnPageChangeListener() {

        @Override
        public void onPageSelected(int position) {
            // on changing the page
            // make respected tab selected
            actionBar.setSelectedNavigationItem(position);
        }

        @Override
        public void onPageScrolled(int arg0, float arg1, int arg2) {
        }

        @Override
        public void onPageScrollStateChanged(int arg0) {
        }
    });
}

@Override
public void onTabReselected(Tab tab, FragmentTransaction ft) {
}

@Override
public void onTabSelected(Tab tab, FragmentTransaction ft) {
    // on tab selected
    // show respected fragment view
    viewPager.setCurrentItem(tab.getPosition());
}

@Override
public void onTabUnselected(Tab tab, FragmentTransaction ft) {
}

}

Answer 1

1. Make sure you have downloaded the Android Support Repository using the SDK Manager.
2. Open the build.gradle file for your application.

3. Add the support library to the dependencies section. For example, to add the v4 support library, add the following lines:

   dependencies { ... compile "com.android.support:support-v4:18.0.+" }

Answer 2

I have solved it. I installed everything but I did not import the external library into my library. It was not installed automatically during creation of the new project. So I just opened the project structure and imported the dependencies -> add support-v4 library.

Btw, thanks you guys for helping me a lot and posting the suggestion to me.