《Android 基础（十七）》 ViewPager

package mraz.com.opensourcedemo;

import android.support.v4.view.ViewPager;
import android.support.v4.widget.ViewDragHelper;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.util.Log;
import android.view.View;
import android.view.Window;

import java.util.ArrayList;

public class MainActivity extends AppCompatActivity {

    ArrayList<String> sourceList;
    private static final float MIN_SCALE = 0.5f;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);

        setContentView(R.layout.activity_main);
        ViewPager viewPager = (ViewPager) findViewById(R.id.viewpager);
        MyPagerAdapter myPagerAdapter = new MyPagerAdapter(getSupportFragmentManager());
        viewPager.setAdapter(myPagerAdapter);

    }

}

package mraz.com.opensourcedemo;

import android.support.v4.app.Fragment;
import android.support.v4.app.FragmentManager;
import android.support.v4.app.FragmentPagerAdapter;

/**
 * Created by Mraz on 2016/7/8.
 */
public class MyPagerAdapter extends FragmentPagerAdapter {

    public static final String[] titles = {"Android"," Pet","Gift"};

    public MyPagerAdapter(FragmentManager fm) {
        super(fm);
    }

    @Override
    public Fragment getItem(int position) {
        switch (position) {
            case 0:
                return new FirstFragment();
            case 1:
                return new SecondFragment();
            case 2:
                return new ThreeFragment();
        }
        return null;
    }

    @Override
    public int getCount() {
        return 3;
    }
}

private static final float MIN_SCALE = 0.5f;
...
viewPager.setPageTransformer(true, new ViewPager.PageTransformer() {
    @Override
    public void transformPage(View view, float position) {

        int pageWidth = view.getWidth();

        if (position < -1) { // [-Infinity,-1)
            // This page is way off-screen to the left.
            view.setAlpha(0);

        } else if (position <= 0) { // [-1,0]
            // Use the default slide transition when moving to the left page
            view.setAlpha(1 + position);
            view.setTranslationX(0);

            float scaleFactor = MIN_SCALE
                    + (1 - MIN_SCALE) * (1 - Math.abs(position));
            view.setScaleX(scaleFactor);
            view.setScaleY(scaleFactor);

        } else if (position <= 1) { // (0,1]
            // Fade the page out.
            view.setAlpha(1 - position);

            // Counteract the default slide transition
            view.setTranslationX(pageWidth * -position);

            // Scale the page down (between MIN_SCALE and 1)
            float scaleFactor = MIN_SCALE
                    + (1 - MIN_SCALE) * (1 - Math.abs(position));
            view.setScaleX(scaleFactor);
            view.setScaleY(scaleFactor);

        } else { // (1,+Infinity]
            // This page is way off-screen to the right.
            view.setAlpha(0);
        }
    }
});

/**
 * A PageTransformer is invoked whenever a visible/attached page is scrolled.
 * This offers an opportunity for the application to apply a custom transformation
 * to the page views using animation properties.
 *
 * <p>As property animation is only supported as of Android 3.0 and forward,
 * setting a PageTransformer on a ViewPager on earlier platform versions will
 * be ignored.</p>
 */
public interface PageTransformer {
    /**
     * Apply a property transformation to the given page.
     *
     * @param page Apply the transformation to this page
     * @param position Position of page relative to the current front-and-center
     *                 position of the pager. 0 is front and center. 1 is one full
     *                 page position to the right, and -1 is one page position to the left.
     */
    public void transformPage(View page, float position);
}

viewPager.addOnPageChangeListener(new ViewPager.OnPageChangeListener() {
    @Override
    public void onPageScrolled(int position, float positionOffset, int positionOffsetPixels) {
        Log.e(TAG, "onPageScrolled position = " + position + " positionOffset = " + positionOffset + " positionOffsetPixels = " + positionOffsetPixels);
    }

    @Override
    public void onPageSelected(int position) {
        Log.e(TAG, "onPageSelected position = " + position);
    }

    @Override
    public void onPageScrollStateChanged(int state) {
        Log.e(TAG, "onPageScrollStateChanged state = " + state);
    }
});

/**
 * Callback interface for responding to changing state of the selected page.
 */
public interface OnPageChangeListener {

    /**
     * This method will be invoked when the current page is scrolled, either as part
     * of a programmatically initiated smooth scroll or a user initiated touch scroll.
     *
     * @param position Position index of the first page currently being displayed.
     *                 Page position+1 will be visible if positionOffset is nonzero.
     * @param positionOffset Value from [0, 1) indicating the offset from the page at position.
     * @param positionOffsetPixels Value in pixels indicating the offset from position.
     */
    public void onPageScrolled(int position, float positionOffset, int positionOffsetPixels);

    /**
     * This method will be invoked when a new page becomes selected. Animation is not
     * necessarily complete.
     *
     * @param position Position index of the new selected page.
     */
    public void onPageSelected(int position);

    /**
     * Called when the scroll state changes. Useful for discovering when the user
     * begins dragging, when the pager is automatically settling to the current page,
     * or when it is fully stopped/idle.
     *
     * @param state The new scroll state.
     * @see ViewPager#SCROLL_STATE_IDLE
     * @see ViewPager#SCROLL_STATE_DRAGGING
     * @see ViewPager#SCROLL_STATE_SETTLING
     */
    public void onPageScrollStateChanged(int state);
}