Android ViewPager Implementation of Carousel Effect

First, let's take a look at an effect diagram:

When it comes to implementing the carousel effect of ViewPager, PagerAdapter will definitely be used. Let's first introduce this class.

Introduction to PagerAdapter

PagerAdapter is Android.support.v4The classes in the package are an abstract class, directly inheriting from Object, and importing package android.support.v4.view.PagerAdapter can be used.

PagerAdapter is the adapter of viewPager, and viewPager is also in android.support.v4A powerful control added in the extended package, which can realize the sliding effect of the control, such as the sliding effect of the advertisement bar commonly seen in our software, which can be realized by viewPager. Today, we mainly introduce how to use viewPager and override PagerAdapter to realize the sliding effect of the common advertisement bar.

Since it is an abstract class, we create a new class to inherit it and override four methods:

　1.public Object instantiateItem(ViewGroup container, int position)

　2.public void destroyItem(ViewGroup container, int position, Object object)

　3.public int getCount()

　4.public boolean isViewFromObject(View arg0, Object arg1)

MyViewPagerAdapter class:

public class MyViewPagerAdapter extends PagerAdapter {
private List<ImageView> mList;
public MyViewPagerAdapter(List<ImageView> mList){
 this.mList=mList;
}
//When the image to be displayed is cached, this method will be called to initialize the image display
//We add the ImageView we want to display to the ViewGroup
public Object instantiateItem(ViewGroup container, int position) {
 // TODO Auto-generated method stub
 container.addView(mList.get(position));
 return mList.get(position);
}
@Override
//PagerAdapter caches only three images to be displayed, if the sliding image exceeds the cache range, this method will be called to destroy the image
public void destroyItem(ViewGroup container, int position, Object object) {
 // TODO Auto-generated method stub
 container.removeView(mList.get(position));
}
//Get the number of controls to be scrolled
public int getCount() {
 // TODO Auto-generated method stub
 return mList.size();
}
//to determine whether the same photo is displayed, we will compare the two images and then return
public boolean isViewFromObject(View arg0, Object arg1) {
 // TODO Auto-generated method stub
 return arg0==arg1;
}
}

activity_main.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" >
<android.support.v4.view.ViewPager
 android:id="@"+id/vp"
 android:layout_width="match_parent"
 android:layout_height="200dp" />
<LinearLayout
 android:layout_width="match_parent"
 android:layout_height="wrap_content"
 android:layout_alignBottom="@id/vp"
 android:background="#33000000"
 android:orientation="vertical"
 android:paddingBottom="10dp" >
 <LinearLayout
 android:id="@"+id/ll_points"
 android:layout_width="match_parent"
 android:layout_height="wrap_content"
 android:gravity="center_horizontal"
 android:orientation="horizontal"
 android:paddingBottom="10dp" >
 </LinearLayout>
</LinearLayout>
</RelativeLayout>

MainActivity：

public class MainActivity extends Activity {
private ViewPager mVp;
//private TextView tvTitle;
private LinearLayout llPoints;
//private String[] titles;// Store all the titles to be displayed
private int[] images;// Store all the image resource IDs to be displayed
private List<ImageView> list = new ArrayList<ImageView>();;// Store all ImageView objects to be displayed in the ViewPager object
private int prevPosition = 0;
private Handler handler = new Handler() {
 @SuppressLint("HandlerLeak") 
 public void handleMessage(android.os.Message msg) {
 switch (msg.what) {
 case 0:
  // Get the index of the current page of mvp
  int currentItem = mVp.getCurrentItem();
  // The index of the next page to be displayed
  currentItem++;
  // Set the page displayed by ViewPager
  mVp.setCurrentItem(currentItem % list.size());
  break;
 default:
  break;
 }
 };
};
@SuppressWarnings("deprecation")
protected void onCreate(Bundle savedInstanceState) {
 super.onCreate(savedInstanceState);
 setContentView(R.layout.activity_main);
 initView(); 
 // titles = getTitles();
 images = getImages();
 for (int i = 0; i < images.length; i++) {
 ImageView iv = new ImageView(this);
 iv.setBackgroundResource(images[i]);
 list.add(iv);
 //Generate the corresponding number of small dots according to the number of images
 final View view = new View(this);
 view.setBackgroundResource(R.drawable.login__05);
 DisplayMetrics metrics = new DisplayMetrics();
 float width=TypedValue.applyDimension(TypedValue.COMPLEX_UNIT_PX,30, metrics);
 float height=TypedValue.applyDimension(TypedValue.COMPLEX_UNIT_PX, 30, metrics);
 LinearLayout.LayoutParams params=new LinearLayout.LayoutParams((int)width,(int)height);
 params.leftMargin=5;
 view.setLayoutParams(params);
 llPoints.addView(view);
 }
 //Set the title displayed on the first page
 //tvTitle.setText(titles[0]);
 //Set the background image of the small dot when the first page is set
 llPoints.getChildAt(0).setBackgroundResource(R.drawable.login__03);
 //The following encapsulates the ViewPager adapter
 MyViewPagerAdapter adapter=new MyViewPagerAdapter(list);
 mVp.setAdapter(adapter);
 //Set the listener for page changes of the ViewPager object
 mVp.setOnPageChangeListener(new OnPageChangeListener() {
 @Override
 //When the next page is selected
 public void onPageSelected(int arg0) {
  // TODO Auto-generated method stub
  //tvTitle.setText(titles[arg0%list.size()]);
  llPoints.getChildAt(prevPosition).setBackgroundResource(R.drawable.login__05);
  llPoints.getChildAt(arg0).setBackgroundResource(R.drawable.login__03);
  //Set the current point position as the previous point position for the next change
  prevPosition=arg0;
 }
 @Override
 public void onPageScrolled(int arg0, float arg1, int arg2) {
  // TODO Auto-generated method stub
 }
 @Override
 public void onPageScrollStateChanged(int arg0) {
  // TODO Auto-generated method stub
 }
 });
 new Thread(new Runnable() {
 @Override
 public void run() {
  // TODO Auto-generated method stub
  while (true) {
  SystemClock.sleep(3000);
  handler.sendEmptyMessage(0);
  }
 }
 }).start();
}
private void initView() {
 // TODO Auto-generated method stub
 mVp = (ViewPager) findViewById(R.id.vp);
 //tvTitle = (TextView) findViewById(R.id.tv_title);
 llPoints = (LinearLayout) findViewById(R.id.ll_points);
}
private int[] getImages(){
 return new int[]{R.drawable.banner_01,R.drawable.banner_02,R.drawable.banner_03};
}
}

That's all for this article. I hope it will be helpful to everyone's learning and that everyone will support the Yelling Tutorial more.

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