Android ViewPager小圆点指示器

一个很常用的功能，一个ViewPager会自动滚动，并且有一排小圆点黑和白来指示当前的滚动进度

首先写一个ViewPager的适配器，这里这个适配器为了方便里面的元素全都是ImageView

import android.content.Context;
import android.os.Handler;
import android.support.v4.view.PagerAdapter;
import android.support.v4.view.ViewPager;
import android.view.View;
import android.view.ViewGroup;
import android.view.animation.Interpolator;
import android.widget.ImageView;
import android.widget.LinearLayout;
import android.widget.Scroller;

/**
 * Created by Administrator on 2016/2/24.
 */
public class HomeHomeBannerAdapter extends PagerAdapter{
    private Context context;
    private ImageView[] eventImageViews;
    private String[] eventUrls;
    int destWidth,destHeight;

    public HomeHomeBannerAdapter(Context context, String[] eventUrls,int destWidth,int destHeight) {
        this.context = context;
        this.eventUrls = eventUrls;
        this.destHeight = destHeight;
        this.destWidth = destWidth;
        initImageViews();
    }

    /**
     * 初始化viewPager里的几张图
     */
    private void initImageViews(){
        if(eventUrls==null)return;
        eventImageViews = new ImageView[eventUrls.length];
        for (int i=0;i<eventUrls.length;i++) {
            eventImageViews[i] = new ImageView(context);
            eventImageViews[i].setLayoutParams(new LinearLayout.LayoutParams(destWidth, destHeight));
            eventImageViews[i].setPadding(0, 0, 0, 0);
            eventImageViews[i].setScaleType(ImageView.ScaleType.FIT_XY);
            JImageUtils.loadImageFromServerByUrl(context,eventImageViews[i],eventUrls[i]);
        }//显示图片
    }

    @Override
    public void destroyItem(ViewGroup container, int position, Object object) {
        if (eventImageViews != null && eventImageViews.length > position && position >= 0)
            container.removeView(eventImageViews[position]);

    }

    @Override
    public Object instantiateItem(ViewGroup container, int position) {
        container.addView(eventImageViews[position], 0);
        return eventImageViews[position];
    }

    @Override
    public int getCount() {return eventUrls==null?0:eventUrls.length;}

    @Override
    public boolean isViewFromObject(View arg0, Object arg1) {
        return arg0 == arg1;
    }
//ViewPager监听器集成到内部类去
    static public class EventViewPagerChangeListener implements ViewPager.OnPageChangeListener {
        LinearLayout llGuideGroup;
        int oldEventPosition;
        int currentItem;

        public EventViewPagerChangeListener(LinearLayout llGuideGroup){
            this.llGuideGroup = llGuideGroup;
        }

        @Override
        public void onPageScrolled(int position, float positionOffset, int positionOffsetPixels) {}

        /**
         * 控制小点的白色还是黑色的显示
         * @param position
         */
        public void onPageSelected(int position) {
            llGuideGroup.getChildAt(oldEventPosition).setBackgroundResource(R.drawable.dot_normal);//黑色点
            llGuideGroup.getChildAt(position).setBackgroundResource(R.drawable.dot_focused);//白色点
            oldEventPosition = position;
            currentItem = position;
        }

        @Override
        public void onPageScrollStateChanged(int state) {

        }
    }

    /**
     * 控制viewpager自动滑动的定时任务
     */
    public static class ScrollTask implements Runnable {
        EventViewPagerChangeListener listener;
        ViewPager vpEvent;
        int eventSize;
        Handler handler;
        public ScrollTask(EventViewPagerChangeListener listener,final ViewPager vpEvent, int eventSize){
            this.listener = listener;
            this.vpEvent = vpEvent;
            this.eventSize = eventSize;
            handler = new Handler();
        }
        public void run() {
            if(listener==null||vpEvent==null||eventSize==0)return;
            listener.currentItem = (listener.currentItem + 1) % eventSize;
            Log.i("Alex","currentItem是"+listener.currentItem);
            handler.post(new Runnable() {
                @Override
                public void run() {
                    vpEvent.setCurrentItem(listener.currentItem); // 通过Handler切换图片
                }
            });
        }
    }

    public static class FixedSpeedScroller extends Scroller {
        private static final int mDuration = 400;
        private int eventCount;

        public FixedSpeedScroller(Context context, Interpolator interpolator,int eventCount) {
            super(context, interpolator);
            this.eventCount = eventCount;
        }

        @Override
        public void startScroll(int startX, int startY, int dx, int dy, int duration) {
            if (duration % 100 == 0 && duration > 0) {
                //"现在是自动划"
                if (duration / 100 == eventCount) super.startScroll(startX, startY, dx, dy, 1);//如果是最后一张
                else super.startScroll(startX, startY, dx, dy, mDuration);

            } else {
                // "现在是手动划"
                super.startScroll(startX, startY, dx, dy, 80);
            }
        }
    }
}

在上面适配器的内部类有一个监听器，这个监听器里有一个成员LinearLayout llGuideGroup，这个线性布局里面装有几个小点，下面是这个布局的定义：

<RelativeLayout
        android:id="@+id/rlEvents"
        android:layout_width="match_parent"
        android:layout_height="200dp"
        android:visibility="gone">

        <android.support.v4.view.ViewPager
            android:id="@+id/vpEvent"
            android:layout_width="match_parent"
            android:layout_height="200dp"
            android:background="@color/black666666" />

        <LinearLayout
            android:id="@+id/llGuideGroup"
            android:layout_width="match_parent"
            android:layout_height="10dp"
            android:layout_alignParentBottom="true"
            android:layout_marginBottom="10dp"
            android:layout_centerHorizontal="true"
            android:gravity="center"
            android:orientation="horizontal" >

        </LinearLayout>
</RelativeLayout>

设置小圆点的数量并初始化监听器

/**
     * 向一个线性布局里添加小圆点，具体的控制逻辑在listener里
     * @param llGuideGroup
     * @param count 要添加多少个小圆点
     */
    public EventViewPagerChangeListener addViewPagerDots(LinearLayout llGuideGroup,ViewPager vpEvents,int count){
        if(llGuideGroup==null||vpEvents==null||count<1)return null;
        LinearLayout.LayoutParams lp = new LinearLayout.LayoutParams(15, 15);
        lp.leftMargin = 5;
        lp.rightMargin = 5;
        for(int i=0;i<count;i++){
            ImageView imageView = new ImageView(llGuideGroup.getContext());
            imageView.setLayoutParams(lp);
            imageView.setBackgroundResource(i==0?R.drawable.dot_focused:R.drawable.dot_normal);
            llGuideGroup.addView(imageView);
        }
        //控制小圆点显示的监听器
        EventViewPagerChangeListener listener = new EventViewPagerChangeListener(llGuideGroup);
        vpEvents.addOnPageChangeListener(listener);
        return listener;
    }

通过多线程实现定时切换页面

HomeHomeBannerAdapter.EventViewPagerChangeListener listener = producer.addViewPagerDots(holder.llGuideGroup,holder.viewPager,eventUrls.length);//添加用于指示的小圆点
                    // 当Activity显示出来后，每3秒钟切换一次图片显示
                    ScheduledExecutorService scheduledExecutorService = Executors.newSingleThreadScheduledExecutor();
                    scheduledExecutorService.scheduleAtFixedRate(new HomeHomeBannerAdapter.ScrollTask(listener,holder.viewPager,eventUrls.length), 3, 3, TimeUnit.SECONDS);

设置自定义滚动器降低viewPager的切换速度

/**
     * 给ViewPager设置自定义的滚动器，降低默认的滚动速度
     * @param vpEvent
     */
    public void setViewPagerScroller(ViewPager vpEvent){
        if(vpEvent==null)return;
        Field mField;
        Scroller mScroller;
        try {
            mField = ViewPager.class.getDeclaredField("mScroller");
            mField.setAccessible(true);
            mScroller = new HomeHomeBannerAdapter.FixedSpeedScroller(vpEvent.getContext(), new AccelerateInterpolator(),vpEvent.getChildCount());
            try {
                mField.set(vpEvent, mScroller);
            } catch (IllegalAccessException e) {
                e.printStackTrace();
            }
        } catch (NoSuchFieldException e) {
            e.printStackTrace();
        }
    }

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