用viewpager实现图片轮播

应用中常常遇到图片轮播的需求，这时候就需要用到viewpager这个组件。viewpager是android support v4 中提供的一个组件。viewpager使用需要以下几步骤：

1.在布局文件中添加viewpager组件

<android.support.v4.view.ViewPager
        android:id="@+id/vp_adv"
        android:layout_width="match_parent"
        android:layout_height="match_parent">
    </android.support.v4.view.ViewPager>

ViewPager路径要写完整，否则会出现问题；

2.创建PagerAdapter,PagerAdapter是viewPager的内容提供者，这里我们的图片就是由PagerAdapter提供给viewpager展示的。同样PagerAdapter也在support v4包中。具体如下所示：

public class AdvertisingAdapter extends PagerAdapter {

    private List<View> mList;

    public AdvertisingAdapter() {
        mList = new ArrayList<View>();
    }

    public void setData(List<View> list) {
        if (list != null) {
            mList.clear();
            mList.addAll(list);
            notifyDataSetChanged();
        }
    }

    @Override
    public int getCount() {
        return mList.size();
    }

    @Override
    public boolean isViewFromObject(View view, Object object) {
        return object == view;
    }

    @Override
    public void destroyItem(ViewGroup container, int position, Object object) {
        container.removeView(mList.get(position));
    }

    @Override
    public Object instantiateItem(ViewGroup container, int position) {
        container.addView(mList.get(position), 0);
        return mList.get(position);
    }
}

3.初始化ViewPager,PagerAdapter

    protected void setupView() {
        mPagerAdapter = new AdvertisingAdapter();
        mViewPager = (ViewPager) findViewById(R.id.vp_adv);
        mViewPager .setAdapter(mPagerAdapter );
        mAdvertising.addOnPageChangeListener(this);
    }    

待PagerAdapter填充图片数据后，ViewPager便可以将图片展示出来。

4.添加“.”。基本所有应用使用到ViewPager都会使用“.”标识当前坐标，即展示到哪一页。如下代码添加点号：

添加布局文件

<LinearLayout
        android:id="@+id/viewGroup"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_alignParentBottom="true"
        android:layout_alignParentRight="true"
        android:layout_marginBottom="20dp"
        android:layout_marginRight="20dp"
        android:orientation="horizontal"></LinearLayout>

在布局里面动态添加“点”的view

        imageViews = new ImageView[advPics.size()];
        ImageView imageView;
        for (int i = 0; i < advPics.size(); i++) {
            imageView = new ImageView(this);
            imageView.setLayoutParams(new LinearLayout.LayoutParams(50, 50));
            imageView.setPadding(15, 15, 15, 15);
            imageViews[i] = imageView;
            if (i == 0) {
                imageViews[i].setImageResource(R.drawable.dot_focus);
            } else {
                imageViews[i].setImageResource(R.drawable.dot_blur);
            }
            llDot.addView(imageViews[i]);
        }

拖动ViewPager时，坐标点动态改变

　　@Override
    public void onPageSelected(int position) {
        LogUtils.d("enter onPageSelected method");
        
        for (int i = 0; i < advPics.size(); i++) {
            imageViews[position].setImageResource(R.drawable.dot_focus);
            if (position != i) {
                imageViews[i].setImageResource(R.drawable.dot_blur);
            }
        }
    }

5.自动轮播。大多数时候，我们展示图片时需要其自动轮播的。

启动线程，控制轮播时间，及发出轮播请求给UI线程

private void initAutoThread() {
        Runnable runnable = new Runnable() {
            @Override
            public void run() {
                while (true) {
                    if (!isPlayPaused.get()) {
                        sendUiMessage(MSG_UI_CHANGE_ADV_PIC, what.get(), 0, null);
                        what.incrementAndGet();
                        if (what.get() > advPics.size() - 1) {
                            what.getAndAdd(-advPics.size());
                        }
                    }
                    if (needExit.get()) {
                        break;
                    }
                    try {
                        Thread.sleep(8000);
                    } catch (InterruptedException e) {
                        e.printStackTrace();
                    }
                }
            }
        };
        Thread thread = new Thread(runnable);
        thread.setName("Carousel");
        thread.start();
    }

UI 线程收到请求后，对显示的图片进行更改

 mViewPager.setCurrentItem(msg.arg1);