本文转自:http://blog.csdn.net/smartbetter/article/details/53083816
我们经常会看到有一些app的banner界面可以实现循环播放多个广告图片和手动滑动循环的效果。看到那样的效果,相信大家都会想到ViewPager,但是ViewPager并不支持循环翻页,所以要实现循环还得需要自己去动手。最后还有一个问题就是翻页到最后一页如何平滑过渡到首页的问题。这些都源于有人私信问我ViewPager广告条如何平滑过渡的问题,出于这个问题,我想着亲自实现并分享下吧,本篇就是为了解决这些问题而写的。
1.初始化布局
我们先来写一个ViewPager广告条的布局:
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android" 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="210dp"/> <LinearLayout android:layout_width="match_parent" android:layout_height="wrap_content" android:layout_alignBottom="@id/vp" android:background="#55000000" android:gravity="center_horizontal" android:orientation="vertical" android:padding="5dp"> <TextView android:id="@+id/tv_img_desc" android:layout_width="wrap_content" android:layout_height="wrap_content" android:text="这里是广告标题" android:textColor="#ffffff" android:textSize="16sp"/> <LinearLayout android:id="@+id/ll_dot_group" android:layout_width="wrap_content" android:layout_height="wrap_content" android:orientation="horizontal"/> </LinearLayout></RelativeLayout>
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此时的效果如下,是不是已经有了点模样:
2.Activity实现
接下来进入到关键的实现代码,当然,Activity实现也难不倒我们,其中ViewPager数据,为了方便,本篇就直接用本地数据进行模拟了。而在实际项目开发数据大都来自网络。
public class MainActivity extends AppCompatActivity implements ViewPager.OnPageChangeListener { private List<ImageView> vpLists; private LinearLayout ll_dot_group; private String[] imageDescArrs; private TextView tv_img_desc; private ViewPager vp; private boolean isSwitchPager = false; private int previousPosition = 0; private Handler handler = new Handler() { public void handleMessage(android.os.Message msg) { vp.setCurrentItem(vp.getCurrentItem() + 1); } }; @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.activity_main); initView(); } /** * 初始化view */ private void initView() { vp = (ViewPager) findViewById(R.id.vp); ll_dot_group = (LinearLayout) findViewById(R.id.ll_dot_group); tv_img_desc = (TextView) findViewById(R.id.tv_img_desc); initViewPagerData(); vp.setAdapter(new ViewpagerAdapter()); int item = Integer.MAX_VALUE / 2 - (Integer.MAX_VALUE / 2 % vpLists.size()); vp.setCurrentItem(item); ll_dot_group.getChildAt(previousPosition).setEnabled(true); tv_img_desc.setText(imageDescArrs[previousPosition]); vp.addOnPageChangeListener(this); new Thread() { public void run() { while (!isSwitchPager) { SystemClock.sleep(3000); handler.sendEmptyMessage(0); } } }.start(); } /** * 初始化ViewPager的数据 */ private void initViewPagerData() { imageDescArrs = new String[]{"标题1", "标题2", "标题3", "标题4", "标题5"}; vpLists = new ArrayList<ImageView>(); int imgIds[] = {R.drawable.a, R.drawable.b, R.drawable.c, R.drawable.d, R.drawable.e}; ImageView iv; View dotView; for (int i = 0; i < imgIds.length; i++) { iv = new ImageView(this); iv.setBackgroundResource(imgIds[i]); vpLists.add(iv); dotView = new View(getApplicationContext()); dotView.setBackgroundResource(R.drawable.selector_dot); LayoutParams params = new LayoutParams(15, 15); if (i != 0) { params.leftMargin = 15; } dotView.setLayoutParams(params); dotView.setEnabled(false); ll_dot_group.addView(dotView); } } /** * 定义数据适配器 */ private class ViewpagerAdapter extends PagerAdapter { @Override public int getCount() { return Integer.MAX_VALUE; } @Override public boolean isViewFromObject(View arg0, Object arg1) { return arg0 == arg1; } @Override public Object instantiateItem(ViewGroup container, int position) { int newposition = position % vpLists.size(); ImageView iv = vpLists.get(newposition); container.addView(iv); return iv; } @Override public void destroyItem(ViewGroup container, int position, Object object) { container.removeView((View) object); } } @Override public void onPageSelected(int position) { int newposition = position % vpLists.size(); ll_dot_group.getChildAt(newposition).setEnabled(true); ll_dot_group.getChildAt(previousPosition).setEnabled(false); tv_img_desc.setText(imageDescArrs[newposition]); previousPosition = newposition; } @Override protected void onDestroy() { isSwitchPager = true; super.onDestroy(); } @Override public void onPageScrollStateChanged(int state) { } @Override public void onPageScrolled(int position, float positionOffset, int positionOffsetPixels) { }}
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如上我们就解决了平滑过渡的问题,关键的地方就是ViewpagerAdapter:
getCount方法我们返回Integer.MAX_VALUE
public int getCount() { return Integer.MAX_VALUE;}
初始化每个条目要显示的内容,我们拿着position位置 % 集合.size
@Overridepublic Object instantiateItem(ViewGroup container, int position) { int newposition = position % vpLists.size(); ImageView iv = vpLists.get(newposition); container.addView(iv); return iv;}
此时我们发现已经最后一个广告可以平滑过渡了,但是还有一个问题就是,那从第一张开始,我们往左滑呢?其实也很容易解决,就是设置第一个条目为Integer.MAX_VALUE的中间位置就可以了,我们来到initView方法中,设置当前viewpager要显示第几个条目:
int item = Integer.MAX_VALUE / 2 - (Integer.MAX_VALUE / 2 % vpLists.size())vp.setCurrentItem(item)
问题完美解决。
用到的Shape相关资源如下:
selector_dot.xml
<?xml version="1.0" encoding="utf-8"?><selector xmlns:android="http://schemas.android.com/apk/res/android"> <item android:drawable="@drawable/dot_enable" android:state_enabled="true"></item> <item android:drawable="@drawable/dot_normal" android:state_enabled="false"></item></selector>
dot_enable.xml
<?xml version="1.0" encoding="utf-8"?><shape xmlns:android="http://schemas.android.com/apk/res/android" > <corners android:radius="5dp"/> <solid android:color="@android:color/white"/></shape>
dot_normal.xml
<?xml version="1.0" encoding="utf-8"?><shape xmlns:android="http://schemas.android.com/apk/res/android" > <corners android:radius="5dp"/> <solid android:color="@android:color/darker_gray"/></shape>
来看看效果图:
到此,一个平滑过渡的ViewPager广告条已经完美实现了。
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