Android借助Handler,实现ViewPager中页面的自动切换

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在很多电商网页及app上都有自动切换的商品的推广快,感觉体验挺不错的,正好今天学习使用ViewPager,因此也实现了一个功能类似的demo。

下面是其中的两个截图:

Android借助Handler,实现ViewPager中页面的自动切换         Android借助Handler,实现ViewPager中页面的自动切换

实现一个自动播放功能的ViewPager,要做的主要有以下的几个部分:



  • 实现一个ViewPagerAdapter,用于为ViewPager提供展示内容(例如上面的两张小猫图片)
public class ViewPagerAdapter extends PagerAdapter {
private List<View> mData;
public ViewPagerAdapter(List<View> mData) {
this.mData = mData;
}
@Override
public int getCount() {
return mData.size();
}
@Override
public boolean isViewFromObject(View arg0, Object arg1) {
return arg0 == arg1;
}
@Override
public Object instantiateItem(ViewGroup container, int position) {
View v = mData.get(position);
container.addView(v);
return v;
}
@Override
public void destroyItem(ViewGroup container, int position, Object object) {
//			super.destroyItem(container, position, object);
container.removeView(mData.get(position));
}
}


  • 实现一个OnPageChangeListener,这样在页面切换后可以提示当前页面所在的位置(例如上图中,左下角的3个圆点,红色表示当前页面)
private class ViewPageChangeListener implements OnPageChangeListener {
@Override
public void onPageScrollStateChanged(int arg0) {
}
@Override
public void onPageScrolled(int arg0, float arg1, int arg2) {
}
//监听页面改变事件来改变viewIndicator中的指示图片
@Override
public void onPageSelected(int arg0) {
int len = viewIndicator.getChildCount();
for(int i = 0; i < len; ++i)
viewIndicator.getChildAt(i).setBackgroundResource(R.drawable.tip_normal);
viewIndicator.getChildAt(arg0).setBackgroundResource(R.drawable.tip_select);
}
}


  • 实现一个Handler,用于在一定的时间间隔后修改UI(将当前显示的图片切换到下一个)

private Handler mHandler = new Handler() {
public void handleMessage(android.os.Message msg) {
switch(msg.what) {
case 1:
int totalcount = pagers.size();//autoChangeViewPager.getChildCount();
int currentItem = autoChangeViewPager.getCurrentItem();
int toItem = currentItem + 1 == totalcount ? 0 : currentItem + 1;
Log.i(TAG, "totalcount: " + totalcount + "   currentItem: " + currentItem + "   toItem: " + toItem);
autoChangeViewPager.setCurrentItem(toItem, true);
//每两秒钟发送一个message,用于切换viewPager中的图片
this.sendEmptyMessageDelayed(1, 2000);
}
}
	};



上面这3段就是主要的代码,除此之外,还需要在onResume()中发送一个起始message以及在onStop()中停止ViewPager页面的自动切换等内容。

完整的代码如下:

public class MainActivity extends Activity {
	private static final String TAG = MainActivity.class.getSimpleName();
	private ViewPager autoChangeViewPager;
//用来指示当前显示图片所在位置
	private LinearLayout viewIndicator;
//包含要在ViewPager中显示的图片
	private List<View> pagers;
	@Override
	protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
autoChangeViewPager = (ViewPager) findViewById(R.id.autoVP);
viewIndicator = (LinearLayout) findViewById(R.id.vpindicator);
initAdapter();
//监听页面改变事件来改变viewIndicator中的指示图片
autoChangeViewPager.setOnPageChangeListener(new ViewPageChangeListener());
}
private void initAdapter() {
//即将在viewPager中展示的图片资源
int[] imgs = {R.drawable.i1, R.drawable.i2, R.drawable.i3};
//init pagers;
pagers = new ArrayList<View>();
LinearLayout.LayoutParams img_params = new LayoutParams(
LayoutParams.MATCH_PARENT, LayoutParams.MATCH_PARENT
);
for(int i = 0; i < imgs.length; ++i) {
ImageView iv = new ImageView(this);
iv.setBackgroundResource(imgs[i]);
iv.setLayoutParams(img_params);
final int index = i;
iv.setOnClickListener(new OnClickListener() {
//当viewPager中的图片被点击后,跳转到新的activity
@Override
public void onClick(View v) {
Intent i = new Intent(MainActivity.this, InvokedActivity.class);
i.putExtra("name", "cat " + index);
MainActivity.this.startActivity(i);
}
});
pagers.add(iv);
}
autoChangeViewPager.setAdapter(new ViewPagerAdapter(pagers));
//init indicator
LinearLayout.LayoutParams ind_params = new LayoutParams(
LayoutParams.WRAP_CONTENT, LayoutParams.WRAP_CONTENT
);
for(int i = 0; i < imgs.length; ++i) {
ImageView iv = new ImageView(this);
if(i == 0)
iv.setBackgroundResource(R.drawable.tip_select);
else
iv.setBackgroundResource(R.drawable.tip_normal);
iv.setLayoutParams(ind_params);
viewIndicator.addView(iv);
}
	}
@Override
	protected void onResume() {
super.onResume();
//activity启动两秒钟后,发送一个message,用来将viewPager中的图片切换到下一个
mHandler.sendEmptyMessageDelayed(1, 2000);
	}
@Override
	protected void onStop() {
super.onStop();
//停止viewPager中图片的自动切换
mHandler.removeMessages(1);
	}
public class ViewPagerAdapter extends PagerAdapter {
private List<View> mData;
public ViewPagerAdapter(List<View> mData) {
this.mData = mData;
}
@Override
public int getCount() {
return mData.size();
}
@Override
public boolean isViewFromObject(View arg0, Object arg1) {
return arg0 == arg1;
}
@Override
public Object instantiateItem(ViewGroup container, int position) {
View v = mData.get(position);
container.addView(v);
return v;
}
@Override
public void destroyItem(ViewGroup container, int position, Object object) {
//			super.destroyItem(container, position, object);
container.removeView(mData.get(position));
}
}
private class ViewPageChangeListener implements OnPageChangeListener {
@Override
public void onPageScrollStateChanged(int arg0) {
}
@Override
public void onPageScrolled(int arg0, float arg1, int arg2) {
}
//监听页面改变事件来改变viewIndicator中的指示图片
@Override
public void onPageSelected(int arg0) {
int len = viewIndicator.getChildCount();
for(int i = 0; i < len; ++i)
viewIndicator.getChildAt(i).setBackgroundResource(R.drawable.tip_normal);
viewIndicator.getChildAt(arg0).setBackgroundResource(R.drawable.tip_select);
}
}
private Handler mHandler = new Handler() {
public void handleMessage(android.os.Message msg) {
switch(msg.what) {
case 1:
int totalcount = pagers.size();//autoChangeViewPager.getChildCount();
int currentItem = autoChangeViewPager.getCurrentItem();
int toItem = currentItem + 1 == totalcount ? 0 : currentItem + 1;
Log.i(TAG, "totalcount: " + totalcount + "   currentItem: " + currentItem + "   toItem: " + toItem);
autoChangeViewPager.setCurrentItem(toItem, true);
//每两秒钟发送一个message,用于切换viewPager中的图片
this.sendEmptyMessageDelayed(1, 2000);
}
}
	};
}




布局文件如下:(上面代码中的InvokedActivity非常简单,此处就省略了)

<FrameLayout 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/autoVP"
android:layout_width="match_parent"
android:layout_height="match_parent" />
<LinearLayout
android:id="@+id/vpindicator"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:layout_gravity="bottom"
android:orientation="horizontal" />
</FrameLayout>



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