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

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

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

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