原理图
ViewPager循环、自动滚动，这种效果很常见，一般app首页都会有焦点图、或者用户引导页面。第三方比较好用的我推荐阿里开源的UltraViewPager，毕竟大公司的，用着放心吧。轮子虽好，不过自己也还是需要会写吧。
有2种方案实现循环滚动，一种是在PagerAdapter设置最大数量为int最大值，另一种就是本文实现的。前一种感觉有点奇怪，如果不带自动循环滚动的话还可以用，毕竟用户一般不会切换这么多次能看到头。而对于循环滚动的话，需要本文的类似思路实现起来比较好一点吧，原理看上图即可。例子效果图在最后。
import android.content.Context;import android.os.Handler;import android.os.Message;import android.support.annotation.AttrRes;import android.support.annotation.NonNull;import android.support.annotation.Nullable;import android.support.v4.view.PagerAdapter;import android.support.v4.view.ViewPager;import android.util.AttributeSet;import android.util.Log;import android.view.Gravity;import android.view.View;import android.view.ViewGroup;import android.widget.FrameLayout;import android.widget.LinearLayout;/**
* 封装的viewpager
* Created by WZH on 2017/12/14.
*/public class AutoScrollViewPager<T extends PagerAdapter> extends FrameLayout { private ViewPager viewPager ; private PagerAdapter mAdapter ; private LinearLayout mLinearLayout ; private Context mContext ; private int pageMargin = 0 ; private int oldPosition = 0 ; //上一个位置
private int currentIndex = 1 ; //当前位置
private static long time = 3000 ; //自动播放时间
private static boolean autoPlay = true ; //是否自动播放
private Handler handler = new Handler(){ @Override
public void handleMessage(Message msg) {
play();
}
}; private Runnable runnable = new Runnable() { @Override
public void run() {
viewPager.setCurrentItem(++currentIndex);
}
}; public AutoScrollViewPager(@NonNull Context context) { this(context,null);
} public AutoScrollViewPager(@NonNull Context context, @Nullable AttributeSet attrs) { this(context, attrs,0);
} public AutoScrollViewPager(@NonNull Context context, @Nullable AttributeSet attrs, @AttrRes int defStyleAttr) { super(context, attrs, defStyleAttr);
init();
} /**
* 动态添加viewpager和小圆点
*/
private void init() {
mContext = getContext() ;
setLayerType(View.LAYER_TYPE_SOFTWARE, null);
setClipChildren(false);
pageMargin = getResources().getDimensionPixelSize(R.dimen.page_margin);
viewPager = new ViewPager(mContext);
LayoutParams vparams = new LayoutParams(ViewGroup.LayoutParams.MATCH_PARENT,
ViewGroup.LayoutParams.MATCH_PARENT);
vparams.leftMargin = pageMargin * 2;
vparams.rightMargin = pageMargin * 2 ;
viewPager.setLayoutParams(vparams);
addView(viewPager);
mLinearLayout = new LinearLayout(mContext);
LayoutParams params = new LayoutParams(ViewGroup.LayoutParams.MATCH_PARENT,
ViewGroup.LayoutParams.WRAP_CONTENT);
params.gravity = Gravity.BOTTOM ;
mLinearLayout.setGravity(Gravity.CENTER);
mLinearLayout.setOrientation(LinearLayout.HORIZONTAL);
addView(mLinearLayout,params);
} @Override
protected void onAttachedToWindow() { super.onAttachedToWindow();
play();
} @Override
protected void onDetachedFromWindow() { super.onDetachedFromWindow();
cancel();
} /**
* 初始化viewpager
*/
private void initViewPager() { if (mAdapter==null){ return;
}
viewPager.setCurrentItem(currentIndex); //设置红缓存的页面数
viewPager.setOffscreenPageLimit(1); // 设置2张图之前的间距。
viewPager.setPageMargin(pageMargin);// viewPager.setPageTransformer(true, new ZoomOutPageTransformer());
viewPager.addOnPageChangeListener(new ViewPager.OnPageChangeListener() { @Override
public void onPageScrolled(int position, float positionOffset,int positionOffsetPixels) {
} @Override
public void onPageSelected(int position) { if (position==0){
currentIndex = mAdapter.getCount()-2 ;
}else if (position == mAdapter.getCount()-1){
currentIndex = 1 ;
}else {
currentIndex = position ;
} //此处currentIndex是从1开始的，要注意
mLinearLayout.getChildAt(oldPosition).setEnabled(false);
mLinearLayout.getChildAt(currentIndex-1).setEnabled(true);
oldPosition = currentIndex-1 ;
Log.e("wenzhihao","position=="+position+",currentIndex="+currentIndex);
} @Override
public void onPageScrollStateChanged(int state) { if(state==ViewPager.SCROLL_STATE_IDLE){
viewPager.setCurrentItem(currentIndex,false);
play();
}else if(state==ViewPager.SCROLL_STATE_DRAGGING){
cancel();
}
}
});
setIndicatorDot();
mLinearLayout.getChildAt(0).setEnabled(true);
} /**
* 播放，根据autoplay
*/
public void play(){ if (autoPlay){
handler.postDelayed(runnable,time);
}else {
handler.removeCallbacks(runnable);
}
} /**
* 取消播放
*/
public void cancel(){
handler.removeCallbacks(runnable);
} /**
* 设置小圆点
*/
private void setIndicatorDot() { for (int i = 0;i<mAdapter.getCount()-2;i++){ //添加底部灰点
View v = new View(mContext);
v.setBackgroundResource(R.drawable.bg_dot);
v.setEnabled(false); //指定其大小
LinearLayout.LayoutParams params = new LinearLayout.LayoutParams(20,20); if (i != 0)
params.leftMargin = 20;
params.bottomMargin = 20;
v.setLayoutParams(params);
mLinearLayout.addView(v);
}
} /**
* 设置适配器
* @param adpter
*/
public void setAdapter(T adpter){
mAdapter = adpter ;
viewPager.setAdapter(mAdapter);
initViewPager();
} /**
* 设置是否自动播放
* @param autoPlay
*/
public void setAutoPlay(boolean autoPlay) {
AutoScrollViewPager.autoPlay = autoPlay; if (!autoPlay){
handler.removeCallbacks(runnable);
}
}
}注意主要几点
组合控件，一个FrameLayout布局包含ViewPager和一个小圆点指示器。
自动循环用handler实现，循环发送消息。
这里需要注意的是setAdapter( )方法，只要正常写PageAdapter传入即可;
在OnPageChangeListener中，onPageSelected的时候去处理位置问题，就是图中所说的，从左往右滑动，position==0的时候切换到4的位置，当从右往左滑动的时候，positon==5的时候切换到1的位置。onPageScrollStateChanged状态改变的时候，即停止滑动的时候滑到指定位置，当手指拖动的时候需要停止自动播放；
小圆点指示器，是一个线性布局根据图片数量添加原点，原点背景为selector；
在屏幕显示的时候设置自动播放，离开屏幕时候停止播放；
如果想显示3个page需要在viewpager父容器设置
android:clipChildren="false"android:layerType="hardware"http://代码如下setLayerType(View.LAYER_TYPE_SOFTWARE, null); setClipChildren(false);
并且设置viewPager.setPageMargin(pageMargin);，需要加其他特效可以自定义PageTransformer。
setAutoPlay方法可以设置不自动循环 viewPager.setAutoPlay(false);
例子
activity_main.xml
<?xml version="1.0" encoding="utf-8"?><LinearLayout xmlns:android="http://schemas.android.com/apk/res/android" android:layout_width="match_parent" android:orientation="horizontal" android:layout_height="match_parent"> <com.wzh.AutoScrollViewPager android:id="@+id/viewpager" android:layout_width="match_parent" android:layout_height="300dp"> </com.wzh.AutoScrollViewPager></LinearLayout>
MainActivity.java
import android.os.Bundle;import android.support.v7.app.AppCompatActivity;public class MainActivity extends AppCompatActivity { private AutoScrollViewPager viewPager ; private ViewPagerAdapter adapter ; @Override
protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
viewPager = (AutoScrollViewPager) findViewById(R.id.viewpager);
adapter = new ViewPagerAdapter(this);
viewPager.setAdapter(adapter);
viewPager.setAutoPlay(true);
}
}ViewPagerAdapter.java
import android.content.Context;import android.support.v4.view.PagerAdapter;import android.view.View;import android.view.ViewGroup;import android.widget.ImageView;import com.bumptech.glide.Glide;/**
* Created by WZH on 2018/4/14.
*/public class ViewPagerAdapter extends PagerAdapter { private String[] resIds = { //最后一张图片
"https://timgsa.baidu.com/timg?image&quality=80&size=b9999_10000&sec=1523772064849&di=7502440dd81352d3e3d584eb810e0acc&imgtype=0&src=http%3A%2F%2Fimage.tianjimedia.com%2FuploadImages%2F2012%2F265%2F5432CKKPF561_1000x500.jpg", //正真的5张图片
"https://timgsa.baidu.com/timg?image&quality=80&size=b9999_10000&sec=1523772064850&di=dd3588fdf916fce1527f7b53cc536293&imgtype=0&src=http%3A%2F%2Fimage.tianjimedia.com%2FuploadImages%2F2012%2F088%2F9KF35LBMFO74.jpg", "https://timgsa.baidu.com/timg?image&quality=80&size=b9999_10000&sec=1523772064854&di=165a16c1167b38b067b3c82cb830c347&imgtype=0&src=http%3A%2F%2Fattachments.gfan.com%2Fforum%2Fattachments2%2F201303%2F18%2F110902j0e5zjwj0yutt00j.jpg", "https://timgsa.baidu.com/timg?image&quality=80&size=b9999_10000&sec=1523772064877&di=dac68b830070fb6dbf1a9d71fc6b2772&imgtype=0&src=http%3A%2F%2Fi3.download.fd.pchome.net%2Fg1%2FM00%2F0D%2F18%2FoYYBAFS8sGGIUf9wAAJfpTlwpsgAACPGwFaL6cAAl-9928.jpg", "https://timgsa.baidu.com/timg?image&quality=80&size=b9999_10000&sec=1523772294591&di=9633b23326710637bda3b511c87e0fdb&imgtype=jpg&src=http%3A%2F%2Fimg0.imgtn.bdimg.com%2Fit%2Fu%3D1163084700%2C3470735618%26fm%3D214%26gp%3D0.jpg", "https://timgsa.baidu.com/timg?image&quality=80&size=b9999_10000&sec=1523772064849&di=7502440dd81352d3e3d584eb810e0acc&imgtype=0&src=http%3A%2F%2Fimage.tianjimedia.com%2FuploadImages%2F2012%2F265%2F5432CKKPF561_1000x500.jpg", //第一张图片
"https://timgsa.baidu.com/timg?image&quality=80&size=b9999_10000&sec=1523772064850&di=dd3588fdf916fce1527f7b53cc536293&imgtype=0&src=http%3A%2F%2Fimage.tianjimedia.com%2FuploadImages%2F2012%2F088%2F9KF35LBMFO74.jpg",
}; private Context context ; public ViewPagerAdapter(Context context) { this.context = context ;
} @Override
public int getCount() { return resIds.length;
} @Override
public Object instantiateItem(ViewGroup container, int position) {
View view = View.inflate(context, R.layout.vp_item, null);
ImageView imageView = (ImageView) view.findViewById(R.id.image);
Glide.with(context)
.load(resIds[position])
.into(imageView);// imageView.setImageResource(resIds[position]);
//添加到容器中
container.addView(view); return view;
} @Override
public void destroyItem(ViewGroup container, int position, Object object) {
container.removeView((View) object);
} @Override
public boolean isViewFromObject(View view, Object object) { return view==object;
}
}// bg_while.xml<?xml version="1.0" encoding="utf-8"?><shape xmlns:android="http://schemas.android.com/apk/res/android" android:shape="oval"> <size android:width="30dp" android:height="30dp"/> <!--白色--> <solid android:color="#ffffff" /> <!--半径--> <corners android:radius="10dp" /></shape>//bg_gray.xml<?xml version="1.0" encoding="utf-8"?><shape xmlns:android="http://schemas.android.com/apk/res/android" android:shape="oval"> <size android:width="20dp" android:height="20dp"/> <!--灰色--> <solid android:color="#88aaaaaa" /> <!--半径--> <corners android:radius="10dp" /></shape>//bg_dot.xml<?xml version="1.0" encoding="utf-8"?><selector xmlns:android="http://schemas.android.com/apk/res/android"> <item android:drawable="@drawable/bg_while" android:state_enabled="true" /> <item android:drawable="@drawable/bg_gray" android:state_enabled="false" /></selector>
效果图
最近在整理并复习一些Android基础知识点，有问题希望大家够指出，谢谢。
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