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怎么在Android中利用Viewpager实现一个无限循环轮播图？很多新手对此不是很清楚，为了帮助大家解决这个难题，下面小编将为大家详细讲解，有这方面需求的人可以来学习下，希望你能有所收获。
在网上找了很多viewpager实现图片轮播的，但是大多数通过以下方式在PagerAdapter的getCount()返回一个无限大的数，来实现 伪无限
@Override
public int getCount() {
return Integer.MAX_VALUE;//返回一个无限大的值，可以 无限循环
}虽然通过这种方式是能达到效果，但是从严格意义上来说并不是真正的无限。
假如有五张轮播图 item的编号为（0,1,2,3,4） 要想实现 无限循环 我们在这五张的头部和尾部各加一张即（5+2）张,item编号为（0,1,2,3,4,5,6）其中编号为0,6的两张不做展示只是为了做循环轮播的铺垫，使得播放更加平滑。
1、当我们从编号为5 右滑的时候到了编号6 这时候就将当前页面设置为1
2、当我们从编号为1左滑的时候到了编号0 这时候就将当前页面设置为5
这么做之后就可以实现无限轮播 怎么保证从编号6跳转编号1的时候不出现页面停顿 突然跳到下一页的现象呢？
public Object instantiateItem (ViewGroup container, int position)
在指定的位置创建页面；适配器负责添加view到这个容器中，然而它只保证在finishUpdate(ViewGroup)返回时才完成。
public void destroyItem (ViewGroup container, int position, Object object)
删除指定位置的页面；适配器负责从view容器中删除view，然而它只保证在finishUpdate(ViewGroup)返回时才完成。
所以说 重点就在于finishUpdate(ViewGroup)这个方法 其实无论是创建view添加到容器中 还是 销毁view 都是在此方法结束之后执行的
换句话说 就是 我在这个方法里让页面完成从 编号5跳转到编号1 或者从编号1跳转到编号5，此方法完成时 视图还未完成创建或者 销毁 这样也就不会出现 页面停顿 突然跳到下一页的现象。
@Override
public void finishUpdate(ViewGroup container) {
super.finishUpdate(container);
int position = viewPager.getCurrentItem();
if (position == 0) {
position = simpleDraweeViewList.size() - 2;
viewPager.setCurrentItem(position,false);
} else if (position == simpleDraweeViewList.size() - 1) {
position = 1;
viewPager.setCurrentItem(position,false);
}
}话不多说，上代码：
布局文件：
<?xml version="1.0" encoding="utf-8"?> <android.support.constraint.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android" xmlns:app="http://schemas.android.com/apk/res-auto" xmlns:tools="http://schemas.android.com/tools" android:layout_width="match_parent" android:layout_height="match_parent" tools:context=".MainActivity"> <FrameLayout android:id="@+id/frameLayout" android:layout_width="0dp" android:layout_height="200dp" app:layout_constraintEnd_toEndOf="parent" app:layout_constraintHorizontal_bias="0.0" app:layout_constraintStart_toStartOf="parent" app:layout_constraintTop_toTopOf="parent"> <android.support.v4.view.ViewPager android:id="@+id/viewPager" android:layout_width="match_parent" android:layout_height="match_parent" tools:layout_editor_absoluteX="8dp" tools:layout_editor_absoluteY="0dp" /> <LinearLayout android:layout_width="match_parent" android:layout_height="35dip" android:layout_gravity="bottom" android:background="#33000000" android:gravity="center_vertical" android:orientation="horizontal" android:weightSum="10"> <TextView android:id="@+id/tv_pager_title" android:layout_width="0dp" android:layout_height="35dip" android:layout_weight="8" android:gravity="center_vertical" android:paddingLeft="8dip" android:text="加载图片轮播失败" android:textColor="@android:color/white" /> <LinearLayout android:id="@+id/lineLayout_dot" android:layout_width="0dp" android:layout_height="match_parent" android:layout_marginRight="5dp" android:layout_weight="2" android:gravity="center|right" android:orientation="horizontal" android:paddingLeft="3dp" android:paddingRight="3dp" /> </LinearLayout> </FrameLayout> </android.support.constraint.ConstraintLayout>
最主要的PagerAdapter：
import android.content.Context;
import android.support.v4.view.PagerAdapter;
import android.support.v4.view.ViewPager;
import android.util.Log;
import android.view.View;
import android.view.ViewGroup;
import com.facebook.drawee.view.SimpleDraweeView;
import java.util.List;
public class ImagesPagerAdapter extends PagerAdapter {
private List<SimpleDraweeView> simpleDraweeViewList;
private ViewPager viewPager;
private Context context;
private SimpleDraweeView simpleDraweeView;
public ImagesPagerAdapter(List<SimpleDraweeView> simpleDraweeViewList, ViewPager viewPager, Context context) {
this.simpleDraweeViewList = simpleDraweeViewList;
this.viewPager = viewPager;
this.context = context;
}
@Override
public int getCount() {
return simpleDraweeViewList.size();
}
//删除指定位置的页面；适配器负责从view容器中删除view，然而它只保证在finishUpdate(ViewGroup)返回时才完成。
@Override
public void destroyItem(ViewGroup container, int position, Object object) {
// 把ImageView从ViewPager中移除掉
viewPager.removeView(simpleDraweeViewList.get(position));
//super.destroyItem(container, position, object);
}
//是否获取缓存
@Override
public boolean isViewFromObject(View view, Object object) {
return view == object;
}
//实例化Item
//在指定的位置创建页面；适配器负责添加view到这个容器中，然而它只保证在finishUpdate(ViewGroup)返回时才完成。
@Override
public Object instantiateItem(ViewGroup container, int position) {
simpleDraweeView = simpleDraweeViewList.get(position);
viewPager.addView(simpleDraweeView);
return simpleDraweeView;
}
@Override
public int getItemPosition(Object object) {
return POSITION_NONE;
}
//无论是创建view添加到容器中 还是 销毁view 都是在此方法结束之后执行的
@Override
public void finishUpdate(ViewGroup container) {
super.finishUpdate(container);
int position = viewPager.getCurrentItem();
if (position == 0) {
position = simpleDraweeViewList.size() - 2;
viewPager.setCurrentItem(position,false);
} else if (position == simpleDraweeViewList.size() - 1) {
position = 1;
viewPager.setCurrentItem(position,false);
}
}
/* private int mChildCount = 0;
@Override
public void notifyDataSetChanged() {
mChildCount = getCount();
super.notifyDataSetChanged();
}
@Override
public int getItemPosition(Object object) {
if (mChildCount > 0) {
mChildCount--;
Log.e("image","getItemPosition");
return POSITION_NONE;
}
return super.getItemPosition(object);
}*/
}import android.app.Activity;
import android.content.Context;
import android.graphics.drawable.Drawable;
import android.support.v4.content.ContextCompat;
import android.support.v4.view.ViewPager;
import android.util.Log;
import android.view.View;
import android.view.ViewGroup;
import android.widget.LinearLayout;
import android.widget.TextView;
import com.facebook.drawee.view.SimpleDraweeView;
import java.util.ArrayList;
import java.util.List;
public class ImageCarousel {
private Context context;
private ViewPager viewPager;
private TextView tvTitle;
private LinearLayout dotsRoot;
private int time;
private List<View> dots;//小点
private int previousPosition = 1;//前一个被选中的position
private List<SimpleDraweeView> simpleDraweeViewList;
private String[] titles;//标题数组
private ImagesPagerAdapter adapter;
private AutoPlayThread autoPlayThread;
private volatile boolean isExit = true;
private static final int FIRST_PAGE = 1;
public ImageCarousel(Context context, ViewPager viewPager, TextView tvTitle,
List<View> dots, int time) {
this.context = context;
this.viewPager = viewPager;
this.tvTitle = tvTitle;
this.dots = dots;
this.time = time;
Log.e("image", "构造方法");
}
/**
* 传入数据
*
* @param simpleDraweeViewList SimpleDraweeView集合
* @param titles 标题数组
* @return this 本身
*/
public ImageCarousel init(List<SimpleDraweeView> simpleDraweeViewList, String[] titles) {
this.simpleDraweeViewList = simpleDraweeViewList;
this.titles = titles;
Log.e("image", "init");
autoPlayThread = new AutoPlayThread();
return this;
}
/**
* 重新加载，有待考验...
*
* @param simpleDraweeViewList SimpleDraweeView集合
* @param titles 标题数组
*/
public void reload(List<SimpleDraweeView> simpleDraweeViewList, String[] titles) {
init(simpleDraweeViewList, titles);
previousPosition = 0;
start();
}
/**
* 设置设配器，并实现轮播功能
*/
public void start() {
if (adapter != null) {
adapter = null;
}
adapter = new ImagesPagerAdapter(this.simpleDraweeViewList, viewPager, context);
viewPager.setAdapter(adapter);
viewPager.addOnPageChangeListener(new ViewPager.OnPageChangeListener() {
@Override
public void onPageScrolled(int position, float positionOffset, int positionOffsetPixels) {
}
//当被选择
@Override
public void onPageSelected(int position) {
int currentPosition = 1;
if (position == simpleDraweeViewList.size() - 1) {
// 设置当前值为1
currentPosition = FIRST_PAGE;
} else if (position == 0) {
// 如果索引值为0了,就设置索引值为倒数第二个
currentPosition = simpleDraweeViewList.size() - 2;
} else {
currentPosition = position;
}
// 把当前选中的点给切换了, 还有描述信息也切换
tvTitle.setText(titles[currentPosition]);//图片下面设置显示文本
//设置轮播点 可设置成传入的图
Log.d("dots", "previousPosition=" + previousPosition + " currentPosition=" + currentPosition);
dots.get(previousPosition-1).setBackgroundResource(R.drawable.ic_dot_focused);
dots.get(currentPosition-1).setBackgroundResource(R.drawable.ic_dot_normal);
// 把当前的索引赋值给前一个索引变量, 方便下一次再切换.
previousPosition = currentPosition;
}
@Override
public void onPageScrollStateChanged(int state) {
// SCROLL_STATE_IDLE ：空闲状态
// SCROLL_STATE_DRAGGING ：滑动状态
// SCROLL_STATE_SETTLING ：滑动后滑翔的状态
if (state == ViewPager.SCROLL_STATE_DRAGGING) {
} else if(state == ViewPager.SCROLL_STATE_IDLE){
}
}
});
setFirstLocation();
//autoPlayThread.start();
}
/**
* 设置刚打开app时显示的图片和文字
*/
private void setFirstLocation() {
tvTitle.setText(titles[0]);
dots.get(0).setBackgroundResource(R.drawable.ic_dot_normal);
viewPager.setCurrentItem(1);
}
/**
* 设置是否轮播
*
* @param b
*/
private void setAutoPlay(boolean b) {
/*if (b && suspendRequested) {
autoPlayThread.requestResume();
} else if (!b){
autoPlayThread.requestSuspend();
}*/
}
public void stopAutoPlay() {
if (autoPlayThread != null) {
Log.e("thrad", "暂停");
isExit = true;
autoPlayThread.interrupt();
autoPlayThread = null;
}
}
/**
* 请求继续
*/
public void startAutoPlay() {
Log.e("thrad", "开始");
isExit = false;
autoPlayThread = null;
autoPlayThread = new AutoPlayThread();
autoPlayThread.start();
}
/**
* 自动播放线程，添加暂停和继续方法
*/
class AutoPlayThread extends Thread {
@Override
public synchronized void run() {
while (!isExit) {
try {
Thread.sleep(time);
} catch (InterruptedException e) {
Log.e("thrad", "强制请求退出线程");
break;
}
((Activity) context).runOnUiThread(new Runnable() {
@Override
public void run() {
viewPager.setCurrentItem(viewPager.getCurrentItem() + 1);
}
});
if (this.interrupted()) {
Log.e("thrad", "已经是停止状态了，我要退出了");
break;
}
}
}
}
}mainActivity.java:
import android.app.Activity;
import android.content.Context;
import android.graphics.drawable.Drawable;
import android.net.Uri;
import android.support.v4.content.ContextCompat;
import android.support.v4.view.ViewPager;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.View;
import android.view.ViewGroup;
import android.widget.AbsListView;
import android.widget.LinearLayout;
import android.widget.TextView;
import com.facebook.drawee.backends.pipeline.Fresco;
import com.facebook.drawee.backends.pipeline.PipelineDraweeController;
import com.facebook.drawee.drawable.ScalingUtils;
import com.facebook.drawee.generic.GenericDraweeHierarchy;
import com.facebook.drawee.generic.GenericDraweeHierarchyBuilder;
import com.facebook.drawee.view.SimpleDraweeView;
import com.facebook.imagepipeline.common.ResizeOptions;
import com.facebook.imagepipeline.request.ImageRequest;
import com.facebook.imagepipeline.request.ImageRequestBuilder;
import java.util.ArrayList;
import java.util.List;
public class MainActivity extends AppCompatActivity implements View.OnClickListener {
// 图片轮播控件
private ViewPager mViewPager;
private TextView mTvPagerTitle;
private LinearLayout mLineLayoutDot;
private ImageCarousel imageCarousel;
private List<View> dots;//小点
// 图片数据，包括图片标题、图片链接、数据、点击要打开的网站（点击打开的网页或一些提示指令）
private List<ImageInfo> imageInfoList;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
initView();
initEvent();
imageStart();
}
@Override
public void onClick(View v) {
}
/**
* 初始化事件
* 左右多添加一张图片
*/
private void initEvent() {
imageInfoList = new ArrayList<>();
imageInfoList.add(new ImageInfo(1, "图片5，公告5啦啦啦啦", "", "http://e.hiphotos.baidu.com/image/h%3D300/sign=73443062281f95cab9f594b6f9177fc5/72f082025aafa40fafb5fbc1a664034f78f019be.jpg", ""));
imageInfoList.add(new ImageInfo(2, "图片1，公告1啦啦啦啦", "", "http://d.hiphotos.baidu.com/image/pic/item/6159252dd42a2834a75bb01156b5c9ea15cebf2f.jpg", ""));
imageInfoList.add(new ImageInfo(3, "图片2，公告2啦啦啦啦", "", "http://c.hiphotos.baidu.com/image/h%3D300/sign=cfce96dfa251f3dedcb2bf64a4eff0ec/4610b912c8fcc3ce912597269f45d688d43f2039.jpg", ""));
imageInfoList.add(new ImageInfo(4, "图片3，公告3啦啦啦啦", "", "http://e.hiphotos.baidu.com/image/pic/item/6a600c338744ebf85ed0ab2bd4f9d72a6059a705.jpg", ""));
imageInfoList.add(new ImageInfo(5, "图片4，公告4啦啦啦啦", "", "http://b.hiphotos.baidu.com/image/h%3D300/sign=8ad802f3801001e9513c120f880e7b06/a71ea8d3fd1f4134be1e4e64281f95cad1c85efa.jpg", ""));
imageInfoList.add(new ImageInfo(6, "图片5，公告5啦啦啦啦", "", "http://e.hiphotos.baidu.com/image/h%3D300/sign=73443062281f95cab9f594b6f9177fc5/72f082025aafa40fafb5fbc1a664034f78f019be.jpg", ""));
imageInfoList.add(new ImageInfo(7, "图片1，公告1啦啦啦啦", "", "http://d.hiphotos.baidu.com/image/pic/item/6159252dd42a2834a75bb01156b5c9ea15cebf2f.jpg", ""));
}
/**
* 初始化控件
*/
private void initView() {
mViewPager = findViewById(R.id.viewPager);
mTvPagerTitle = findViewById(R.id.tv_pager_title);
mLineLayoutDot = findViewById(R.id.lineLayout_dot);
}
private void imageStart() {
//设置图片轮播
int[] imgaeIds = new int[]{R.id.pager_image1, R.id.pager_image2, R.id.pager_image3, R.id.pager_image4,
R.id.pager_image5, R.id.pager_image6, R.id.pager_image7, R.id.pager_image8};
String[] titles = new String[imageInfoList.size()];
List<SimpleDraweeView> simpleDraweeViewList = new ArrayList<>();
for (int i = 0; i < imageInfoList.size(); i++) {
titles[i] = imageInfoList.get(i).getTitle();
SimpleDraweeView simpleDraweeView = new SimpleDraweeView(this);
simpleDraweeView.setAspectRatio(1.78f);
// 设置一张默认的图片
GenericDraweeHierarchy hierarchy = new GenericDraweeHierarchyBuilder(this.getResources())
.setPlaceholderImage(ContextCompat.getDrawable(this, R.drawable.defult), ScalingUtils.ScaleType.CENTER_CROP).build();
simpleDraweeView.setHierarchy(hierarchy);
simpleDraweeView.setLayoutParams(new AbsListView.LayoutParams(AbsListView.LayoutParams.MATCH_PARENT, AbsListView.LayoutParams.WRAP_CONTENT));
//加载高分辨率图片;
ImageRequest imageRequest = ImageRequestBuilder.newBuilderWithSource(Uri.parse(imageInfoList.get(i).getImage()))
.setResizeOptions(new ResizeOptions(1280, 720))
.build();
PipelineDraweeController controller = (PipelineDraweeController) Fresco.newDraweeControllerBuilder()
//.setLowResImageRequest(ImageRequest.fromUri(Uri.parse(listItemBean.test_pic_low))) //在加载高分辨率图片之前加载低分辨率图片
.setImageRequest(imageRequest)
.setOldController(simpleDraweeView.getController())
.build();
simpleDraweeView.setController(controller);
simpleDraweeView.setId(imgaeIds[i]);//给view设置id
simpleDraweeView.setTag(imageInfoList.get(i));
simpleDraweeView.setOnClickListener(this);
titles[i] = imageInfoList.get(i).getTitle();
simpleDraweeViewList.add(simpleDraweeView);
}
dots = addDots(mLineLayoutDot, fromResToDrawable(this, R.drawable.ic_dot_focused), simpleDraweeViewList.size());
imageCarousel = new ImageCarousel(this, mViewPager, mTvPagerTitle, dots, 5000);
imageCarousel.init(simpleDraweeViewList, titles)
.startAutoPlay();
imageCarousel.start();
}
/**
* 动态添加一个点
*
* @param linearLayout 添加到LinearLayout布局
* @param backgount 设置
* @return 小点的Id
*/
private int addDot(final LinearLayout linearLayout, Drawable backgount) {
final View dot = new View(this);
LinearLayout.LayoutParams dotParams = new LinearLayout.LayoutParams(ViewGroup.LayoutParams.MATCH_PARENT,
ViewGroup.LayoutParams.WRAP_CONTENT);
dotParams.width = 16;
dotParams.height = 16;
dotParams.setMargins(4, 0, 4, 0);
dot.setLayoutParams(dotParams);
dot.setBackground(backgount);
dot.setId(View.generateViewId());
((Activity) this).runOnUiThread(new Runnable() {
@Override
public void run() {
linearLayout.addView(dot);
}
});
return dot.getId();
}
/**
* 资源图片转Drawable
*
* @param context 上下文
* @param resId 资源ID
* @return 返回Drawable图像
*/
public static Drawable fromResToDrawable(Context context, int resId) {
return ContextCompat.getDrawable(context, resId);
}
/**
* 添加多个轮播小点到横向线性布局
*
* @param linearLayout 线性横向布局
* @param backgount 小点资源图标
* @param number 数量
* @return 返回小点View集合
*/
private List<View> addDots(final LinearLayout linearLayout, Drawable backgount, int number) {
List<View> dots = new ArrayList<>();
for (int i = 2; i < number; i++) { // 注意这里的 i 从 2 开始，只画出5个点
int dotId = addDot(linearLayout, backgount);
dots.add(findViewById(dotId));
}
return dots;
}
}ic_dot_focused.xml：
<vector android:height="5dp" android:viewportHeight="24.0" android:viewportWidth="24.0" android:width="5dp" xmlns:android="http://schemas.android.com/apk/res/android"> <path android:fillColor="#c8ffffff" android:pathData="M12,12m-8,0a8,8 0,1 1,16 0a8,8 0,1 1,-16 0"/> </vector>
ic_dot_normal.xml：
<vector android:height="5dp" android:viewportHeight="24.0" android:viewportWidth="24.0" android:width="5dp" xmlns:android="http://schemas.android.com/apk/res/android"> <path android:fillColor="#c8fd8888" android:pathData="M12,12m-8,0a8,8 0,1 1,16 0a8,8 0,1 1,-16 0"/> </vector>
Android是一种基于Linux内核的自由及开放源代码的操作系统，主要使用于移动设备，如智能手机和平板电脑，由美国Google公司和开放手机联盟领导及开发。
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