Android使用ViewPager实现轮播图（自动和手动）

Posted 2023-02-19

参考技术A 源码链接
效果图

1.自动轮播

2.手动轮播

3.监听点击事件跳转界面

4.每个图片可加标题（我的图片颜色太鲜艳了，就没有让文字显示）

接口回调步骤：

如果界面滚动了，获取当前的item,如果item==0,就设置为最后一个，如果，item==count+1,就设置为第一个，这样可以实现第一个图片和最后一个图片切换时不会出现闪现或卡顿的画面

这里用到了SparseBooleanArray，它是用来存储布尔值的，类似于key,value,根据其中存放的值来判断是否被选中

Android 使用ViewPager和自定义PagerAdapter实现轮播图效果

一、首先是布局页面activity_main.xml

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout 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="200dp"
    android:background="#DFDFDF"
    tools:context=".MainActivity">

    <androidx.viewpager.widget.ViewPager
        android:id="@+id/viewPager"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:background="@color/white" />

    <LinearLayout
        android:id="@+id/viewGroup"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_alignParentBottom="true"
        android:layout_centerHorizontal="true"
        android:layout_marginBottom="3dp"
        android:orientation="horizontal" />
</RelativeLayout>

二、自定义MyPagerAdapter类继承与PagerAdapter

public class MyPagerAdapter extends PagerAdapter {
    private int[] banners = new int[]{R.mipmap.banner_one, R.mipmap.banner_two, R.mipmap.banner_three};
    private Context context;
    private View.OnClickListener onBannerClickListener;
    private static final String TAG = "MyPagerAdapter";

    public MyPagerAdapter(Context context) {
        this.context = context;
    }

    @Override
    public int getCount() {
    	//返回int的最大值 可以一直滑动
        return Integer.MAX_VALUE;
    }

    @Override
    public boolean isViewFromObject(@NonNull View view, @NonNull Object object) {
        return view == object;
    }

    @NonNull
    @Override
    public Object instantiateItem(@NonNull ViewGroup container, int position) {
        Log.e(TAG, "instantiateItem1: " + position);
        position %= banners.length;
        Log.e(TAG, "instantiateItem2: " + position);
        ImageView imageView = new ImageView(context);
        //设置图片缩放类型
        imageView.setScaleType(ImageView.ScaleType.CENTER_CROP);
        //把当前的下标通过setTag方法设置进去
        imageView.setTag(position);
        imageView.setImageResource(banners[position]);
        imageView.setOnClickListener(onClickListener);
        container.addView(imageView);
        return imageView;
    }

    private View.OnClickListener onClickListener = new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            onBannerClickListener.onClick(v);
        }
    };

    @Override
    public void destroyItem(@NonNull ViewGroup container, int position, @NonNull Object object) {
        container.removeView((View) object);
    }

    public void setOnBannerClickListener(View.OnClickListener onBannerClickListener) {
        this.onBannerClickListener = onBannerClickListener;
    }

    public int[] getBanners() {
        return banners;
    }
}

三、MainActivity.java代码如下，注释已经在代码中给出

public class MainActivity extends AppCompatActivity {
    private static final String TAG = "MainActivity";
    private MyPagerAdapter myPagerAdapter;
    private ViewPager viewPager;
    private LinearLayout viewGroup;

    private int currentItem = 0;
    private final Handler handler = new Handler();
    private static final int CAROUSEL_TIME = 3000;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        viewPager = findViewById(R.id.viewPager);
        viewGroup = findViewById(R.id.viewGroup);
        myPagerAdapter = new MyPagerAdapter(this);
        myPagerAdapter.setOnBannerClickListener(onBannerClickListener);
        //设置缓存页数
        viewPager.setOffscreenPageLimit(myPagerAdapter.getBanners().length - 1);
        viewPager.setAdapter(myPagerAdapter);
        //添加页面更改监听器
        viewPager.addOnPageChangeListener(onPageChangeListener);

        //将点点的图添加到视图ViewGroup中
        for (int i = 0; i < myPagerAdapter.getBanners().length; i++) {
            ImageView imageView = new ImageView(this);
            //设置图片的宽高 为10像素
            imageView.setLayoutParams(new ViewGroup.LayoutParams(10, 10));
            if (i == 0) {
                //第一个为默认选中状态
                imageView.setImageResource(R.drawable.icon_page_select);
            } else {
                imageView.setImageResource(R.drawable.icon_page_normal);
            }
            LinearLayout.LayoutParams params = new LinearLayout.LayoutParams(ViewGroup.LayoutParams.WRAP_CONTENT, ViewGroup.LayoutParams.WRAP_CONTENT);
            params.leftMargin = 5;
            params.rightMargin = 5;
            viewGroup.addView(imageView, params);
        }
        //给ViewPager设置当前页，这样刚打开软件也能向左滑动
        currentItem = myPagerAdapter.getBanners().length * 50;
        viewPager.setCurrentItem(currentItem);
        handler.postDelayed(mTicker, CAROUSEL_TIME);
    }

    private final Runnable mTicker = new Runnable() {
        @Override
        public void run() {
            long now = SystemClock.uptimeMillis();
            Log.d(TAG, "now:" + now);
//            long next = now + (CAROUSEL_TIME - now % CAROUSEL_TIME);
            //等同于
            long next = now + CAROUSEL_TIME;
            Log.d(TAG, "next: " + next);
            //回调应该运行的绝对时间 3秒后发送消息
            handler.postAtTime(mTicker, next);
            currentItem++;
            viewPager.setCurrentItem(currentItem);
        }
    };

    private View.OnClickListener onBannerClickListener = new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            int position = (int) v.getTag();
            Toast.makeText(MainActivity.this, "当前点击位置：" + position, Toast.LENGTH_SHORT).show();
        }
    };

    private ViewPager.OnPageChangeListener onPageChangeListener = new ViewPager.OnPageChangeListener() {
        @Override
        public void onPageScrolled(int position, float positionOffset, int positionOffsetPixels) {

        }

        @Override
        public void onPageSelected(int position) {
            Log.e(TAG, "onPageSelected: MainActivity" + position);
            currentItem = position;
            //当新页面选中时调用此方法，position 为新选中页面的位置索引
            //在所选页面的时候,点点图片也要发生变化
            setImageBackground(position %= myPagerAdapter.getBanners().length);
            Log.e(TAG, "onPageSelected: " + myPagerAdapter.getBanners().length);
        }

        @Override
        public void onPageScrollStateChanged(int state) {

        }
    };

    /**
     * 改变点点点的切换效果
     *
     * @param selectItem 当前选中的页面索引
     */
    private void setImageBackground(int selectItem) {
        for (int i = 0; i < myPagerAdapter.getBanners().length; i++) {
            ImageView imageView = (ImageView) viewGroup.getChildAt(i);
            imageView.setBackground(null);
            if (i == selectItem) {
                imageView.setImageResource(R.drawable.icon_page_select);
            } else {
                imageView.setImageResource(R.drawable.icon_page_normal);
            }
        }
    }
}

效果如图所示：