博客

0.实现效果

1.添加依赖

dependencies {
    ...
    implementation 'androidx.viewpager2:viewpager2:1.0.0'
}

2.设计布局

使用CardView实现圆角的效果，并在父布局的右下角放一个线性布局，用来动态添加指示点。

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    android:padding="10dp">

    <RelativeLayout
        android:layout_width="match_parent"
        android:layout_height="200dp">

        <androidx.cardview.widget.CardView
            android:layout_width="match_parent"
            android:layout_height="match_parent"
            app:cardCornerRadius="10dp"
            app:cardElevation="0dp">

            <androidx.viewpager2.widget.ViewPager2
                android:id="@+id/viewpager2"
                android:layout_width="match_parent"
                android:layout_height="match_parent" />

        </androidx.cardview.widget.CardView>

        <LinearLayout
            android:id="@+id/container_indicator"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:orientation="horizontal"
            android:layout_alignParentEnd="true"
            android:layout_alignParentBottom="true"
            android:layout_marginEnd="5dp"
            android:layout_marginBottom="5dp"/>

     </RelativeLayout>

</RelativeLayout>

3.实现Adapter

ViewPager2是使用RecyclerView实现的，适配器的写法与使用RecyclerView类似。

要实现”无限”轮播，需要在getItemCount()方法中返回一个较大的值，这里返回的是Integer.MAX_VALUE.

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout
    android:id="@+id/container"
    xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent">

    <TextView
        android:id="@+id/tv_title"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_centerInParent="true"
        android:textSize="20sp"/>

</RelativeLayout>

public class ViewPagerAdapter extends RecyclerView.Adapter<ViewPagerAdapter.ViewHolder> {

    private List<Integer> colors;

    ViewPagerAdapter(List<Integer> colors){
        this.colors = colors;
    }

    @NonNull
    @Override
    public ViewHolder onCreateViewHolder(@NonNull ViewGroup parent, int viewType) {
        return new ViewHolder(LayoutInflater.from(parent.getContext()).inflate(R.layout.item,parent,false));
    }

    @Override
    public void onBindViewHolder(@NonNull ViewHolder holder, int position) {
        int i = position % 4;
        holder.titleTv.setText("item " + i);
        holder.container.setBackgroundColor(colors.get(i));
    }

    @Override
    public int getItemCount() {
        //实现无限轮播
        return Integer.MAX_VALUE;
    }

    class ViewHolder extends RecyclerView.ViewHolder{

        RelativeLayout container;
        TextView titleTv;

        public ViewHolder(@NonNull View itemView) {
            super(itemView);
            container = itemView.findViewById(R.id.container);
            titleTv = itemView.findViewById(R.id.tv_title);
        }
    }
}

4.绘制指示点

绘制一个白色的点和一个蓝色的点用于指示。

<?xml version="1.0" encoding="utf-8"?>
<shape xmlns:android="http://schemas.android.com/apk/res/android">
    <size
        android:width="8dp"
        android:height="8dp"/>
    <corners
        android:radius="8dp"/>
    <solid
        android:color="#ffffff"/>
</shape>

<?xml version="1.0" encoding="utf-8"?>
<shape xmlns:android="http://schemas.android.com/apk/res/android">
    <size
        android:width="8dp"
        android:height="8dp"/>
    <corners
        android:radius="8dp"/>
    <solid
        android:color="#00ccff"/>
</shape>

5.实现

public class MainActivity extends AppCompatActivity {

    private ViewPager2 viewPager2;
    private int lastPosition;                           //记录轮播图最后所在的位置
    private List<Integer> colors = new ArrayList<>();   //轮播图的颜色
    private LinearLayout indicatorContainer;            //填充指示点的容器
    private Handler mHandler = new Handler();

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        //初始化组件
        viewPager2 = findViewById(R.id.viewpager2);
        indicatorContainer = findViewById(R.id.container_indicator);

        initColors();
        //初始化指示点
        initIndicatorDots();
		
		//添加适配器
        ViewPagerAdapter viewPagerAdapter = new ViewPagerAdapter(colors);
        viewPager2.setAdapter(viewPagerAdapter);
        //设置轮播图初始位置在500,以保证可以手动前翻
        viewPager2.setCurrentItem(500);
        //最后所在的位置设置为500
        lastPosition = 500;
	
		//注册轮播图的滚动事件监听器
        viewPager2.registerOnPageChangeCallback(new ViewPager2.OnPageChangeCallback() {

            @Override
            public void onPageSelected(int position) {
                super.onPageSelected(position);
                //轮播时，改变指示点
                int current = position % 4;
                int last = lastPosition % 4;
                indicatorContainer.getChildAt(current).setBackgroundResource(R.drawable.shape_dot_selected);
                indicatorContainer.getChildAt(last).setBackgroundResource(R.drawable.shape_dot);
                lastPosition = position;
            }
        });
    }

    private void initColors(){
        colors.add(Color.BLUE);
        colors.add(Color.YELLOW);
        colors.add(Color.GREEN);
        colors.add(Color.RED);
    }

    /**
     * 初始化指示点
     */
    private void initIndicatorDots(){
        for(int i = 0; i < colors.size(); i++){
            ImageView imageView = new ImageView(this);
            if (i == 0) imageView.setBackgroundResource(R.drawable.shape_dot_selected);
            else imageView.setBackgroundResource(R.drawable.shape_dot);
            //为指示点添加间距
            LinearLayout.LayoutParams layoutParams = new LinearLayout.LayoutParams(LinearLayout.LayoutParams.WRAP_CONTENT,LinearLayout.LayoutParams.WRAP_CONTENT);
            layoutParams.setMarginEnd(4);
            imageView.setLayoutParams(layoutParams);
            //将指示点添加进容器
            indicatorContainer.addView(imageView);
        }
    }

    /* 当应用被唤醒时，让轮播图开始轮播 */
    @Override
    protected void onResume() {
        super.onResume();
        mHandler.postDelayed(runnable,5000);
    }

    /* 当应用被暂停时，让轮播图停止轮播 */
    @Override
    protected void onPause() {
        super.onPause();
        mHandler.removeCallbacks(runnable);
    }

    private final Runnable runnable = new Runnable() {
        @Override
        public void run() {
            //获得轮播图当前的位置
            int currentPosition = viewPager2.getCurrentItem();
            currentPosition++;
            viewPager2.setCurrentItem(currentPosition,true);
            mHandler.postDelayed(runnable,5000);
        }
    };
}