ViewPager指示器，随页面滑动指示器跟随滑动效果

刚做安卓一直百度找轮子，现在可以尝试自己实现了，虽然实现方式很烂，但是效果实现了，还是挺有意思的

image.png Screenshot_2022_0908_172239.gif

指示器：

import android.content.Context;
import android.util.AttributeSet;
import android.view.View;
import android.view.ViewGroup;
import android.widget.ImageView;

import androidx.annotation.Nullable;
import androidx.appcompat.content.res.AppCompatResources;

/**
 * Time:2022/9/8
 * Author:ypf
 * Description:viewpager指示器
 */
public class ViewPagerIndicator extends ViewGroup {


    private Context context;

    private int parentWidth;

    private int parentHeight;

    private int position;

    private float positionOffset;

    public ViewPagerIndicator(Context context) {
        super(context);
        init(context);
    }

    public ViewPagerIndicator(Context context, @Nullable AttributeSet attrs) {
        super(context, attrs);
        init(context);
    }

    public ViewPagerIndicator(Context context, @Nullable AttributeSet attrs, int defStyleAttr) {
        super(context, attrs, defStyleAttr);
        init(context);
    }

    private void init(Context context) {
        this.context = context;
    }

    public void initIndicator(int viewPagerSize) {
        initIndicator(viewPagerSize, R.mipmap.ic_2, R.mipmap.ic_1);
    }

    public void initIndicator(int viewPagerSize, int unSelectIndicatorResId, int selectedIndicatorResId) {
        int size = viewPagerSize + 1;
        for (int i = 0; i < size; i++) {
            ImageView imageView = new ImageView(context);
            LayoutParams params = new LayoutParams(0, 0);
            imageView.setLayoutParams(params);
            if (i == viewPagerSize) {
                imageView.setImageDrawable(AppCompatResources.getDrawable(context, selectedIndicatorResId));
            } else {
                imageView.setImageDrawable(AppCompatResources.getDrawable(context, unSelectIndicatorResId));
            }
            addView(imageView);
        }
    }

    @Override
    protected void onLayout(boolean changed, int l, int t, int r, int b) {

        int childCount = getChildCount() - 1;

        //指示器宽高 1/2高
        int indicatorWidthHeight = parentHeight / 2;

        //间隔距离
        int indicatorSpace = (parentWidth - indicatorWidthHeight * childCount) / (childCount + 1);

        int childLeft = indicatorSpace;
        int childTop = parentHeight / 4;
        int childRight = childLeft + indicatorWidthHeight;
        int childBottom = parentHeight - childTop;

        for (int i = 0; i < childCount; i++) {
            View childAt = getChildAt(i);
            LayoutParams layoutParams = childAt.getLayoutParams();
            layoutParams.width = indicatorWidthHeight;
            layoutParams.height = indicatorWidthHeight;
            childAt.setLayoutParams(layoutParams);
            childAt.layout(childLeft + (indicatorWidthHeight + indicatorSpace) * i, childTop, childRight + (indicatorWidthHeight + indicatorSpace) * i, childBottom);
        }

        //绘制指引器指引
        childLeft = (int) (indicatorSpace + (indicatorWidthHeight + indicatorSpace) * positionOffset) + (indicatorWidthHeight + indicatorSpace) * position;

        View childAt = getChildAt(childCount);
        LayoutParams layoutParams = childAt.getLayoutParams();
        layoutParams.width = indicatorWidthHeight;
        layoutParams.height = indicatorWidthHeight;
        childAt.setLayoutParams(layoutParams);
        childAt.layout(childLeft, childTop, childLeft + indicatorWidthHeight, childBottom);
    }

    @Override
    protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
        super.onMeasure(widthMeasureSpec, heightMeasureSpec);
        //ViewGroup解析的父亲给我的宽度
        parentWidth = MeasureSpec.getSize(widthMeasureSpec);
        // ViewGroup解析的父亲给我的高度
        parentHeight = MeasureSpec.getSize(heightMeasureSpec);
    }

    public void moveIndicator(int position, float positionOffset) {
        this.position = position;
        this.positionOffset = positionOffset;
        requestLayout();
    }

}

主页面

import android.os.Bundle;

import androidx.appcompat.app.AppCompatActivity;
import androidx.viewpager.widget.ViewPager;

public class MainActivity extends AppCompatActivity {

    private ViewPager mViewPager;

    private ViewPagerIndicator mViewPagerIndicator;

    private GuidePageAdapter guidePageAdapter;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        mViewPager = findViewById(R.id.viewpager);
        mViewPagerIndicator = findViewById(R.id.viewPagerIndicator);
        loadGuideDataToView();
    }

    private void loadGuideDataToView() {

        guidePageAdapter = new GuidePageAdapter();
        mViewPager.setCurrentItem(0);
        mViewPager.setAdapter(guidePageAdapter);

        mViewPagerIndicator.initIndicator(guidePageAdapter.getCount());

        mViewPager.addOnPageChangeListener(new ViewPager.OnPageChangeListener() {
            @Override
            public void onPageScrolled(int position, float positionOffset, int positionOffsetPixels) {
                mViewPagerIndicator.moveIndicator(position, positionOffset);
            }

            @Override
            public void onPageSelected(int position) {

            }

            @Override
            public void onPageScrollStateChanged(int state) {

            }
        });

    }

}

<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.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">

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

    <com.pf.bannerviewpager.ViewPagerIndicator
        android:id="@+id/viewPagerIndicator"
        android:layout_width="300dp"
        android:layout_height="40dp"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent" />

</androidx.constraintlayout.widget.ConstraintLayout>

public class GuidePageAdapter extends PagerAdapter {

    private final SparseArray<ImageView> mHolderArray = new SparseArray<>();

    private int mSize;

    private int[] drawableId = new int[]{R.mipmap.guide_1, R.mipmap.guide_2, R.mipmap.guide_3, R.mipmap.guide_4};

    /**
     *  GuidePageAdapter
     */
    public GuidePageAdapter() {
        mSize = drawableId.length;
    }

    @Override
    public int getCount() {
        return mSize;
    }

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

    @Override
    public Object instantiateItem(ViewGroup view, int position) {

        ImageView imageView = new ImageView(view.getContext());
        imageView.setScaleType(ImageView.ScaleType.CENTER_CROP);
        imageView.setImageResource(drawableId[position]);


        view.addView(imageView, ViewGroup.LayoutParams.MATCH_PARENT, ViewGroup.LayoutParams.MATCH_PARENT);
        mHolderArray.put(position, imageView);
        return imageView;
    }

    @Override
    public void destroyItem(ViewGroup view, int position, Object object) {
        view.removeView(mHolderArray.get(position));
    }

    @Override
    public int getItemPosition(Object object) {
        return POSITION_NONE;
    }
}