℃江让您从精通到入门：Android Studio 简单实现ViewPager，可做APP操作提示

阳光穿透心脏的1/2处 2022-06-17 10:09 123阅读 0赞

*  前期准备，如下图：![这里写图片描述][SouthEast]
 *  第一步、先书写布局文件：activity\_main.xml文件如下：

<?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">
    
        <android.support.v4.view.ViewPager android:id="@+id/viewpager" android:layout_width="match_parent" android:layout_height="match_parent">
    
        </android.support.v4.view.ViewPager>
    
    </RelativeLayout>

*  第二步、在MainAvtivity中声明控件并使用自带的适配器操作List的方式，操作页面切换。MainActivity代码如下：

package com.example.dujiang0311.viewpager;
    
    import android.support.v4.view.PagerAdapter;
    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.ImageView;
    
    import java.util.ArrayList;
    import java.util.List;
    
    public class MainActivity extends AppCompatActivity { 
    
        private ViewPager mViewPager;
        private int[] mImgId = new int[]{R.drawable.p1, R.drawable.p2, R.drawable.p3};
    
        private List<ImageView> mList = new ArrayList<>();
    
        @Override
        protected void onCreate(Bundle savedInstanceState) {
            super.onCreate(savedInstanceState);
            setContentView(R.layout.activity_main);
    
            mViewPager = (ViewPager) findViewById(R.id.viewpager);
            //为ViewPager添加动画效果
            mViewPager.setPageTransformer(true,new ZoomOutPageTransformer());
            mViewPager.setAdapter(new PagerAdapter() {
    
                @Override
                public void destroyItem(ViewGroup container, int position, Object object) {
                  container.removeView(mList.get(position));
                }
    
                @Override
                public Object instantiateItem(ViewGroup container, int position) {
                    ImageView imageView = new ImageView(MainActivity.this);
                    imageView.setImageResource(mImgId[position]);
                    imageView.setScaleType(ImageView.ScaleType.CENTER_CROP);
                    container.addView(imageView);
                    mList.add(imageView);
                    return imageView;
                }
    
                @Override
                public int getCount() {
                    return mImgId.length;
                }
    
                @Override
                public boolean isViewFromObject(View view, Object object) {
                    return view == object;
                }
            });
        }
    }

*  动画切换类的书写（官方文档的例子）：ZoomOutPageTransformer代码书写如下：

package com.example.dujiang0311.viewpager;
    
    /** * 项目名： ViewPager * 包名： com.example.dujiang0311.viewpager * 创建者： Dujiang0311 * 创建时间：2017/4/23 19:38 * 描述： TODO */
    
    import android.annotation.SuppressLint;
    import android.support.v4.view.ViewPager;
    import android.util.Log;
    import android.view.View;
    
    public class ZoomOutPageTransformer implements ViewPager.PageTransformer { 
        private static final float MIN_SCALE = 0.85f;
        private static final float MIN_ALPHA = 0.5f;
    
        @SuppressLint("NewApi")
        public void transformPage(View view, float position)
        {
            int pageWidth = view.getWidth();
            int pageHeight = view.getHeight();
    
            Log.e("TAG", view + " , " + position + "");
    
            if (position < -1)
            { // [-Infinity,-1)
                // This page is way off-screen to the left.
                view.setAlpha(0);
    
            } else if (position <= 1) //a页滑动至b页 ； a页从 0.0 -1 ；b页从1 ~ 0.0
            { // [-1,1]
                // Modify the default slide transition to shrink the page as well
                float scaleFactor = Math.max(MIN_SCALE, 1 - Math.abs(position));
                float vertMargin = pageHeight * (1 - scaleFactor) / 2;
                float horzMargin = pageWidth * (1 - scaleFactor) / 2;
                if (position < 0)
                {
                    view.setTranslationX(horzMargin - vertMargin / 2);
                } else
                {
                    view.setTranslationX(-horzMargin + vertMargin / 2);
                }
    
                // Scale the page down (between MIN_SCALE and 1)
                view.setScaleX(scaleFactor);
                view.setScaleY(scaleFactor);
    
                // Fade the page relative to its size.
                view.setAlpha(MIN_ALPHA + (scaleFactor - MIN_SCALE)
                        / (1 - MIN_SCALE) * (1 - MIN_ALPHA));
    
            } else
            { // (1,+Infinity]
                // This page is way off-screen to the right.
                view.setAlpha(0);
            }
        }
    }

*  注意：如果想做闪屏的操作提示模块，可以在FlashActivity中加判断，判断用户是否是第一次打开APP，然后就可以了。

[SouthEast]: /images/20220617/a2a70853cf5a4da1bc87a3b24d340f08.png