<span role="heading" aria-level="2">ViewPager基本用法

大家好，又见面了，我是你们的朋友全栈君。

step1：在layout中定义一个ViewPager组件。

<android.support.v4.view.ViewPager>

step2：在Activity中获取ViewPager的引用。

pager=(ViewPager) findViewById(R.id.view_pager);

step3: 为ViewPager设置适配器，

PagerAdapter adapter=new ViewAdapter(pages); pager.setAdapter(adapter);

step4：为ViewPager设置滑动特效

浮现特效：Google为我们提供了API,android.support.v4.view.ViewPager.PageTransformer接口

public void transformPage(View page, float position)

page表示ViewPager中的一页，position[0,0]表示当前屏幕的一页，[0，-1]表示屏幕左边第一页，【0,1】表示屏幕右边第一页

当`page`向左边滑动时，`position`从0向-1变化，当`position==-1`时完全不可见；当`page`向右滑动时，`position`从0向1变化，当`position==1`时完全不可见。

//滑动特效

public class ScalePageTransformer implements ViewPager.PageTransformer { private static final float MIN_SCALE=0.75f; @Override public void transformPage(View page, float position) { //Log.d("TAG", "<"+page.hashCode()+", "+position+">"); // out of left screen if(position<-1.0f) { page.setScaleX(MIN_SCALE); page.setScaleY(MIN_SCALE); } // slide left else if(position<=0.0f) { page.setAlpha(1.0f); page.setTranslationX(0.0f); page.setScaleX(1.0f); page.setScaleY(1.0f); } // slide right else if(position<=1.0f) { page.setAlpha(1.0f-position); page.setTranslationX(-page.getWidth()*position); float scale=MIN_SCALE+(1.0f-MIN_SCALE)*(1.0f-position); page.setScaleX(scale); page.setScaleY(scale); } // out of right screen else { page.setScaleX(MIN_SCALE); page.setScaleY(MIN_SCALE); } } } //旋转特效 public class RotatePageTransformer implements ViewPager.PageTransformer { private static final float MAX_ROTATION=20.0f; @Override public void transformPage(View page, float position) { if(position<-1) rotate(page, -MAX_ROTATION); else if(position<=1) rotate(page, MAX_ROTATION*position); else rotate(page, MAX_ROTATION); } private void rotate(View view, float rotation) { view.setPivotX(view.getWidth()*0.5f); view.setPivotY(view.getHeight()); view.setRotation(rotation); } } // 3d相册---1.围绕Y轴旋转一定的角度 public class GalleryPageTransformer implements ViewPager.PageTransformer { private static final float MAX_ROTATION=20.0f; private static final float MIN_SCALE=0.75f; private static final float MAX_TRANSLATE=20.0f; @Override public void transformPage(View page, float position) { if(position<-1) { page.setTranslationX(MAX_TRANSLATE); page.setScaleX(MIN_SCALE); page.setScaleY(MIN_SCALE); page.setRotationY(-MAX_ROTATION); } else if(position<=0) { page.setTranslationX(-MAX_TRANSLATE*position); float scale=MIN_SCALE+(1-MIN_SCALE)*(1.0f+position); page.setScaleX(scale); page.setScaleY(scale); page.setRotationY(MAX_ROTATION*position); } else if(position<=1) { page.setTranslationX(-MAX_TRANSLATE*position); float scale=MIN_SCALE+(1-MIN_SCALE)*(1.0f-position); page.setScaleX(scale); page.setScaleY(scale); page.setRotationY(MAX_ROTATION*position); } else { page.setTranslationX(-MAX_TRANSLATE); page.setScaleX(MIN_SCALE); page.setScaleY(MIN_SCALE); page.setRotationY(MAX_ROTATION); } } } // 3d相册---2.生成有倒影的图片 public static Bitmap getReverseBitmapById(Context context, int resId, float percent) { // get the source bitmap  Bitmap srcBitmap=BitmapFactory.decodeResource(context.getResources(), resId); // get the tow third segment of the reverse bitmap  Matrix matrix=new Matrix(); matrix.setScale(1, -1); Bitmap rvsBitmap=Bitmap.createBitmap(srcBitmap, 0, (int) (srcBitmap.getHeight()*(1-percent)), srcBitmap.getWidth(), (int) (srcBitmap.getHeight()*percent), matrix, false); // combine the source bitmap and the reverse bitmap  Bitmap comBitmap=Bitmap.createBitmap(srcBitmap.getWidth(), srcBitmap.getHeight()+rvsBitmap.getHeight()+20, srcBitmap.getConfig()); Canvas gCanvas=new Canvas(comBitmap); gCanvas.drawBitmap(srcBitmap, 0, 0, null); gCanvas.drawBitmap(rvsBitmap, 0, srcBitmap.getHeight()+20, null); Paint paint=new Paint(); LinearGradient shader=new LinearGradient(0, srcBitmap.getHeight()+20, 0, comBitmap.getHeight(), Color.BLACK, Color.TRANSPARENT, Shader.TileMode.CLAMP); paint.setShader(shader); paint.setXfermode(new PorterDuffXfermode(PorterDuff.Mode.DST_IN)); gCanvas.drawRect(0, srcBitmap.getHeight()+20, srcBitmap.getWidth(), comBitmap.getHeight(), paint); return comBitmap; } // 3d相册---3.对原图进行处理 private List<View> getPages() { List<View> pages=new ArrayList<>(); Field[] fields=R.drawable.class.getDeclaredFields(); try { for (Field field : fields) { if (field.getName().startsWith("page")) { ImageView view = new ImageView(this); view.setImageBitmap(ImageUtils.getReverseBitmapById(this, field.getInt(null), 0.5f)); pages.add(view); } } } catch (IllegalAccessException e) { e.printStackTrace(); } return pages; } step5：为这个pager添加这个特效 pager.setPageTransformer(true, new ScalePageTransformer()); step6: 设置监听 mViewPager.addOnPageChangeListener(new ViewPager.OnPageChangeListener() { @Override public void onPageScrolled(int position, float positionOffset, int positionOffsetPixels) { } @Override public void onPageSelected(int position) { mBottomNavigationBar.selectTab(position); setDarkStatusIcon(position != 2); } @Override public void onPageScrollStateChanged(int state) { } });