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android千变万化的ViewPager之二
之一已经说了，怎么实现图片的切换。这里我说下怎么给切换的动画添加动画，对！你没听错，我们要给ViewPager加动画了。
首先贴上源代码代码
1 package com.example.android_viewpager; 2 3 import java.util.ArrayList; 4 import java.util.List; 5 6 import android.app.Activity; 7 import android.os.Bundle; 8 import android.support.v4.view.PagerAdapter; 9 import android.support.v4.view.ViewPager;10 import android.view.View;11 import android.view.ViewGroup;12 import android.widget.ImageView;13 import android.widget.ImageView.ScaleType;14 15 public class MainActivity extends Activity {16 private ViewPager viewpager = null;17 private int[] res = new int[] { R.drawable.guide_image1, R.drawable.guide_image2, R.drawable.guide_image3 };18 private List<ImageView>list = new ArrayList<ImageView>();19 protected void onCreate(Bundle savedInstanceState) {20 super.onCreate(savedInstanceState);21 setContentView(R.layout.activity_main);22 viewpager = (ViewPager) findViewById(R.id.viewpager);23 viewpager.setPageTransformer(true, new DepthPageTransformer());24 viewpager.setAdapter(new PagerAdapter() {25 @Override26 public Object instantiateItem(ViewGroup container, int position) {27 ImageView imageview = new ImageView(MainActivity.this);28 imageview.setImageResource(res[position]);29 imageview.setScaleType(ScaleType.CENTER_CROP);30 container.addView(imageview);31 list.add(imageview);32 return imageview;33 }34 @Override35 public void destroyItem(ViewGroup container, int position, Object object) {36 // TODO Auto-generated method stub37 container.removeView(list.get(position));38 }39 public boolean isViewFromObject(View arg0, Object arg1) {40 // TODO Auto-generated method stub41 return arg0 == arg1;42 }43 44 @Override45 public int getCount() {46 // TODO Auto-generated method stub47 return res.length;48 }49 });50 }51 }
看上面的代码，我们会发现比原来的代码多了一行，这就是会ViewPager设置了动画，但是那个莫名其妙的类从哪里来的？
从API中可以看出setPageTransformer方法原型是：setPageTransformer(boolean reverseDrawingOrder, ViewPager.PageTransformer transformer)；第一个参数是布尔类型，就不用说了，而第二个参数是啥？PageTransformer类型参数？
我来解释下PageTransformer类，它是一个接口，专门用来给ViewPager添加动画的。它里面只有一个抽象方法public void transformPage(View view, float position)。我们通常操作这个方法来给ViewPager添加动画。
然后，我们来看看怎么怎么使用PageTransformer类。首先我们使用的它的子类，而且是自定义的子类，为什么？因为它没有系统的子类。那怎么创建它的子类呢？我从安卓官方的API上抄来了两个代码，供大家参考
1.DepthPageTransformer类
1 private static final float MIN_SCALE = 0.75f; 2 3 public void transformPage(View view, float position) { 4 int pageWidth = view.getWidth(); 5 6 if (position < -1) { // [-Infinity,-1) 7 // This page is way off-screen to the left. 8 view.setAlpha(0); 9 10 } else if (position <= 0) { // [-1,0]11 // Use the default slide transition when moving to the left page12 view.setAlpha(1);13 view.setTranslationX(0);14 view.setScaleX(1);15 view.setScaleY(1);16 17 } else if (position <= 1) { // (0,1]18 // Fade the page out.19 view.setAlpha(1 - position);20 21 // Counteract the default slide transition22 view.setTranslationX(pageWidth * -position);23 24 // Scale the page down (between MIN_SCALE and 1)25 float scaleFactor = MIN_SCALE26 + (1 - MIN_SCALE) * (1 - Math.abs(position));27 view.setScaleX(scaleFactor);28 view.setScaleY(scaleFactor);29 30 } else { // (1,+Infinity]31 // This page is way off-screen to the right.32 view.setAlpha(0);33 }34 }
2.ZoomOutPageTransformer类
1 private static final float MIN_SCALE = 0.85f; 2 private static final float MIN_ALPHA = 0.5f; 3 4 public void transformPage(View view, float position) { 5 int pageWidth = view.getWidth(); 6 int pageHeight = view.getHeight(); 7 8 if (position < -1) { // [-Infinity,-1) 9 // This page is way off-screen to the left.10 view.setAlpha(0);11 12 } else if (position <= 1) { // [-1,1]13 // Modify the default slide transition to shrink the page as well14 float scaleFactor = Math.max(MIN_SCALE, 1 - Math.abs(position));15 float vertMargin = pageHeight * (1 - scaleFactor) / 2;16 float horzMargin = pageWidth * (1 - scaleFactor) / 2;17 if (position < 0) {18 view.setTranslationX(horzMargin - vertMargin / 2);19 } else {20 view.setTranslationX(-horzMargin + vertMargin / 2);21 }22 23 // Scale the page down (between MIN_SCALE and 1)24 view.setScaleX(scaleFactor);25 view.setScaleY(scaleFactor);26 27 // Fade the page relative to its size.28 view.setAlpha(MIN_ALPHA +29 (scaleFactor - MIN_SCALE) /30 (1 - MIN_SCALE) * (1 - MIN_ALPHA));31 32 } else { // (1,+Infinity]33 // This page is way off-screen to the right.34 view.setAlpha(0);35 }36 }
我们可以通过这两个代码来给ViewPager加上动画。
android千变万化的ViewPager之二
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