1、概述
之前寫過一篇博文:Android 自定義 ViewPager 打造千變萬化的圖片切換效果。有兄弟提出,ViewPager自帶了一個setPageTransformer用於設置切換動畫~
本篇博文,將:
1、介紹如何使用setPageTransformer設置切換動畫;
2、自定義PageTransformer實現個性的切換動畫;
3、該方法在SDK11以下的版本不起作用,我們會對其做一定修改,讓其向下兼容。
官方示例地址:http://developer.android.com/training/animation/screen-slide.html 有興趣的可以去看看~~
好了,下面開始編寫代碼~~
2、setPageTransformer的使用
首先我們迅速的實現一個傳統的ViewPager效果~
1、佈局文件
- <RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
- xmlns:tools="http://schemas.android.com/tools"
- android:layout_width="match_parent"
- android:layout_height="match_parent" >
- <android.support.v4.view.ViewPager
- android:id="@+id/id_viewpager"
- android:layout_width="fill_parent"
- android:layout_height="fill_parent" />
- </RelativeLayout>
2、MainActivity
- package com.zhy.demo_zhy_08_viewpageranim;
- import java.util.ArrayList;
- import java.util.List;
- import android.app.Activity;
- import android.os.Bundle;
- import android.support.v4.view.PagerAdapter;
- import android.support.v4.view.ViewPager;
- import android.view.View;
- import android.view.ViewGroup;
- import android.view.Window;
- import android.widget.ImageView;
- import android.widget.ImageView.ScaleType;
- public class MainActivity extends Activity
- {
- private ViewPager mViewPager;
- private int[] mImgIds = new int[] { R.drawable.guide_image1,
- R.drawable.guide_image2, R.drawable.guide_image3 };
- private List<ImageView> mImageViews = new ArrayList<ImageView>();
- @Override
- protected void onCreate(Bundle savedInstanceState)
- {
- super.onCreate(savedInstanceState);
- requestWindowFeature(Window.FEATURE_NO_TITLE);
- setContentView(R.layout.activity_main);
- initData();
- mViewPager = (ViewPager) findViewById(R.id.id_viewpager);
- mViewPager.setAdapter(new PagerAdapter()
- {
- @Override
- public Object instantiateItem(ViewGroup container, int position)
- {
- container.addView(mImageViews.get(position));
- return mImageViews.get(position);
- }
- @Override
- public void destroyItem(ViewGroup container, int position,
- Object object)
- {
- container.removeView(mImageViews.get(position));
- }
- @Override
- public boolean isViewFromObject(View view, Object object)
- {
- return view == object;
- }
- @Override
- public int getCount()
- {
- return mImgIds.length;
- }
- });
- }
- private void initData()
- {
- for (int imgId : mImgIds)
- {
- ImageView imageView = new ImageView(getApplicationContext());
- imageView.setScaleType(ScaleType.CENTER_CROP);
- imageView.setImageResource(imgId);
- mImageViews.add(imageView);
- }
- }
- }
好了,這樣一個傳統ViewPager就實現了~~大家對上面代碼應該不會有任何陌生的感覺~運行效果也不用貼圖了,大家肯定知道~~
3、PageTransformer
ViewPager有個方法叫做:
setPageTransformer(boolean reverseDrawingOrder, PageTransformer transformer) 用於設置ViewPager切換時的動畫效果,並且google官方還給出了兩個示例。
只需要在上述代碼中調用setPageTransformer即可添加切換動畫效果~~下面演示google的兩個PageTransformer的代碼,以及運行效果。
1、DepthPageTransformer
- public class DepthPageTransformer implements ViewPager.PageTransformer {
- private static final float MIN_SCALE = 0.75f;
- public void transformPage(View view, float position) {
- int pageWidth = view.getWidth();
- if (position < -1) { // [-Infinity,-1)
- // This page is way off-screen to the left.
- view.setAlpha(0);
- } else if (position <= 0) { // [-1,0]
- // Use the default slide transition when moving to the left page
- view.setAlpha(1);
- view.setTranslationX(0);
- view.setScaleX(1);
- view.setScaleY(1);
- } else if (position <= 1) { // (0,1]
- // Fade the page out.
- view.setAlpha(1 - position);
- // Counteract the default slide transition
- view.setTranslationX(pageWidth * -position);
- // Scale the page down (between MIN_SCALE and 1)
- float scaleFactor = MIN_SCALE
- + (1 - MIN_SCALE) * (1 - Math.abs(position));
- view.setScaleX(scaleFactor);
- view.setScaleY(scaleFactor);
- } else { // (1,+Infinity]
- // This page is way off-screen to the right.
- view.setAlpha(0);
- }
- }
- }
調用代碼:
- mViewPager.setPageTransformer(true, new DepthPageTransformer());
效果:
2、ZoomOutPageTransformer
- package com.zhy.view;
- 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頁滑動至b頁 ; a頁從 0.0 -1 ;b頁從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);
- }
- }
- }
調用代碼:
- mViewPager.setPageTransformer(true, new ZoomOutPageTransformer());
效果:
效果圖都是google官網上的,我們的測試圖會在兼容3.0以下貼出來,不然就重複了~~
爲ViewPager添加切換就一行代碼是不是很happy,可惜是不兼容3.0以下的版本的,該方法的註釋上寫到:
setting a PageTransformer prior to Android 3.0 (API 11) will have no effect 在3.0之前的版本設置此方法是沒有效果的,那麼下面我們就看如何讓其兼容3.0以下版本。
3、版本的向下兼容
1、不兼容的原因
首先看下爲什麼不兼容,3.0以下呢?
看上面的兩個示例代碼,代碼中View的動畫使用的是屬性動畫,而屬性動畫是3.0才推出的,那麼這麼寫肯定是不兼容3.0以下了~
那麼我們首先引入nineoldandroids,讓動畫先能在3.0以下跑再說:
修改DepthPageTransformer
- package com.zhy.view;
- import com.nineoldandroids.view.ViewHelper;
- import android.annotation.SuppressLint;
- import android.support.v4.view.ViewPager;
- import android.view.View;
- public class DepthPageTransformer implements ViewPager.PageTransformer
- {
- private static final float MIN_SCALE = 0.75f;
- public void transformPage(View view, float position)
- {
- int pageWidth = view.getWidth();
- if (position < -1)
- { // [-Infinity,-1)
- // This page is way off-screen to the left.
- // view.setAlpha(0);
- ViewHelper.setAlpha(view, 0);
- } else if (position <= 0)// a頁滑動至b頁 ; a頁從 0.0 -1 ;b頁從1 ~ 0.0
- { // [-1,0]
- // Use the default slide transition when moving to the left page
- // view.setAlpha(1);
- ViewHelper.setAlpha(view, 1);
- // view.setTranslationX(0);
- ViewHelper.setTranslationX(view, 0);
- // view.setScaleX(1);
- ViewHelper.setScaleX(view, 1);
- // view.setScaleY(1);
- ViewHelper.setScaleY(view, 1);
- } else if (position <= 1)
- { // (0,1]
- // Fade the page out.
- // view.setAlpha(1 - position);
- ViewHelper.setAlpha(view, 1 - position);
- // Counteract the default slide transition
- // view.setTranslationX(pageWidth * -position);
- ViewHelper.setTranslationX(view, pageWidth * -position);
- // Scale the page down (between MIN_SCALE and 1)
- float scaleFactor = MIN_SCALE + (1 - MIN_SCALE) * (1 - position);
- // view.setScaleX(scaleFactor);
- ViewHelper.setScaleX(view, scaleFactor);
- // view.setScaleY(1);
- ViewHelper.setScaleY(view, scaleFactor);
- } else
- { // (1,+Infinity]
- // This page is way off-screen to the right.
- // view.setAlpha(0);
- ViewHelper.setAlpha(view, 1);
- }
- }
- }
很簡單,把所有屬性動畫換成ViewHelper去設置就好了。現在我們去3.0以下的機子上去運行,發現還是沒有效果~~~
爲什麼呢?
我們再去看看setPageTransformer的源碼:
- public void setPageTransformer(boolean reverseDrawingOrder, PageTransformer transformer) {
- if (Build.VERSION.SDK_INT >= 11) {
- final boolean hasTransformer = transformer != null;
- final boolean needsPopulate = hasTransformer != (mPageTransformer != null);
- mPageTransformer = transformer;
- setChildrenDrawingOrderEnabledCompat(hasTransformer);
- if (hasTransformer) {
- mDrawingOrder = reverseDrawingOrder ? DRAW_ORDER_REVERSE : DRAW_ORDER_FORWARD;
- } else {
- mDrawingOrder = DRAW_ORDER_DEFAULT;
- }
- if (needsPopulate) populate();
- }
- }
終於發現原因了,原來在此方法內部判斷了如果是11以上的版本才讓動畫生效~~
那麼,沒辦法了,如果想兼容,必須修改ViewPager的源碼了~~
2、完美向下兼容
我們將ViewPager的源碼拷貝一份至我們的項目中,修改名稱爲ViewPagerCompat;然後註釋掉SDK版本判斷那一句
public class ViewPagerCompat extends ViewGroup {
- public void setPageTransformer(boolean reverseDrawingOrder, ViewPager.PageTransformer transformer) {
- // if (Build.VERSION.SDK_INT >= 11)
- {
- final boolean hasTransformer = transformer != null;
- final boolean needsPopulate = hasTransformer != (mPageTransformer != null);
- mPageTransformer = transformer;
- setChildrenDrawingOrderEnabledCompat(hasTransformer);
- if (hasTransformer) {
- mDrawingOrder = reverseDrawingOrder ? DRAW_ORDER_REVERSE : DRAW_ORDER_FORWARD;
- } else {
- mDrawingOrder = DRAW_ORDER_DEFAULT;
- }
- if (needsPopulate) populate();
- }
- }
}
注意,所有的PageTransformer使用ViewPager.PageTransformer
然後我們把項目中的ViewPager改爲ViewPagerCompat;記得修改佈局文件,以及MainActivity中的ViewPager爲ViewPagerCompat
我們在2.3.3的模擬器上測試下效果:
可以看到,我們的切換動畫完美的運行在2.3.3的機器上~~so happy ~~沒有ViewPager源碼的童鞋不要緊,我會在文末的源碼下載中加入ViewPager源碼,讓你可以盡情去測試~~
當然了,僅僅是兼容當然不能滿足我們的好奇心,難道我們做到了兼容,還只能使用Google給的示例動畫麼~~我們強大的創新呢~~下面帶領大家分析setPageTransformer方法,然後設計一個個性的動畫切換效果
4、自定義PageTransformer實現個性切換動畫
- public interface PageTransformer {
- /**
- * Apply a property transformation to the given page.
- *
- * @param page Apply the transformation to this page
- * @param position Position of page relative to the current front-and-center
- * position of the pager. 0 is front and center. 1 is one full
- * page position to the right, and -1 is one page position to the left.
- */
- public void transformPage(View page, float position);
- }
可以看到該接口只有一個方法,第一個是我們的view,第二個是position~~
當我們滑動時:會打印出當然ViewPager中存活的每個View以及它們的position的變化~~注意是每一個,所以建議別隻log position,不然你會覺得莫名其妙的輸出~~
position的可能性的值有,其實從官方示例的註釋就能看出:
[-Infinity,-1) 已經看不到了
(1,+Infinity] 已經看不到了
[-1,1]
重點看[-1,1]這個區間 , 其他兩個的View都已經看不到了~~
假設現在ViewPager在A頁現在滑出B頁,則:
A頁的position變化就是( 0, -1]
B頁的position變化就是[ 1 , 0 ]
知道了我們滑動時position的變化~~那麼就開始設計我們的個性的切換效果;
官方給的例子,有變化透明度、偏移量、縮放的,我們準備來個不一樣的,我們變化角度,即rotation;
大概的效果是這樣的:
下面我們分析代碼:
我們設置View的旋轉中心爲:
ViewHelper.setPivotX(view, view.getMeasuredWidth() * 0.5f);
ViewHelper.setPivotY(view, view.getMeasuredHeight());
依然是ViewPager在A頁現在滑出B頁
那麼A頁應當在滑動過程中0度到-20度的偏移,B頁應當在滑動過程中+20度到0度的偏移
結合
A頁的position變化就是( 0, -1]
B頁的position變化就是[ 1 , 0 ]
那麼旋轉的角度即:mRot = (20 * position); A頁 mRot :0 ,~ -20 ; B頁 mRot :20 ~ 0 ;
瞬間覺得好簡單:
完整代碼:
- package com.zhy.view;
- import com.nineoldandroids.view.ViewHelper;
- import android.annotation.SuppressLint;
- import android.support.v4.view.ViewPager;
- import android.util.Log;
- import android.view.View;
- public class RotateDownPageTransformer implements ViewPager.PageTransformer
- {
- private static final float ROT_MAX = 20.0f;
- private float mRot;
- public void transformPage(View view, float position)
- {
- Log.e("TAG", view + " , " + position + "");
- if (position < -1)
- { // [-Infinity,-1)
- // This page is way off-screen to the left.
- ViewHelper.setRotation(view, 0);
- } else if (position <= 1) // a頁滑動至b頁 ; a頁從 0.0 ~ -1 ;b頁從1 ~ 0.0
- { // [-1,1]
- // Modify the default slide transition to shrink the page as well
- if (position < 0)
- {
- mRot = (ROT_MAX * position);
- ViewHelper.setPivotX(view, view.getMeasuredWidth() * 0.5f);
- ViewHelper.setPivotY(view, view.getMeasuredHeight());
- ViewHelper.setRotation(view, mRot);
- } else
- {
- mRot = (ROT_MAX * position);
- ViewHelper.setPivotX(view, view.getMeasuredWidth() * 0.5f);
- ViewHelper.setPivotY(view, view.getMeasuredHeight());
- ViewHelper.setRotation(view, mRot);
- }
- // Scale the page down (between MIN_SCALE and 1)
- // Fade the page relative to its size.
- } else
- { // (1,+Infinity]
- // This page is way off-screen to the right.
- ViewHelper.setRotation(view, 0);
- }
- }
- }
你沒看錯,if else 裏面代碼是一樣的,爲了好理解特意沒有合併到一起~~~
到此,我們從setPageTransformer使用,到修改ViewPager做到向下兼容,直至自己定義出個性的切換效果 都已經介紹完畢~~
大家可以發揮自己的創造力,做出各種神奇的動畫效果,ok,就到這裏!
如果你喜歡自定義ViewPager來實現,請移步:Android 自定義 ViewPager 打造千變萬化的圖片切換效果