1、概述
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"
tools:context="com.example.viewpageranimation.MainActivity" >
<android.support.v4.view.ViewPager
android:id="@+id/view_pager"
android:layout_width="match_parent"
android:layout_height="match_parent"/>
</RelativeLayout>
2.MainActivity.java
public class MainActivity extends Activity {
private ViewPager viewPager;
//這裏是爲了兼容3.0版本下設置動畫效果從新改寫的ViewPager
// private ViewPagerCompat viewPager;
private int[] mImgId = new int[]{R.drawable.guide_image1,R.drawable.guide_image2,R.drawable.guide_image3};
List<ImageView> mImages = new ArrayList<ImageView>();
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
// viewPager = (ViewPagerCompat)findViewById(R.id.view_pager);
viewPager = (ViewPager)findViewById(R.id.view_pager);
viewPager.setAdapter(new PagerAdapter() {
//實例化 Item 創建ImageView
@Override
public Object instantiateItem(ViewGroup container, int position) {
ImageView imageView = new ImageView(MainActivity.this);
imageView.setImageResource(mImgId[position]);
imageView.setScaleType(ScaleType.CENTER_CROP);
container.addView(imageView);
mImages.add(imageView);
return imageView;
}
@Override
public boolean isViewFromObject(View arg0, Object arg1) {
//判斷view是否來自於 arg1 arg1 是初始化的時候添加進去的
return arg0 == arg1;
}
@Override
public int getCount() {
//獲取視圖的長度
return mImgId.length;
}
@Override
public void destroyItem(ViewGroup container, int position,
Object object) {
//移除視圖
container.removeView(mImages.get(position));
}
});
}
}
這樣一個傳統ViewPager就實現了
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。代碼的位置在我們的SDK doc裏面(我用的是6.0)
file:///C:/ProgramFilesWork/android-sdk/docs/training/animation/screen-slide.html
1.Zoom-out page transformer
This page transformer shrinks and fades pages when scrolling between adjacent pages. As a page gets closer to the center, it grows back to its normal size and fades in.
public class ZoomOutPageTransformer implements ViewPager.PageTransformer {
private static final float MIN_SCALE = 0.85f;
private static final float MIN_ALPHA = 0.5f;
public void transformPage(View view, float position) {
int pageWidth = view.getWidth();
int pageHeight = view.getHeight();
if (position < -1) { // [-Infinity,-1)
// This page is way off-screen to the left.
view.setAlpha(0);
} else if (position <= 1) { // [-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:
viewPager.setPageTransformer(true, new ZoomOutPageTransformer());
效果:
2.Depth page transformer
This page transformer uses the default slide animation for sliding pagesto the left, while using a "depth" animation for sliding pages to theright. This depth animation fades the page out, and scales it down linearly.
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:
viewPager.setPageTransformer(true, new DepthPageTransformer());
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ZoomOutPageTransformer
public class ZoomOutPageTransformer implements ViewPager.PageTransformer {
private static final float MIN_SCALE = 0.85f;
private static final float MIN_ALPHA = 0.5f;
public void transformPage(View view, float position) {
/*
* 第一頁向第二頁滑動時,一頁的的position從0到-1,第二頁是從1到0變化
*/
Log.i("meng.li","view = "+view+" position= "+position);
int pageWidth = view.getWidth();
int pageHeight = view.getHeight();
//小於 -1 表示看不見
if (position < -1) { // [-Infinity,-1)
// This page is way off-screen to the left.
// view.setAlpha(0);
ViewHelper.setAlpha(view, 0);
} else if (position <= 1) { // [-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);
ViewHelper.setTranslationX(view, horzMargin-vertMargin/2);
} else {
// view.setTranslationX(-horzMargin + vertMargin / 2);
ViewHelper.setTranslationX(view, -horzMargin + vertMargin / 2);
}
// Scale the page down (between MIN_SCALE and 1)
// view.setScaleX(scaleFactor);
// view.setScaleY(scaleFactor);
ViewHelper.setScaleX(view, scaleFactor);
ViewHelper.setScaleY(view, scaleFactor);
// Fade the page relative to its size.
/* view.setAlpha(MIN_ALPHA +
(scaleFactor - MIN_SCALE) /
(1 - MIN_SCALE) * (1 - MIN_ALPHA));*/
ViewHelper.setAlpha(view, MIN_ALPHA +
(scaleFactor - MIN_SCALE) /
(1 - MIN_SCALE) * (1 - MIN_ALPHA));
} else { // (1,+Infinity] //1 - 無窮表示看不見
// This page is way off-screen to the right.
// view.setAlpha(0);
//使用第三方jar實現3.0以下動畫切換效果
ViewHelper.setAlpha(view, 0);
}
}
}
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 {
/**
* 修改所有 PageTransformer transformer 爲ViewPager.PageTransformer transformer
* 註釋掉版本判斷的代碼
*
*/
public void setPageTransformer(boolean reverseDrawingOrder, ViewPager.PageTransformer transformer) {
//兼容3.0以下也可以使用
// 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
在2.2上測試效果:
可以看到,我們的切換動畫完美的運行在2.2的機器上~~so happy ~~沒有ViewPager源碼的童鞋不要緊,後面會提供ViewPager和屬性動畫Jar包的下載。
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;
效果如下:
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:
/*
* 自定義動畫切換效果,旋轉效果
*/
public class RotatePageTransform implements ViewPager.PageTransformer{
//A頁角度變化從 0 - 負20 度, B頁角度變化從 正20 - 0
private static final float MAX_ROTATE = 20;
private float mRoat = 0;
@Override
public void transformPage(View view, float position) {
int pageWidth = view.getWidth();
int pageHeight = view.getHeight();
//小於 -1 表示看不見
if (position < -1) { // [-Infinity,-1)
ViewHelper.setAlpha(view, 0);
} else if (position <= 0) {
/*
* A頁切換到B頁 A頁的position 0 - -1; B頁的position 1- 0
*/
//0 到 -20
mRoat = position *MAX_ROTATE;
ViewHelper.setPivotX(view, pageWidth/2);
ViewHelper.setPivotY(view, view.getMeasuredHeight());
ViewHelper.setRotation(view, mRoat);
}else if(position <= 1){
// (0,1]
mRoat = position * MAX_ROTATE;
ViewHelper.setPivotX(view, pageWidth/2);
ViewHelper.setPivotY(view, view.getMeasuredHeight());
ViewHelper.setRotation(view, mRoat);
}else { // (1,+Infinity] //1 - 無窮表示看不見
// This page is way off-screen to the right.
// view.setAlpha(0);
//使用第三方jar實現3.0以下動畫切換效果
ViewHelper.setAlpha(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~~
ViewPager 源碼和第三方Jar包下載地址:http://download.csdn.net/detail/u010583599/9587239本文轉載自:http://blog.csdn.net/lmj623565791/article/details/40411921