Android 動畫分析之翻轉效果
大家一定看到過三維的翻轉效果,所以今天在這裡簡單的給大家分析一下,我們怎麼樣才能實現Android中的翻轉動畫效果的實現,首先看一下執行效果如下圖所示。
效果圖:
Android中並沒有提供直接做3D翻轉的動畫,所以關於3D翻轉的動畫效果需要我們自己實現,那麼我們首先來分析一下Animation 和 Transformation。
Animation動畫的主要介面,其中主要定義了動畫的一些屬性比如開始時間,持續時間,是否重複播放等等。而Transformation中則包含一個矩陣和alpha值,矩陣是用來做平移,旋轉和縮放動畫的,而alpha值是用來做alpha動畫的,要實現3D旋轉動畫我們需要繼承自Animation類來實現,我們需要過載getTransformation和applyTransformation,在getTransformation中Animation會根據動畫的屬性來產生一系列的差值點,然後將這些差值點傳給applyTransformation,這個函式將根據這些點來生成不同的Transformation。下面是具體實現:
public class Rotate3dAnimation extends Animation { // 開始角度 private final float mFromDegrees; // 結束角度 private final float mToDegrees; // 中心點 private final float mCenterX; private final float mCenterY; private final float mDepthZ; // 是否需要扭曲 private final boolean mReverse; // 攝像頭 private Camera mCamera; public Rotate3dAnimation(float fromDegrees, float toDegrees, float centerX, float centerY, float depthZ, boolean reverse) { mFromDegrees = fromDegrees; mToDegrees = toDegrees; mCenterX = centerX; mCenterY = centerY; mDepthZ = depthZ; mReverse = reverse; } @Override public void initialize(int width, int height, int parentWidth, int parentHeight) { super.initialize(width, height, parentWidth, parentHeight); mCamera = new Camera(); } // 生成Transformation @Override protected void applyTransformation(float interpolatedTime, Transformation t) { final float fromDegrees = mFromDegrees; // 生成中間角度 float degrees = fromDegrees + ((mToDegrees - fromDegrees) * interpolatedTime); final float centerX = mCenterX; final float centerY = mCenterY; final Camera camera = mCamera; final Matrix matrix = t.getMatrix(); camera.save(); if (mReverse) { camera.translate(0.0f, 0.0f, mDepthZ * interpolatedTime); } else { camera.translate(0.0f, 0.0f, mDepthZ * (1.0f - interpolatedTime)); } camera.rotateY(degrees); // 取得變換後的矩陣 camera.getMatrix(matrix); camera.restore(); matrix.preTranslate(-centerX, -centerY); matrix.postTranslate(centerX, centerY); } }
其中包括了旋轉的開始和結束角度,中心點、是否扭曲、和一個Camera,這裡我們主要分析applyTransformation函式,其中第一個引數就是通過getTransformation函式傳遞的差指點,然後我們根據這個差值通過線性差值演算法計算出一箇中間角度degrees,Camera類是用來實現繞Y軸旋轉後透視投影的,因此我們首先通過t.getMatrix()取得當前的矩陣,然後通過camera.translate來對矩陣進行平移變換操作,camera.rotateY進行旋轉。這樣我們就可以很輕鬆的實現3D旋轉效果了,該例子的原意是通過一個列表來供使用者選擇要實現翻轉的影象,所以我們分析至少需要定義兩個控制元件:ListView和ImageView(要翻轉的影象),主介面的xml佈局定義如下所示。
<FrameLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:id="@+id/container"
android:layout_width="match_parent"
android:layout_height="match_parent" >
<ListView
android:id="@android:id/list"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:layoutAnimation="@anim/layout_bottom_to_top_slide"
android:persistentDrawingCache="animation|scrolling" />
<ImageView
android:id="@+id/picture"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:scaleType="fitCenter"
android:visibility="gone" />
</FrameLayout>
然後準備好需要的資源,在onCreate函式中準備好ListView和ImageView,因為要旋轉所以我們需要儲存檢視的快取資訊,通過setPersistentDrawingCache(ViewGroup.PERSISTENT_ANIMATION_CACHE);可以設定該功能,當我們選擇列表中的影象資源後在onItemClick中將選擇的資源Id對應的影象設定到ImageView中,然後通過applyRotation來啟動一個動畫,前面有了Rotate3dAnimation的實現,我們要完成3D翻轉動畫就很簡單,直接構建一個Rotate3dAnimation物件,設定其屬性(包括動畫監聽),這裡將動畫的監聽設定為DisplayNextView,可以用來顯示下一個檢視,在其中的動畫結束監聽(onAnimationEnd)中,通過一個縣城SwapViews來交換兩個畫面,交換過程則是設定ImageView和ListView的顯示相關屬性,並構建一個Rotate3dAnimation物件,對另一個介面進行旋轉即可,然後啟動動畫,整個轉換過程實際上就是將第一個介面從0度轉好90度,然後就愛你過第二個介面從90度轉到0度,這樣就形成了一個翻轉動畫,完整程式碼如下,我們也加入了一些必要的註解。
public class Transition3d extends Activity implements
AdapterView.OnItemClickListener, View.OnClickListener {
// 照片列表
private ListView mPhotosList;
private ViewGroup mContainer;
private ImageView mImageView;
// 照片的名字,用於顯示在list中
private static final String[] PHOTOS_NAMES = new String[] { "Lyon",
"Livermore", "Tahoe Pier", "Lake Tahoe", "Grand Canyon", "Bodie" };
// 資源id
private static final int[] PHOTOS_RESOURCES = new int[] {
R.drawable.photo1, R.drawable.photo2, R.drawable.photo3,
R.drawable.photo4, R.drawable.photo5, R.drawable.photo6 };
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.animations_main_screen);
mPhotosList = (ListView) findViewById(android.R.id.list);
mImageView = (ImageView) findViewById(R.id.picture);
mContainer = (ViewGroup) findViewById(R.id.container);
// 準備ListView
final ArrayAdapter<String> adapter = new ArrayAdapter<String>(this,
android.R.layout.simple_list_item_1, PHOTOS_NAMES);
mPhotosList.setAdapter(adapter);
mPhotosList.setOnItemClickListener(this);
// 準備ImageView
mImageView.setClickable(true);
mImageView.setFocusable(true);
mImageView.setOnClickListener(this);
// 設定需要儲存快取
mContainer.setPersistentDrawingCache(ViewGroup.PERSISTENT_ANIMATION_CACHE);
}
/**
* Setup a new 3D rotation on the container view.
* @param position
* the item that was clicked to show a picture, or -1 to show the
* list
* @param start
* the start angle at which the rotation must begin
* @param end
* the end angle of the rotation
*/
private void applyRotation(int position, float start, float end) {
// 計算中心點
final float centerX = mContainer.getWidth() / 2.0f;
final float centerY = mContainer.getHeight() / 2.0f;
// Create a new 3D rotation with the supplied parameter
// The animation listener is used to trigger the next animation
final Rotate3dAnimation rotation = new Rotate3dAnimation(start, end,
centerX, centerY, 310.0f, true);
rotation.setDuration(500);
rotation.setFillAfter(true);
rotation.setInterpolator(new AccelerateInterpolator());
// 設定監聽
rotation.setAnimationListener(new DisplayNextView(position));
mContainer.startAnimation(rotation);
}
public void onItemClick(AdapterView parent, View v, int position, long id) {
// 設定ImageView
mImageView.setImageResource(PHOTOS_RESOURCES[position]);
applyRotation(position, 0, 90);
}
// 點選影象時,返回listview
public void onClick(View v) {
applyRotation(-1, 180, 90);
}
/**
* This class listens for the end of the first half of the animation. It
* then posts a new action that effectively swaps the views when the
* container is rotated 90 degrees and thus invisible.
*/
private final class DisplayNextView implements Animation.AnimationListener {
private final int mPosition;
private DisplayNextView(int position) {
mPosition = position;
}
public void onAnimationStart(Animation animation) {
}
// 動畫結束
public void onAnimationEnd(Animation animation) {
mContainer.post(new SwapViews(mPosition));
}
public void onAnimationRepeat(Animation animation) {
}
}
/**
* This class is responsible for swapping the views and start the second
* half of the animation.
*/
private final class SwapViews implements Runnable {
private final int mPosition;
public SwapViews(int position) {
mPosition = position;
}
public void run() {
final float centerX = mContainer.getWidth() / 2.0f;
final float centerY = mContainer.getHeight() / 2.0f;
Rotate3dAnimation rotation;
if (mPosition > -1) {
// 顯示ImageView
mPhotosList.setVisibility(View.GONE);
mImageView.setVisibility(View.VISIBLE);
mImageView.requestFocus();
rotation = new Rotate3dAnimation(90, 180, centerX, centerY, 310.0f, false);
} else {
// 返回listview
mImageView.setVisibility(View.GONE);
mPhotosList.setVisibility(View.VISIBLE);
mPhotosList.requestFocus();
rotation = new Rotate3dAnimation(90, 0, centerX, centerY, 310.0f, false);
}
rotation.setDuration(500);
rotation.setFillAfter(true);
rotation.setInterpolator(new DecelerateInterpolator());
// 開始動畫
mContainer.startAnimation(rotation);
}
}
}