實現需求是：
在商品列表頁面，從列表Item 添加商品的時候，需要一個動畫，彷彿是是往購物車裏添加商品。實現思路：
- 獲取起始點與終點的座標，利用PathMeasure 繪製貝塞爾曲線；
- 爲點擊的Item 商品View 設置屬性動畫；
- 監聽屬性動畫的update，改變View 的座標；
實現效果如下：
實現中會用到 PathMeasure 類：
我們主要使用它兩個方法：
1、獲取長度：
/** //獲取弧線的總長度（周長）
* Return the total length of the current contour, or 0 if no path is
* associated with this measure object.
*/
public float getLength() {
return native_getLength(native_instance);//系統調用native 方法；
}2、獲取座標:
/**
* Pins distance to 0 <= distance <= getLength(), and then computes the
* corresponding position and tangent. Returns false if there is no path,
* or a zero-length path was specified, in which case position and tangent
* are unchanged.
*
* @param distance The distance along the current contour to sample
* @param pos If not null, eturns the sampled position (x==[0], y==[1])
* @param tan If not null, returns the sampled tangent (x==[0], y==[1])
* @return false if there was no path associated with this measure object
*/
public boolean getPosTan(float distance, float pos[], float tan[]) {
if (pos != null && pos.length < 2 ||
tan != null && tan.length < 2) {
throw new ArrayIndexOutOfBoundsException();
}
return native_getPosTan(native_instance, distance, pos, tan);
}方法 getPosTan(float distance, float pos[],float tan[]) － path 爲 null ，返回 false
distance 爲一個 0 － getLength() 之間的值，根據這個值 PathMeasure 會計算出當前點的座標封裝到 pos 中。上面這句話我們可以這麼來理解，不管實際 Path 多麼的複雜，PathMeasure 都相當於做了一個事情，就是把 Path “拉直”，然後給了我們一個接口(getLength)告訴我們path的總長度，然後我們想要知道具體某一點的座標，只需要用相對的distance去取即可，這樣就省去了自己用函數模擬path，然後計算獲取點座標的過程。
代碼如下：
public class GoodsListActivity extends AppCompatActivity {
private RelativeLayout mRootRl;
private RecyclerView mGoodsRecyclerView;
private ImageView mCarImageView;
private TextView mCountTv;
private List<Bitmap> mBitmapList = new ArrayList<>();
private PathMeasure mPathMeasure;
private float[] mCurrentPosition = new float[2];
private int mCount = 0;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_goods_list);
initView();
initData();
GoodsAdapter goodsAdapter = new GoodsAdapter(mBitmapList);
mGoodsRecyclerView.setLayoutManager(new LinearLayoutManager(this));
mGoodsRecyclerView.setAdapter(goodsAdapter);
}
private void initView(){
mGoodsRecyclerView = (RecyclerView)findViewById(R.id.recyclerView);
mCarImageView = (ImageView)findViewById(R.id.imageview_shop_car);
mCountTv = (TextView)findViewById(R.id.tv_count);
mRootRl = (RelativeLayout)findViewById(R.id.rl_root);
}
private void initData(){
mBitmapList.add(BitmapFactory.decodeResource(getResources(), R.drawable.car));
mBitmapList.add(BitmapFactory.decodeResource(getResources(), R.drawable.car));
mBitmapList.add(BitmapFactory.decodeResource(getResources(), R.drawable.car));
}
class GoodsAdapter extends RecyclerView.Adapter<GoodsViewHolder>{
private List<Bitmap> mData;
public GoodsAdapter(List<Bitmap> data) {
mData = data;
}
@Override
public GoodsViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
View itemView = LayoutInflater.from(GoodsListActivity.this)
.inflate(R.layout.rv_goods_item, parent, false);
return new GoodsViewHolder(itemView);
}
@Override
public void onBindViewHolder(final GoodsViewHolder holder, int position) {
holder.ivGood.setImageBitmap(mData.get(position));
holder.tvBuy.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
addGoodToCar(holder.ivGood);
}
});
}
@Override
public int getItemCount() {
return mData != null ? mData.size() : 0;
}
}
private void addGoodToCar(ImageView imageView){
final ImageView view = new ImageView(GoodsListActivity.this);
view.setImageDrawable(imageView.getDrawable());
RelativeLayout.LayoutParams layoutParams = new RelativeLayout.LayoutParams(100, 100);
mRootRl.addView(view, layoutParams);
//二、計算動畫開始/結束點的座標的準備工作
//得到父佈局的起始點座標（用於輔助計算動畫開始/結束時的點的座標）
int[] parentLoc = new int[2];
mRootRl.getLocationInWindow(parentLoc);
//得到商品圖片的座標（用於計算動畫開始的座標）
int startLoc[] = new int[2];
imageView.getLocationInWindow(startLoc);
//得到購物車圖片的座標(用於計算動畫結束後的座標)
int endLoc[] = new int[2];
mCarImageView.getLocationInWindow(endLoc);
float startX = startLoc[0] - parentLoc[0] + imageView.getWidth()/2;
float startY = startLoc[1] - parentLoc[1] + imageView.getHeight()/2;
//商品掉落後的終點座標：購物車起始點-父佈局起始點+購物車圖片的1/5
float toX = endLoc[0] - parentLoc[0] + mCarImageView.getWidth() / 5;
float toY = endLoc[1] - parentLoc[1];
//開始繪製貝塞爾曲線
Path path = new Path();
path.moveTo(startX, startY);
//使用二次薩貝爾曲線：注意第一個起始座標越大，貝塞爾曲線的橫向距離就會越大，一般按照下面的式子取即可
path.quadTo((startX + toX) / 2, startY, toX, toY);
mPathMeasure = new PathMeasure(path, false);
//屬性動畫
ValueAnimator valueAnimator = ValueAnimator.ofFloat(0, mPathMeasure.getLength());
valueAnimator.setDuration(1000);
valueAnimator.setInterpolator(new LinearInterpolator());
valueAnimator.addUpdateListener(new ValueAnimator.AnimatorUpdateListener() {
@Override
public void onAnimationUpdate(ValueAnimator animation) {
float value = (float)animation.getAnimatedValue();
mPathMeasure.getPosTan(value, mCurrentPosition, null);
view.setTranslationX(mCurrentPosition[0]);
view.setTranslationY(mCurrentPosition[1]);
}
});
valueAnimator.addListener(new Animator.AnimatorListener() {
@Override
public void onAnimationStart(Animator animation) {
}
@Override
public void onAnimationEnd(Animator animation) {
// 購物車的數量加1
mCount++;
mCountTv.setText(String.valueOf(mCount));
// 把移動的圖片imageview從父佈局裏移除
mRootRl.removeView(view);
//shopImg 開始一個放大動畫
Animation scaleAnim = AnimationUtils.loadAnimation(GoodsListActivity.this, R.anim.shop_car_scale);
mCarImageView.startAnimation(scaleAnim);
}
@Override
public void onAnimationCancel(Animator animation) {
}
@Override
public void onAnimationRepeat(Animator animation) {
}
});
valueAnimator.start();
}
class GoodsViewHolder extends RecyclerView.ViewHolder{
private ImageView ivGood;
private TextView tvBuy;
public GoodsViewHolder(View itemView) {
super(itemView);
ivGood = (ImageView)itemView.findViewById(R.id.iv_goods);
tvBuy = (TextView) itemView.findViewById(R.id.tv_buy);
}
}
}