Android开发中实现一个头像滑动变大变小功能

public class MainActivity extends AppCompatActivity {

 private CircleImageView ivPortrait;
 private ObservableScrollView scrollView;

 private ViewGroup.MarginLayoutParams marginLayoutParams;

 @Override
 protected void onCreate(Bundle savedInstanceState) {
 super.onCreate(savedInstanceState);
 setContentView(R.layout.activity_main);

 initView();
 }

 private void initView() {
 ivPortrait = (CircleImageView) findViewById(R.id.iv_portrait);
 scrollView = (ObservableScrollView) findViewById(R.id.scrollView);

 marginLayoutParams = new ViewGroup.MarginLayoutParams(ivPortrait.getLayoutParams());

 scrollView.setScrollViewListener(new ObservableScrollView.ScrollViewListener() {
 @Override
 public void onScrollChanged(ObservableScrollView scrollView, int x, int y, int oldx, int oldy) {
 // 设置头像距离顶部的距离
 int top = dp2px(70) - y;
 if (top < dp2px(10)) {
  // 固定在标题栏
  marginLayoutParams.setMargins(dp2px(20), dp2px(10), 0, 0);
 } else {
  // 向上移动
  marginLayoutParams.setMargins(dp2px(20), dp2px(70) - y, 0, 0);
 }

 // 根据向上滑动的距离设置头像的大小
 FrameLayout.LayoutParams layoutParams = new FrameLayout.LayoutParams(marginLayoutParams);
 // 头像最大为45dp，最小为30dp
 int height = dp2px(45) - y < dp2px(30) ? dp2px(30) : dp2px(45) - y;
 layoutParams.height = height;
 layoutParams.width = height;
 ivPortrait.setLayoutParams(layoutParams);
 }
 });
 }

 private int dp2px(float dp) {
 return (int) TypedValue.applyDimension(TypedValue.COMPLEX_UNIT_DIP, dp,
 getResources().getDisplayMetrics());
 }
}

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public class ObservableScrollView extends ScrollView {

 private ScrollViewListener scrollViewListener;

 public ObservableScrollView(Context context) {
 super(context);
 }

 public ObservableScrollView(Context context, AttributeSet attrs, int defStyle) {
 super(context, attrs, defStyle);
 }

 public ObservableScrollView(Context context, AttributeSet attrs) {
 super(context, attrs);
 }

 public void setScrollViewListener(ScrollViewListener scrollViewListener) {
 this.scrollViewListener = scrollViewListener;
 }

 @Override
 protected void onScrollChanged(int x, int y, int oldx, int oldy) {
 super.onScrollChanged(x, y, oldx, oldy);
 if (scrollViewListener != null) {
 scrollViewListener.onScrollChanged(this, x, y, oldx, oldy);
 }
 }

 public interface ScrollViewListener {
 void onScrollChanged(ObservableScrollView scrollView, int x, int y, int oldx, int oldy);
 }
}