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) &#63; 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()); }}