Android实现动画效果的自定义下拉菜单功能

public class SpinnerDemo extends Activity {
  private static final String[] countries = {"北京", "上海", "广州", "深圳", "成都", "杭州"};

  private TextView mTextView;
  private Spinner mSpinner;
  private ArrayAdapter<String> mAdapter;
  private Animation mAnimation;

  @Override
  protected void onCreate(Bundle onSavedInstance) {
    super.onCreate(onSavedInstance);
    setContentView(R.layout.spinner_demo);

    mTextView = findViewById(R.id.textView9);
    mSpinner = findViewById(R.id.spinner);

    mAdapter = new ArrayAdapter<>(this, android.R.layout.simple_spinner_item, countries);

    // 自定义的下拉视图布局样式
    mAdapter.setDropDownViewResource(R.layout.spinner_drop_down);

    // 设置数据的适配器
    mSpinner.setAdapter(mAdapter);

    mSpinner.setOnItemSelectedListener(new AdapterView.OnItemSelectedListener() {
      @Override
      public void onItemSelected(AdapterView<?> parent, View view, int position, long id) {
        mTextView.setText("你选择的是：" + countries[position]);

        // 一定要设置父视图可见，否则 在选择后，Spinner会消失
        parent.setVisibility(View.VISIBLE);
      }

      @Override
      public void onNothingSelected(AdapterView<?> parent) {
      }
    });

    // 通过 xml 的形式来定义动画
    mAnimation = AnimationUtils.loadAnimation(this, R.anim.my_anim);
    mSpinner.setOnTouchListener(new Spinner.OnTouchListener() {
      @Override
      public boolean onTouch(View v, MotionEvent event) {
        // 点击 Spinner 后，运行动画
        v.startAnimation(mAnimation);
        return false;
      }
    });
  }
}

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
       android:layout_width="match_parent"
       android:layout_height="match_parent"
       android:orientation="vertical">

  <TextView android:layout_width="wrap_content"
       android:layout_height="wrap_content"
       android:layout_gravity="center"
       android:id="@+id/textView9"/>

  <Spinner android:layout_width="wrap_content"
       android:layout_height="wrap_content"
       android:id="@+id/spinner"
       android:layout_gravity="center"
       android:layout_marginTop="15dp"/>

</LinearLayout>

<?xml version="1.0" encoding="utf-8"?>
<TextView xmlns:android="http://schemas.android.com/apk/res/android"
       android:layout_width="wrap_content"
       android:layout_height="50dp"
       android:textColor="@color/colorBlue"
       android:singleLine="true"
       style="?android:attr/spinnerDropDownItemStyle">
</TextView>

<?xml version="1.0" encoding="utf-8"?>
<set xmlns:android="http://schemas.android.com/apk/res/android">
  <translate
    android:fromXDelta="0"
    android:toXDelta="50%p"
    android:duration="2000"/>

  <alpha
    android:fromAlpha="0.0"
    android:toAlpha="1.0"
    android:duration="2000"/>
</set>