Android下拉列表选项框及指示箭头动画

android原生的Spinner提供了下拉列表选项框，但在一些流行的APP中，原生的Spinner似乎不太受待见，而通常会有下图所示的下拉列表选项框：

初始化状态：

点击弹出下拉选择选项框：

选中后：

注意那个指示箭头，如果把这个控件写的比较精细的话，在下拉-选择-复位过程中箭头是应该有动画旋转效果的。

这种样式的选择框实现方案很多，并且常见、常用，我自己写了一个，我写的这个例子的代码运行结果就是上图所示。

首先是MainActivity.Java：

package zhangphil.app;

import android.content.Context;
import android.graphics.Color;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.support.v7.widget.ListPopupWindow;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.AdapterView;
import android.widget.ArrayAdapter;
import android.widget.ImageView;
import android.widget.LinearLayout;
import android.widget.PopupWindow;
import android.widget.TextView;
import android.widget.Toast;

public class MainActivity extends AppCompatActivity {

  private ListPopupWindow listPopupWindow = null;

  private ImageView arrowImageView;
  private TextView chooseText;
  private LinearLayout linearLayout;
  private SortAadapter adapter = null;

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

    linearLayout= (LinearLayout) findViewById(R.id.linearLayout);

    arrowImageView = (ImageView)findViewById(R.id.arrow);
    chooseText= (TextView) findViewById(R.id.chooseText);

    linearLayout.setOnClickListener(new View.OnClickListener() {
      @Override
      public void onClick(View view) {
        showListPopupWindow(linearLayout);
      }
    });
  }

  private class SortAadapter extends ArrayAdapter {

    private String[] strs = {"最新", "推荐", "全部", "最热"};
    private LayoutInflater inflater;
    private int res;

    public SortAadapter(Context context, int resource) {
      super(context, resource);
      inflater = LayoutInflater.from(context);
      res = resource;
    }

    @Override
    public View getView(int position, View convertView, ViewGroup parent) {
      if (convertView == null)
        convertView = inflater.inflate(res, null);

      TextView text = (TextView) convertView.findViewById(android.R.id.text1);
      text.setText(getItem(position));
      text.setTextColor(Color.WHITE);
      text.setTextSize(10);

      convertView.setBackgroundColor(Color.RED);

      return convertView;
    }

    @Override
    public String getItem(int position) {
      return strs[position];
    }

    @Override
    public int getCount() {
      return strs.length;
    }
  }

  public void showListPopupWindow(View view) {
    if (listPopupWindow == null)
      listPopupWindow = new ListPopupWindow(this);

    if (adapter == null) {
      adapter = new SortAadapter(this, android.R.layout.simple_list_item_1);

      // ListView适配器
      listPopupWindow.setAdapter(adapter);

      // 选择item的监听事件
      listPopupWindow.setOnItemClickListener(new AdapterView.OnItemClickListener() {
        @Override
        public void onItemClick(AdapterView<?> parent, View view, int pos, long id) {
          Toast.makeText(getApplicationContext(), adapter.getItem(pos), Toast.LENGTH_SHORT).show();
          chooseText.setText(adapter.getItem(pos));

          listPopupWindow.dismiss();
        }
      });

      listPopupWindow.setOnDismissListener(new PopupWindow.OnDismissListener() {
        @Override
        public void onDismiss() {
          //旋转0度是复位ImageView
          arrowImageView.animate().setDuration(500).rotation(0).start();
        }
      });
    }

    // ListPopupWindow的锚,弹出框的位置是相对当前View的位置
    listPopupWindow.setAnchorView(view);

    listPopupWindow.setVerticalOffset(dip2px(this,5));

    // 对话框的宽高
    listPopupWindow.setWidth(view.getWidth());

    listPopupWindow.setModal(true);

    listPopupWindow.show();
    arrowImageView.animate().setDuration(500).rotation(180).start();
  }

  public static int dip2px(Context context, float dipValue) {
    float sDensity = context.getResources().getDisplayMetrics().density;
    final float scale = sDensity;
    return (int) (dipValue * scale + 0.5f);
  }
}

布局文件：

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

  <LinearLayout
    android:id="@+id/linearLayout"
    android:layout_width="wrap_content"
    android:layout_height="24dp"
    android:background="@drawable/round_corner_line_radius_3dp"
    android:orientation="horizontal"
    android:paddingLeft="8dp"
    android:paddingRight="8dp"
    android:layout_centerInParent="true">

    <TextView
      android:id="@+id/chooseText"
      android:layout_width="wrap_content"
      android:layout_height="wrap_content"
      android:layout_gravity="center_vertical"
      android:text="分类"
      android:textColor="@android:color/holo_orange_dark"
      android:textSize="12dp" />

    <ImageView
      android:id="@+id/arrow"
      android:layout_width="14dp"
      android:layout_height="14dp"
      android:layout_gravity="center_vertical"
      android:layout_marginLeft="8dp"
      android:src="@drawable/icon" />

  </LinearLayout>

</RelativeLayout>

LinearLayout的背景需要一个圆角背景res/drawable/round_corner_line_radius_3dp.xml：

<?xml version="1.0" encoding="UTF-8"?>
<shape
  xmlns:android="http://schemas.android.com/apk/res/android"
  android:shape= "rectangle">

  <stroke android:color="@android:color/holo_orange_dark"
    android:width="2px"/>

  <solid android:color="@android:color/transparent"/>
  <corners android:radius="3dp" />

</shape>

箭头icon.png：

附：Android第三方开源下拉框NiceSpinner

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