实现安卓Spinner控件hint提示效果

效果图：

1.定义一个Spinner控件：

<Spinner
    android:layout_width="150dp"
    android:layout_height="match_parent"
    android:id="@+id/spinner_car">

2.Activity代码：

Spinner spinner_car;

List<String> cars = new ArrayList<>();

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    spinner_car = findViewById(R.id.spinner_car);
    myadapter();
}

public void myadapter()
{
    cars.add("1号爪黄飞电");
    cars.add("2号卷毛赤兔");
    cars.add("3号绝影");
    cars.add("请选择车辆");
    Myadapter myadapter = new Myadapter(thisR.layout.support_simple_spinner_dropdown_item,cars);
    spinner_car.setAdapter(myadapter);
    //默认选中最后一项
    spinner_car.setSelection(cars.size()-1,true);
}

/**
 * 定义一个Myadapter类继承ArrayAdapter
 * 重写以下两个方法
 * */
class Myadapter<T> extends ArrayAdapter{
    public Myadapter(@NonNull Context context, int resource, @NonNull List<T> objects) {
        super(context, resource, objects);
    }

    @Override
    public int getCount() {
        //返回数据的统计数量，大于0项则减去1项，从而不显示最后一项
        int i = super.getCount();
        return i>0?i-1:i;
    }
}