重复造轮子？

也不算是。
Bigkoo的Android-PickerView库，很好的支持了日期、时间、地区等各种类型的联动选择。目前的需求是只需要年月二级联动查询，不想集成整个Android-PickerView，毕竟大部分功能用不到，白白增加代码量，于是就基于Bigkoo的WheelView库实现了一个简便的年月选择器DatePicker。

说一说实现过程

集成WheelView库

implementation 'com.contrarywind:wheelview:4.0.9'

Bigkoo的Github地址：Bigkoo Github
他的Android-PickerView库写的很棒，功能全，性能好，单看看Star数，就知道此库得到了Android开发者的广泛认可。
WheelView内置于Android-PickerView，也可单独集成。它是一个自定义View，800行源码，立一个flag：读它的源码，下周内出一篇源码分析的文章。

DatePicker的实现

DatePicker

DatePicker继承于DialogFragment。采用Fragment弹出框，更便于自定义DatePicker布局，以及在任意页面进行调用，并可像管理Fragment一样管理DatePicker，很方便。

Builder

在DatePicker中用了一个静态内部类Builder，用于构建DatePicker及初始化。在Builder中开放了几个方法：

setYearRange(int minYear, int maxYear)
设定年份可选择的范围
setCancelable(boolean cancelable)
设定点击DatePicker外区域是否可取消DatePicker
loopYear(boolean loop)
设置年份是否可循环展示，默认为true
loopMonth(boolean loop)
设置月份是否可循环展示，默认为true
build()
构建并初始化DatePicker

public static class Builder {        private OnDatePickedListener listener;        public Builder(OnDatePickedListener listener) {            this.listener = listener;        }        private int minYear;        private int maxYear;        private boolean loopYear;        private boolean loopMonth;        private boolean cancelable;        public Builder setYearRange(int minYear, int maxYear) {            this.minYear = minYear;            this.maxYear = maxYear;            return this;        }        public Builder setCancelable(boolean cancelable) {            this.cancelable = cancelable;            return this;        }        public Builder loopYear(boolean loop) {            this.loopYear = loop;            return this;        }        public Builder loopMonth(boolean loop) {            this.loopMonth = loop;            return this;        }        public DatePicker build() {            if (minYear > maxYear) {                throw new IllegalArgumentException();//不允许minYear > maxYear            }            return DatePicker.newInstance(this);        }    }

OnDatePickedListener

DatePicker的监听接口，内有一回调方法onDatePickCompleted(int year, int month)，用于年月选择后的选择值回传。

public interface OnDatePickedListener {   void onDatePickCompleted(int year, int month);}

WheelView

xml布局：

Java代码：

WheelView wheelView = findViewById(R.id.wheelview);        wheelView.setCyclic(false); //是否循环展示        final List mOptionsItems = new ArrayList<>();        mOptionsItems.add("item0");        mOptionsItems.add("item1");        mOptionsItems.add("item2");          wheelView.setAdapter(new ArrayWheelAdapter(mOptionsItems));        wheelView.setOnItemSelectedListener(new OnItemSelectedListener() {            @Override            public void onItemSelected(int index) {                Toast.makeText(MainActivity.this, "" + mOptionsItems.get(index), Toast.LENGTH_SHORT).show();            }        });

DatePicker的使用

private String TAG = DemoActivity.class.getName();

DatePicker datePicker = new DatePicker.Builder(new DatePicker.OnDatePickedListener() {                    @Override                    public void onDatePickCompleted(int year, int month) {                        Toast.makeText(LoginStatisticsActivity.this, "selectedYear:" + year + "--selectedMonth" + month, Toast.LENGTH_SHORT).show();                    }                })                  .setYearRange(1990, Calendar.getInstance().get(Calendar.YEAR))//1990——当前年份                  .setCancelable(true)                  .loopYear(false)                  .loopMonth(false)                  .build();datePicker.showPicker(DemoActivity.this, TAG);

附以完整源码

DatePicker.class

package com.gd.terminalmanager.view;import android.app.Activity;import android.app.DialogFragment;import android.graphics.Color;import android.graphics.drawable.ColorDrawable;import android.os.Bundle;import android.support.annotation.NonNull;import android.support.annotation.Nullable;import android.util.DisplayMetrics;import android.view.LayoutInflater;import android.view.View;import android.view.ViewGroup;import android.view.Window;import android.widget.TextView;import com.contrarywind.adapter.WheelAdapter;import com.contrarywind.listener.OnItemSelectedListener;import com.contrarywind.view.WheelView;import com.gd.terminalmanager.R;import java.util.ArrayList;import java.util.Calendar;import java.util.List;/** * 只提供年和月的选择 * * @author ZuoHailong * @date 2019/3/19. */public class DatePicker extends DialogFragment {    private static final int DEFAULT_MAX_YEAR = 2050;    private static final int DEFAULT_MIN_YEAR = 1900;    private WheelView wheelViewYear, wheelViewMonth;    private TextView tv_sure, tv_cancle;    private int minYear; // min year    private int maxYear; // max year    private boolean cancelable, loopYear, loopMonth;    private OnDatePickedListener listener;    private int selectedYear, selectedMonth;    private static Calendar calendar;    //private，只允许通过Builder构建DatePicker    private static DatePicker newInstance(Builder builder) {        calendar = Calendar.getInstance();        DatePicker datePicker = new DatePicker();        datePicker.minYear = builder.minYear < DatePicker.DEFAULT_MIN_YEAR ? DatePicker.DEFAULT_MIN_YEAR : builder.minYear;        datePicker.maxYear = builder.maxYear > DatePicker.DEFAULT_MAX_YEAR ? DatePicker.DEFAULT_MAX_YEAR : builder.maxYear;        datePicker.cancelable = builder.cancelable;        datePicker.loopYear = builder.loopYear;        datePicker.loopMonth = builder.loopMonth;        datePicker.listener = builder.listener;        return datePicker;    }    @Override    public void onStart() {        super.onStart();        DisplayMetrics dm = new DisplayMetrics();        getActivity().getWindowManager().getDefaultDisplay().getMetrics(dm);        getDialog().getWindow().setLayout(dm.widthPixels, getDialog().getWindow().getAttributes().height);    }    @Nullable    @Override    public View onCreateView(@NonNull LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) {        View view = inflater.inflate(R.layout.layout_datepicker, container);        tv_cancle = view.findViewById(R.id.tv_cancle);        tv_cancle.setOnClickListener(new View.OnClickListener() {            @Override            public void onClick(View v) {                dismiss();            }        });        tv_sure = view.findViewById(R.id.tv_sure);        tv_sure.setOnClickListener(new View.OnClickListener() {            @Override            public void onClick(View v) {                listener.onDatePickCompleted(selectedYear, selectedMonth);                dismiss();            }        });        wheelViewYear = view.findViewById(R.id.wheelViewYear);        wheelViewMonth = view.findViewById(R.id.wheelViewMonth);        //设置DialogFragment所在窗口的背景透明        getDialog().getWindow().setBackgroundDrawable(new ColorDrawable(Color.TRANSPARENT));        getDialog().requestWindowFeature(Window.FEATURE_NO_TITLE);        initView();        return view;    }    private void initView() {        setCancelable(cancelable);        initYear(minYear, maxYear);        initMonth();        //默认选择当前年份        selectedYear = calendar.get(Calendar.YEAR);        //position = 当前年份 - minYear        wheelViewYear.setCurrentItem(selectedYear - minYear);        //设置是否循环显示年份        wheelViewYear.setCyclic(loopYear);        wheelViewYear.setOnItemSelectedListener(new OnItemSelectedListener() {            @Override            public void onItemSelected(int position) {                selectedYear = yearList.get(position);            }        });        //月份是从0到11，实际选择月份要+1        selectedMonth = calendar.get(Calendar.MONTH) + 1;        //position = 实际选择月份 - 1        wheelViewMonth.setCurrentItem(selectedMonth - 1);        //设置是否循环显示月份        wheelViewMonth.setCyclic(loopMonth);        wheelViewMonth.setOnItemSelectedListener(new OnItemSelectedListener() {            @Override            public void onItemSelected(int position) {                selectedMonth = monthList.get(position);            }        });    }    //存储可供选择的 年份/月份 集合    private List yearList, monthList;    private void initYear(int minYear, int maxYear) {        //避免传入顺序有误        minYear = Math.min(minYear, maxYear);        maxYear = Math.max(minYear, maxYear);        yearList = new ArrayList<>();        for (int i = 0; i < maxYear + 1 - minYear; i++) {            yearList.add(minYear + i);        }        wheelViewYear.setAdapter(new WheelAdapter() {            @Override            public int getItemsCount() {                return yearList.size();            }            @Override            public Object getItem(int index) {                return yearList.get(index);            }            @Override            public int indexOf(Object o) {                return yearList.indexOf(o);            }        });    }    private void initMonth() {        monthList = new ArrayList<>();        monthList.add(1);        monthList.add(2);        monthList.add(3);        monthList.add(4);        monthList.add(5);        monthList.add(6);        monthList.add(7);        monthList.add(8);        monthList.add(9);        monthList.add(10);        monthList.add(11);        monthList.add(12);        wheelViewMonth.setAdapter(new WheelAdapter() {            @Override            public int getItemsCount() {                return monthList.size();            }            @Override            public Object getItem(int index) {                return monthList.get(index);            }            @Override            public int indexOf(Object o) {                return monthList.indexOf(o);            }        });    }    //显示DatePicker    public void showPicker(Activity mActivity, String TAG) {        show(mActivity.getFragmentManager(), TAG);    }    public interface OnDatePickedListener {        void onDatePickCompleted(int year, int month);    }    public static class Builder {        private OnDatePickedListener listener;        public Builder(OnDatePickedListener listener) {            this.listener = listener;        }        private int minYear;        private int maxYear;        private boolean loopYear;        private boolean loopMonth;        private boolean cancelable;        public Builder setYearRange(int minYear, int maxYear) {            this.minYear = minYear;            this.maxYear = maxYear;            return this;        }        public Builder setCancelable(boolean cancelable) {            this.cancelable = cancelable;            return this;        }        public Builder loopYear(boolean loop) {            this.loopYear = loop;            return this;        }        public Builder loopMonth(boolean loop) {            this.loopMonth = loop;            return this;        }        public DatePicker build() {            if (minYear > maxYear) {                throw new IllegalArgumentException();//不允许minYear > maxYear            }            return DatePicker.newInstance(this);        }    }}

layout_datepicker.xml

<?xml version="1.0" encoding="utf-8"?>

Android(安卓)年月选择器，基于必酷公司的竖直滑动选择器WheelView进行实现

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