Android使用GridView实现日历的简单功能

简单的日历实现，只是显示了每一个月，没有显示当天和记事这些功能

主要是计算月初是周几，月末是周几，然后相应的显示上一月多少天和下一月多少天。

先看一下关于日期的用到的几个工具类

 /**
   * 获取该月天数
   */
  public static int getCurrentMonthDay(long millSec) {
    Calendar calendar = Calendar.getInstance();
    calendar.setTimeInMillis(millSec);
    calendar.set(Calendar.DATE, 1);
    calendar.roll(Calendar.DATE, -1);
    int dateCount = calendar.get(Calendar.DATE);
    return dateCount;
  }

  /**
   * 获取当月第一天
   */
  public static long getFirOfMonth(long millSec) {
    Calendar calendar = Calendar.getInstance();
    calendar.setTimeInMillis(millSec);
    calendar.set(Calendar.DATE, 1);
    return calendar.getTimeInMillis();
  }

  /**
   * 获取当前时间戳
   */
  public static long getCurrentTime() {
    Calendar calendar = Calendar.getInstance();
    return calendar.getTimeInMillis();
  }

  /**
   * 获取上一月/下一月
   */
  public static long getLastOrNextMonth(long millSec, int count) {
    Calendar calendar = Calendar.getInstance();
    calendar.setTimeInMillis(millSec);
    calendar.add(Calendar.MONTH, count);
    return calendar.getTimeInMillis();
  }

  /**
   * 格式化到月份
   */
  public static String long2str(long millSec) {
    SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM");
    return sdf.format(new Date(millSec));
  }

用一个List存放每一天，因为之前考虑到每一天有记事这些，所以封装了一个类，如果不需要的话可以直接一个时间戳就可以。
打开之后先获取当前的时间戳，然后初始化到当前月份的第一天，通过工具类中方法。
然后就是计算了，把上月结余的、本月所有、下月的一起添加到List中。

 private void setCalendarList(long millSecs) {
    beans.clear();
    Calendar calendar = Calendar.getInstance();
    calendar.setTimeInMillis(millSecs);
//    int nor = today.getDay();
    int max = DateUtil.getCurrentMonthDay(millSecs);
    /**
     * 当月日历
     */
    for (int i = 1; i <= max; i++) {
      DayBean bean = new DayBean();
      Calendar cc = Calendar.getInstance();
      cc.setTimeInMillis(millSecs);
      cc.add(Calendar.DAY_OF_MONTH, i - 1);
      setBean(bean, cc);
      bean.setIsCurrentMonth(true);
      beans.add(bean);
    }
    //上月结余
    int fir_day_of_week = beans.get(0).getCalendar().get(Calendar.DAY_OF_WEEK);
    Log.e("AAA", "week_last:" + fir_day_of_week);
    if (fir_day_of_week != 2) {
      if(fir_day_of_week == 1){
        for (int i = 0; i < 6; i++) {
          DayBean bean = new DayBean();
          Calendar cc = Calendar.getInstance();
          cc.setTimeInMillis(millSecs);
          cc.add(Calendar.DAY_OF_MONTH, -i -1);
          setBean(bean, cc);
          Log.e("AAA", "last:" + bean.getDay());
          bean.setIsCurrentMonth(false);
          beans.add(0, bean);
        }
      }else{
        for (int i = 0; i < fir_day_of_week-2; i++) {
          DayBean bean = new DayBean();
          Calendar cc = Calendar.getInstance();
          cc.setTimeInMillis(millSecs);
          cc.add(Calendar.DAY_OF_MONTH, -i-1);
          setBean(bean, cc);
          Log.e("AAA", "last:" + bean.getDay());
          bean.setIsCurrentMonth(false);
          beans.add(0, bean);
        }
      }

    }
    //下月
    int last_day_of_week = beans.get(beans.size() - 1).getCalendar().get(Calendar.DAY_OF_WEEK);
    Log.e("AAA", "week_next:" + last_day_of_week);
    if (last_day_of_week != 1) {
      for (int i = last_day_of_week; i < 8; i++) {
        DayBean bean = new DayBean();
        Calendar cc = Calendar.getInstance();
        cc.setTimeInMillis(millSecs);
        cc.add(Calendar.DAY_OF_MONTH, i - last_day_of_week);
        setBean(bean, cc);
        Log.e("AAA", "next:" + bean.getDay());
        bean.setIsCurrentMonth(false);
        beans.add(bean);
      }
    }
    GridViewAdapter adapter = new GridViewAdapter(this, beans);
    mGridView.setAdapter(adapter);
  }

  private void setBean(DayBean bean, Calendar cc) {
    bean.setCalendar(cc);
    bean.setDay(cc.get(Calendar.DAY_OF_MONTH));
  }

设置每一天时设置了一个字段为是否为本月，如果是，则设置为黑色，否则设为灰色显示，在Adapter中的getView方法中设置即可。

  @Override
  public View getView(int position, View convertView, ViewGroup parent) {
    ViewHolder holder;
    if (convertView == null) {
      convertView = inflater.inflate(R.layout.item_layout, null);
      holder = new ViewHolder();
      holder.day_text = (TextView) convertView.findViewById(R.id.day_text);
      convertView.setTag(holder);
    } else {
      holder = (ViewHolder) convertView.getTag();
    }
    holder.day_text.setText(beans.get(position).getDay() + "");
    if (beans.get(position).isToday()) {
      holder.day_text.setBackgroundColor(Color.RED);
    } else {
      holder.day_text.setBackgroundColor(Color.WHITE);
    }
    if (beans.get(position).isCurrentMonth()) {
      holder.day_text.setTextColor(Color.BLACK);
    } else {
      holder.day_text.setTextColor(Color.GRAY);
    }

    return convertView;
  }

  class ViewHolder {
    TextView day_text;
  }

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