广播的动态注册

先前我们的每个Activity都要在AndroidMainfest.xml文件中注册才能使用，这属于静态注册。现在我们学习一种新的注册方法，动态注册。

动态注册有很多好处，在新版本的安卓中，推荐全部使用动态注册，动态注册也利于大型项目的开发。

我们以Broadcast为例，我们需要在OnCreate和OnStop中注册和取消注册；取消注册是必要的，否则会导致内存溢出

声明广播

private SetTimeActivity.AlarmReceiver alarmReceiver;

注册广播

@Override
    public void onStart() {
        super.onStart();
        alarmReceiver = new SetTimeActivity.AlarmReceiver(); // 创建一个闹钟的广播接收器
        // 创建一个意图过滤器，只处理指定事件来源的广播
        IntentFilter filter = new IntentFilter("ALARM");
        registerReceiver(alarmReceiver, filter); // 注册接收器，注册之后才能正常接收广播
    }

取消注册：

 @Override
    public void onStop() {
        super.onStop();
        unregisterReceiver(alarmReceiver); // 注销接收器，注销之后就不再接收广播
    }

 在此次的安卓打卡app中，我发现必须使用动态注册，才能成功使用广播触发AlertDialog

下面是我用AlertDialog实现定时提醒的具体代码:

package com.example.clockappliction;

import static android.icu.text.DateTimePatternGenerator.DAY;
import static androidx.constraintlayout.helper.widget.MotionEffect.TAG;

import android.annotation.SuppressLint;
import android.app.AlarmManager;
import android.app.AlertDialog;
import android.app.PendingIntent;
import android.app.TimePickerDialog;
import android.content.BroadcastReceiver;
import android.content.Context;
import android.content.DialogInterface;
import android.content.Intent;
import android.content.IntentFilter;
import android.content.SharedPreferences;
import android.icu.util.TimeZone;
import android.os.Bundle;
import android.os.SystemClock;
import android.util.Log;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import android.widget.TextView;
import android.widget.TimePicker;
import android.widget.Toast;

import androidx.annotation.NonNull;
import androidx.annotation.Nullable;
import androidx.appcompat.app.AppCompatActivity;

import java.util.Calendar;

public class SetTimeActivity extends AppCompatActivity implements View.OnClickListener , TimePickerDialog.OnTimeSetListener {

    private int hour,minute;
    private TextView tv_time;
    private Button btn_send;
    private EditText et_remind;
    public String mess = null;
    private SetTimeActivity.AlarmReceiver alarmReceiver;
    @SuppressLint("MissingInflatedId")
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_time_picker);

        tv_time = findViewById(R.id.tv_time);
        findViewById(R.id.btn_time).setOnClickListener(this);
        btn_send = (Button) findViewById(R.id.btn_send);
        btn_send.setOnClickListener(this);

        et_remind = (EditText) findViewById(R.id.et_remind);

    }

    @Override
    public void onStart() {
        super.onStart();
        alarmReceiver = new SetTimeActivity.AlarmReceiver(); // 创建一个闹钟的广播接收器
        // 创建一个意图过滤器，只处理指定事件来源的广播
        IntentFilter filter = new IntentFilter("ALARM");
        registerReceiver(alarmReceiver, filter); // 注册接收器，注册之后才能正常接收广播
    }
    @Override
    public void onStop() {
        super.onStop();
        unregisterReceiver(alarmReceiver); // 注销接收器，注销之后就不再接收广播
    }
    @Override
    public void onClick(View view) {
        if (view.getId()==R.id.btn_time){
            Calendar calendar = Calendar.getInstance();
            TimePickerDialog dialog = new TimePickerDialog(this,this,
                    calendar.get(Calendar.HOUR_OF_DAY),
                    calendar.get(Calendar.MINUTE),
                    true);
            dialog.show();
        }
        else if (view.getId()==R.id.btn_send) {


            Intent intent = new Intent("ALARM");
            mess = et_remind.getText().toString();

            PendingIntent sender = PendingIntent.getBroadcast(this,0, intent,PendingIntent.FLAG_MUTABLE);

            long firstTime = SystemClock.elapsedRealtime();    // 开机之后到现在的运行时间(包括睡眠时间)
            long systemTime = System.currentTimeMillis();

            android.icu.util.Calendar calendar = android.icu.util.Calendar.getInstance();
            calendar.setTimeInMillis(System.currentTimeMillis());
// 这里时区需要设置一下，不然会有8个小时的时间差
            calendar.setTimeZone(TimeZone.getTimeZone("GMT+8"));
            calendar.set(android.icu.util.Calendar.MINUTE,getMinute());
            calendar.set(android.icu.util.Calendar.HOUR_OF_DAY,getHours());
            calendar.set(android.icu.util.Calendar.SECOND,0);
            calendar.set(android.icu.util.Calendar.MILLISECOND,0);
// 选择的定时时间
            long selectTime = calendar.getTimeInMillis();
// 如果当前时间大于设置的时间，那么就从第二天的设定时间开始
            if(systemTime > selectTime) {
                Toast.makeText(this," ", Toast.LENGTH_SHORT).show();//设置的时间小于当前时间
                calendar.add(android.icu.util.Calendar.DAY_OF_MONTH,0);
                selectTime = calendar.getTimeInMillis();
            }
// 计算现在时间到设定时间的时间差
            long time = selectTime - systemTime;
            firstTime += time;
// 进行闹铃注册
            AlarmManager manager = (AlarmManager)getSystemService(ALARM_SERVICE);
            manager.setRepeating(AlarmManager.ELAPSED_REALTIME_WAKEUP,
                    time, DAY, sender);
            Log.i(TAG,"time ==== " + time +", selectTime ===== "
                    + selectTime + ", systemTime ==== " + systemTime +", firstTime === " + firstTime);
            Toast.makeText(this,"设置提醒闹铃成功! ", Toast.LENGTH_LONG).show();


        }
    }

    @Override
    public void onTimeSet(TimePicker timePicker, int hours_of_day, int minute) {
        String desc = String.format("你选择的时间是%d时%d分",hours_of_day,minute);
        tv_time.setText(desc);
        setHours(hours_of_day);
        setMinute(minute);
    }

    public int getHours(){
        return hour;
    }

    public int getMinute(){
        return minute;
    }
    public void setHours(int hour){
        this.hour=hour;
    }
    public void setMinute(int minute){
        this.minute=minute;
    }

    public void tipDialog(Context context) {
        AlertDialog.Builder builder = new AlertDialog.Builder(context);
        builder.setTitle("事件闹钟：");
        builder.setMessage("提醒您:"+mess);
        builder.setIcon(R.mipmap.ic_launcher);
        builder.setCancelable(false);            //点击对话框以外的区域是否让对话框消失
        //设置正面按钮
        builder.setPositiveButton("确定", new DialogInterface.OnClickListener() {
            @Override
            public void onClick(DialogInterface dialog, int which) {
                dialog.dismiss();
            }
        });
        AlertDialog dialog = builder.create();      //创建AlertDialog对象

        dialog.show();                              //显示对话框
    }

    public class AlarmReceiver extends BroadcastReceiver {

        @Override
        public void onReceive(Context context, Intent intent) {

            tipDialog(context);

        }

    }


}