Broadcast基础（使用广播，发送临时广播，注册接收器，通过定时器设置定时广播）

举例场景：

碎片将信息传回页面,适配器向页面传回消息

（一）Fragment提供了onAttach(）方法，onAttach方法指定结合了Activity对象。定义一个回调接口，把Activity对象强制转换为回调接口就可以在碎片中调用页面方法

（二）Broadcast

特点：一对多

发送者不需要考虑接受者在不在工作，在工作就接收广播，不在就不接收广播

接收者自行过滤符合条件的广播，进行解包处理

有关方法：

sendBroadcast:发送广播

registerReceiver:注册接收器 onStart()或onResume()中注册

unregisterReceiver:注销接收器 onStop()或onPause()中注销

1、应用内使用广播

在Fragment页面点击事件中发送广播

public class BroadcastFragment extends Fragment {

    private View view;
    private Context context;


    public final static String EVENT = "com.example.yejiajia.myapplication.fragment.BroadcastFragment";
    private String[] mColorNameArray = {"红色","黄色","绿色","青色","蓝色"};
    private int[] mColorArray = {Color.RED,Color.YELLOW,Color.GREEN,Color.CYAN,Color.BLUE};

    @Nullable
    @Override
    public View onCreateView(@NonNull LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) {
        context = getActivity();
        view = inflater.inflate(R.layout.broadcastfragment,container,false);
        Spinner spinner = view.findViewById(R.id.spinner);
        ArrayAdapter<String> startAdapter = new ArrayAdapter<>(getActivity(),R.layout.spinner_layout,mColorNameArray);

        spinner.setAdapter(startAdapter);
        spinner.setOnItemSelectedListener(new AdapterView.OnItemSelectedListener() {
            @Override
            public void onItemSelected(AdapterView<?> parent, View view, int position, long id) {
                Intent intent = new Intent(BroadcastFragment.EVENT);
                intent.putExtra("color",mColorArray[position]);
                LocalBroadcastManager.getInstance(getContext()).sendBroadcast(intent);
            }

            @Override
            public void onNothingSelected(AdapterView<?> parent) {

            }
        });
        return view;
    }

    @Override
    public void onCreate(@Nullable Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
    }
}

注册和注销广播（在需要变化的Activity页面）

@Override
protected void onStart() {
    super.onStart();
    bgChangeReceiver = new BgChangeReceiver();
    IntentFilter filter = new IntentFilter(BroadcastFragment.EVENT);
    LocalBroadcastManager.getInstance(this).registerReceiver(bgChangeReceiver,filter);
}

@Override
protected void onStop() {
    LocalBroadcastManager.getInstance(this).unregisterReceiver(bgChangeReceiver);
    super.onStop();
}

private BgChangeReceiver bgChangeReceiver;
private class BgChangeReceiver extends BroadcastReceiver{

    @Override
    public void onReceive(Context context, Intent intent) {
        if(intent != null){
            int color = intent.getIntExtra("color", Color.WHITE);
            ll_bg.setBackgroundColor(color);

        }
    }
}

2、定时器AlarmManager

全局定时器，利用系统闹钟定时发送广播。即使App退出，依然会被唤醒响应广播事件

静态注册

<receiver android:name=".AlermActivity$AlermReceiver">
    <intent-filter>
        <action android:name="com.example.yejiajia.myapplication.AlermActivity.AlermReceiver"/>
    </intent-filter>
</receiver>

/**
 * 定时器发送广播
 */
public class AlermActivity extends AppCompatActivity {

    private String ALARM_ENENT  = "com.example.yejiajia.myapplication.AlermActivity.AlermReceiver";
    private static String mDesc = "";
    private static boolean bArrived = false;
    private static TextView tv_setting;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_alerm);
        tv_setting = findViewById(R.id.tv_setting);
        tv_setting.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                Intent intent = new Intent(ALARM_ENENT);
                PendingIntent pendingIntent = PendingIntent.getBroadcast(AlermActivity.this,0,intent,PendingIntent.FLAG_UPDATE_CURRENT);
                AlarmManager alarmManager = (AlarmManager) getSystemService(ALARM_SERVICE);
                Calendar calendar = Calendar.getInstance();
                calendar.setTimeInMillis(System.currentTimeMillis());
                calendar.add(Calendar.SECOND,1);
                alarmManager.set(AlarmManager.RTC_WAKEUP,calendar.getTimeInMillis(),pendingIntent);

                tv_setting.setText("设置时间");
            }
        });
    }

    public static class AlermReceiver extends BroadcastReceiver{


        @Override
        public void onReceive(Context context, Intent intent) {
            if(intent != null) {
                if(tv_setting != null && bArrived == false) {
                    bArrived = true;
                    tv_setting.setText("时间到");
                }
            }
        }
    }
}