Notification通知

Notification：
例子的NotificationCompat使用的是v4包下的，稍微有点老，如果大家使用的话，建议使用v7包下的，通知也没什么好介绍的，直接看代码
MainActivity：

package com.fitsoft;

import android.app.Notification;
import android.app.NotificationManager;
import android.app.PendingIntent;
import android.content.Context;
import android.content.Intent;
import android.os.Bundle;
import android.support.v4.app.NotificationCompat;
import android.support.v7.app.AppCompatActivity;
import android.view.View;
import android.widget.Button;

public class MainActivity extends AppCompatActivity {

    private int notificationId = 100;
    private static int times = 0;
    Button button;
    Context context;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        context = this;  //设置上下文对象

        button = findViewById(R.id.btn);
        button.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                times++;
                if(times%2 == 1){
                    button.setText("销毁通知");
                    createNotification();  //创建通知
                }else {
                    button.setText("创建通知");
                    destroyNotification(); //取消通知
                }
            }
        });
    }

    /**
     * 创建通知
     */
    private void createNotification() {
        //创建builder
        NotificationCompat.Builder builder = new NotificationCompat.Builder(context, "my_notifications");
        //设置属性
        builder.setSmallIcon(R.mipmap.ic_launcher_round);  //设置图标
        builder.setContentTitle("这是通知的标题");     //设置标题
        builder.setContentText("这是通知的具体内容");  //设置内容
        builder.setNumber(1);    //设置通知次数
        builder.setAutoCancel(true);   //设置是否自动取消
        //构建启动意图
        PendingIntent pendingIntent = PendingIntent.getActivity(context, 1,
                new Intent(this, SecondActivity.class), PendingIntent.FLAG_UPDATE_CURRENT);
        //设置启动意图
        builder.setContentIntent(pendingIntent);
        Notification notification = builder.build();
        //获取系统服务
        NotificationManager notificationManager = (NotificationManager) getSystemService(NOTIFICATION_SERVICE);
        //系统创建通知
        notificationManager.notify(notificationId, notification);
    }

    /**
     * 取消通知
     */
    private void destroyNotification() {
        NotificationManager notificationManager = (NotificationManager) getSystemService(NOTIFICATION_SERVICE);
        //取消通知
        notificationManager.cancel(notificationId);
    }
}

布局文件使用的是上一次的只有一个按钮的状态选择器的布局，具体请查看上一篇。
这里的方法都很好理解，只是其中有一个构建启动意图的时候的PendingIntent.getActivity()方法，我们具体看一下：

/**
 * Retrieve a PendingIntent that will start a new activity, like calling
 * {@link Context#startActivity(Intent) Context.startActivity(Intent)}.
 * Note that the activity will be started outside of the context of an
 * existing activity, so you must use the {@link Intent#FLAG_ACTIVITY_NEW_TASK
 * Intent.FLAG_ACTIVITY_NEW_TASK} launch flag in the Intent.
 *
 * <p class="note">For security reasons, the {@link android.content.Intent}
 * you supply here should almost always be an <em>explicit intent</em>,
 * that is specify an explicit component to be delivered to through
 * {@link Intent#setClass(android.content.Context, Class) Intent.setClass}</p>
 *
 * @param context The Context in which this PendingIntent should start
 * the activity.
 * @param requestCode Private request code for the sender
 * @param intent Intent of the activity to be launched.
 * @param flags May be {@link #FLAG_ONE_SHOT}, {@link #FLAG_NO_CREATE},
 * {@link #FLAG_CANCEL_CURRENT}, {@link #FLAG_UPDATE_CURRENT},
 * or any of the flags as supported by
 * {@link Intent#fillIn Intent.fillIn()} to control which unspecified parts
 * of the intent that can be supplied when the actual send happens.
 *
 * @return Returns an existing or new PendingIntent matching the given
 * parameters.  May return null only if {@link #FLAG_NO_CREATE} has been
 * supplied.
 */
public static PendingIntent getActivity(Context context, int requestCode,
        Intent intent, @Flags int flags) {
    return getActivity(context, requestCode, intent, flags, null);
}

这里的第四个参数flags值得注意，我们点击这个@Flags注解进行查看：

/** @hide */
@IntDef(flag = true,
        value = {
                FLAG_ONE_SHOT,
                FLAG_NO_CREATE,
                FLAG_CANCEL_CURRENT,
                FLAG_UPDATE_CURRENT,
                FLAG_IMMUTABLE,

                Intent.FILL_IN_ACTION,
                Intent.FILL_IN_DATA,
                Intent.FILL_IN_CATEGORIES,
                Intent.FILL_IN_COMPONENT,
                Intent.FILL_IN_PACKAGE,
                Intent.FILL_IN_SOURCE_BOUNDS,
                Intent.FILL_IN_SELECTOR,
                Intent.FILL_IN_CLIP_DATA
        })
@Retention(RetentionPolicy.SOURCE)
public @interface Flags {}

这是一个源码级的注解，有五个常用的值以及一些Intent的常用值，这五个值的含义大致如下：

1. FLAG_ONE_SHOT：表明这里构建的PendingIntent只能使用一次
2. FLAG_NO_CREATE：如果前一个PendingIntent已经不存在，将不再构建它
3. FLAG_CANCEL_CURRENT：如果构建的PendingIntent已经存在，则取消前一个，重新构建一个
4. FLAG_UPDATE_CURRENT：如果构建的PendingIntent已经存在，则替换它
5. FLAG_IMMUTABLE：已经构建的PendingIntent不可更改

这里我们使用第4个，因为它比较常用。
效果图：