为什么addPeriodicSync（）无法正常工作？

Question

我需要每10秒触发一次syncAdapter类中的performSync，但它甚至一次也不会触发。为此，使用contentResolver的addPeriodicSync函数。我还具有触发contentResolver的requestSync的按钮。单击我的按钮performSync被执行后，这个效果很好，但是为什么periodicSync功能不起作用。

这是我的主要活动代码。

package com.stalnobcrs.syncadapdemo;

import android.accounts.Account;
import android.accounts.AccountManager;
import android.content.ContentResolver;
import android.content.Context;
import android.database.ContentObserver;
import android.net.Uri;
import android.support.v4.app.FragmentActivity;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.util.Log;
import android.view.View;
import android.widget.Button;

public class MainActivity extends AppCompatActivity {
    //...
    // Constants
    public static String AUTHORITY="";
    public static final String ACCOUNT = "default_account";
    // An account type, in the form of a domain name
    public static String ACCOUNT_TYPE="";
    private static final String TAG=MainActivity.class.getName();
    // Global variables
    ContentResolver mResolver;
    Button sync;
    //...
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        //...
        // Get the content resolver object for your app
        AUTHORITY=getApplicationContext().getString(R.string.content_authority);
        ACCOUNT_TYPE=getApplicationContext().getString(R.string.sync_account_type);
        mResolver = getContentResolver();
        mAccount=CreateSyncAccount(this);
        setContentView(R.layout.activity_main);
        ContentResolver.setIsSyncable(mAccount,AUTHORITY, 1);

        // Inform the system whether this account is eligible for auto sync when the network 
        // is up. In your case should be false
        ContentResolver.setSyncAutomatically(mAccount, AUTHORITY, false);

        // Add a schedule for automatic synchronisation. The system may call the sync function
        // a few seconds early or late for battery and network optimisation.
        ContentResolver.addPeriodicSync(mAccount, AUTHORITY, Bundle.EMPTY,
                10);
    }
    //...
    // Constants
    // Instance fields
    Account mAccount;
   // ...
    /**
     * Create a new dummy account for the sync adapter
     *
     * @param context The application context
     */
    public static Account CreateSyncAccount(Context context) {
        // Create the account type and default account
        Log.i(TAG,ACCOUNT+"  "+ACCOUNT_TYPE);
        Account newAccount = new Account(ACCOUNT,ACCOUNT_TYPE);
        // Get an instance of the Android account manager
        AccountManager accountManager =
                (AccountManager) context.getSystemService(
                        ACCOUNT_SERVICE);
        /*
         * Add the account and account type, no password or user data
         * If successful, return the Account object, otherwise report an error.
         */
        assert accountManager != null;
        if (accountManager.addAccountExplicitly(newAccount, "", null)) {
            /*
             * If you don't set android:syncable="true" in
             * in your <provider> element in the manifest,
             * then call context.setIsSyncable(account, AUTHORITY, 1)
             * here.
             */
            Log.i(TAG, "CreateSyncAccount Successful");
            return newAccount;
        } else {
            /*
             * The account exists or some other error occurred. Log this, report it,
             * or handle it internally.

             */
            Log.i(TAG,"Already account exist or some error occurred in CreateSyncAccount");
            return newAccount;
        }
    }
    public void onRefreshButtonClick(View v) {
        //...
        // Pass the settings flags by inserting them in a bundle
        Bundle settingsBundle = new Bundle();
        settingsBundle.putBoolean(
                ContentResolver.SYNC_EXTRAS_MANUAL, true);
        settingsBundle.putBoolean(
                ContentResolver.SYNC_EXTRAS_EXPEDITED, true);
        /*
         * Request the sync for the default account, authority, and
         * manual sync settings
         */
        Log.i(TAG,"Button clicked");
        Log.i(TAG,AUTHORITY+" "+mAccount);
        ContentResolver.requestSync(mAccount, AUTHORITY, settingsBundle);
    }
}

这是我的清单文件。

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
package="com.stalnobcrs.syncadapdemo">

<uses-permission
    android:name="android.permission.INTERNET"/>
<uses-permission
    android:name="android.permission.READ_SYNC_SETTINGS"/>
<uses-permission
    android:name="android.permission.WRITE_SYNC_SETTINGS"/>
<uses-permission
    android:name="android.permission.AUTHENTICATE_ACCOUNTS"
    android:maxSdkVersion="22" />
<application
    android:allowBackup="true"
    android:icon="@mipmap/ic_launcher"
    android:label="@string/app_name"
    android:roundIcon="@mipmap/ic_launcher_round"
    android:supportsRtl="true"
    android:theme="@style/AppTheme">
    <activity android:name=".MainActivity">
        <intent-filter>
            <action android:name="android.intent.action.MAIN" />

            <category android:name="android.intent.category.LAUNCHER" />
        </intent-filter>
    </activity>
    <service
        android:name="com.stalnobcrs.syncadapdemo.SyncService"
        android:exported="true">
        <intent-filter>
            <action android:name="android.content.SyncAdapter"/>
        </intent-filter>
        <meta-data android:name="android.content.SyncAdapter"
            android:resource="@xml/syncadapter" />
    </service>
    <service
        android:name="com.stalnobcrs.syncadapdemo.AuthenticatorService">
        <intent-filter>
            <action android:name="android.accounts.AccountAuthenticator"/>
        </intent-filter>
        <meta-data
            android:name="android.accounts.AccountAuthenticator"
            android:resource="@xml/authenticator" />
    </service>
    <provider
        android:name="com.stalnobcrs.syncadapdemo.StubProvider"
        android:authorities="com.stalnobcrs.syncadapdemo"
        android:exported="false"
        android:syncable="true"/>
</application>

这是我的syncAdapter xml

<?xml version="1.0" encoding="utf-8"?>
<sync-adapter xmlns:android="http://schemas.android.com/apk/res/android"
android:contentAuthority="@string/content_authority"
android:accountType="@string/sync_account_type"
android:userVisible="false"
android:supportsUploading="false"
android:allowParallelSyncs="false"
android:isAlwaysSyncable="false"/>

有人可以帮我吗？