设置中添加UI修改系统默认NTP服务器

经常遇到客户在内网中使用无法与ntp服务器通讯导致系统时间错乱，他们想自己替换ntp地址要么是用adb命令要么是重新刷机，这样比较浪费客户的时间。
看了一下Android系统中选择ntp地址的逻辑，发现在framework中已经有了个ntp地址那么系统将会选择framework中默认的ntp服务器作为系统ntp服务器，如果framework中没有那么将会选择settings数据库中存储的ntp服务器作为系统ntp服务器
framework/base/core/java/android/util/NtpTrustedTime.java
根据上面逻辑咋们可以推断，是可以在app中通过写数据库的值来更改系统的ntp地址。
以下代码是在设置中添加UI来更改ntp地址（基于MTK6771 Android10）

vendor/mediatek/proprietary/packages/apps/MtkSettings/res/values-zh-rCN/strings.xml
+	<string name="date_and_time_ntp_server">NTP服务器</string>

vendor/mediatek/proprietary/packages/apps/MtkSettings/res/values/strings.xml
+	<string name="date_and_time_ntp_server">NTP server</string>

vendor/mediatek/proprietary/packages/apps/MtkSettings/res_ext/xml/date_time_ext_prefs.xml
+	<com.android.settings.widget.ValidatedEditTextPreference
+        android:key="ntp_server"
+        android:title="@string/date_and_time_ntp_server"
+        android:summary="@string/summary_placeholder"
+		settings:controller="com.android.settings.datetime.NtpServerPreferenceController"
+        settings:enableCopying="true"/>

新建文件
vendor/mediatek/proprietary/packages/apps/MtkSettings/src/com/android/settings/datetime/NtpServerPreferenceController.java
package com.android.settings.datetime;


import android.content.Context;
import android.os.Build;
import android.os.Bundle;
import android.provider.Settings;
import android.text.SpannedString;
import androidx.preference.Preference;
import androidx.preference.PreferenceScreen;
import com.android.settings.R;
import com.android.settings.core.BasePreferenceController;
import com.android.settings.widget.ValidatedEditTextPreference;
import com.android.settingslib.core.lifecycle.LifecycleObserver;
import com.android.settingslib.core.lifecycle.events.OnCreate;
import com.android.settingslib.core.lifecycle.events.OnSaveInstanceState;
import android.util.Log;


public class NtpServerPreferenceController extends BasePreferenceController
        implements ValidatedEditTextPreference.Validator,
        Preference.OnPreferenceChangeListener,
        LifecycleObserver,
        OnSaveInstanceState{ 
		
    private String defaultServer;
	private String secureServer = null;
	private String mPendingNtpName;
    private ValidatedEditTextPreference mPreference;
	private String TAG = "NtpServerPreferenceController";
	
    public NtpServerPreferenceController(Context context, String key) {
        super(context, key);
		//Log.d(TAG,"NtpServerPreferenceController is run..");
		initializeDeviceName();
    }

    private void initializeDeviceName(){
		defaultServer = Settings.Global.getString(mContext.getContentResolver(), Settings.Global.NTP_SERVER);
	    //Log.d(TAG,"defaultserver=" + defaultServer);
		if(defaultServer == null){
			Log.d(TAG,"defaultservr is null");
		}
		//Settings.Global.getString(resolver, Settings.Global.NTP_SERVER);
	}

    @Override
    public void displayPreference(PreferenceScreen screen) {
        super.displayPreference(screen);
		mPreference = screen.findPreference(getPreferenceKey());
		final CharSequence ntpserverName = getSummary();
		if(ntpserverName != null){ 
			//Log.d(TAG,"ntpserverName=" + ntpserverName);
			mPreference.setSummary(ntpserverName);
			mPreference.setText(ntpserverName.toString());
			mPreference.setValidator(this);
		} else {
		    Log.d(TAG,"ntpserverName is null");
		}

    }
	
	@Override
	public CharSequence getSummary() {
	     return defaultServer;
	}
	
	public void updateDeviceName(boolean update) {
	 
	}
	
	private void setSettingsGlobalDeviceName(String ntpserver) {
	    Settings.Global.putString(mContext.getContentResolver(), Settings.Global.NTP_SERVER,ntpserver);
		//Log.d(TAG,"set ntpserver is:" + ntpserver);
	}
 
	
	@Override
    public int getAvailabilityStatus() {
        return 0;
    }
	
	@Override
    public boolean onPreferenceChange(Preference preference, Object newValue) {
		//Log.d(TAG,"newValue=" + newValue);
		mPendingNtpName = (String) newValue; 
		setSettingsGlobalDeviceName(mPendingNtpName);
        return true;
    }
	
	@Override
    public boolean isTextValid(String deviceName) {
        // BluetoothNameDialogFragment describes BT name filter as a 248 bytes long cap.
        // Given the restrictions presented by the SSID name filter (32 char), I don't believe it is
        // possible to construct an SSID that is not a valid Bluetooth name.
        return true;
    }
	

    @Override
    public void onSaveInstanceState(Bundle outState) {

    }
}

实际效果如下：

设置ntp地址后需要重启系统新设置的ntp地址才生效

此功能实现并无难度，好在方便了用户使用。