APN 开关实现原理

关闭APN的原理是在APN信息表(content://telephony/carriers/current)的apn, type字段添加自定义的后缀（参考自APNDroid）

package com.android.settings.widget;
 
import android.content.ContentResolver;
import android.content.ContentValues;
import android.content.Context;
import android.database.Cursor;
import android.net.Uri;
import android.provider.BaseColumns;
 
/**
 * Utility class for changing APN state
 */
public class ApnUtils {
    private static final String SUFFIX_APN = "_suffix_apn"; // type 1
 
    private static final String MMS = "mms";
 
    private static final String COLUMN_ID = BaseColumns._ID;
    private static final String COLUMN_APN = "apn";
    private static final String COLUMN_TYPE = "type";
    private static final String COLUMN_APN_ID = "apn_id"; // for preferred APN
 
    private static final String[] PROJECTION = new String[] { COLUMN_ID,
            COLUMN_APN, COLUMN_TYPE };
    private static final Uri CURRENT_APNS = Uri
            .parse("content://telephony/carriers/current");
    private static final Uri PREFERRED_APN = Uri
            .parse("content://telephony/carriers/preferapn");
    
    /**
     * Gets the state of APN
     * 
     * @param context
     * @return true if enabled
     */
    public static boolean getApnState(Context context) {
        
        ContentResolver resolver = context.getContentResolver();
        int counter = 0;
        Cursor cursor = null;
        try {
            cursor = resolver.query(CURRENT_APNS, PROJECTION, null, null, null);
            int typeIndex = cursor.getColumnIndex(COLUMN_TYPE);
            cursor.moveToNext();
            while (!cursor.isAfterLast()) {
                String type = cursor.getString(typeIndex);
 
                if (isDisabled(type)) {
                    return false; // no need to continue
                }
 
                if (!isMms(type) || /* this is MMM and we */shouldDisableMms()) {
                    counter++;
                }
 
                cursor.moveToNext();
            }
        } finally {
            if (cursor != null) {
                cursor.close();
            }
        }
        return counter != 0;
    }
    
    private static boolean isMms(String type) {
        return type != null && type.toLowerCase().endsWith(MMS);
    }
 
    private static boolean shouldDisableMms() {
        // TODO Auto-generated method stub
        return false;
    }
    
    private static boolean isDisabled(String value) {
        return value != null && value.endsWith(SUFFIX_APN);
    }
    
    /**
     * Set APN State
     * 
     * @param context
     * @param enabled
     */
    public static void setApnState(Context context, boolean enabled) {
        boolean shouldDisableMms = shouldDisableMms();
        
        ContentResolver resolver = context.getContentResolver();
        ContentValues values = new ContentValues();
        Cursor cursor = null;
 
        String[] args = new String[1];
        try {
            // COLUMN_ID{0}, COLUMN_APN{1}, COLUMN_TYPE{2}
            cursor = resolver.query(CURRENT_APNS, PROJECTION, null, null, null);
            int idIndex = cursor.getColumnIndex(COLUMN_ID);
            int apnIndex = cursor.getColumnIndex(COLUMN_APN);
            int typeIndex = cursor.getColumnIndex(COLUMN_TYPE);
            cursor.moveToFirst();
            while (!cursor.isAfterLast()) {
 
                String typeValue = cursor.getString(typeIndex);
                if (!enabled // we should disable
                        && isMms(typeValue) // and this is MMS
                        && !shouldDisableMms) { // but users disallow us to
                                                // disable MMS
                    // ignore
                    cursor.moveToNext();
                    continue;
                }
 
                args[0] = String.valueOf(cursor.getInt(idIndex)); // id
                values.put(COLUMN_APN, getAdaptedValue(cursor.getString(apnIndex), enabled));
                values.put(COLUMN_TYPE, getAdaptedValue(typeValue, enabled));
 
                resolver.update(CURRENT_APNS, values, COLUMN_ID + "=?", args);
 
                // move to next
                cursor.moveToNext();
            }
 
        } catch (Exception e) {
            throw new RuntimeException(e);
        } finally {
            if (cursor != null) {
                cursor.close();
            }
        }        
    }
    
    private static String getAdaptedValue(String value, boolean enable) {
        
        final String modifier = SUFFIX_APN;
        
        // handle null-value
        if (value == null) return enable ? value : modifier;
        
        // remove any modifier so that value becomes enabled in any case
        value = removeModifiers(value); 
        
        if (!enable) { // add required modifier
            value = addModifier(value);
        }
        
        return value;
    }
    
    private static String removeModifiers(String value) {
        if (value.endsWith(SUFFIX_APN)) 
            return value.substring(0, value.length() - SUFFIX_APN.length());
        else 
            return value;
    }
    
    private static String addModifier(String value) {
        return value + SUFFIX_APN;
    }
}