Android设置里面默认存储器选项（default write disk）的实现

    原生的Android设置里面没有默认存储器的选项，但是MTK偏偏加上了这个功能，可能MTK觉得这个比较有用吧，所以，他们在原生的基础上面做了修改，加上了这个功能。但是高通平台没有这个功能，相对MTK来说，高通比较严谨一点，不会随随便便加上一些功能，但是MTK平台优化了很多东西（有有点也有缺点），开发者这可能是很多山寨手机选择MTK平台的原因吧。

     我给“默认存储器”做了一个简单的定义：一些内置应用的数据存放位置。当然，如果其他应用知道这个接口（不是标准接口，所以只有开发者本人知道，或者MTK的人），也可以使用该功能。

    之前接到一个在高通平台上的手机里面加上默认存储器的选项，即如果选择本地内存，一些内置应用的数据将存储到本地内存里面，如果选择SD卡存储，则这些应用的数据将会存储到SD卡里面。借鉴MTK平台的实现方法，整理其思路是：通过SystemProperties接口往系统内存里面写入存储路径（set），然后在一些指定应用里面存储数据的时候判断当前默认存储器,使用get方法读取这个属性。为什么使用SystemProperties，因为其设置的值全局都可以使用，即不同应用都可以通过共享内存取出其值，解决了进程间通信的问题。

    1：我们先在framework层加上一些自定义的接口文件。我加的位置是 ....../frameworks/base/core/java/android/os/storage/，添加的文件名StorageManagerEx.java,内容如下：

package android.os.storage;	
import android.util.Log;	
import com.android.internal.R;	
import android.os.SystemProperties;	
import java.io.File;	
import android.os.Environment;	


public class StorageManagerEx {	
»       private static final String TAG ="StorageManagerEx";	
»       private static final String PROP_SD_DEFAULT_PATH = "persist.sys.sd.defaultpath";	
»       	
»       private static final String STORAGE_PATH_SD1 ="/storage/sdcard0";	
»       private static final String STORAGE_PATH_SD2 ="/storage/sdcard1";	
»       private static final String STORAGE_PATH_SD1_ICS = "/mnt/sdcard";	
»       private static final String STORAGE_PATH_SD2_ICS = "/mnt/sdcard2";	
»       	
»       private static final String STORAGE_PATH_SHARE_SD = "/storage/emulated/0";	
»       	
»       /**	
»        * Return default path for writing.	
»        * @return default path.	
»        * @hide	
»        * @internal	
»        */	
   public static String getDefaultPath(){
»          String path = STORAGE_PATH_SD1;	
»          try {	
»       »          path = SystemProperties.get(PROP_SD_DEFAULT_PATH);	
»       »          Log.i(TAG,"default path = "+path);	
»          } catch (IllegalArgumentException e) {	
»       »          Log.e(TAG,"IllegalArgumentException when get default path:"+e);	
»          }	
»          //Property will be empty when first boot should set to default 	
»          if(path.equals("")){	
»       »          Log.i(TAG,"getDefaultPath empty! set to default");	
»       »          //Here may be some problems.refer to MTK:only share sd and no swap,internal path 
is 	
»       »          //"/storage/emulated/0",i don't know "share" and "no swap",so i skip. 	
»       »          //           if (FeatureOption.MTK_SHARED_SDCARD && !FeatureOption.MTK_2SDCARD_SW
AP) {»       »       
»       »          //               setDefaultPath(STORAGE_PATH_SHARE_SD); 	
»       »          //               path = STORAGE_PATH_SHARE_SD; 	
»       »          //           } else { 	
»       »          //               setDefaultPath(STORAGE_PATH_SD1); 	
»       »          //               path = STORAGE_PATH_SD1; 	
»       »          //           } 	
»       »          setDefaultPath(STORAGE_PATH_SD1);	
»       »          path = STORAGE_PATH_SD1;	
»          }	
»          	
»          //Here we don't care multi user which will be used by google,ignore and go on. 	
»          	
»          //MOTA upgrade from ICS to JB,update defaultPath to JB. 	
»          if(path.equals(STORAGE_PATH_SD1_ICS)){	
»       »          path = STORAGE_PATH_SD1;	
»       »          setDefaultPath(path);	
»          }else if(path.equals(STORAGE_PATH_SD2_ICS)){	
»       »          path = STORAGE_PATH_SD2;	
»       »          setDefaultPath(path);	
»          }	
»          	
»          Log.i(TAG,"getDefaultPath path="+path);	
»          return path;	
   }	
   	
   /**	
    * set default path for Appto storage data	
    * this only can used by settings.	
    * 	
    * @param path	
    * @hide	
    * @internal	
    */	
   public static void setDefaultPath(String path){	
»          Log.i(TAG,"setDefaultPath path = " + path);	
»          if (path == null) {	
»       »          Log.e(TAG,"setDefaultPath error! path = null");	
»       »          return;	
»          }	
»          	
»          try {	
»       »          SystemProperties.set(PROP_SD_DEFAULT_PATH,path);	
»          } catch (IllegalArgumentException e) {	
»       »          Log.e(TAG,"IllegalArgumentException when setDefaultPath:" + e);	
»          }	
   }	
   	
   /**	
    * Returns external SD card path.»       /sdcard2	
    * @hide	
    * @internal	
    */	
//   public static String getExternalStoragePath(){»       //method 1: 	
//»          String sdCardDir = null; 	
//       android.os.storage.StorageManager storageManager = 	
//               (android.os.storage.StorageManager) context 	
//                       .getSystemService(Context.STORAGE_SERVICE); 	
//       StorageVolume[] volumes = storageManager.getVolumeList(); 	
//       for (int i = 0; i < volumes.length; i++) { 	
//           if (volumes[i].isRemovable() && volumes[i].allowMassStorage()) { 	
//               sdCardDir = volumes[i].getPath(); 	
//               break; 	
//           } 	
//       } 	
//       return sdCardDir; 	
//   } 
   	
 public static String getExternalStoragePath(){»       //method 2: 	
   String sdCardDir = null;	
   String state = Environment.getStorageState(new File(STORAGE_PATH_SD2));	
   	
   if(state.equals(Environment.MEDIA_MOUNTED)){	
»          sdCardDir = STORAGE_PATH_SD2;	
   }else if(state.equals(Environment.MEDIA_UNMOUNTED)){	
»          sdCardDir = Environment.MEDIA_UNMOUNTED;	
   }else{	
»          sdCardDir = STORAGE_PATH_SD2;	
   }	
   return sdCardDir;  	
}	
   	
   	
   /**	
    * Returns internal storage path.	
    * @return	
    * @hide	
    * @internal	
    */	
   public static String getInternalStoragePath(){	
»          String sdCardDir = null;	
»          String state = Environment.getStorageState(new File(STORAGE_PATH_SHARE_SD));	
»          	
»          if(state.equals(Environment.MEDIA_MOUNTED)){	
»       »          sdCardDir = STORAGE_PATH_SD1;	
»          }else if(state.equals(Environment.MEDIA_UNMOUNTED)){	
»       »          sdCardDir = Environment.MEDIA_UNMOUNTED;	
»          }else{	
»       »          sdCardDir = STORAGE_PATH_SD1;	
»          }	
»          return sdCardDir;  	
   }	1
   	
} 

    定义的主要作用是往系统内存的属性里面添加属性presist.sys.sd.default.我们可以进入adb里面查看和修改一些属性1：adb shell 2：getprop + 键（或不加） tip:我们也可以setprop + 键 +值

     2：在设置里面添加默认存储器的选项：

在Settings的工程里面的.....res/xml/device_info_memory.xml的文件里面添加

......<span style="white-space:pre">	</span><PreferenceCategory 	
        android:key="memory_select"	
        android:title="@string/select_memory" />     ......

在Memroy.java文件里面添加

private void initDefaultWriteDisk(){	
    »       mDefaultWriteCategory = (PreferenceCategory)findPreference(DEFAULT_WRITE_CATEGORY_KEY);	
        List<RadioButtonPreference> defaultWritePreference = new ArrayList<RadioButtonPreference>();	
        StorageVolume[] volumes = mStorageManager.getVolumeList();	
        List<StorageVolume> storageVolumesEx = initVolumeList(volumes);	
        for (int i = 0; i < storageVolumesEx.size(); i++) {	
        »       StorageVolume volumn = storageVolumesEx.get(i);	
        »       RadioButtonPreference avalibileDisk = new RadioButtonPreference(getActivity());	
        »       String path = volumn.getPath();»       //volumn path 	
        »       android.util.Log.i("haiyong.liu","volumn.path="+path);	
        »       String state = Environment.getStorageState(new File(path));	
        »       	
        »       avalibileDisk.setKey(path);	
        »       avalibileDisk.setTitle(volumn.getDescription(getActivity()));	
        »       avalibileDisk.setPath(path);	
        »       avalibileDisk.setOnPreferenceChangeListener(this);	
        »       defaultWritePreference.add(avalibileDisk);	
        »       android.util.Log.e("haiyong.liu","Environment="+state);	
        »       if(state.equals(Environment.MEDIA_UNMOUNTED)||state.equals(Environment.MEDIA_REMOVED
)){	
        »       »       	
        »       }else {	
        »       »       mDefaultWriteCategory.addPreference(avalibileDisk);	
        »       »       if(path.equals(StorageManagerEx.getDefaultPath())){	
        »       »       »       avalibileDisk.setChecked(true);	
        »       »       »       mDeafultWritePathPref = avalibileDisk;	
        »       »       }else{	
        »       »       »       avalibileDisk.setChecked(false);	
        »       »       }	
        »       }	
»       »       }	
    }	
    	
    private List<StorageVolume> initVolumeList(StorageVolume[] volumes){	
    »       List<StorageVolume> storageVolumes = new ArrayList<StorageVolume>();	
    »       /*if(UserManager.supportsMultipleUsers()){»       //return the current user's volumn lis
t if supported,otherwise ignore.	
    »       »       StorageVolume[] sv = mStorageManager.getVolumeListAsUser();	
    »       »       for (int i = 0; i < sv.length; i++) {	
                if (!"not_present".equals(mStorageManager.getVolumeState(volumes[i].getPath()))) {	
                    storageVolumes.add(volumes[i]);	
                }	
            }	
    »       »       return storageVolumes;	
    »       }*/	
    »       	
        for (int i = 0; i < volumes.length; i++) {	
            if (!"not_present".equals(mStorageManager.getVolumeState(volumes[i].getPath()))) {	
                storageVolumes.add(volumes[i]);	
            }	
        }	
        	
        return storageVolumes;	
    }	
    	
    @Override	
    public boolean onPreferenceChange(Preference preference, Object newValue) {	

        if (preference != null && preference instanceof RadioButtonPreference) {	
            if (mDeafultWritePathPref != null) {	
                mDeafultWritePathPref.setChecked(false);	
            }	
            StorageManagerEx.setDefaultPath(preference.getKey());	
            mDeafultWritePathPref = (RadioButtonPreference) preference;	
            return true;	
        }	
        return false;	
    }

initDefaultWriteDisk（）

    3：找到对应需要添加该功能的工程，我们需要添加的是Camrea2，蓝牙，下载器，录音这几个Apk，找到这几个源码存储数据的地方，将存储位置改为StorageManagerEx.getDefaultPath()