进行如下操作：
设置->应用->选择一个应用->应用信息
会到达如下界面：
可以看到这个应用占用的磁盘空间。
先说结果，这几项会计算哪些文件（夹）。
1.应用，由三项相加组成
- /data/data/com.myapp/lib，即so库文件夹大小
- /data/app/com.myapp-1.apk，原始apk文件的复制
- [email protected]@[email protected]，dalvik虚拟机对dex文件的缓存
2.USB存储（应用）。把程序装到（或移到）sd卡后的大小。/sdcard/Android/...，参考“应用”项。
3.数据 = /data/data/com.myapp/目录大小 - cache子目录大小 - lib子目录大小
4.SD 卡 = /sdcard/Android/data/com.myapp/目录大小 - /sdcard/Android/data/com.myapp/cache目录大小
（总计是以上4个之和）
5.缓存 = /data/data/com.myapp/cache目录大小 + /sdcard/Android/data/com.myapp/cache目录大小
下面是分析Android4.2源码怎么做的。比较详细说分析过程，会累赘些，授之以渔吧。
根据应用信息的界面Settings这个名字，猜测到源码
android4.2/packages/apps/Settings/src/com/android/settings/applications/InstalledAppDetails.java
负责，对应的xml是
android4.2/packages/apps/Settings/res/layout/installed_app_details.xml
刷新磁盘占用大小的函数是
InstalledAppDetaileds.refreshSizeInfo()
根据代码线索反查
mDataSize.setText(getSizeStr(dataSize));
->
long dataSize = mAppEntry.dataSize;
->
mAppEntry = mState.getEntry(packageName);
->
mState.requestSize(mAppEntry.info.packageName);
ApplicationsState mState
->
android4.2/packages/apps/Settings/src/com/android/settings/applications/ApplicationState.java
mPm.getPackageSizeInfo(packageName, mBackgroundHandler.mStatsObserver);
final PackageManager mPm
->
android4.2/frameworks/base/core/java/android/app/ApplicationPackageManager.java
public void getPackageSizeInfo(String packageName, int userHandle,
IPackageStatsObserver observer) {
mPM.getPackageSizeInfo(packageName, userHandle, observer);
private final IPackageManager mPM;
->
IPackageManager是个接口，用查找文件内容的方式搜索它的实现，根据java语法，可用关键字“extends IPackageManager”
用shell命令行可得到这样的结果：
[email protected] ~/Desktop/android4.2 $ grep -rnsw "extends IPackageManager" *
frameworks/base/services/java/com/android/server/pm/PackageManagerService.java:172:public class PackageManagerService extends IPackageManager.Stub {
->
android4.2/frameworks/base/services/java/com/android/server/pm/PackageManagerService.java
public void getPackageSizeInfo(
Message msg = mHandler.obtainMessage(INIT_COPY);
msg.obj = new MeasureParams(stats, observer);
mHandler.sendMessage(msg);
->
内部类class MeasureParams
void handleStartCopy() throws RemoteException {
mSuccess = getPackageSizeInfoLI(mStats.packageName, mStats.userHandle, mStats);
->
getPackageSizeInfoLI函数
int res = mInstaller.getSizeInfo(packageName, userHandle, p.mPath, publicSrcDir,
asecPath, pStats);
final Installer mInstaller
->
frameworks/base/services/java/com/android/server/pm/Installer.java
public int getSizeInfo(
String s = transaction(builder.toString());
->
private synchronized String transaction(String cmd) {
if (!writeCommand(cmd)) {
->
private boolean writeCommand(String _cmd)
mOut.write(buf, 0, 2);
mOut.write(cmd, 0, len);
->
OutputStream mOut;
LocalSocketAddress address = new LocalSocketAddress("installd",
LocalSocketAddress.Namespace.RESERVED);
mSocket.connect(address);
mOut = mSocket.getOutputStream();
到此很无语，用socket的方式来通信。
->
查找文件内容，关键字为 "installd"， 注意包含双引号
得到结果：
[email protected] ~/Desktop/android4.2 $ grep -rnsw "\"installd\"" *
cts/tools/device-setup/TestDeviceSetup/src/android/tests/getinfo/RootProcessScanner.java:33: "installd",
frameworks/base/services/java/com/android/server/pm/Installer.java:51: LocalSocketAddress address = new LocalSocketAddress("installd",
frameworks/base/cmds/installd/installd.h:18:#define LOG_TAG "installd"
frameworks/base/cmds/installd/installd.h:49:#define SOCKET_PATH "installd"
sdk/files/ant/build.xml:1355: <condition property="tested.project.install.target" value="installi" else="installd">
sdk/files/ant/build.xml:1392: <target name="installd" depends="-set-debug-files, install"
->
frameworks/base/cmds/installd/installd.h
int get_size(const char *pkgname, int persona, const char *apkpath, const char *fwdlock_apkpath,
const char *asecpath, int64_t *codesize, int64_t *datasize, int64_t *cachesize,
int64_t *asecsize);
或
frameworks/base/cmds/installd/installd.c
static int do_get_size(char **arg, char reply[REPLY_MAX])
res = get_size(arg[0], atoi(arg[1]), arg[2], arg[3], arg[4],
&codesize, &datasize, &cachesize, &asecsize);
->
看到在installd.c没有实现get_size函数。可以根据函数声明搜索文件内容，不过既然是c语言，那可能是把函数分离实现。
所以在installd.c的目录下，看到另一个代码文件里实现了。转载请注明出处：http://blog.csdn.net/hursing
->
frameworks/base/cmds/installd/commands.c
这里就是计算的源码了。
int get_size(const char *pkgname, int persona, const char *apkpath, const char *fwdlock_apkpath, const char *asecpath, int64_t *_codesize, int64_t *_datasize, int64_t *_cachesize, int64_t* _asecsize){ DIR *d; int dfd; struct dirent *de; struct stat s; char path[PKG_PATH_MAX]; int64_t codesize = 0; int64_t datasize = 0; int64_t cachesize = 0; int64_t asecsize = 0; /* count the source apk as code -- but only if it's not * on the /system partition and its not on the sdcard. */ if (validate_system_app_path(apkpath) && strncmp(apkpath, android_asec_dir.path, android_asec_dir.len) != 0) { if (stat(apkpath, &s) == 0) { codesize += stat_size(&s); } } /* count the forward locked apk as code if it is given */ if (fwdlock_apkpath != NULL && fwdlock_apkpath[0] != '!') { if (stat(fwdlock_apkpath, &s) == 0) { codesize += stat_size(&s); } } /* count the cached dexfile as code */ if (!create_cache_path(path, apkpath)) { if (stat(path, &s) == 0) { codesize += stat_size(&s); } } /* add in size of any libraries */ if (!create_pkg_path_in_dir(path, &android_app_lib_dir, pkgname, PKG_DIR_POSTFIX)) { d = opendir(path); if (d != NULL) { dfd = dirfd(d); codesize += calculate_dir_size(dfd); closedir(d); } } /* compute asec size if it is given */ if (asecpath != NULL && asecpath[0] != '!') { if (stat(asecpath, &s) == 0) { asecsize += stat_size(&s); } } if (create_pkg_path(path, pkgname, PKG_DIR_POSTFIX, persona)) { goto done; } d = opendir(path); if (d == NULL) { goto done; } dfd = dirfd(d); /* most stuff in the pkgdir is data, except for the "cache" * directory and below, which is cache, and the "lib" directory * and below, which is code... */ while ((de = readdir(d))) { const char *name = de->d_name; if (de->d_type == DT_DIR) { int subfd; int64_t statsize = 0; int64_t dirsize = 0; /* always skip "." and ".." */ if (name[0] == '.') { if (name[1] == 0) continue; if ((name[1] == '.') && (name[2] == 0)) continue; } if (fstatat(dfd, name, &s, AT_SYMLINK_NOFOLLOW) == 0) { statsize = stat_size(&s); } subfd = openat(dfd, name, O_RDONLY | O_DIRECTORY); if (subfd >= 0) { dirsize = calculate_dir_size(subfd); } if(!strcmp(name,"lib")) { codesize += dirsize + statsize; } else if(!strcmp(name,"cache")) { cachesize += dirsize + statsize; } else { datasize += dirsize + statsize; } } else if (de->d_type == DT_LNK && !strcmp(name,"lib")) { // This is the symbolic link to the application's library // code. We'll count this as code instead of data, since // it is not something that the app creates. if (fstatat(dfd, name, &s, AT_SYMLINK_NOFOLLOW) == 0) { codesize += stat_size(&s); } } else { if (fstatat(dfd, name, &s, AT_SYMLINK_NOFOLLOW) == 0) { datasize += stat_size(&s); } } } closedir(d);done: *_codesize = codesize; *_datasize = datasize; *_cachesize = cachesize; *_asecsize = asecsize; return 0;}以上是计算了内部磁盘的占用，还不齐，还有线索：PackageManagerService.java的内部类MeasureParams.handleStartCopy()函数：
void handleStartCopy() throws RemoteException { synchronized (mInstallLock) { mSuccess = getPackageSizeInfoLI(mStats.packageName, mStats.userHandle, mStats); } final boolean mounted; if (Environment.isExternalStorageEmulated()) { mounted = true; } else { final String status = Environment.getExternalStorageState(); mounted = (Environment.MEDIA_MOUNTED.equals(status) || Environment.MEDIA_MOUNTED_READ_ONLY.equals(status)); } if (mounted) { final UserEnvironment userEnv = new UserEnvironment(mStats.userHandle); final File externalCacheDir = userEnv .getExternalStorageAppCacheDirectory(mStats.packageName); final long externalCacheSize = mContainerService .calculateDirectorySize(externalCacheDir.getPath()); mStats.externalCacheSize = externalCacheSize; final File externalDataDir = userEnv .getExternalStorageAppDataDirectory(mStats.packageName); long externalDataSize = mContainerService.calculateDirectorySize(externalDataDir .getPath()); if (externalCacheDir.getParentFile().equals(externalDataDir)) { externalDataSize -= externalCacheSize; } mStats.externalDataSize = externalDataSize; final File externalMediaDir = userEnv .getExternalStorageAppMediaDirectory(mStats.packageName); mStats.externalMediaSize = mContainerService .calculateDirectorySize(externalMediaDir.getPath()); final File externalObbDir = userEnv .getExternalStorageAppObbDirectory(mStats.packageName); mStats.externalObbSize = mContainerService.calculateDirectorySize(externalObbDir .getPath()); } }这里计算了sd卡上的磁盘占用。内部磁盘的计算，是用linux的stat函数。
一些目录和文件的常量，定义在installd.h
认真看代码，则会得到文章开头的结果。
代码计算的结果得到的是占用磁盘的大小，但由于存储器有"4K对齐”的概念，所以占用磁盘大小不等于文件大小。例如一个实际为2.98K的文件，会在应用信息里显示为4K。
转载请注明出处：http://blog.csdn.net/hursing