Android 系统缓存扫描与清理方法分析

	public void someFunc() {
	    IPackageStatsObserver.Stub observer = new PackageSizeObserver();
	    getPackageInfo("com.tencent.mobileqq", observer);
	}
	
	public void getPackageInfo(String packageName, IPackageStatsObserver.Stub observer) {
	    try {
	        PackageManager pm = ContextUtil.applicationContext.getPackageManager();
	        Method getPackageSizeInfo = pm.getClass()
	                .getMethod("getPackageSizeInfo", String.class, IPackageStatsObserver.class);
	
	        getPackageSizeInfo.invoke(pm, packageName, observer);
	    } catch (NoSuchMethodException e ) {
	        e.printStackTrace();
	    } catch (IllegalAccessException e) {
	        e.printStackTrace();
	    } catch (InvocationTargetException e) {
	        e.printStackTrace();
	    }
	}
	
	private class PackageSizeObserver extends IPackageStatsObserver.Stub {
	    @Override
	    public void onGetStatsCompleted(PackageStats packageStats, boolean succeeded)
	            throws RemoteException {
	        if (packageStats == null || !succeeded) {
	        } else {
	            AppEntry entry = new AppEntry();
	            entry.packageName = packageStats.packagename;
	            entry.cacheSize = packageStats.cacheSize + packageStats.externalCacheSize;
	            // do something else，比如把 entry 通过消息发送给需要的地方，或者添加到你的列表里
	        }
	    }
	}

	private void initData() {
        new Thread(new Runnable() {
            @Override
            public void run() {
                mPackageManager = getPackageManager();
                List<ApplicationInfo> installedApplications = mPackageManager.getInstalledApplications(PackageManager.GET_UNINSTALLED_PACKAGES);
                pb_cacheclean.setMax(installedApplications.size());
                int index = 1;

                for (ApplicationInfo info : installedApplications) {
                    try {
                        Thread.sleep(20+ new Random().nextInt(50));
                        getPackageCache(info);
                        pb_cacheclean.setProgress(index++);

                        Message msg = Message.obtain();
                        msg.what = CHECK_APP_CACHE;
                        msg.obj = info.packageName;
                        mHandler.sendMessage(msg);

                    } catch (InterruptedException e) {
                        e.printStackTrace();
                    }
                }
                Message msg = Message.obtain();
                msg.what = SCAN_FINISH;
                mHandler.sendMessage(msg);
            }

        }).start();
    }

    


    private void getPackageCache(final ApplicationInfo info) {

        mPm = getPackageManager();
        //引入IPackageStatsObserver.stub 类的aidl文件，并实现 onGetStatsCompleted 方法
        IPackageStatsObserver.Stub mStatsObserver = new IPackageStatsObserver.Stub() {

            public void onGetStatsCompleted(PackageStats stats, boolean succeeded) {

                Message msg = Message.obtain();
                msg.what = ADD_CACHE_VIEW;
                AppCacheViewInfo viewInfo = new AppCacheViewInfo();
                //缓存大小的过程
                if (stats.cacheSize > 0) {
                    String cacheSize = Formatter.formatFileSize(getApplicationContext(), stats.cacheSize);
                    viewInfo.setName(info.loadLabel(mPackageManager).toString());
                    viewInfo.setPkgName(info.packageName);
                    viewInfo.setCachaSize(cacheSize);
                    viewInfo.setIcon(info.loadIcon(mPackageManager));
                    msg.obj = viewInfo;
                    mHandler.sendMessage(msg);
                }
            }
        };

        //函数被隐藏，需要通过反射获取方法
	//        mPm.getPackageSizeInfo("com.android.browser", mStatsObserver);
        try {
            Class<?> clazz = Class.forName("android.content.pm.PackageManager");
            Method method = clazz.getMethod("getPackageSizeInfo", String.class, IPackageStatsObserver.class);
            method.invoke(mPm, info.packageName, mStatsObserver);

        } catch (Exception e) {
            e.printStackTrace();
        }
    }

class AppCacheViewInfo {
	        private String name;
	        private String pkgName;
	        private Drawable icon;
	        private String cachaSize;
	
	        public String getName() {
	            return name;
	        }
	
	        public void setName(String name) {
	            this.name = name;
	        }
	
	        public String getPkgName() {
	            return pkgName;
	        }
	
	        public void setPkgName(String pkgName) {
	            this.pkgName = pkgName;
	        }
	
	        public Drawable getIcon() {
	            return icon;
	        }
	
	        public void setIcon(Drawable icon) {
	            this.icon = icon;
	        }
	
	        public String getCachaSize() {
	            return cachaSize;
	        }
	
	        public void setCachaSize(String cachaSize) {
	            this.cachaSize = cachaSize;
	        }
	    }

public class InstalledAppDetails extends Fragment
 implements View.OnClickListener, CompoundButton.OnCheckedChangeListener,
        ApplicationsState.Callbacks {
    ......
    private Button mClearCacheButton;
    ......
    class ClearCacheObserver extends IPackageDataObserver.Stub {
        public void onRemoveCompleted(final String packageName, final boolean succeeded) {
            final Message msg = mHandler.obtainMessage(CLEAR_CACHE);
            msg.arg1 = succeeded ? OP_SUCCESSFUL:OP_FAILED;
            mHandler.sendMessage(msg);
         }
     }
    ......
    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
        ......
        mClearCacheButton = (Button) view.findViewById(R.id.clear_cache_button);
        ......
    }
    ......
    private void refreshSizeInfo() {
        ......
        if (cacheSize <= 0) {
            mClearCacheButton.setEnabled(false);
        } else {
            mClearCacheButton.setEnabled(true);
            mClearCacheButton.setOnClickListener(this);
        }
    }
    ......
    public void onClick(View v) {
        ......
        } else if (v == mClearCacheButton) {
            // Lazy initialization of observer
            if (mClearCacheObserver == null) {
                mClearCacheObserver = new ClearCacheObserver();
            }
            mPm.deleteApplicationCacheFiles(packageName, mClearCacheObserver);
        }
        ......
    } 这个类定义在文件 packages/apps/Settings/src/com/android/settings/applications/InstalledAppDetails.java 中。

/**
 * Attempts to delete the cache files associated with an application.
 * Since this may take a little while, the result will
 * be posted back to the given observer.  A deletion will fail if the calling context
 * lacks the {@link android.Manifest.permission#DELETE_CACHE_FILES} permission, if the
 * named package cannot be found, or if the named package is a "system package".
 *
 * ......
 *
 * @hide
 */ 没错它又是一个 @hide 方法，关键是它需要 DELETE_CACHE_FILES 权限，而该权限的相关声明如下：

<!-- Allows an application to delete cache files. -->
<permission android:name="android.permission.DELETE_CACHE_FILES"
    android:label="@string/permlab_deleteCacheFiles"
    android:description="@string/permdesc_deleteCacheFiles"
    android:protectionLevel="signature|system" />

/**
 * Free storage by deleting LRU sorted list of cache files across
 * all applications. If the currently available free storage
 * on the device is greater than or equal to the requested
 * free storage, no cache files are cleared. If the currently
 * available storage on the device is less than the requested
 * free storage, some or all of the cache files across
 * all applications are deleted (based on last accessed time)
 * to increase the free storage space on the device to
 * the requested value. There is no guarantee that clearing all
 * the cache files from all applications will clear up
 * enough storage to achieve the desired value.
 * @param freeStorageSize The number of bytes of storage to be
 * freed by the system. Say if freeStorageSize is XX,
 * and the current free storage is YY,
 * if XX is less than YY, just return. if not free XX-YY number
 * of bytes if possible.
 * @param observer call back used to notify when
 * the operation is completed
 *
 * @hide
 */ public abstract void freeStorageAndNotify(long freeStorageSize, IPackageDataObserver observer); 从解释来看它是用来在必要时释放所有应用的缓存所占空间的，在 Android 源码里搜索一下它被调用的地方，有一处是在 frameworks/base/services/java/com/android/server/DeviceStorageMonitorService.java 中，大致的逻辑是在系统空间不够的时候，提示用户清理系统缓存。

public class PackageManagerService extends IPackageManager.Stub {
    ......
    public void freeStorageAndNotify(final long freeStorageSize, final IPackageDataObserver observer) {
        mContext.enforceCallingOrSelfPermission(
                android.Manifest.permission.CLEAR_APP_CACHE, null);
        // Queue up an async operation since clearing cache may take a little while.
        mHandler.post(new Runnable() {
            public void run() {
                mHandler.removeCallbacks(this);
                int retCode = -1;
                retCode = mInstaller.freeCache(freeStorageSize);
                if (retCode < 0) {
                    Slog.w(TAG, "Couldn't clear application caches");
                }
                if (observer != null) {
                    try {
                        observer.onRemoveCompleted(null, (retCode >= 0));
                    } catch (RemoteException e) {
                        Slog.w(TAG, "RemoveException when invoking call back");
                    }
                }
            }
        });
    }
    ......
}