每個安裝使用者都知道安卓程式的安裝步驟，下載，點選安裝包，安裝。那麼這些步驟在安卓核心中是如何執行的？我們先從安卓原始碼中的系統軟體PackageInstaller入手，來分析軟體安裝的執行步驟。
PackageInstaller的原始碼packages/apps下。其中的源程式包含如下幾個原始檔：

我們從PackageInstallerActivity入手：
找到oncreate入口：

 protected void onCreate(Bundle icicle) {
        super.onCreate(icicle);

        // get intent information
      //  **首先是從Intent當中讀取包資訊**
        final Intent intent = getIntent();
 

        mPackageURI = intent.getData();
        mOriginatingURI = intent.getParcelableExtra(Intent.EXTRA_ORIGINATING_URI);
        mReferrerURI = intent.getParcelableExtra(Intent.EXTRA_REFERRER);
        mPm = getPackageManager();
      /*  **判斷是否來自未知包源，看是否是非官網上下載下來的APP**
        軟體安裝，app-store安裝，普通應用安裝--通過PackageInstallerActivity，Runtime.getRuntime().exec(pm install -r $app)需要安裝許可權
        Android應用安裝有如下四種方式
        1. 系統應用安裝――開機時完成，沒有安裝介面
        2. 網路下載應用安裝――通過market應用完成，沒有安裝介面
        3. ADB工具安裝――沒有安裝介面。
        4. 第三方應用安裝――通過SD卡里的APK檔案安裝，有安裝介面，由packageinstaller.apk應用處理安裝及解除安裝過程的介面。*/
 

        boolean requestFromUnknownSource = isInstallRequestFromUnknownSource(intent);
        安裝包資訊流分析：請移步到1.安裝包資訊流分析
        mInstallFlowAnalytics = new InstallFlowAnalytics();
        mInstallFlowAnalytics.setContext(this);
        mInstallFlowAnalytics.setStartTimestampMillis(SystemClock.elapsedRealtime
 
());
        mInstallFlowAnalytics.setInstallsFromUnknownSourcesPermitted(
                isInstallingUnknownAppsAllowed());
        mInstallFlowAnalytics.setInstallRequestFromUnknownSource(requestFromUnknownSource);
        mInstallFlowAnalytics.setVerifyAppsEnabled(isVerifyAppsEnabled());
        mInstallFlowAnalytics.setAppVerifierInstalled(isAppVerifierInstalled());
        mInstallFlowAnalytics.setPackageUri(mPackageURI.toString());
//如果連線的開頭不是file或者package，結束安裝
        final String scheme = mPackageURI.getScheme();
        if (scheme != null && !"file".equals(scheme) && !"package".equals(scheme)) {
            Log.w(TAG, "Unsupported scheme " + scheme);
            setPmResult(PackageManager.INSTALL_FAILED_INVALID_URI);
            mInstallFlowAnalytics.setFlowFinished(
                    InstallFlowAnalytics.RESULT_FAILED_UNSUPPORTED_SCHEME);
            finish();
            return;
        }

        final PackageUtil.AppSnippet as;
        if ("package".equals(mPackageURI.getScheme())) {
            mInstallFlowAnalytics.setFileUri(false);
            try {
                mPkgInfo = mPm.getPackageInfo(mPackageURI.getSchemeSpecificPart(),
                        PackageManager.GET_PERMISSIONS | PackageManager.GET_UNINSTALLED_PACKAGES);
            } catch (NameNotFoundException e) {
            }
            if (mPkgInfo == null) {
                Log.w(TAG, "Requested package " + mPackageURI.getScheme()
                        + " not available. Discontinuing installation");
                showDialogInner(DLG_PACKAGE_ERROR);
                setPmResult(PackageManager.INSTALL_FAILED_INVALID_APK);
                mInstallFlowAnalytics.setPackageInfoObtained();
                mInstallFlowAnalytics.setFlowFinished(
                        InstallFlowAnalytics.RESULT_FAILED_PACKAGE_MISSING);
                return;
            }
            as = new PackageUtil.AppSnippet(mPm.getApplicationLabel(mPkgInfo.applicationInfo),
                    mPm.getApplicationIcon(mPkgInfo.applicationInfo));
        } else {
            mInstallFlowAnalytics.setFileUri(true);
            final File sourceFile = new File(mPackageURI.getPath());
            PackageParser.Package parsed = PackageUtil.getPackageInfo(sourceFile);

            // Check for parse errors
            if (parsed == null) {
                Log.w(TAG, "Parse error when parsing manifest. Discontinuing installation");
                showDialogInner(DLG_PACKAGE_ERROR);
                setPmResult(PackageManager.INSTALL_FAILED_INVALID_APK);
                mInstallFlowAnalytics.setPackageInfoObtained();
                mInstallFlowAnalytics.setFlowFinished(
                        InstallFlowAnalytics.RESULT_FAILED_TO_GET_PACKAGE_INFO);
                return;
            }
            mPkgInfo = PackageParser.generatePackageInfo(parsed, null,
                    PackageManager.GET_PERMISSIONS, 0, 0, null,
                    new PackageUserState());
            mPkgDigest = parsed.manifestDigest;
            as = PackageUtil.getAppSnippet(this, mPkgInfo.applicationInfo, sourceFile);
        }
        mInstallFlowAnalytics.setPackageInfoObtained();

        //set view
        setContentView(R.layout.install_start);
        mInstallConfirm = findViewById(R.id.install_confirm_panel);
        mInstallConfirm.setVisibility(View.INVISIBLE);
        PackageUtil.initSnippetForNewApp(this, as, R.id.app_snippet);

        mOriginatingUid = getOriginatingUid(intent);

        // Block the install attempt on the Unknown Sources setting if necessary.
        if ((requestFromUnknownSource) && (!isInstallingUnknownAppsAllowed())) {
            //ask user to enable setting first
            showDialogInner(DLG_UNKNOWN_APPS);
            mInstallFlowAnalytics.setFlowFinished(
                    InstallFlowAnalytics.RESULT_BLOCKED_BY_UNKNOWN_SOURCES_SETTING);
            return;
        }
        initiateInstall();
    }

1.安裝包資訊流分析