解析xml android Android源代码解析之（十三）(4)

消息弹窗的主要作用，用于提示用户当前安装apk文件的特性。都知道android系统在android apk文件之前会解析器manifest文件，这个操作也是早onCreate方法中运行的：

PackageParser.Package parsed = PackageUtil.getPackageInfo(sourceFile);

我们详细看一下getPackageInfo方法的实现：

public static PackageParser.Package getPackageInfo(File sourceFile) {
        final PackageParser parser = new PackageParser();
        try {
            PackageParser.Package pkg = parser.parseMonolithicPackage(sourceFile, 0);
            parser.collectManifestDigest(pkg);
            return pkg;
        } catch (PackageParserException e) {
            return null;
        }
    }

好吧，到了这里是不是代码变得非常熟悉了？parseMonolithicPackage就是我们上一节分析的android系统解析manifest文件的过程，详细的可参考：

而collectManifestDigest方法，我们这里简单的介绍一下。其主要是要争apk的签名是否正确。好吧通过这两部我们就把apk文件的manifest和签名信息都解析完毕并保存在了Package中。

接着往下走，在全部的解析完毕之后我们会在onCreate方法中运行initiateInstall();方法。刚方法的主要作用是初始化安装。

private void initiateInstall() {
        String pkgName = mPkgInfo.packageName;
        // Check if there is already a package on the device with this name
        // but it has been renamed to something else.
        String[] oldName = mPm.canonicalToCurrentPackageNames(new String[] { pkgName });
        if (oldName != null && oldName.length > 0 && oldName[0] != null) {
            pkgName = oldName[0];
            mPkgInfo.packageName = pkgName;
            mPkgInfo.applicationInfo.packageName = pkgName;
        }
        // Check if package is already installed. display confirmation dialog if replacing pkg
        try {
            // This is a little convoluted because we want to get all uninstalled
            // apps, but this may include apps with just data, and if it is just
            // data we still want to count it as "installed".
            mAppInfo = mPm.getApplicationInfo(pkgName,
                    PackageManager.GET_UNINSTALLED_PACKAGES);
            if ((mAppInfo.flags&ApplicationInfo.FLAG_INSTALLED) == 0) {
                mAppInfo = null;
            }
        } catch (NameNotFoundException e) {
            mAppInfo = null;
        }

        mInstallFlowAnalytics.setReplace(mAppInfo != null);
        mInstallFlowAnalytics.setSystemApp(
                (mAppInfo != null) && ((mAppInfo.flags & ApplicationInfo.FLAG_SYSTEM) != 0));

        // If we have a session id, we're invoked to verify the permissions for the given
        // package. Otherwise, we start the install process.
        if (mSessionId != -1) {
            startInstallConfirm();
        } else {
            startInstall();
        }
    }

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