Framework基础：运行时权限的弹框是谁弹出来的？

女神.png

Android 6.0的权限不再是在安装的时候一股脑给你了。需要权限的话，需要代码中去获取。而对于用户，获取权限会弹框，用户可以醒目地知道应用拿了什么权限，用户进而可以决定给不给这个权限。

例如下面的例子是一个垃圾程序要获取短信的权限

获取权限.png

在代码只需要加一句就可以了,参数里面了的2我是随便乱写的，就是要输入一个整形，代表request code。

    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        this.requestPermissions(
                new String[]{Manifest.permission.SEND_SMS},
                2);
    }

这篇文章不说太多，就说下这个弹框是怎么出来的好了。
首先入口是Activity类，调用requestPermissions获取权限。可以看到他启动了另一个Activity。可以想象，这个弹框就是在这个Activity里面。我们看看这个Intent是什么，找出Intent的包名与Action。
/frameworks/base/core/java/android/app/Activity.java

    public final void requestPermissions(@NonNull String[] permissions, int requestCode) {
        Intent intent = getPackageManager().buildRequestPermissionsIntent(permissions);
        startActivityForResult(REQUEST_PERMISSIONS_WHO_PREFIX, intent, requestCode, null);
    }

通过ContextImpl.getPackageManager()获取到的是ApplicationPackageManager，他的父类是PackageManager。
/frameworks/base/core/java/android/app/ContextImpl.java

    @Override
    public PackageManager getPackageManager() {
        if (mPackageManager != null) {
            return mPackageManager;
        }

        IPackageManager pm = ActivityThread.getPackageManager();
        if (pm != null) {
            // Doesn't matter if we make more than one instance.
            return (mPackageManager = new ApplicationPackageManager(this, pm));
        }

        return null;
    }

ApplicationPackageManager获取到这个intent的action是android.content.pm.action.REQUEST_PERMISSIONS，包名要再看看，是通过getPermissionControllerPackageName()获取的。
/frameworks/base/core/java/android/app/ApplicationPackageManager.java

    public static final String ACTION_REQUEST_PERMISSIONS =
            "android.content.pm.action.REQUEST_PERMISSIONS";
    public static final String EXTRA_REQUEST_PERMISSIONS_NAMES =
            "android.content.pm.extra.REQUEST_PERMISSIONS_NAMES";

    public Intent buildRequestPermissionsIntent(@NonNull String[] permissions) {
        if (ArrayUtils.isEmpty(permissions)) {
           throw new NullPointerException("permission cannot be null or empty");
        }
        Intent intent = new Intent(ACTION_REQUEST_PERMISSIONS);
        intent.putExtra(EXTRA_REQUEST_PERMISSIONS_NAMES, permissions);
        intent.setPackage(getPermissionControllerPackageName());
        return intent;
    }

getPermissionControllerPackageName()会进一步调用mPM.getPermissionControllerPackageName()，这个mPM是系统服务PackageManagerService的远程代理。

    @Override
    public String getPermissionControllerPackageName() {
        synchronized (mLock) {
            if (mPermissionsControllerPackageName == null) {
                try {
                    mPermissionsControllerPackageName = mPM.getPermissionControllerPackageName();
                } catch (RemoteException e) {
                    throw new RuntimeException("Package manager has died", e);
                }
            }
            return mPermissionsControllerPackageName;
        }
    }

最后包名通过PackageManagerService的getRequiredInstallerLPr获取到，看这个函数名，可以顾名思义下，就是安装器，就是安装apk那个玩意。

安装器.png
/frameworks/base/services/core/java/com/android/server/pm/PackageManagerService.java

    private String getRequiredInstallerLPr() {
        Intent installerIntent = new Intent(Intent.ACTION_INSTALL_PACKAGE);
        installerIntent.addCategory(Intent.CATEGORY_DEFAULT);
        installerIntent.setDataAndType(Uri.fromFile(new File("foo.apk")), PACKAGE_MIME_TYPE);

        final List<ResolveInfo> installers = queryIntentActivities(installerIntent,
                PACKAGE_MIME_TYPE, 0, 0);

        String requiredInstaller = null;

        final int N = installers.size();
        for (int i = 0; i < N; i++) {
            final ResolveInfo info = installers.get(i);
            final String packageName = info.activityInfo.packageName;

            if (!info.activityInfo.applicationInfo.isSystemApp()) {
                continue;
            }

            if (requiredInstaller != null) {
                throw new RuntimeException("There must be one required installer");
            }

            requiredInstaller = packageName;
        }

        if (requiredInstaller == null) {
            throw new RuntimeException("There must be one required installer");
        }

        return requiredInstaller;
    }

所以，最后的组合而成的intent的包名是com.android.packageinstaller，action是android.content.pm.action.REQUEST_PERMISSIONS。

应用安装器.png

这个Action会启动应用安装器的GrantPermissionsActivity 进行授权

清单.png

所以啦，这个弹框是由GrantPermissionsActivity中弹出的。分析完毕！