android动态权限的源码解析

android 动态权限

android权限的类型

在android9.0中定义了很多权限，如下：

    <attr name="protectionLevel">
    <!-- <strong>Base permission type</strong>: a lower-risk permission that gives
         an application access to isolated application-level features, with minimal
         risk to other applications, the system, or the user. The system
         automatically grants this type of permission to a requesting application at
         installation, without asking for the user's explicit approval (though the
         user always has the option to review these permissions before installing). -->
    <flag name="normal" value="0" />
    <!-- <strong>Base permission type</strong>: a higher-risk permission that
         would give a requesting application access to private user data or
         control over the device that can negatively impact the user.  Because
         this type of permission introduces potential risk, the system may
         not automatically grant it to the requesting application.  For example,
         any dangerous permissions requested by an application may be displayed
         to the user and require confirmation before proceeding, or some other
         approach may be taken to avoid the user automatically allowing
         the use of such facilities.  -->
    <flag name="dangerous" value="1" />
    <!-- <strong>Base permission type</strong>: a permission that the system is
         to grant only if the requesting application is signed with the same
         certificate as the application that declared the permission. If the
         certificates match, the system automatically grants the permission
         without notifying the user or asking for the user's explicit approval. -->
    <flag name="signature" value="2" />
    <!-- Old synonym for "signature|privileged". Deprecated in API level 23.
         Base permission type: a permission that the system is to grant only
         to packages in the Android system image <em>or</em> that are signed
         with the same certificates. Please avoid using this option, as the
         signature protection level should be sufficient for most needs and
         works regardless of exactly where applications are installed.  This
         permission is used for certain special situations where multiple
         vendors have applications built in to a system image which need
         to share specific features explicitly because they are being built
         together. -->
    <flag name="signatureOrSystem" value="3" />
    <!-- Additional flag from base permission type: this permission can also
         be granted to any applications installed as privileged apps on the system image.
         Please avoid using this option, as the
         signature protection level should be sufficient for most needs and
         works regardless of exactly where appl