Content Provider Permissions
A provider's application can specify permissions that other applications must have in order to access the provider's data. These permissions ensure that the user knows what data an application will try to access. Based on the provider's requirements, other applications request the permissions they need in order to access the provider. End users see the requested permissions when they install the application.
发布provider的应用可以给它指定个权限，没有这个权限，外部应用不可访问这个provider。
If a provider's application doesn't specify any permissions, then other applications have no access to the provider's data. However, components in the provider's application always have full read and write access, regardless of the specified permissions.
如果没有定义权限，那么只能本应用内访问这个 provider。
As noted previously, the User Dictionary Provider requires the android.permission.READ_USER_DICTIONARY permission to retrieve data from it. The provider has the separate android.permission.WRITE_USER_DICTIONARY permission for inserting, updating, or deleting data.
To get the permissions needed to access a provider, an application requests them with a <uses-permission> element in its manifest file. When the Android Package Manager installs the application, a user must approve all of the permissions the application requests. If the user approves all of them, Package Manager continues the installation; if the user doesn't approve them, Package Manager aborts the installation.
The following <uses-permission> element requests read access to the User Dictionary Provider:
<uses-permission android:name="android.permission.READ_USER_DICTIONARY">
The impact of permissions on provider access is explained in more detail in the Security and Permissions guide.
