应用程序权限

Many features of today's devices and operating systems can have significant privacy, security, and performance implications if misused. It's therefore increasingly common for platforms to require explicit consent from the user before accessing these features.

The Qt permission APIs allow the application to check or request permission for such features in a cross platform manner.

用法

A feature that commonly requires user consent is access to the microphone of the device. An application for recording voice memos would perhaps look something like this initially:

void VoiceMemoWidget::onRecordingInitiated()
{
    m_microphone->startRecording();
}

To ensure this application works well on platforms that require user consent for microphone access we would extend it like this:

void VoiceMemoWidget::onRecordingInitiated()
{
#if QT_CONFIG(permissions)
    QMicrophonePermission microphonePermission;
    switch (qApp->checkPermission(microphonePermission)) {
    case Qt::PermissionStatus::Undetermined:
        qApp->requestPermission(microphonePermission, this,
                    &VoiceMemoWidget::onRecordingInitiated);
        return;
    case Qt::PermissionStatus::Denied:
        m_permissionInstructionsDialog->show();
        return;
    case Qt::PermissionStatus::Granted:
        break; // Proceed
    }
#endif
    m_microphone->startRecording();
}

We first check if we already know the status of the microphone permission. If we don't we initiate a permission request to determine the current status, which will potentially ask the user for consent. We connect the result of the request to the slot we're already in, so that we get another chance at evaluating the permission status.

Once the permission status is known, either because we had been granted or denied permission at an earlier time, or after getting the result back from the request we just initiated, we redirect the user to a dialog explaining why we can not record voice memos at this time (if the permission was denied), or proceed to using the microphone (if permission was granted).

The use of the QT_CONFIG(permissions) macro ensures that the code will work as before on platforms where permissions are not available.

注意： On macOS and iOS permissions can currently only be requested for GUI applications.

声明权限

Some platforms require that the permissions you request are declared up front at build time.

Apple 平台

Each permission you request must be accompanied by a so called usage description string in the application's Info.plist file, describing why the application needs to access the given permission. For example:

<key>NSMicrophoneUsageDescription</key>
<string>The microphone is used to record voice memos.</string>

The relevant usage description keys are described in the documentation for each permission type.

Android

Each permission you request must be accompanied by a uses-permission entry in the application's AndroidManifest.xml 文件。例如：

<manifest ...>
    <uses-permission android:name="android.permission.RECORD_AUDIO"/>
</manifest>

The relevant permission names are described in the documentation for each permission type.

可用权限

下列权限类型可用：

QBluetoothPermission	访问蓝牙外围设备
QCalendarPermission	访问用户的日历
QCameraPermission	访问摄像头为取得图片 (或视频)
QContactsPermission	访问用户的联系人
QLocationPermission	访问用户的位置
QMicrophonePermission	为监视访问麦克风 (或录制声音)

最佳实践

To ensure the best possible user experience for the end user we recommend adopting the following best practices for managing application permissions:

Request the minimal set of permissions needed. For example, if you only need access to the microphone, do not request camera permission just in case. Use the properties of individual permission types to limit the permission scope even further, for example QContactsPermission::setReadOnly() to request read only access.
Request permissions in response to specific actions by the user. For example, defer requesting microphone permission until the user presses the button to record audio. Associating the permission request to a specific action gives the user a clearer context of why the permission is needed. Do not request all needed permission on startup.
Present extra context and explanation if needed. Sometimes the action by the user is not enough context. Consider presenting an explanation-dialog after the user has initiated the action, but before requesting the permission, so the user is aware of what's about to happen when the system permission dialog subsequently pops up.
Be transparent and explicit about why permissions are needed. In explanation dialogs and usage descriptions, be transparent about why the particular permission is needed for your application to provide a specific feature, so users can make informed decisions.
Account for denied permissions. The permissions you request may be denied for various reasons. You should always account for this situation, by gracefully degrading the experience of your application, and presenting clear explanations the user about the situation.
Never request permissions from a library. The request of permissions should be done as close as possible to the user, where the information needed to make good decisions on the points above is available. Libraries can check permissions, to ensure they have the prerequisites for doing their work, but if the permission is undetermined or denied this should be reflected through the library's API, so that the application in turn can request the necessary permissions.

另请参阅 信息特性列表文件 and Qt Creator：编辑清单文件 .