如何检查 ViewModel 中授予的权限？

Question

我需要为联系人请求权限，当应用程序启动时我在询问，在 ViewModel 部分我需要调用需要权限的方法。我需要检查权限是否由用户授予然后调用，但是为了检查权限我需要访问活动。而在我的 ViewModel 中，我没有对 Activity 的引用并且不想有，我该如何克服这个问题？

Answer 1

我已经修改了解决方案。 PermissionRequester 对象是您从至少具有应用程序上下文的任何位置请求权限所需的一切。它使用它的助手PermissionRequestActivity 来完成这项工作。

@Parcelize
class PermissionResult(val permission: String, val state: State) : Parcelable
enum class State { GRANTED, DENIED_TEMPORARILY, DENIED_PERMANENTLY }
typealias Cancellable = () -> Unit
private const val PERMISSIONS_ARGUMENT_KEY = "PERMISSIONS_ARGUMENT_KEY"
private const val REQUEST_CODE_ARGUMENT_KEY = "REQUEST_CODE_ARGUMENT_KEY"

object PermissionRequester {
    private val callbackMap = ConcurrentHashMap<Int, (List<PermissionResult>) -> Unit>(1)
    private var requestCode = 256
    get() {
        requestCode = field--
        return if (field < 0) 255 else field
    }

    fun requestPermissions(context: Context, vararg permissions: String, callback: (List<PermissionResult>) -> Unit): Cancellable {
        val intent = Intent(context, PermissionRequestActivity::class.java)
                .putExtra(PERMISSIONS_ARGUMENT_KEY, permissions)
                .putExtra(REQUEST_CODE_ARGUMENT_KEY, requestCode)
                .addFlags(Intent.FLAG_ACTIVITY_NEW_TASK)
        context.startActivity(intent)
        callbackMap[requestCode] = callback
        return { callbackMap.remove(requestCode) }
    }

    internal fun onPermissionResult(responses: List<PermissionResult>, requestCode: Int) {
        callbackMap[requestCode]?.invoke(responses)
        callbackMap.remove(requestCode)
    }
}

class PermissionRequestActivity : AppCompatActivity() {

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        if (savedInstanceState == null) {
            requestPermissions()
        }
    }

    private fun requestPermissions() {
        val permissions = intent?.getStringArrayExtra(PERMISSIONS_ARGUMENT_KEY) ?: arrayOf()
        val requestCode = intent?.getIntExtra(REQUEST_CODE_ARGUMENT_KEY, -1) ?: -1
        when {
            permissions.isNotEmpty() && requestCode != -1 -> ActivityCompat.requestPermissions(this, permissions, requestCode)
            else -> finishWithResult()
        }
    }

    override fun onRequestPermissionsResult(requestCode: Int, permissions: Array<String>, grantResults: IntArray) {
        super.onRequestPermissionsResult(requestCode, permissions, grantResults)

        val permissionResults = grantResults.zip(permissions).map { (grantResult, permission) ->
            val state =  when {
                grantResult == PackageManager.PERMISSION_GRANTED -> State.GRANTED
                ActivityCompat.shouldShowRequestPermissionRationale(this, permission) -> State.DENIED_TEMPORARILY
                else -> State.DENIED_PERMANENTLY
            }
            PermissionResult(permission, state)
        }

        finishWithResult(permissionResults)
    }

    private fun finishWithResult(permissionResult: List<PermissionResult> = listOf()) {
        val requestCode = intent?.getIntExtra(REQUEST_CODE_ARGUMENT_KEY, -1) ?: -1
        PermissionRequester.onPermissionResult(permissionResult, requestCode)
        finish()
    }
}

用法：

class MyViewModel(application: Application) : AndroidViewModel(application) {

    private val cancelRequest: Cancellable = requestPermission()

    private fun requestPermission(): Cancellable {
        return PermissionRequester.requestPermissions(getApplication(), "android.permission.SEND_SMS") {
            if (it.firstOrNull()?.state == State.GRANTED) {
                Toast.makeText(getApplication(), "GRANTED", Toast.LENGTH_LONG).show()
            } else {
                Toast.makeText(getApplication(), "DENIED", Toast.LENGTH_LONG).show()
            }
        }
    }

    override fun onCleared() {
        super.onCleared()
        cancelRequest()
    }
}

Answer 2

我刚遇到这个问题，我决定改用LiveData。

核心理念：

• ViewModel 有一个 LiveData 说明需要提出什么权限请求

• ViewModel 有一个方法（本质上是回调），如果授予或不授予权限，则返回

SomeViewModel.kt:

class SomeViewModel : ViewModel() {
    val permissionRequest = MutableLiveData<String>()

    fun onPermissionResult(permission: String, granted: Boolean) {
        TODO("whatever you need to do")
    }
}

FragmentOrActivity.kt

class FragmentOrActivity : FragmentOrActivity() {
    private viewModel: SomeViewModel by lazy {
        ViewModelProviders.of(this).get(SomeViewModel::class.java)
    }

    override fun onCreate(savedInstanceState: Bundle?) {
        ......
        viewModel.permissionRequest.observe(this, Observer { permission -> 
            TODO("ask for permission, and then call viewModel.onPermissionResult aftwewards")
        })
        ......
    }
}

Answer 3

我做了这样的事情：

创建一个扩展 AndroidViewModel 的抽象类，让您可以访问应用程序上下文：

abstract class BaseViewModel(application: Application) : AndroidViewModel(application), CoroutineScope {

    private val job = Job()

    override val coroutineContext: CoroutineContext
        get() = job + Dispatchers.Main

    override fun onCleared() {
        super.onCleared()
        job.cancel()
    }
}

现在，通过扩展 BaseViewModel 类创建您的视图模型，您将可以访问应用程序上下文

class AdminViewModel(application: Application) : BaseViewModel(application) {
    .....
}

现在您始终可以访问可用于访问资源的 Context。