[英]LiveData onChanged called multiple times with the same data when using FirebaseAuth
我有一個登錄活動,它使用 email 和密碼實現 Firebase 身份驗證。 它所做的是將用戶輸入的 email 和密碼發送到 FirebaseAuth function 並通過 LiveData 檢索響應,然后觀察它。
問題是,當登錄失敗或憑證無效時,它應該烤一次消息,但真正發生的是多次烤,可能超過4次(它使烤顯示很長時間)。
登錄活動
private fun signInWithEmailAndPassword(email: String, password: String){
val authResult = viewModel.authWithEmailPassword(email, password)
handleAuthenticationResult(authResult)
}
private fun handleAuthenticationResult(authResult: LiveData<Resource<AuthResult>>){
authResult.observe(this, object : Observer<Resource<AuthResult>>{
override fun onChanged(it: Resource<AuthResult>?) {
when(it){
is Resource.Loading -> {
toggleLoadingIndicator(true)
}
is Resource.Success -> {
toggleLoadingIndicator(false)
val isNewUser = it.data.additionalUserInfo?.isNewUser ?: true
if(isNewUser) gotoIntroActivity()
else gotoMainActivity()
}
is Resource.Failure -> {
toggleLoadingIndicator(false)
when(it.throwable){
is FirebaseAuthException -> Toast.makeText(this@LoginActivity, getString(R.string.error_credentials_invalid), Toast.LENGTH_SHORT).show()
else -> Toast.makeText(this@LoginActivity, getString(R.string.error_login_failed), Toast.LENGTH_SHORT).show()
}
}
}
}
})
}
視圖模型
fun authWithEmailPassword(email: String, password: String): LiveData<Resource<AuthResult>>{
return AuthRepository.signInWithEmailAndPassword(email, password)
}
Firebase 身份驗證
private var authResult: MutableLiveData<Resource<AuthResult>> = MutableLiveData()
fun signInWithEmailAndPassword(email: String, password: String): LiveData<Resource<AuthResult>>{
authResult.value = Resource.Loading()
mAuth.signInWithEmailAndPassword(email, password)
.addOnCompleteListener{
if(it.isSuccessful) authResult.value = Resource.Success(it.result!!)
else authResult.value = Resource.Failure(it.exception!!)
}
return authResult
}
資源
sealed class Resource<out T> {
class Loading<out T> : Resource<T>()
data class Success<out T>(val data: T) : Resource<T>()
data class Failure<out T>(val throwable: Throwable) : Resource<T>()
}
為什么會發生這種情況以及如何解決這個問題? 每次觸發Resource.Failure
時我應該刪除觀察者嗎?
LiveData 是您只創建和訂閱一次的東西。 在您的情況下,每次獲得身份驗證結果時都會訂閱它,因此會出現多個重復事件。
為了解決這個問題,請執行以下操作:
val authResult: MutableLiveData<Resource<AuthResult>> = MutableLiveData()
viewModel.authResult.observe(this, ... [the rest of your code]
authResult.postValue(resource)
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