Bad return type in lambda expression: void cannot be converted to Unit

news2024/11/22 14:06:19

1.背景

当kotlin中声明需要传入一个返回值为空(Unit)的方法引用.

代码示例:

下方第二个参数为一个方法引用,(参数为BiometricPrompt.AuthenticationResult, 返回类型为Unit).

object BiometricPromptUtil {
    private const val TAG = "BiometricPromptUtil"

    fun createBiometricPrompt(
        activity: AppCompatActivity,
        processSuccess: (BiometricPrompt.AuthenticationResult) -> Unit
    ): BiometricPrompt {
        val executor = ContextCompat.getMainExecutor(activity)

        val callback = object : BiometricPrompt.AuthenticationCallback() {

            override fun onAuthenticationError(errCode: Int, errString: CharSequence) {
                super.onAuthenticationError(errCode, errString)
                Log.d(TAG, "errCode is $errCode and errString is: $errString")
            }

            override fun onAuthenticationFailed() {
                super.onAuthenticationFailed()
                Log.d(TAG, "User biometric rejected.")
            }

            override fun onAuthenticationSucceeded(result: BiometricPrompt.AuthenticationResult) {
                super.onAuthenticationSucceeded(result)
                Log.d(TAG, "Authentication was successful")
                processSuccess(result)
            }
        }
        return BiometricPrompt(activity, executor, callback)
    }
}

2. kotlin调用传参

如果调用方是kotlin代码示例, 只需要直接定义一个默认返回为Unit的函数并将其传入即可.

private fun showBiometricPromptForEncryption() {
        val canAuthenticate = BiometricManager.from(applicationContext).canAuthenticate()
        if (canAuthenticate == BiometricManager.BIOMETRIC_SUCCESS) {
            val secretKeyName = getString(R.string.secret_key_name)
            cryptographyManager = CryptographyManager()
            val cipher = cryptographyManager.getInitializedCipherForEncryption(secretKeyName)
            val biometricPrompt =
                BiometricPromptUtils.createBiometricPrompt(this, ::encryptAndStoreServerToken) //重点关注第二个参数
            val promptInfo = BiometricPromptUtils.createPromptInfo(this)
            biometricPrompt.authenticate(promptInfo, BiometricPrompt.CryptoObject(cipher))
        }
    }

    private fun encryptAndStoreServerToken(authResult: BiometricPrompt.AuthenticationResult) { // 用于做形参的函数,函数返回类型是默认的Unit.
        authResult.cryptoObject?.cipher?.apply {
            SampleAppUser.fakeToken?.let { token ->
                Log.d(TAG, "The token from server is $token")
                val encryptedServerTokenWrapper = cryptographyManager.encryptData(token, this)
                cryptographyManager.persistCiphertextWrapperToSharedPrefs(
                    encryptedServerTokenWrapper,
                    applicationContext,
                    SHARED_PREFS_FILENAME,
                    Context.MODE_PRIVATE,
                    CIPHERTEXT_WRAPPER
                )
            }
        }
        finish()
    }