Android Kotlin 无法从另一个活动中获取结果

Question

我需要从我的主要活动开始一个活动，第二个活动必须进行 REST 调用（我正在使用 OkHttp）并将结果返回给主要活动。我实际上能够完成所有过程，但是当我回到主要活动时，我无法获得结果数据。代码如下：

class MainActivity : AppCompatActivity() {
    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)

        var resultLauncher = registerForActivityResult(ActivityResultContracts.StartActivityForResult()) { result: ActivityResult ->
            val data: Intent? = result.data
            Log.d("Main", data.toString())
        }

        findViewById<Button>(R.id.button).setOnClickListener {

            val intent = Intent(this, SecondActivity::class.java)
            resultLauncher.launch(intent)
        }
    }
}

class SecondActivity : AppCompatActivity() {
    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.second_activity)
            
        customFunction(this)
    }
    
    private fun customFunction(activity: Activity) {
        var json: String? = ""

        val payload = "custom payload"

        val okHttpClient = OkHttpClient()
        val requestBody = payload.toRequestBody()
        val request = Request.Builder()
            .header("Authorization", "Basic mytoken")
            .header("Content-Type", "application/x-www-form-urlencoded")
            .url("myurl")
            .method("POST", requestBody)
            .build()

        okHttpClient.newCall(request).enqueue(object : Callback {
            override fun onFailure(call: Call, e: IOException) {
                Log.d("SecondActivity", "onFailure")
                activity.finish()
            }

            override fun onResponse(call: Call, response: Response) {
                json = response.body?.string()
                Log.d("SecondActivity", "$json")

                val data = Intent()
                data.putExtra("json", json)
                Log.d("SecondActivity", data.toString())
                activity.setResult(Activity.RESULT_OK, data)
                activity.finish()
            }
        })
    }
}

所以，在customFunction() 中，我能够获取该json 并将其放入数据意图中。事实上，当我用Log.d() 打印它时，它会显示Intent { (has extras) }，所以没关系。但是当我在 registerForActivityResult 的 MainActivity 中收到它时，它会打印出 null。我做错了什么？

Answer 1

在这种情况下，您必须在MainActivity 的启动器活动中获得额外的Intent，即

而不是

var resultLauncher = registerForActivityResult(ActivityResultContracts.StartActivityForResult()) { result: ActivityResult ->
            val data: Intent? = result.data
            Log.d("Main", data.toString())
        }

使用

var resultLauncher = registerForActivityResult(ActivityResultContracts.StartActivityForResult()) { result: ActivityResult ->
            val data: Intent? = result.data
            val actualExtraData = data.getExtra("json") // Here is your actual data 
            Log.d("Main", data.toString())
        }

Answer 2

在 SecondActivity 中，您正在使用方法 putExtra 并将值 json 作为 String 传递。所以在 MainActivity 中得到它

val data = result.data?.getStringExtra("json")

var resultLauncher = registerForActivityResult(ActivityResultContracts.StartActivityForResult()) { result: ActivityResult ->
       // val data: Intent? = result.data
        val data = result.data?.getStringExtra("json")
        Log.d("Main", data.toString())
    }