Android Activity Result API

最近准备开始新的项目，在编写base类复写onActivityResult方法时，发现已经提示deprecation了。于是去官网查找了一下，发现现在官方推荐做法是使用 Activity Result API。

本篇文章用来记录一下 Activity Result API 如何使用。

以往的实现方式

以往，A Activity获取B Activity的返回值的实现方法是，A通过startActivityForResult()来启动B，然后B在finish()之前通过setResult()方法来设置结果值，A就可以在onActivityResult()方法中获取到B在setResult()方法中设置的参数。简单示例如下：

class A : Activity() {


    override fun onCreate(savedInstanceState: Bundle?) {

        super.onCreate(savedInstanceState)

        startActivityForResult(Intent(this,B::class.java))

    }


    override fun onActivityResult(requestCode: Int, resultCode: Int, data: Intent?) {

        super.onActivityResult(requestCode, resultCode, data)

        //从B返回后这里就可以获取到resultCode为Activity.RESULT_OK

    }

}


class B: Activity() {


    override fun onCreate(savedInstanceState: Bundle?) {

        super.onCreate(savedInstanceState)

        setResult(Activity.RESULT_OK)

        finish()

    }

}

Activity Result API

现在，在Activity和Fragment中，Activity Result API提供了registerForActivityResult()方法，该方法用于注册获取结果的回调。

registerForActivityResult可以传入ActivityResultContract、ActivityResultRegistry、ActivityResultCallback等3个参数，并返回ActivityResultLauncher。

• ActivityResultContract：ActivityResult合约，约定输入的参数和输出的参数。包含默认合约和自定义合约。
• ActivityResultRegistry：存储已注册的ActivityResultCallback的记录表，可以在非Activity和Fragment的类中借用此类获取ActivityResult。
• ActivityResultCallback：ActivityResult回调，用于获取返回结果。
• ActivityResultLauncher：启动器，根据合约规定的输入参数来启动页面。

Activity Result API的简单使用示例：

class A : Activity() {


    //默认合约

    var forActivityResultLauncher = registerForActivityResult(ActivityResultContracts.StartActivityForResult()) { activityResult ->

        launcher?.text="lanuncher callback value : resultCode:$resultCode data$data"

    }


    //自定义合约（输入输出类型均为String）

    var forActivityResultLauncher1 = registerForActivityResult(object : ActivityResultContract<String, String>() {

        override fun createIntent(context: Context, input: String?): Intent {

            return Intent(this@AActivity, B::class.java).apply {

                putExtra("inputParams", input)

            }

        }


        override fun parseResult(resultCode: Int, intent: Intent?): String {

            return if (resultCode == Activity.RESULT_OK) {

                intent?.getStringExtra("result") ?: "empty result"

            } else {

                ""

            }

        }

    }) { resultString ->

        launcher1?.text = "lanuncher1 callback value : reslutString:$reslutString"

    }


    var launcher: TextView? = null

    var launcher1: TextView? = null


    override fun onCreate(savedInstanceState: Bundle?) {

        super.onCreate(savedInstanceState)

        setContentView(R.layout.layout_a_activity)

        launcher = findViewById(R.id.tv_launcher_callback)

        launcher1 = findViewById(R.id.tv_launcher_callback1)

        val btnLauncher = findViewById<Button>(R.id.launcher)

        val btnLauncher1 = findViewById<Button>(R.id.launcher1)

        btnLauncher.setOnClickListener {

            //默认合约

            forActivityResultLauncher.launch(Intent(this@AActivity, B::class.java))

        }


        btnLauncher1.setOnClickListener {

            //自定义合约

            forActivityResultLauncher1.launch("inputParams from A")

        }

    }

}


class B: Activity() {


    override fun onCreate(savedInstanceState: Bundle?) {

        super.onCreate(savedInstanceState)

        setContentView(R.layout.layout_b_activity)

        val btnBack = findViewById<Button>(R.id.back)

        val inputParams = intent.getStringExtra("inputParams")

        btnBack.setOnClickListener {

            if (TextUtils.isEmpty(inputParams)) {

                setResult(Activity.RESULT_OK, Intent())

            } else {

                setResult(Activity.RESULT_OK, Intent().apply {

                    putExtra("result", "result from A")

                })

            }

            finish()

        }

    }

}

示例效果图： 

在非Activity和Fragment的类中接收ActivityResult

示例代码如下:

class A : Activity() {


    override fun onCreate(savedInstanceState: Bundle?) {

        super.onCreate(savedInstanceState)

        val myActivityResultObserver = MyActivityResultObserver(activityResultRegistry)

        lifecycle.addObserver(myActivityResultObserver)

    }

}


class MyActivityResultObserver(private val registry: ActivityResultRegistry) : DefaultLifecycleObserver {


    override fun onCreate(owner: LifecycleOwner) {

        super.onCreate(owner)

        registry.register("MyActivityResultReceiver", owner, ActivityResultContracts.StartActivityForResult()) {


        }

    }

}