startActivityForResult废弃了，用Activity Result API吧

因为项目中突然需要用到两个activity之间进行数据交互，脑子里第一想法就是用EventBus来实现，但是需求仅仅只有2个activity之间进行交互（神奇的需求？），所以考虑几百年前用过的startActivityForResult来实现，但撸代码的时候发现，它过时了！！！

 如果你将项目中的appcompat库升级到1.3.0或更高的版本,startActivityForResult()方法就已经显示被废弃了，因为项目中引入的就是1.3.0的

所以才发现过时的，如果版本低了，我还蒙在鼓里。

     废弃了，自然有替代品。新欢胜旧爱，官网建议用Activity Result API来取代startActivityForResult了。

   OK，先回顾下startActivityForResult的用法，它主要作用就是用于两个activity之间传递数据，例如：

class MainActivity : AppCompatActivity() {
    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)
        findViewById(R.id.btn1).setOnClickListener {
            val intent = Intent(this, SecondActivity::class.java)
            val  bundle=Bundle()
            bundle.putString("key","from MainActivity data")
            intent.putExtras(bundle)
            startActivityForResult(intent, 1)
        }
 
    }
 
    override fun onActivityResult(requestCode: Int, resultCode: Int, data: Intent?) {
        super.onActivityResult(requestCode, resultCode, data)
        when (requestCode) {
            1 ->
                if (resultCode == RESULT_OK) {
                    val stringExtra = data?.getStringExtra("data")
                    Log.e("TAG", "onActivityResult: $stringExtra")
                }
        }
    }
}

在MainActivity里通过点击一个按钮，往Bundle里添加数据，然后放到intent里，通过startActivityForResult向SecondActivity传递数据，并且重写了onActivityResult（）方法去解析SecondActivity返回来的数据。

SecondActivity就稍微简单点了，先获取到MainActivity传递过来的数据，然后再点击一个按钮，发送新的数据返回给MainActivity。

class SecondActivity : AppCompatActivity() {
    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_second)
        val extras = intent.extras
        val data = extras?.getString("key")
        Log.e("SecondActivity", "onCreate: $data" )
        findViewById(R.id.btn).setOnClickListener {
            val intent = Intent()
            intent.putExtra("data", "data from SecondActivity")
            setResult(RESULT_OK, intent)
            finish()
        }
    }
}

以上代码应该没毛病，早几年每个项目百分百会用到的.

结果显而易见，从MainActivity点击按钮跳转到SecondActivity界面会打印 

SecondActivity: onCreate: from MainActivity data

然后在SecondActivity点击按钮回到MainActivity打印

TAG: onActivityResult: data from SecondActivity

接着我们学习一下如何使用Activity Result API来实现同样的功能。

import androidx.activity.result.contract.ActivityResultContracts
 
class MainActivity : AppCompatActivity() {
 
    private val requestDataLauncher = registerForActivityResult(ActivityResultContracts.StartActivityForResult()) { result ->
        if (result.resultCode == RESULT_OK) {
            val data = result.data?.getStringExtra("data")
            Log.e("TAG", "registerForActivityResult: $data")
        }
    }
 
    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)
        findViewById(R.id.btn1).setOnClickListener {
            val intent = Intent(this, SecondActivity::class.java)
            val bundle = Bundle()
            bundle.putString("key", "from MainActivity data")
            intent.putExtras(bundle)
            requestDataLauncher.launch(intent)
           // startActivityForResult(intent, 1)
        }
 
    }
}

SecondActivity完全不用动，代码不用变。主要看下MainActivity的代码改动，移除了对onActivityResult()方法的重写，而是调用registerForActivityResult()方法来注册一个对Activity结果的监听。registerForActivityResult()方法接收两个参数，第一个参数是一种Contract类型，由于我们是希望从另外一个Activity中请求数据，因此这里使用了StartActivityForResult这种Contract。第二个参数是一个Lambda表达式，当有结果返回时则会回调到这里，然后我们在这里获取并处理数据即可。

  @NonNull
    @Override
    public final  ActivityResultLauncher registerForActivityResult(
            @NonNull ActivityResultContract contract,
            @NonNull ActivityResultCallback callback) {
        return registerForActivityResult(contract, mActivityResultRegistry, callback);
    }

class MainActivity : AppCompatActivity() {
 
    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)
        findViewById(R.id.btn1).setOnClickListener {
            val intent = Intent(this, SecondActivity::class.java)
            val bundle = Bundle()
            bundle.putString("key", "from MainActivity data1")
            intent.putExtras(bundle)
            startActivityForResult(intent, 1)
        }
        findViewById(R.id.btn2).setOnClickListener {
            val intent = Intent(this, ThreeActivity::class.java)
            val bundle = Bundle()
            bundle.putString("key", "from MainActivity data2")
            intent.putExtras(bundle)
            startActivityForResult(intent, 2)
        }
    }
 
    override fun onActivityResult(requestCode: Int, resultCode: Int, data: Intent?) {
        super.onActivityResult(requestCode, resultCode, data)
        when (requestCode) {
            1 -> {
                if (resultCode == RESULT_OK) {
                    val stringExtra = data?.getStringExtra("data")
                    Log.e("TAG", "onActivityResult: 1$stringExtra")
                }
            }
            2 ->
                if (resultCode == RESULT_OK) {
                    val stringExtra = data?.getStringExtra("data")
                    Log.e("TAG", "onActivityResult: 2 $stringExtra")
                }
        }
    }
}

class MainActivity : AppCompatActivity() {
 
    private val requestDataOneLauncher =
        registerForActivityResult(ActivityResultContracts.StartActivityForResult()) { result ->
            if (result.resultCode == RESULT_OK) {
                val data = result.data?.getStringExtra("data")
                Log.e("TAG", "registerForActivityResult:one  $data")
            }
        }
    private val requestDataTwoLauncher =
        registerForActivityResult(ActivityResultContracts.StartActivityForResult()) { result ->
            if (result.resultCode == RESULT_OK) {
                val data = result.data?.getStringExtra("data")
                Log.e("TAG", "registerForActivityResult:two  $data")
            }
        }
    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)
        findViewById(R.id.btn1).setOnClickListener {
            val intent = Intent(this, SecondActivity::class.java)
            val bundle = Bundle()
            bundle.putString("key", "from MainActivity data1")
            intent.putExtras(bundle)
            requestDataOneLauncher.launch(intent)
          
        }
        findViewById(R.id.btn2).setOnClickListener {
            val intent = Intent(this, SecondActivity::class.java)
            val bundle = Bundle()
            bundle.putString("key", "from MainActivity data2")
            intent.putExtras(bundle)
            requestDataTwoLauncher.launch(intent)
 
        }
    }
}