ResultAPI：告别onActivityResult，拥抱ActivityResultContract

港控/mmm° 2023-03-01 10:16 25阅读 0赞

![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3ZpdGF2aXZh_size_16_color_FFFFFF_t_70]  
很多开发者对`onActivityResult`抱怨已久：需要定义`resultCode`和`requestCode`，使用繁琐且容易出错。现在通过KTX新发布的`ActivityResultContract`可以很多好地解决上述烦恼

# 基本使用 #

--------------------

## Before ##

传统的`onActivityResult`写法

class MainActivity : AppCompatActivity() { 
    
        companion object { 
            private const val REQUEST_CODE = 1234
        }
    
        override fun onCreate(savedInstanceState: Bundle?) { 
            super.onCreate(savedInstanceState)
            setContentView(R.layout.activity_main)
    
            button_open.setOnClickListener { 
                startActivityForResult(
                        SecondActivity.createIntent(this),
                        REQUEST_CODE
                )
            }
        }
    
        override fun onActivityResult(requestCode: Int, resultCode: Int, data: Intent?) { 
            super.onActivityResult(requestCode, resultCode, data)
            Log.d("MainActivity", "requestCode: $requestCode, resultCode: $resultCode, data: $data")
        }
    }

SecondActivity需要finish之前需要`setResult`

setResult(Activity.RESULT_OK, intent)
    finish()

## After ##

引入gradle

implementation "androidx.activity:activity-ktx:$latest_vsersion"
      or
    implementation "androidx.fragment:fragment-ktx:$latest_vsersion"

class MainActivity : AppCompatActivity() { 
    
        private val launcher: ActivityResultLauncher<Intent> =
                registerForActivityResult(ActivityResultContracts.StartActivityForResult()) {  activityResult ->
                    Log.d("MainActivity", activityResult.toString())
                }
    
        override fun onCreate(savedInstanceState: Bundle?) { 
            super.onCreate(savedInstanceState)
            setContentView(R.layout.activity_main)
    
            button_open.setOnClickListener { 
                launcher.launch(SecondActivity.createIntent(this))
            }
        }
    }

省掉了烦人的`resultCode`和`requestCode`，代码更优雅  
![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3ZpdGF2aXZh_size_16_color_FFFFFF_t_70 1]

# 其他场景 #

--------------------

看几个常见场景中如何使用ActivityResultContract：

## 选择文件 ##

打开文件管理器选择图片并返回`uri`，首先看一下基于onActivityResult的实现：

class MainActivity : AppCompatActivity() { 
        companion object { 
            private const val REQUEST_CODE_CHOOSER = 1234
        }
    
        override fun onCreate(savedInstanceState: Bundle?) { 
            super.onCreate(savedInstanceState)
            setContentView(R.layout.activity_main)
    
            button_get_content.setOnClickListener { 
                startActivityForResult(
                        Intent(Intent.ACTION_GET_CONTENT).apply { 
                            addCategory(Intent.CATEGORY_OPENABLE)
                            type = "image/*"
                        },
                        REQUEST_CODE_CHOOSER
                )
            }
        }
    
        override fun onActivityResult(requestCode: Int, resultCode: Int, data: Intent?) { 
            super.onActivityResult(requestCode, resultCode, data)
            if (requestCode == REQUEST_CODE_CHOOSER && resultCode == Activity.RESULT_OK) { 
                Log.d("MainActivity", "uri: ${ data?.data}")
            }
        }
    }

基于ActivityResultContracts实现后：

class MainActivity : AppCompatActivity() { 
    
        private val launcher = registerForActivityResult(ActivityResultContracts.GetContent()) {  uri ->
            Log.d("MainActivity", "uri: $uri")
        }
    
        override fun onCreate(savedInstanceState: Bundle?) { 
            super.onCreate(savedInstanceState)
            setContentView(R.layout.activity_main)
    
            button_get_content.setOnClickListener { 
                launcher.launch("image/*")
            }
        }
    }

`ActivityResultContracts.GetContent`是系统预置的几种Contracts之一：  
![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3ZpdGF2aXZh_size_16_color_FFFFFF_t_70 2]  
当然除以上预置的`Contracts`以外，也可以通过继承`ActivityResultContracts`自定义自己的Contracts

## 权限请求 ##

requestPermission与startActivityForResult的过程比较类似：

//权限请求
    ActivityCompat.requestPermissions(this, arrayOf(WRITE_EXTERNAL_STORAGE), REQUEST_CODE)

//返回结果
    override fun onRequestPermissionsResult(
        requestCode: Int,
        permissions: Array<out String>,
        grantResults: IntArray
    ) { 
        if (requestCode == REQUEST_CODE) { 
            if (grantResults[0] == PackageManager.PERMISSION_GRANTED) { 
                Toast.makeText(this, "result: granted", Toast.LENGTH_LONG).show()
            }
            return
        }
        super.onRequestPermissionsResult(requestCode, permissions, grantResults)
    }

基于ActivityResultContract的实现：

// 设置回调
    private val launcher = registerForActivityResult(RequestPermission()) { 
        if (it) { 
            Toast.makeText(this, "result: granted", Toast.LENGTH_LONG).show()
        }
    }

// 请求权限
    launcher.launch(WRITE_EXTERNAL_STORAGE)

# 实现原理 #

--------------------

关于ActivityResultContract的原理比较简单，有兴趣的同学可以参考[深入理解ActivityResultContracts][ActivityResultContracts]

[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3ZpdGF2aXZh_size_16_color_FFFFFF_t_70]: /images/20230209/7a22e02ff7164eeb896ee44a93e23f11.png
[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3ZpdGF2aXZh_size_16_color_FFFFFF_t_70 1]: /images/20230209/d77a9fb838474d10b93a15dcdadee447.png
[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3ZpdGF2aXZh_size_16_color_FFFFFF_t_70 2]: /images/20230209/58289bbc549d4e37a6b217cd47b81009.png
[ActivityResultContracts]: https://blog.csdn.net/vitaviva/article/details/105014966