Jetpack architecture component learning (3) -- activity results API usage

Original address :Jetpack Architecture component learning (3)——Activity Results API Use - Stars-One My groceries nest

Technology keeps pace with the times , Page Jump value transfer has been using startActivityForResult Method , Now there is a new API Realization way , Learn and summarize

startActivityForResult review

MainActivity Code :

Main2Activity Code :

effect :

The above code should be the basic code , I won't go into details here

Mainly about some shortcomings

All logic is in onActivityResult() The method is used to judge , according to requestCode and resultCode Judge

If it's OK to say , But if there are more , You will see onActivityResult() In a pile if Logic , It is very tedious to read , And maintenance is difficult

Google officials also took this into account , So we launched a new version Activity Results API To replace the way described above , Here's how to use

Easy to use

1. Introduce dependencies

First , We need to introduce dependencies :

implementation 'androidx.appcompat:appcompat:1.3.1'

PS: Please use 1.3.1 Above version , The lower version does not have this enumeration class ActivityResultContracts

Let's start with the above example , Use Activity Results API

Main2Acitivity The code doesn't move , We just need to adjust MainActivity The code in the file , As shown below :

2. Create a contract

val contract = ActivityResultContracts.StartActivityForResult()

contract The object class name of the variable is ActivityResultContract

ActivityResultContracts Equivalent to an enumeration class , It's officially sealed by Google , There are some commonly used ActivityResultContract Class object for us to use

Like taking pictures , Apply for permission , You can see from the code prompt , As shown in the figure below :

Here we choose StartActivityForResult(), The literal meaning should be easy to understand , It is applied in the scenario that the page jumps and returns data

PS: According to our choice ActivityResultContracts, Will affect the 4 The parameter type in the step

The corresponding selection instructions are supplemented below :

StartActivityForResult: General purpose Contract, No conversion ,Intent As input ,ActivityResult As the output , This is also the most commonly used protocol .
CreateDocument: Prompt the user to select a document , Return to one (file:/http:/content:) At the beginning Uri.
GetContent: Prompt to select a content , Return a pass through ContentResolver#openInputStream(Uri) Access to native data Uri Address （content:// form ） . By default , It increases the Intent#CATEGORY_OPENABLE, Return the content that can represent the stream .
GetMultipleContents: Get multiple items
OpenDocument: Prompt the user to select a file of the specified type ( Input parameter is mimeType), Returns the file selected by the user Uri
OpenDocumentTree: Prompt the user to select a directory , And return the user selected as a Uri return , The application can fully manage the documents returned to the directory .
OpenMultipleDocuments: Prompt the user to select a document （ Multiple can be selected ）, Return their... Respectively Uri, With List In the form of .
PickContact: From address book APP Get contacts
RequestMultiplePermissions： Used to request a set of permissions
RequestPermission: Used to request a single permission
TakePicturePreview: call MediaStore.ACTION_IMAGE_CAPTURE Taking pictures , The return value is Bitmap picture
TakePicture: call MediaStore.ACTION_IMAGE_CAPTURE Taking pictures , And save the picture to the given Uri Address , return true Indicates that the save was successful .
TakeVideo: call MediaStore.ACTION_VIDEO_CAPTURE Take a video , Save to given Uri Address , Return a thumbnail .

See the documentation when specific parameters and descriptions can be used ~

actually , If the above list does not meet our needs , Then we can also customize the contract operation , The following part of the article will be supplemented , I won't extend it here

3. Build a contract ( register Contact)

// register ActivityResultContract

val myLauncher = registerForActivityResult(contract){

    if (it.resultCode==2) {

        val data = it.data

        if (data != null) {

            val resultData = data.getStringExtra("mydata")

            Toast.makeText(this, resultData, Toast.LENGTH_SHORT).show()

        }

    }

}

Use Activity Class registerForActivityResult() Method , Register the deed , In fact, it is equivalent to registering a listener , After from Main2Activity Page back MainActivity page , Will call back the methods in this

Be careful : Here's a variable myLauncher, The third step is to use

4. Initiate page Jump

val intent = Intent(this, Main2Activity::class.java)

myLauncher.launch(intent)

call myLauncher Object's launch() Method , take intent Object transfer can realize the operation of page Jump

PS: This is still in the button click event , Easy to read omits

After from Main2Activity After the page returns , The operation in step 2 will be recalled , The effect is consistent with the above dynamic illustration , There is no need to re post a picture here

Customize ActivityResultContract

ActivityResultContract There are actually two generic types , Complete should be like this ActivityResultContract<I,O>

I by input It means , Meaning for Input parameter type
O by output It means , Meaning for Output parameter type

ActivityResultContract<I,O> It's an abstract class , We want to implement customization , Then inherit it directly

class MyContract: ActivityResultContract<String, String>() {

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

        // here input The type of , Just as mentioned above I

    }

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

        // Here, the result type returned by the method , Just as mentioned above O

    }

}

Inheritance discovery , We need to implement two methods ,createIntent() and parseResult()

A glance at the past is actually easy to understand ,createIntent() To create a intent object , call launch() Method time ( The number used above 4 Step by step ), It will be based on this intent Jump to the page

and parseResult() Method , It is the step of establishing the contract , The data type of callback inside

Let's take the example above , It is found that we have to make a statement Intent Object delivery , And when you send it back, you have to pass intent Object to get data , A little fussy , Some of the code can be encapsulated into generic

According to this idea , We can achieve one Customize ActivityResultContract, Pass the page parameters to get Main2Activity Returned data , The code is as follows :

class MyContract: ActivityResultContract<KClass<out Activity>, String>() {

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

        if (resultCode == 2 && intent!=null) {

            return intent.getStringExtra("mydata")

        }

        return null

    }

    override fun createIntent(context: Context, input: KClass<out Activity>?): Intent {

        val intent = Intent(context,input?.java)

        return intent

    }

}

Use :

//1. Create a contract 

val contract = MyContract()

//2. register ActivityResultContract

val myLauncher = registerForActivityResult(contract){

    Toast.makeText(this, it, Toast.LENGTH_SHORT).show()

}

btnGo.setOnClickListener {

    //2. Initiate page Jump 

    myLauncher.launch(Main2Activity::class)

}

Of course , You can also optimize , If we let MyContract Multiple constructors , This is the value key This can also be used to define

class MyContract(val key: String) : ActivityResultContract<KClass<out Activity>, String>() {

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

        if (resultCode == 2 && intent != null) {

            return intent.getStringExtra(key)

        }

        return null

    }

    override fun createIntent(context: Context, input: KClass<out Activity>?): Intent {

        val intent = Intent(context, input?.java)

        return intent

    }

}

Use :

// Create a contract and transfer parameters 

val contract = MyContract("mydata")

Reference resources

bye ！onActivityResult！ Hello ,Activity Results API！ - Nuggets
Activity Result Api Use _Sz_pine The blog of -CSDN Blog

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