Activity間のObject引き渡し（Gson）

 方法

以前ObjectでSerializableをimplementsした方法を記載しました。
Activity間のObject引き渡し

今回はGsonを使用してObjectを引き渡します。

実装

Gradle

build.gradle

dependencies {
    // Gson
    compile 'com.google.code.gson:gson:2.8.0'
}

Object

Activity間で引き渡すobject

DataState.kt

data class DataState(
    val id: Int,
    val name: String
)

Activity

引き渡し元

MainActivity.kt

class MainActivity : AppCompatActivity() {

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

        val intent = Intent(this, SecondActivity::class.java)
        val state = DataState(0, "name0")
        // Gsonで Object → String
        intent.putString(SecondActivity.KEY_STATE, Gson().toJson(state)) 
        startActivity(intent)
    }
}

引き渡し先

SecondActivity.kt

class SecondActivity : AppCompatActivity() {

    companion object {
        val KEY_STATE = "key_state"
    }

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_second)

        val stateStr = intent.getString(KEY_STATE)
        // Gsonで String → Object
        val state = Gson().fromJson<DataState>(stateStr, DataState::class.java)

        if(state is DataState){
            println(state.id)
            println(state.name)
        }
    }
}

出力結果

0
name0

list objectの引き渡し

Activity

引き渡し元

MainActivity.kt

class MainActivity : AppCompatActivity() {

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

        val states = arrayListOf<DataState>()
        for(i in 0..2){
            val state = DataState(i, "name$i")
            states.add(state)
        }

        val intent = Intent(this, SecondActivity::class.java)
        // Gsonで List<Object> → String
        intent.putExtra(SecondActivity.KEY_STATE, Gson().toJson(states))
        startActivity(intent)
    }
}

引き渡し先

SecondActivity.kt

class SecondActivity : AppCompatActivity() {

    companion object {
        val KEY_STATE = "key_state"
    }

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_second)

        val statesStr = intent.getStringExtra(KEY_STATE)
        // Gsonで String → List<Object>
        val states = Gson().fromJson<List<DataState>>(statesStr, object : TypeToken<List<DataState>>() {}.type)

        states.forEach {
            println(it.id)
            println(it.name)
        }
    }
}

list object 出力結果

0
name0
1
name1
2
name2

まとめ

Serializableをimplementsするより簡単