Android Kotlin 通过 arrayList<object> 到其他活动<div id="text_translate"><p>我想在 2 个活动之间传递对象类型的 arrayList。<br> 通过以下两种方式之一：<br> 要么：有意（我没有找到放置或获得额外）类型的 arrayList ！）<br> 或：OOP。 由 class 使用设置和获取功能。 但是结果还是null<br> （我不知道如何在 kotlin 类中制作 static 变量）。</p><hr><p> 我的数组列表：</p><pre> var listSongs=ArrayList&lt;songInfo&gt;()</pre><p> 里面的 songInfo class：</p><pre> var title:String?=null var authorName:String?=null var songURL:String?=null</pre><p> 通过 class：“ <strong>passing_class</strong> ”</p><p> 你喜欢什么方式？</p></div></object>

Question

I want to pass arrayList of objects type between 2 activities.
By one of 2 ways:
either: By intent (I do not find put or get extra) type of arrayList !)
or: By OOP. By a class using set & get functions. But the result is still null
(I do not know how to make static variables in kotlin class).

---

My array list:

var listSongs=ArrayList<songInfo>()

Inside songInfo class:

var title:String?=null
var authorName:String?=null
var songURL:String?=null

Passing class: " passing_class "

What you prefer any way?

Answer 1

First of all, you have to make sure SongInfo has implemented Parcelable like code below

data class SongInfo(
        var title: String? = null,
        var authorName: String? = null,
        var songURL: String? = null
) : Parcelable {

    constructor(parcel: Parcel) : this(
            parcel.readString(),
            parcel.readString(),
            parcel.readString())

    override fun writeToParcel(parcel: Parcel, flags: Int) {
        parcel.writeString(title)
        parcel.writeString(authorName)
        parcel.writeString(songURL)
    }

    override fun describeContents(): Int {
        return 0
    }

    companion object CREATOR : Parcelable.Creator<SongInfo> {
        override fun createFromParcel(parcel: Parcel): SongInfo {
            return SongInfo(parcel)
        }

        override fun newArray(size: Int): Array<SongInfo?> {
            return arrayOfNulls(size)
        }
    }
}

After that, the code in the first activity should be similar to this

class ActivityOne: AppCompatActivity() {
    override fun onCreate(savedInstanceState: Bundle?, persistentState: PersistableBundle?) {
        super.onCreate(savedInstanceState, persistentState)
        val button = Button(this) // Just for an example

        val arrayList = arrayListOf(
                SongInfo("Love yourself", "Justin Bieber", "https://example.com"),
                SongInfo("Love yourself", "Justin Bieber", "https://example.com"),
                SongInfo("Love yourself", "Justin Bieber", "https://example.com"),
                SongInfo("Love yourself", "Justin Bieber", "https://example.com")
        )

        button.setOnClickListener {
            val intent = Intent(applicationContext, ActivityTwo::class.java)
            intent.putExtra("songs", arrayList)
            startActivity(intent)
        }
    }
}

And then in order to receive your array list from the first activity you need to parse it by using getParcelableArrayListExtra<SongInfo>(..) method.

class ActivityTwo: AppCompatActivity() {
    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        val songs = intent?.getParcelableArrayListExtra<SongInfo>("songs") ?:
                throw IllegalStateException("Songs array list is null")

        println(songs) // There you go
    }
}

Android Studio could help you create a boilerplate code of Parcelable as well by Option + return on Mac.

Answer 2

1.) Create songInfo model class as parcelable.

2.) Pass this parcelbale model class in intent and use Parcelable.putExtra() method using key.

3.) Get Parcelable arraylist into another class by Parcelable.getExtras() using valid key.