Kotlin 无法从 Model Class 与 Putextra 发送数据

Question

I have created a structure like the one below. When I click the list in the first activity, I want the information about that item in the second activity. However, I cannot send data with putextra. I will be very happy if you are interested.I do not know the subject fully. Therefore, if anyone is interested, I will assign the necessary codes.

Customers.kt

    val listView=findViewById<ListView>(R.id.listView)
    val list=ArrayList<CustomerModel>()

    listView.setOnItemClickListener { adapterView, view, i, l ->

        val intent=Intent(applicationContext,CustomersDetails::class.java)
      //I think that's not true   intent.putExtra("Name",list[i])
        startActivity(intent)
    }

CustomersDetails.kt

 val intent=intent
    choosenCustomer= intent.getStringExtra("Name").toString()

CustomerModel.kt

class CustomerModel(val title:String, val description:String,val img:Int): Parcelable {
constructor(parcel: Parcel) : this(
    parcel.readString()!!,
    parcel.readString()!!,
    parcel.readInt()
) {
}

override fun writeToParcel(parcel: Parcel, flags: Int) {
    parcel.writeString(title)
    parcel.writeString(description)
    parcel.writeInt(img)
}

override fun describeContents(): Int {
    return 0
}

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

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

}

CustomerAdapter.kt

class CustomerAdapter(var mCtx:Context,val resources: Int,var items:List<CustomerModel>):
ArrayAdapter<CustomerModel>(mCtx,resources,items) {

override fun getView(position: Int, convertView: View?, parent: ViewGroup): View {
    val layoutInflater: LayoutInflater= LayoutInflater.from(mCtx)
    val view:View=layoutInflater.inflate(resources,null)

    val imageView: ImageView=view.findViewById(R.id.image)
    val titleTextView: TextView=view.findViewById(R.id.cuText)
    val descriptionTextView:TextView=view.findViewById(R.id.ofText)

    var mItem:CustomerModel=items[position]

    imageView.setImageDrawable(mCtx.resources.getDrawable(mItem.img))
    titleTextView.text=mItem.title
    descriptionTextView.text=mItem.description
    return view
}

}

Answer 1

You shouldn't redifine the intent as you did, Instead of

val intent=intent
    choosenCustomer= intent.getStringExtra("Name").toString()

You should use:

choosenCustomer= intent.getStringExtra("Name").toString()

The first snippet the intent value becomes null I think

Answer 2

One option could be letting your custom class implement the Serializable interface and then you can pass object instances in the intent extra using the putExtra(Serializable..) variant of the Intent#putExtra() method.

You can extract Parcelable obj using intent.getParcelableExtra(/ key /"Name")

Answer 3

CustomerModel needs to be serializable.

class CustomerModel : Serializable

See more: https://spin.atomicobject.com/2016/11/28/sending-data-actions-android/

Edited after you edit your question:

• If you use Serializable , then you will just putExtra and getSerializableExtra
• If you use Parcelable , then you will just putExtra and getParcelableExtra

Why do we serialize objects?

Serialization of the object is usually needed when you send your object over a network or store it in files because the network infrastructure and hardware components used for storage understand bits and bytes, but not objects. In Android, when you want to send an object to another activity from any activity, you cannot send it as you do in primitive types.

Differences between Serializable and Parcelable

• Serializable interface is very easy to implement. It is a marker interface and by implementing this, your POJO class is able to be serialized and deserialized; whereas Parcelable is not a marker interface, hence it has some methods that you will have to override when you implement this in your class.
• Serializable interface is not a part of Android SDK and it uses reflection for marshaling operations and creates lots of temp objects. In Parcelable, you are able to choose which field you want to serialize.
• Because of the temp object creation and garbage collection, Serialization is slower than Parcelable.