Android学习笔记04

kotlin+mvvm+databinding+recyclerview
上一篇讲了一般kotlin的recyclereview的写法，这次来整合databinging跟MVVM。
首先是xml(主画面)

<?xml version="1.0" encoding="utf-8"?>
<layout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools">

    <androidx.constraintlayout.widget.ConstraintLayout
        android:layout_width="match_parent"
        android:layout_height="match_parent">
        <androidx.recyclerview.widget.RecyclerView
            android:id="@+id/recyclerView"
            android:layout_width="match_parent"
            android:layout_height="match_parent"
            app:layoutManager="androidx.recyclerview.widget.LinearLayoutManager"
            tools:listitem="@layout/item_view"
            tools:itemCount="5" />
    </androidx.constraintlayout.widget.ConstraintLayout>
</layout>

再来是item_view的xml

<?xml version="1.0" encoding="utf-8"?>
<layout xmlns:app="http://schemas.android.com/apk/res-auto">
    <data>
        <variable
            name="Post"
            type="com.example.myapplication.Post" />
        <variable
            name="listener"
            type="com.example.myapplication.Listener" />
    </data>
    <androidx.constraintlayout.widget.ConstraintLayout
        xmlns:android="http://schemas.android.com/apk/res/android"
        android:orientation="vertical" android:layout_width="match_parent"
        android:layout_height="wrap_content">
        <TextView
            android:layout_width="0dp"
            android:layout_height="wrap_content"
            app:layout_constraintTop_toTopOf="parent"
            app:layout_constraintStart_toStartOf="parent"
            app:layout_constraintEnd_toEndOf="parent"
            app:layout_constraintBottom_toBottomOf="parent"
            android:padding="5dp"
            android:textSize="16sp"
            android:text="@{Post.post}"
            android:onClick="@{()-> listener.onClick(Post)}"/>
    </androidx.constraintlayout.widget.ConstraintLayout>
</layout>

今天主要先说Activity的部分

class Activity:AppCompatActivity() {
    lateinit var binding: ActivityMainBinding

    private val mViewModel by lazy {
        initViewModel(application, ViewModel::class.java)
    }

    private val mAdapter by lazy {
        Adapter<Post>(
            R.layout.item_view,
            listener = object : Listener<Post> {
                override fun onClick(post: Post) {
                    Toast.makeText(this@Activity, post.post, Toast.LENGTH_SHORT).show()
                }
            }
        )
    }

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        binding = DataBindingUtil.setContentView(this, R.layout.activity_main)
        binding.recyclerView.adapter = mAdapter

        mViewModel.data.observe(this, Observer { post ->
            mAdapter.updateData(post)
        })
        mViewModel.fetchData()
    }
}

这边的lazy是让程序执行时，需要的时後在读取，可以提升程序执行速度及记忆体空间的利用
listener是我自定义onclick的interface
因为後面的viewmodel是继承androidviewmodel，所以我用一个扩展含式，去取的程序的application的上下文，也可以直接在manifests里面新增