RecyclerView Sets a fixed number of items

One, foreword

Many times will encounter the use of RecyclerView, the requirements of more than a certain number of items, fixed RecyclerView height, not more than this number on the adaptive height. This is more likely to occur in the dialog box, too many can not let the dialog box take up the entire screen, while the number of items displayed can be controlled, the following for different cases can use different methods.

2. Given the height of Item

When the height of Item layout is known, the maximum height can be set to control the number of items displayed. Since the height of Item is known, the purpose can be achieved by calculating the height well. The following is the specific implementation:

Look at the effect, display a maximum of 3 items, more than scrolling display:

• 1. Layout interface, relatively simple, on a RecyclerView, as long as a maximum height can be set (note: maximum height to use layout_constraintHeight_max)

<? xml version="1.0" encoding="utf-8"? > <androidx.constraintlayout.widget.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"> <! - item high fixed known - > < androidx. Recyclerview. Widget. Recyclerview android: id ="@+id/rv_recycler_fixed_one"
        android:layout_width="match_parent"
        android:layout_height="0dp"
        app:layout_constraintTop_toTopOf="parent"
        app:layout_constraintHeight_max="240dp"
        android:background="@color/yellow_FF9B52"
        />


</androidx.constraintlayout.widget.ConstraintLayout>
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• 2. Activity interface, simple Settings and data Settings, any normal available adapter can be

class RecyclerItemFixedActivity: AppCompatActivity(a){
    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_recycler_item_fixed)

        val list = arrayListOf<String>("Test Data 1"."Test Data 2"."Test Data 3"."Test data 4") val adapter by lazy { RecyclerItemFixedAdapter() } rv_recycler_fixed_one? .let { it.layoutManager = LinearLayoutManager(this)
            it.adapter = adapter
            it.addItemDecoration(DividerItemDecoration(this,LinearLayoutManager.VERTICAL))
        }
        adapter.setList(list)
    }
}
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• 3. Very general Item layout, mainly fixed height

<? xml version="1.0" encoding="utf-8"? > <RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="80dp"
    android:background="@color/green_07C0C2">

    <TextView
        android:id="@+id/tv_item_recycler_fixed_title"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="@string/app_name"
        android:textColor="@color/white"
        android:layout_centerInParent="true"/>
</RelativeLayout>
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<? xml version="1.0" encoding="utf-8"? > <androidx.constraintlayout.widget.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    android:background="@color/red_F7E6ED">


    <androidx.recyclerview.widget.RecyclerView
        android:id="@+id/rv_recycler_wrap_list"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        app:layout_constraintTop_toTopOf="parent"
        />

</androidx.constraintlayout.widget.ConstraintLayout>
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<? xml version="1.0" encoding="utf-8"? > <RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:background="@color/green_07C0C2">

    <TextView
        android:id="@+id/tv_item_recycler_wrap2_title"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="@string/app_name"
        android:textColor="@color/white"
        android:layout_centerInParent="true"
        android:paddingVertical="@dimen/m10"/>
</RelativeLayout>
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class RecyclerWrapAdapter(resId: Int = R.layout.item_recycelr_wrap2) :
    BaseQuickAdapter<String, BaseViewHolder>(resId) {
    override fun convert(holder: BaseViewHolder, item: String) {
        holder.setText(R.id.tv_item_recycler_wrap2_title, item)
    }
}
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class RecyclerWrapActivity: AppCompatActivity(a){
    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_recyclerview_wrap)

        val list = arrayListOf("Test Data 1"."Test Data 2"."Test Data 3"."Test data 4"."Test number five"."Test Data 6") val adapter by lazy { RecyclerWrapAdapter() } rv_recycler_wrap_list? .let { it.layoutManager = LinearLayoutManager(this)
            it.adapter = adapter
            it.addItemDecoration(DividerItemDecoration(this, LinearLayoutManager.VERTICAL))
        }
        adapter.setList(list)

        / / reference https://www.cnblogs.com/guanxinjing/p/13037156.html
        // Set the recyclerView height dynamicallyrv_recycler_wrap_list? .post {// If 4 are fixed, you need to set more than 4
            if (list.size <= 4) {return@post
            }
            val itemView = rv_recycler_wrap_list.getChildAt(0) itemView? .let { val height = it.height *4
                val layoutParems = rv_recycler_wrap_list.layoutParams
                layoutParems.height = height
                rv_recycler_wrap_list.layoutParams = layoutParems
            }
        }
    }
}
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Four, horizontal scrolling

In horizontal scrolling, it is generally required to display a fixed number of items, and if the number exceeds, it will be displayed in scroll. At this time, it is necessary to dynamically set the width of the Item layout to achieve this. The figure below shows 4.5 items beyond scroll:

• 1. Layout interface, same as above

<? xml version="1.0" encoding="utf-8"? > <androidx.constraintlayout.widget.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    android:background="@color/red_F7E6ED">


    <androidx.recyclerview.widget.RecyclerView
        android:id="@+id/rv_recycler_wrap_list"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        app:layout_constraintTop_toTopOf="parent"
        />

</androidx.constraintlayout.widget.ConstraintLayout>
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• 2. Activity, change the orientation to scroll horizontally

class RecyclerViewWrapActivity: AppCompatActivity(a){
    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_recyclerview_wrap)

        val list = arrayListOf("Test Data 1"."Test Data 2"."Test Data 3"."Test data 4"."Test number five"."Test Data 6") val adapter by lazy { RecyclerItemWrapAdapter() } rv_recycler_wrap_list? .let { it.layoutManager = LinearLayoutManager(this,LinearLayoutManager.HORIZONTAL,false)
            it.adapter = adapter
            it.addItemDecoration(DividerItemDecoration(this, LinearLayoutManager.HORIZONTAL))
        }
        adapter.setList(list)
    }
}
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• 3. Adapter, where you set the width of the Item

class RecyclerItemWrapAdapter(resId: Int = R.layout.item_recycelr_wrap)
    : BaseQuickAdapter<String,BaseViewHolder>(resId){
    override fun convert(holder: BaseViewHolder, item: String) {
        holder.setText(R.id.tv_item_recycler_wrap_title,item)

        // Get the width of the screen and allocate it. 4.5 means you can put 4.5 items at any height. In this case, match_parent
        // If margin is set, subtract margin
        / / val width = (context) resources. The displayMetrics. WidthPixels - Utils. Dip2px (context, margin)) / 4.5 f
        / / reference https://blog.csdn.net/qq_32518491/article/details/81033275?utm_medium=distribute.pc_relevant.none-task-blog-BlogComm endFromMachineLearnPai2-1.channel_param&depth_1-utm_source=distribute.pc_relevant.none-task-blog-BlogCommendFromMachineL earnPai2-1.channel_param
        val width = (context.resources.displayMetrics.widthPixels) / 4.5 f
        val params = ViewGroup.LayoutParams(
            width.toInt(),
            ViewGroup.LayoutParams.MATCH_PARENT
        )
        holder.itemView.layoutParams = params

    }
    
}
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• 4. Item layout, height can be fixed or not fixed, width wrap_content

<? xml version="1.0" encoding="utf-8"? > <RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:background="@color/green_07C0C2">

    <TextView
        android:id="@+id/tv_item_recycler_wrap_title"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="@string/app_name"
        android:textColor="@color/white"
        android:layout_centerInParent="true"
        android:paddingVertical="@dimen/m10"
        />
</RelativeLayout>
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