Android中如何让TextView在布局内垂直居中同时保持布局可滚动

解决方案 #

核心实现思路是外层嵌套ScrollView并开启fillViewport属性，既保证内部布局可以撑满全屏让text_no_items垂直居中，内容超过屏幕高度时又能自动滚动：

<?xml version="1.0" encoding="utf-8"?>
<ScrollView xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:fillViewport="true">

    <LinearLayout
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:orientation="vertical">

        <TextView
            android:id="@+id/description"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:gravity="center"
            android:text="This is a sample description about the items you will see below. This text could be very long."
            android:textSize="32sp" />

        <TextView
            android:id="@+id/text_no_items"
            android:layout_width="wrap_content"
            android:layout_height="0dp"
            android:layout_weight="1"
            android:layout_gravity="center_horizontal"
            android:gravity="center"
            android:text="No items"
            android:textSize="48sp" />

    </LinearLayout>
</ScrollView>

关键配置说明

• android:fillViewport="true"：该属性让ScrollView的子布局强制占满ScrollView的可用高度，这是让内部LinearLayout的layout_weight属性生效的前提
• 当description内容较短时，内部LinearLayout高度等于屏幕高度，text_no_items通过layout_weight="1"占满剩余高度，自带的gravity="center"会让文字垂直居中
• 当description内容过长时，内部LinearLayout高度会超过屏幕高度，ScrollView自动进入可滚动状态，用户可以滑动查看完整内容

可选ConstraintLayout实现方案 #

如果你更习惯用约束布局，也可以用以下写法，逻辑更清晰：

<?xml version="1.0" encoding="utf-8"?>
<ScrollView xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:fillViewport="true">

    <androidx.constraintlayout.widget.ConstraintLayout
        android:layout_width="match_parent"
        android:layout_height="match_parent">

        <TextView
            android:id="@+id/description"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:gravity="center"
            android:text="This is a sample description about the items you will see below. This text could be very long."
            android:textSize="32sp"
            app:layout_constraintTop_toTopOf="parent"
            app:layout_constraintStart_toStartOf="parent"
            app:layout_constraintEnd_toEndOf="parent"/>

        <TextView
            android:id="@+id/text_no_items"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="No items"
            android:textSize="48sp"
            app:layout_constraintTop_toBottomOf="@id/description"
            app:layout_constraintBottom_toBottomOf="parent"
            app:layout_constraintStart_toStartOf="parent"
            app:layout_constraintEnd_toEndOf="parent"
            app:layout_constraintVertical_bias="0.5"/>

    </androidx.constraintlayout.widget.ConstraintLayout>
</ScrollView>

内容的提问来源于stack exchange，提问作者Mohit Yadav