在 Android 中垂直居中视图
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Vertically centering a view in Android
提问by Jeremy Logan
I'm trying to center a Viewvertically on screen with the following layout:
我正在尝试View使用以下布局在屏幕上垂直居中：
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:orientation="vertical"
android:layout_width="fill_parent"
android:layout_height="fill_parent" >
<EditText
android:text="example text"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_gravity="center_vertical" />
</LinearLayout>
However it doesn't work. The EditTextis still at the top of the screen. Can someone explain what I'm doing wrong here?
但是它不起作用。在EditText屏幕上方依然。有人可以解释我在这里做错了什么吗？
NOTE:if I add center_horizontalto the layout_gravityattribute then it centers it horizontally, but still does not center vertically.
注意：如果我添加center_horizontal到layout_gravity属性，那么它会水平居中，但仍然不会垂直居中。
UPDATE:using android:gravity="center_vertical"on the parent worked. I still don't understand why android:layout_gravity="center_vertical"on the child didn't work.
更新：android:gravity="center_vertical"在父级上使用有效。我仍然不明白为什么android:layout_gravity="center_vertical"对孩子不起作用。
采纳答案by Bostone
I track the answer on Google groups, here it is© Romain Guy:
我在 Google 群组上跟踪答案，这里是© Romain Guy：
Well, first of all RelativeLayout ignores layout_gravity. Then you need to know that gravity means "apply gravity to the content of this view" whereas layout_gravity means "apply gravity to this view within its parent." So on a TextView, gravity will align the text within the bounds of the TextView whereas layout_gravity will align the TextView within the bounds of its parent.
好吧，首先，RelativeLayout 忽略了 layout_gravity。然后你需要知道引力意味着“将引力应用于此视图的内容”，而 layout_gravity 意味着“将引力应用于其父视图中的此视图”。因此，在 TextView 上，重力将在 TextView 的边界内对齐文本，而 layout_gravity 将在其父级的边界内对齐 TextView。
回答by didxga
The simple and quick answer is to add android:gravity="center_vertical"to the parent(containing) view. For those who want to know why, please refer to @Bostone 's answer.
简单而快速的答案是添加android:gravity="center_vertical"到父（包含）视图。对于那些想知道原因的人，请参阅@Bostone 的回答。
回答by Suragch
There are three ways you can center a view vertically. I recommend using the ConstraintLayout now.
您可以通过三种方式使视图垂直居中。我建议现在使用 ConstraintLayout。
1. Horizontal LinearLayout
1. 水平线性布局
The key is orientation="horizontal". You can't center horizontally for orientation="vertical".
关键是orientation="horizontal"。您不能为orientation="vertical"水平居中。
<LinearLayout
xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="horizontal">
<EditText
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_gravity="center_vertical"
android:text="example text"/>
</LinearLayout>
2. RelativeLayout
2. 相对布局
With a RelativeLayout you can use layout_centerVertical="true".
使用 RelativeLayout，您可以使用layout_centerVertical="true".
<RelativeLayout
xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent">
<EditText
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_centerVertical="true"
android:text="example text"/>
</RelativeLayout>
3. ConstraintLayout
3. 约束布局
It is easiest to show you this one.
向您展示这个是最容易的。
Here is the XML. It still would need a horizontal constraint to be added.
这是 XML。它仍然需要添加水平约束。
<android.support.constraint.ConstraintLayout
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"
android:layout_width="match_parent"
android:layout_height="match_parent"
tools:context="com.example.constraintlayout.MainActivity"
tools:layout_editor_absoluteX="0dp"
tools:layout_editor_absoluteY="81dp">
<EditText
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_marginBottom="8dp"
android:layout_marginTop="8dp"
android:text="example text"
app:layout_constraintBottom_toBottomOf="parent"
app:layout_constraintTop_toTopOf="parent"
tools:layout_editor_absoluteX="16dp"/>
</android.support.constraint.ConstraintLayout>
