实现button在屏幕居中
要实现button在LinearLayout布注意局屏幕中间居中需要做到两点在linearLayout中设置
android:orientantion 竖屏或者横屏居中
android:gravity 设置内容在layout中的位置
例如：
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout 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="fill_parent"
android:gravity="center"
android:orientation="vertical">
<Button
android:id="@+id/button"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_gravity="center"
android:text="Anr Demo" />
><Button
android:id="@+id/button2"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_gravity="center"
android:text="Performace" />
</LinearLayout >
android:orientation
| Constant | Value | Description |
|:---------:|:-------------:|: -----|
|horizontal |0 |Defines an horizontal widget. |
| vertical | 1| Defines a vertical widget.|
android:gravity
| Constant | Value | Description |
|---|---|---|
| bottom | 50 | Push object to the bottom of its container, not changing its size. |
| center | 11 | Place the object in the center of its container in both the vertical and horizontal axis, not changing its size. |
| center_horizontal | 1 | Place object in the horizontal center of its container, not changing its size. |
| center_vertical | 10 | Place object in the vertical center of its container, not changing its size. |
| clip_horizontal | 8 | Additional option that can be set to have the left and/or right edges of the child clipped to its container's bounds. The clip will be based on the horizontal gravity: a left gravity will clip the right edge, a right gravity will clip the left edge, and neither will clip both edges. |
| clip_vertical | 80 | Additional option that can be set to have the top and/or bottom edges of the child clipped to its container's bounds. The clip will be based on the vertical gravity: a top gravity will clip the bottom edge, a bottom gravity will clip the top edge, and neither will clip both edges. |
| end | 800005 | Push object to the end of its container, not changing its size. |
| fill | 77 | Grow the horizontal and vertical size of the object if needed so it completely fills its container. |
| fill_horizontal | 7 | Grow the horizontal size of the object if needed so it completely fills its container. |
| fill_vertical | 70 | Grow the vertical size of the object if needed so it completely fills its container. |
| left | 3 | Push object to the left of its container, not changing its size. |
| right | 5 | Push object to the right of its container, not changing its size. |
| start | 800003 | Push object to the beginning of its container, not changing its size. |
| top | 30 | Push object to the top of its container, not changing its size. |
