RelativeLayout brief description
RelativeLayout inherits from android.widget.ViewGroup and completes layout according to the positional relationship between sub-elements. As the most flexible and commonly used layout method among the five major layouts of the Android system, it is very suitable for some more complex interface designs.
RelativeLayout is similar to LinearLayout, both are ViewGroups and can "accommodate" multiple subviews.
RelativeLayout is a view group that displays subviews in relative positions. Each view's position can be specified relative to a sibling element (for example, to the left or below another view) or relative to the parent RelativeLayout region (for example, aligned to the bottom, left, or center).
The subview can be TextView, Button, or LinearLayout, RelativeLayout, etc. If no other configuration is added, they default to the upper left corner of the RelativeLayout.
In RelativeLayout, a sub-View can be positioned based on another sub-View. But it must be noted that RelativeLayout and its sub-View cannot depend on each other. For example, RelativeLayout sets the height to wrap_content, and the sub-View sets ALIGN_PARENT_BOTTOM, so you will find that RelativeLayout is stretched to the maximum. RelativeLayout eliminates nested view groups and keeps the layout hierarchy flat.
Property introduction
RelativeLayout properties :
RelativeLayout can specify the position of subviews relative to the parent view or to each other (determined by ID). So you can align two elements according to their right borders, or have them one above the other, center on the screen, center on the left, etc. By default, all subviews are drawn in the upper left corner of the layout, so the position of each view must be defined using the various layout properties provided in RelativeLayout.LayoutParams.
There are many layout properties available for views in RelativeLayout, some examples include:
android:layout_alignParentTop
If "true", aligns the top edge of this view to the top edge of the superview.
android:layout_centerVertical
If "true", this child will be vertically centered within the parent.
android:layout_below
Positions the top edge of this view below the view specified with the resource ID.
android:layout_toRightOf
Positions the left edge of this view to the right of the view specified with the resource ID.
Example :
In order to make the UI look better, first define the style and add a new style in the style.xml file.
<style name="RelativeLayoutDemo1Item">
<item name="android:layout_height">wrap_content</item>
<item name="android:layout_width">wrap_content</item>
<item name="android:padding">4dp</item>
<item name="android:background">@color/colorAccent</item>
<item name="android:textColor">#ffffff</item>
<item name="android:textSize">12sp</item>
</style>
Example 1 :
Add RelativeLayout and some sub-Views to the layout. The child View sets different attributes, which are distributed in the top, bottom, left, and right places of the parent View.
<RelativeLayout
android:layout_width="match_parent"
android:layout_height="100dp">
<TextView
style="@style/RelativeLayoutDemo1Item"
android:text="default" />
<TextView
style="@style/RelativeLayoutDemo1Item"
android:layout_alignParentEnd="true"
android:text="layout_alignParentEnd" />
<TextView
style="@style/RelativeLayoutDemo1Item"
android:layout_centerInParent="true"
android:text="layout_centerInParent" />
<TextView
style="@style/RelativeLayoutDemo1Item"
android:layout_alignParentBottom="true"
android:text="layout_alignParentBottom" />
<TextView
style="@style/RelativeLayoutDemo1Item"
android:layout_alignParentEnd="true"
android:layout_alignParentBottom="true"
android:text="layout_alignParentBottom | End" />
</RelativeLayout>
Example 2 :
A sub-View can use another sub-View as a position basis.
<RelativeLayout
android:layout_width="match_parent"
android:layout_height="match_parent"
android:layout_marginTop="120dp">
<TextView
android:id="@+id/tv1"
style="@style/RelativeLayoutDemo1Item"
android:text="天" />
<TextView
android:id="@+id/tv2"
style="@style/RelativeLayoutDemo1Item"
android:layout_below="@id/tv1"
android:layout_toEndOf="@id/tv1"
android:text="天" />
<TextView
android:id="@+id/tv3"
style="@style/RelativeLayoutDemo1Item"
android:layout_below="@id/tv2"
android:layout_toEndOf="@id/tv2"
android:text="向" />
<TextView
android:id="@+id/tv4"
style="@style/RelativeLayoutDemo1Item"
android:layout_below="@id/tv3"
android:layout_toEndOf="@id/tv3"
android:text="上" />
</RelativeLayout>
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