A rich interface consists of many controls, so how can we make each control orderly placed on the interface instead of messy, which needs to be realized with the help of layout

LinearLayout

LinearLayout, also known as linear layout, is a very common layout

android:orientation arrangement
Arranged in vertical order

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:orientation="vertical"
    android:layout_width="match_parent"
    android:layout_height="match_parent">

    <Button
        android:id="@+id/button1"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Button 1"/>

    <Button
        android:id="@+id/button2"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Button 2"/>
    <Button
        android:id="@+id/button3"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Button 3"/>
</LinearLayout>

Arranged horizontally

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:orientation="horizontal"
    android:layout_width="match_parent"
    android:layout_height="match_parent">

    <Button
        android:id="@+id/button1"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Button 1"/>

    <Button
        android:id="@+id/button2"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Button 2"/>
    <Button
        android:id="@+id/button3"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Button 3"/>
</LinearLayout>

android:layout_gravity
If the arrangement is vertical, only the alignment in the horizontal direction will take effect
If the arrangement is horizontal, only the vertical alignment will take effect

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:orientation="horizontal"
    android:layout_width="match_parent"
    android:layout_height="match_parent">

    <Button
        android:id="@+id/button1"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_gravity="top"
        android:text="Button 1"/>

    <Button
        android:id="@+id/button2"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_gravity="center_vertical"
        android:text="Button 2"/>
    <Button
        android:id="@+id/button3"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_gravity="bottom"
        android:text="Button 3"/>
</LinearLayout>

android:layout_weight
This property allows us to specify the size of the control in a proportional manner

Here, we set the width of EditText and Button to 0dp because we use android:layout_weight property. At this time, the width of the control should not be determined by Android: layout_ It's up to width
android:layout_ Setting the weight property to 1 means that EditText and Button will divide the width horizontally

Why divide the screen width equally by specifying 1?
The system will set the layout specified by all controls under LinearLayout_ The weight value is added to get a total value, and then the proportion of the size of each control is the layout of the control_ The weight value is divided by the total value just calculated

Specify only Android: layout of EditText_ Weight attribute and changed the width of the Button back to wrap_content, the interface written in this way can not only adapt to various screens, but also look more comfortable

RelativeLayout

RelativeLayout is also called relative layout. It can make controls appear anywhere in the layout by relative positioning. Therefore, there are many properties in RelativeLayout

Positioning between control and parent layout

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent">
    
    <Button
        android:id="@+id/button1"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_alignParentLeft="true"
        android:layout_alignParentTop="true"
        android:text="Button 1"/>

    <Button
        android:id="@+id/button2"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_alignParentRight="true"
        android:layout_alignParentTop="true"
        android:text="Button 2"/>

    <Button
        android:id="@+id/button3"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_centerInParent="true"
        android:text="Button 3"/>

    <Button
        android:id="@+id/button4"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_alignParentLeft="true"
        android:layout_alignParentBottom="true"
        android:text="Button 4"/>

    <Button
        android:id="@+id/button5"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_alignParentRight="true"
        android:layout_alignParentBottom="true"
        android:text="Button 5"/>

</RelativeLayout>

Positioning between controls

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent">


    <Button
        android:id="@+id/button3"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_centerInParent="true"
        android:text="Button 3"/>

    <Button
        android:id="@+id/button1"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_above="@id/button3"
        android:layout_toLeftOf="@id/button3"
        android:text="Button 1"/>

    <Button
        android:id="@+id/button2"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_below="@id/button3"
        android:layout_toRightOf="@id/button3"
        android:text="Button 2"/>

</RelativeLayout>

FrameLayout

Also known as frame layout, this layout has no rich positioning methods, and all controls will be placed in the upper left corner of the layout by default

<FrameLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent">

    <TextView
        android:id="@+id/textView"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="this is TextView"/>
    <Button
        android:id="@+id/button"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Button"/>
    
</FrameLayout>

The button covers the font, which can be accessed through android:layout_gravity defines the location

<FrameLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent">

    <TextView
        android:id="@+id/textView"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_gravity="left"
        android:text="this is TextView"/>
    <Button
        android:id="@+id/button"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_gravity="right"
        android:text="Button"/>

</FrameLayout>

Due to the lack of positioning methods, FrameLayout has relatively few application scenarios~