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In this tutorial, we will provide an overview of android layout. We will also explore some of the specific layout controls available for organising the screen content namely – Android LinearLayout and Android RelativeLayout.
在本教程中，我们将概述android布局。 我们还将探讨一些可用于组织屏幕内容的特定布局控件，即Android LinearLayout和Android RelativeLayout。
The basic building block for user interface is a View object that is created from the View class and occupies a rectangular area on the screen. Views are the base class for UI components like TextView, Button, EditText etc.
用户界面的基本构建块是一个View对象，该View对象是从View类创建的，并且在屏幕上占据一个矩形区域。 视图是UI组件（如TextView，Button，EditText等）的基类。
The ViewGroup is a subclass of View. One or more Views can be grouped together into a ViewGroup. A ViewGroup provides the android layout in which we can order the appearance and sequence of views. Examples of ViewGroup are LinearLayout, FrameLayout, RelativeLayout etc.
ViewGroup是View的子类。 可以将一个或多个视图组合到一个视图组中。 ViewGroup提供了android布局，我们可以在其中排列视图的外观和序列。 ViewGroup的示例是LinearLayout ， FrameLayout ， RelativeLayout等。
Android provides the following ViewGroups or layouts:
Android提供以下ViewGroup或布局：
LinearLayout : is a ViewGroup that aligns all children in a single direction, vertically or horizontally LinearLayout ：是一个ViewGroup，可在单个方向上垂直或水平对齐所有子级 RelativeLayout : is a ViewGroup that displays child views in relative positions RelativeLayout ：是一个ViewGroup，它在相对位置显示子视图 FrameLayout : is a placeholder on screen that is used to display a single view FrameLayout ：是屏幕上的占位符，用于显示单个视图 ScrollView : is a special type of FrameLayout in that it allows users to scroll through a list of views that occupy more space than the physical display. The ScrollView can contain only one child view or ViewGroup, which normally is a LinearLayout ScrollView ：是FrameLayout的一种特殊类型，它使用户可以滚动浏览比物理显示器占用更多空间的视图列表。 ScrollView只能包含一个子视图或ViewGroup，通常为LinearLayout In this tutorial we’ll focus on the two most used android layout:
在本教程中，我们将重点介绍两个最常用的android布局：
android:marginLeft=20dp, then the view will be arranged after 20dp from left android：layout_margin ：这是视图外部的额外空间。 例如，如果您提供android:marginLeft=20dp ，则视图将从左20dp之后排列 android:layout_width=wrap_content tells the view to size itself to the dimensions required by its content.
android：layout_width = wrap_content告知视图将其自身调整为其内容所需的尺寸。
android:layout_width=match_parent tells the view to become as big as its parent view.
android：layout_width = match_parent告诉视图变得与其父视图一样大。
The syntax for an ID, inside an XML tag is:
XML标记内的ID的语法为：
Android LinearLayout organizes elements along a single line. We can specify whether that line is vertical or horizontal using android:orientation. The orientation is horizontal by default.
Android LinearLayout沿一行组织元素。 我们可以使用android:orientation指定该行是垂直还是水平。 默认情况下方向是水平的。
A vertical LinearLayout will only have one child per row (so it is a column of single elements), and a horizontal LinearLayout will only have one single row of elements on the screen.
垂直LinearLayout每行只有一个子元素（因此它是一列单个元素），而水平LinearLayout在屏幕上将只有一行元素。
android:layout_weight attribute depicts the importance of the element. An element with larger weight occupies more screen space. Here is a sample Layout XML using LinearLayout:
android：layout_weight属性描述了元素的重要性。 重量较大的元素占用更多的屏幕空间。 这是使用LinearLayout的示例布局XML：
layout_linear.xml
layout_linear.xml
In this layout we have a Parent LinearLayout which has a vertical orientation and contains buttons, textviews and a nested Linear Layout(having a horizontal orientation) as child views.
在此布局中，我们有一个Parent LinearLayout ，它具有垂直方向，并包含按钮，文本视图和嵌套的Linear Layout（水平方向）作为子视图。
Note: Nested layouts don’t have to be of one type. We could, for example, have a LinearLayout as one of the children in a RelativeLayout and vice-versa.
注意 ：嵌套布局不必是一种类型。 例如，我们可以将LinearLayout作为RelativeLayout中的子级之一，反之亦然。
Android RelativeLayout lays out elements based on their relationships with one another, and with the parent container. This is one of the most complicated layout and we need several properties to actually get the layout we desire.
Android RelativeLayout根据元素之间的关系以及与父容器的关系来布局元素。 这是最复杂的布局之一，我们需要几个属性才能实际获得所需的布局。
That is, using RelativeLayout we can position a view to be toLeftOf, toRightOf, below or above its siblings.
也就是说，使用RelativeLayout我们可以将视图定位为toLeftOf ， toRightOf ， 位于其同级之下或之上 。
We can also position a view with respect to its parent such as centered horizontally, vertically or both, or aligned with any of the edges of the parent RelativeLayout. If none of these attributes are specified on a child view then the view is by default rendered to the top left position.
我们还可以相对于父视图放置视图，例如水平 ， 垂直或同时居中或与父视图RelativeLayout任何边缘对齐。 如果在子视图上未指定这些属性，则默认情况下将视图渲染到左上角。
The following are the major attributes used across RelativeLayout. They lay across three different categories:
以下是在RelativeLayout中使用的主要属性。 它们分为三个不同的类别：
“@id/XXXXX” is used to reference an element by its id. One thing to remember is that referencing an element before it has been declared will produce an error so @+id/ should be used in such cases.
“ @ id / XXXXX”用于通过元素ID引用元素。 要记住的一件事是，在声明元素之前先引用它会产生错误，因此在这种情况下应使用@ + id /。
The following xml layout uses RelativeLayout:
以下xml布局使用RelativeLayout ：
layout_relative.xml
layout_relative.xml
As you can see we can rearrange elements based on their relative positions.
如您所见，我们可以根据元素的相对位置重新排列元素。
The following xml layout represents a custom layout having nested linear and relative layouts.
以下xml布局表示具有嵌套线性和相对布局的自定义布局。
layout_mixed.xml
layout_mixed.xml
This project consists of three activities and the respective layouts that were discussed above.
该项目包括三个活动和上面讨论的各个布局。
The application launches into the MainActivity which loads the layout_linear.xml contents by the following code:
该应用程序启动进入MainActivity，它通过以下代码加载layout_linear.xml内容：
package com.journaldev.layouts;import android.content.Intent;import android.support.v7.app.AppCompatActivity;import android.os.Bundle;import android.view.Menu;import android.view.MenuItem;import android.view.View;import android.widget.Button;public class MainActivity extends AppCompatActivity { Button back,next; @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.layout_linear); back=(Button)findViewById(R.id.back_button); next=(Button)findViewById(R.id.next_button); next.setOnClickListener(new View.OnClickListener() { @Override public void onClick(View v) { Intent intent=new Intent(MainActivity.this,SecondActivity.class); intent.setFlags(Intent.FLAG_ACTIVITY_CLEAR_TOP); startActivity(intent); } }); back.setOnClickListener(new View.OnClickListener() { @Override public void onClick(View v) { finish(); } }); }} The SecondActivity and ThirdActivity load the layout_relative.xml and layout_mixed.xml layouts respectively as shown below:
SecondActivity和ThirdActivity加载layout_relative.xml和layout_mixed.xml布局，如下所示：
package com.journaldev.layouts;import android.app.Activity;import android.content.Intent;import android.os.Bundle;import android.view.View;import android.widget.Button;public class SecondActivity extends Activity { Button back,next; @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.layout_relative); back=(Button)findViewById(R.id.backbutton); next=(Button)findViewById(R.id.next); next.setOnClickListener(new View.OnClickListener() { @Override public void onClick(View v) { Intent intent=new Intent(SecondActivity.this,ThirdActivity.class); intent.setFlags(Intent.FLAG_ACTIVITY_CLEAR_TOP); startActivity(intent); } }); back.setOnClickListener(new View.OnClickListener() { @Override public void onClick(View v) { Intent intent=new Intent(SecondActivity.this,MainActivity.class); intent.setFlags(Intent.FLAG_ACTIVITY_CLEAR_TOP); startActivity(intent); } }); }} package com.journaldev.layouts;import android.app.Activity;import android.content.Intent;import android.os.Bundle;import android.view.View;import android.widget.Button;public class ThirdActivity extends Activity { Button back; @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.layout_mixed); back=(Button)findViewById(R.id.back_button_pressed); back.setOnClickListener(new View.OnClickListener() { @Override public void onClick(View v) { Intent intent=new Intent(ThirdActivity.this,SecondActivity.class); intent.setFlags(Intent.FLAG_ACTIVITY_CLEAR_TOP); startActivity(intent); } }); }} The image outputs of the three layout files are shown below:
三个布局文件的图像输出如下所示：
layout_linear.xml
layout_linear.xml
As you can see the Parent LinearLayout consists of 6 child elements in a single vertical column among which one is a nested LinearLayout child view containing 4 components in horizontal orientation.
如您所见，Parent LinearLayout在单个垂直列中包含6个子元素，其中一个是嵌套的LinearLayout子视图，其中包含4个水平方向的组件。
layout_relative.xml
layout_relative.xml
The arrows pointing in the image above depict how siblings are positioned relative to each other and relative to the container.
上图中指向的箭头描述了兄弟姐妹如何相对于彼此以及相对于容器定位。
layout_mixed.xml
layout_mixed.xml
This Relative Layout consists of a Vertical LinearLayout within a Nested Horizontal LinearLayout along with a Child RelativeLayout.
此相对布局由嵌套水平LinearLayout中的Vertical LinearLayout以及子RelativeLayout组成。
Note: Components belonging to different layouts are not siblings and hence can’t be positioned relative to each other. It’s their container layouts that are siblings and can be positioned relative to each other.
注意：属于不同布局的组件不是同级组件，因此不能相对放置。 它们的容器布局是同级的并且可以彼此相对放置。
If you are wondering about the blue lined rectangles and arrows, it’s because the images are from xml layouts in graphical view. When you will run the app, these blue lines and rectangles will not be shown.
如果您想知道蓝色的矩形和箭头，那是因为图像来自图形视图中的xml布局。 当您运行应用程序时，这些蓝线和矩形将不会显示。
This brings an end to android layout tutorial. We’ll cover the other android layouts in the next tutorials. You can download the final Android Layout Project from the link below.
这结束了android布局教程。 在接下来的教程中，我们将介绍其他android布局 。 您可以从下面的链接下载最终的Android Layout Project 。
Reference:
参考：
翻译自:
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