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📜  Android-UI布局

📅  最后修改于: 2021-01-05 04:55:03             🧑  作者: Mango

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，并负责绘图和事件处理。 View是窗口小部件的基类，窗口小部件用于创建交互式UI组件，例如按钮，文本字段等。

ViewGroup是View的子类，并提供不可见的容器，用于容纳其他View或其他ViewGroup并定义其布局属性。

在第三层，我们有不同的布局，它们是ViewGroup类的子类，典型的布局定义了Android用户界面的视觉结构，可以在运行时使用View / ViewGroup对象创建，也可以使用简单的XML文件main_layout声明布局。 .xml ，位于项目的res / layout文件夹中。

布局

布局参数

本教程更多关于基于XML文件中定义的布局创建GUI。布局可以包含任何类型的小部件，例如按钮，标签，文本框等。以下是具有LinearLayout的XML文件的简单示例-

创建布局后，您可以在Activity.onCreate()回调实现中从应用程序代码中加载布局资源，如下所示-

public void onCreate(Bundle savedInstanceState) {
   super.onCreate(savedInstanceState);
   setContentView(R.layout.activity_main);
}

Android布局类型

Android提供了许多版式，您几乎可以在所有Android应用程序中使用它们来提供不同的视图，外观和感觉。

Sr.No Layout & Description
1 Linear Layout

LinearLayout is a view group that aligns all children in a single direction, vertically or horizontally.
2 Relative Layout

RelativeLayout is a view group that displays child views in relative positions.
3 Table Layout

TableLayout is a view that groups views into rows and columns.
4 Absolute Layout

AbsoluteLayout enables you to specify the exact location of its children.
5 Frame Layout

The FrameLayout is a placeholder on screen that you can use to display a single view.
6 List View

ListView is a view group that displays a list of scrollable items.
7 Grid View

GridView is a ViewGroup that displays items in a two-dimensional, scrollable grid.

布局属性

每个布局都有一组属性，这些属性定义该布局的视觉属性。在所有布局中，只有很少的公共属性，而其他属性是该布局所特有的。以下是常见属性，这些属性将应用于所有布局：

Sr.No Attribute & Description
1

android:id

This is the ID which uniquely identifies the view.
2

android:layout_width

This is the width of the layout.
3

android:layout_height

This is the height of the layout
4

android:layout_marginTop

This is the extra space on the top side of the layout.
5

android:layout_marginBottom

This is the extra space on the bottom side of the layout.
6

android:layout_marginLeft

This is the extra space on the left side of the layout.
7

android:layout_marginRight

This is the extra space on the right side of the layout.
8

android:layout_gravity

This specifies how child Views are positioned.
9

android:layout_weight

This specifies how much of the extra space in the layout should be allocated to the View.
10

android:layout_x

This specifies the x-coordinate of the layout.
11

android:layout_y

This specifies the y-coordinate of the layout.
12

android:layout_width

This is the width of the layout.
13

android:paddingLeft

This is the left padding filled for the layout.
14

android:paddingRight

This is the right padding filled for the layout.
15

android:paddingTop

This is the top padding filled for the layout.
16

android:paddingBottom

This is the bottom padding filled for the layout.

此处的宽度和高度是布局/视图的尺寸，可以根据dp(与密度无关的像素)，sp(与比例无关的像素)，pt(为1/72英寸的点)，px(像素)，毫米(毫米)，最后以英寸为单位。

您可以通过精确的测量来指定宽度和高度，但是更常见的是，您将使用以下常量之一来设置宽度或高度-

  • android：layout_width = wrap_content告诉您将视图调整为其内容所需的尺寸。

  • android：layout_width = fill_parent告诉您视图变得与其父视图一样大。

重力属性在定位视图对象中起着重要作用，它可以采用以下一个或多个(用“ |”分隔)以下常量值。

Constant Value Description
top 0x30 Push object to the top of its container, not changing its size.
bottom 0x50 Push object to the bottom of its container, not changing its size.
left 0x03 Push object to the left of its container, not changing its size.
right 0x05 Push object to the right of its container, not changing its size.
center_vertical 0x10 Place object in the vertical center of its container, not changing its size.
fill_vertical 0x70 Grow the vertical size of the object if needed so it completely fills its container.
center_horizontal 0x01 Place object in the horizontal center of its container, not changing its size.
fill_horizontal 0x07 Grow the horizontal size of the object if needed so it completely fills its container.
center 0x11 Place the object in the center of its container in both the vertical and horizontal axis, not changing its size.
fill 0x77 Grow the horizontal and vertical size of the object if needed so it completely fills its container.
clip_vertical 0x80 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.
clip_horizontal 0x08 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.
start 0x00800003 Push object to the beginning of its container, not changing its size.
end 0x00800005 Push object to the end of its container, not changing its size.

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视图对象可能具有分配给它的唯一ID，该ID将在树中唯一标识视图。 XML标记内的ID的语法是-

android:id="@+id/my_button"

以下是@和+符号的简要说明-

  • 字符串开头的符号(@)表示XML解析器应解析并扩展ID字符串的其余部分，并将其标识为ID资源。

  • 加号(+)表示这是必须创建并添加到我们资源中的新资源名称。要创建视图对象的实例并从布局中捕获它，请使用以下命令：

Button myButton = (Button) findViewById(R.id.my_button);