Android 简明教程

Android - UI Controls

View 是指用户可以与其交互的屏幕上的绘制对象，而 ViewGroup 是包含其他视图(和视图组)对象以定义用户界面布局的对象。

A View is an object that draws something on the screen that the user can interact with and a ViewGroup is an object that holds other View (and ViewGroup) objects in order to define the layout of the user interface.

您在XML文件中定义布局，该文件为布局提供了人类可读的结构，类似于HTML。例如，带有文本视图和按钮的简单垂直布局如下所示-

You define your layout in an XML file which offers a human-readable structure for the layout, similar to HTML. For example, a simple vertical layout with a text view and a button looks like this −

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
   android:layout_width="fill_parent"
   android:layout_height="fill_parent"
   android:orientation="vertical" >

   <TextView android:id="@+id/text"
      android:layout_width="wrap_content"
      android:layout_height="wrap_content"
      android:text="I am a TextView" />

   <Button android:id="@+id/button"
      android:layout_width="wrap_content"
      android:layout_height="wrap_content"
      android:text="I am a Button" />
</LinearLayout>

Android UI Controls

Android提供了许多UI控件，允许您为应用程序构建图形用户界面。

There are number of UI controls provided by Android that allow you to build the graphical user interface for your app.

Sr.No.	UI Control & Description
1	TextViewThis control is used to display text to the user.
2	EditTextEditText is a predefined subclass of TextView that includes rich editing capabilities.
3	AutoCompleteTextViewThe AutoCompleteTextView is a view that is similar to EditText, except that it shows a list of completion suggestions automatically while the user is typing.
4	ButtonA push-button that can be pressed, or clicked, by the user to perform an action.
5	ImageButtonAn ImageButton is an AbsoluteLayout which enables you to specify the exact location of its children. This shows a button with an image (instead of text) that can be pressed or clicked by the user.
6	CheckBoxAn on/off switch that can be toggled by the user. You should use check box when presenting users with a group of selectable options that are not mutually exclusive.
7	ToggleButtonAn on/off button with a light indicator.
8	RadioButtonThe RadioButton has two states: either checked or unchecked.
9	RadioGroupA RadioGroup is used to group together one or more RadioButtons.
10	ProgressBarThe ProgressBar view provides visual feedback about some ongoing tasks, such as when you are performing a task in the background.
11	SpinnerA drop-down list that allows users to select one value from a set.
12	TimePickerThe TimePicker view enables users to select a time of the day, in either 24-hour mode or AM/PM mode.
13	DatePickerThe DatePicker view enables users to select a date of the day.

Create UI Controls

输入控件是应用程序用户界面中的交互式组件。Android 提供多种控件，可用于您的 UI，例如按钮、文本字段、拖动条、复选框、变焦按钮、切换按钮等。

Input controls are the interactive components in your app’s user interface. Android provides a wide variety of controls you can use in your UI, such as buttons, text fields, seek bars, check box, zoom buttons, toggle buttons, and many more.

如前一章中所述，视图对象可能具有唯一 ID，该 ID 将在树中唯一标识视图。XML 标记内 ID 的语法为 −

As explained in previous chapter, a view object may have a unique ID assigned to it which will identify the View uniquely within the tree. The syntax for an ID, inside an XML tag is −

android:id="@+id/text_id"

要创建 UI 控件/视图/小部件，您必须在布局文件中定义一个视图/小部件，并按如下所示为其分配一个唯一 ID −

To create a UI Control/View/Widget you will have to define a view/widget in the layout file and assign it a unique ID as follows −

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
   android:layout_width="fill_parent"
   android:layout_height="fill_parent"
   android:orientation="vertical" >

   <TextView android:id="@+id/text_id"
      android:layout_width="wrap_content"
      android:layout_height="wrap_content"
      android:text="I am a TextView" />
</LinearLayout>

然后，最后创建控件对象的实例并从布局中获取，使用以下内容 −

Then finally create an instance of the Control object and capture it from the layout, use the following −

TextView myText = (TextView) findViewById(R.id.text_id);