Android UI 设计指南：从基础到进阶

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"Android-UI-Design 是一个关于Android用户界面设计的教程，旨在帮助初学者理解和构建Android应用的UI。内容涵盖了Android UI的基本概念、组件、布局管理器以及Fragment的使用。" Android用户界面（UI）是任何Android应用程序的核心部分，它决定了应用的外观和用户体验。这份资料详细介绍了Android UI设计的各个方面，对于想要学习或提升Android UI设计技能的人来说是非常有价值的。首先，Android UI概述介绍了UI设计的基础，包括UI设计的重要性以及Android应用的结构和UI模式。在Android应用中，常见的UI模式有顶级视图（通常展示概览信息）和详细视图（用于展示特定信息的详细内容）。此外，ActionBar也是一个重要的组件，它提供了导航、操作和定制化的空间。接着，文档深入探讨了Android UI中的视图（Views）系统。视图是构成用户界面的基本元素，如TextView用于显示文本，ImageView用于显示图片，而输入控件如EditText则用于收集用户输入。理解并熟练使用这些组件是创建功能完备的UI的关键。同时，UI事件和监听器的处理也非常重要，它们允许应用响应用户的触摸和其他交互。在UI开发中，理解如何使用View和Adapter至关重要。ListView是展示可滚动列表数据的常用组件，通过适配器（Adapter）可以将数据绑定到视图中。这里还提到了ViewHolder模式，它提高了ListView的性能，减少了视图复用时的内存消耗。接下来，文档详细阐述了各种布局管理器，如LinearLayout（线性布局）、TableLayout（表格布局）、RelativeLayout（相对布局）、FrameLayout（帧布局）和GridLayout（网格布局）。每个布局都有其独特的用途，如LinearLayout用于按行或列排列视图，RelativeLayout允许视图相对于彼此或父容器定位，而GridLayout则按网格组织视图。同时，布局和多设备支持部分解释了如何确保UI在不同尺寸和分辨率的屏幕上都能正确显示。最后，资料涵盖了Fragments，这是Android中处理复杂UI和屏幕适应性的关键组件。Fragments有自己的生命周期，可以在Activity中独立存在和替换，这使得在平板电脑和手机上实现多屏体验成为可能。通过FragmentTransaction和FragmentManager，可以方便地管理Fragment的添加、移除和替换。这份Android-UI-Design教程涵盖了从基础组件到高级布局策略，再到Fragment的全面内容，是Android开发者构建高效、适应性强的UI的宝贵资源。

Android UI Design 9 / 132

Figure 1.7: screenshot

The best practices we have to follow are:

• Don’t use ﬁxed dimensions expressed in pixel, instead we should use dp.

• Provide several layout structures for different screen size, we can do it creating several layout ﬁles.

• Provide several bitmap with different resolution for different screen resolution. We can consider using 9-Patches-Drawables.

Moreover, Android provides a resource qualiﬁer mechanism that helps us to have more control on how the system select the

resource. Usually we can use:

<resource_name>_<qualiﬁer>

where the resource_name can be for example drawable or layout while the qualiﬁer can be hdpi, large and so on. Look here if

you want to have more information.

Even if we follow all the best practices to support multiple screen in our app, there might be some situations where they are

not enough, especially when we want to support smartphones and tablets. In this case, Android has introduced the Fragment

concept. Fragments are available since API 11 and there is a library to maintain the backward compatibility. We will cover

these topics in the next articles. Stay tuned!

Android UI Design 10 / 132

Chapter 2

Android UI: Understanding Views

2.1 Overview

In our previous chapter, we introduced some basic concepts about Android UI patterns and we saw how we can create consistent

UI following those patterns. In this article, we want to explore more about Views and how we can use them to build great user

interfaces. This article will cover concepts about Views and Adapters. Developing a user interface in Android can be quite

simple since we can describe them using XML ﬁles and the system will do the heavy work converting those in real user interface

components, placing them according to the screen size and resolution.

The Android UI framework provides some basic UI components, that are called controls or widgets, helping developers while

coding and building an app.

2.2 Views

The View class is the basic class that all the components extend. A View draws something on a piece of screen and it is

responsible to handle events while user interacts with it. Even the generic ViewGroup class extends View. A ViewGroup

is a special View that holds other views and places these views following some rules. We will see that Android provides some

specialized views that helps us to handle text, images, user inputs, buttons and so on.

All these views have some key aspects in common:

• All views have a set of properties: These properties affect the way the view is rendered. There is a set of properties common

to all views, while there are some other properties depending on the type of view.

• Focus: The system manages the focus on each view and depending on the user input, we can modify and force the focus on a

speciﬁc view.

• Listeners: All views have listeners which are used to handle events when the user interacts with the view. We can register our

app to listen to speciﬁc events that occur on a view.

• Visibility: We can control if a view is visible or not and we can change the view visibility at runtime too.

A view property is a key value pair that we can use to customize the view behavior. The property values can be:

• a number

• a string

• a reference to a value written somewhere else

Android UI Design 11 / 132

The ﬁrst two options are trivial, the third is the most interesting one because we can create a ﬁle (always in XML) that holds a

list of values and we can reference it in our property value. This is the best approach to follow especially when we use themes

and styles or we want to support multi-language apps.

One of the most important property is view id: this is a unique identiﬁer for the view and we can look up a speciﬁc view using

this id. This is a “static” property meaning we cannot change it once we have deﬁned it.

When we want to set a view property, we have two ways to do it:

• using XML while we deﬁne our view

• programmatically

For example, let’s suppose we want to deﬁne a TextView (it writes a text). In XML we have:

<TextView

android:id="@+id/textView1"

android:layout_width="wrap_content"

android:layout_height="wrap_content"

android:text="@string/hello_world" />

As you can notice, we deﬁned an id called textView1, some other properties that have a string values and another property called

android:text that reference a value written somewhere else.

We could do the same thing using just code lines:

TextView tv = new TextView(this);

tv.setText("blabla");

These two approaches are equivalent; however, the ﬁrst one in XML is the preferred one. There is a correspondence between

XML view property and the Java method: usually for each XML property there is a set method that we can use in our code. You

can look here to have more information about this correspondence. In XML, a view property is called attribute.

Two properties that play an important role are layout_width and layout_height. These two properties deﬁne how large

and how tall should be the view. We can use two predeﬁned values:

• MATCH_PARENT

• WRAP_CONTENT

With MATCH_PARENT value, we mean that we want our view as big as its parent that holds it, while with WRAP_CONTENT we

specify that our view must be big enough to hold its content.

There is another option: using a numeric value. In this case, we specify the exact measure of our view. In this case, the best

practice suggests using dp unit measure so that our view can be adapted to different screen density.

Talking about view listeners, this is a well-known approach when we want to be notiﬁed about some events. A listener in Java

is an interface that deﬁnes some methods, which our listener class must implement so that it can receive notiﬁcations when a

speciﬁc event occurs.

The Android SDK has several listener types, so different interfaces can be implemented. Two of the most popular are: View.

OnClickListener, View.OnTouchListener and so on.

Android provides several standard components and of course if we cannot ﬁnd a component that fulﬁlls our needs, we can always

implement a custom view. Using a custom view, we can deﬁne what our view will draw on the screen and its behaviour. We can

even deﬁne custom properties that affect the view’s behavior. In this case, we have to extend the basic View class and override

some methods.

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