【Abstract】： The use of the intelligent mobile phone is quite extensive， it ushered in a new era of interaction design. To adapt to the development of APP is also now， such as bamboo shoots after a spring rain， emerge in an endless stream， constantly upgrading. But how to make high quality， excellent interactive experience， APP has become a problem worth discussing. In this paper， the interface and operation in APP design are discussed from the principles of APP design， UI interface design in order to present some inspiration and guidance.

【Keywords】： interface design， APP， service，

Introduction

Good design is good experience， this is particularly important for the APP designs. IIf you want to stand out from large number of products and to be successful， the most important point is to enhance the user experience.Good user experience derived from the appropriate software of human-computer interaction， logic operation， the nice overall design of the interface.Early in the development of a APP， you should pay attention to choose experienced development team， and master the principle of UI design.

There are many constrains in mobile web design， such as small dimension for less functional keys， small display screen for less information and navigation space， small capacity for less micro-processing and memory volume.

User interface design （UID） or user interface engineering is the design of user interfaces for machines and software， such as computers， home appliances， mobile devices， and other electronic devices， with the focus on maximizing the user experience. The goal of user interface design is to make the user's interaction as simple and efficient as possible， in terms of accomplishing user goals （user-centered design）.

The principles of APP design

2.1 Summarizing the prior design

When it comes to the flat UI design， there are a couple of key characteristics that you need to be aware of. First， there is ZERO use of effects such as shadowing that creates a depth effect. Second， flat UI designs are usually clean with crisp lines and bold colors. Third， words are often the focus as the overall UI has a minimalist look about it. From the above interface designs， it can be carried out the 2 aspects principles.

2.2 The clarity

Clarity is job.Clarity is the first and most important job of any interface. To be effective using an interface you've designed， people must be able to recognize what it is， care about why they would use it， understand what the interface is helping them interact with， predict what will happen when they use it， and then successfully interact with it. While there is room for mystery and delayed gratification in interfaces， there is no room for confusion. Clarity inspires confidence and leads to further use. One hundred clear screens is preferable to a single cluttered one.

The user interface design sources

3.1 User interface design requires a good understanding of user needs

There are several phases and processes in the user interface design， some of which are more demanded upon than others， depending on the project.

Functionality requirements gathering – assembling a list of the functionality required by the system to accomplish the goals of the project and the potential needs of the users.

User and task analysis – a form of field research， it's the analysis of the potential users of the system by studying how they perform the tasks that the design must support， and conducting interviews to elucidate their goals.Typical questions involve：

What would the user want the system to do？

How would the system fit in with the user's normal workflow or daily activities？

How technically savvy is the user and what similar systems does the user already use？

What interface look amp; feel styles appeal to the user？

Prototyping – development of wire-frames， either in the form of paper prototypes or simple interactive screens. These prototypes are stripped of all look amp; feel elements and most content in order to concentrate on the interface.

Usability inspection – letting an evaluator inspect a user interface. This is generally considered to be cheaper to implement than usability testing （see step below）， and can be used early on in the development process since it can be used to evaluate prototypes or specifications for the system， which usually can't be tested on users. Some common usability inspection methods include cognitive walkthrough， which focuses the simplicity to accomplish tasks with the system for new users， heuristic evaluation， in which a set of heuristics are used to identify usability problems in the UI design， and pluralistic walkthrough， in which a selected group of people step through a task scenario and discuss usability issues.

3.2 The dynamic characteristics of a system

Which are described in terms of the dialogue requirements contained in seven principles of part 10 of the ergonomics standard， the ISO 9241. This standard establishes a framework of ergonomic \"principles\" for the dialogue techniques with high-level definitions and illustrative applications and examples of the principles. The principles of the dialogue represent the dynamic aspects of the interface and can be mostly regarded as the \"feel\" of the interface. The seven dialogue principles are：

Suitability for the task： the dialogue is suitable for a task when it supports the user in the effective and efficient completion of the task.

Self-descriptiveness： the dialogue is self-descriptive when each dialogue step is immediately comprehensible through feedback from the system or is explained to the user on request.

Controllability： the dialogue is controllable when the user is able to initiate and control the direction and pace of the interaction until the point at which the goal has been met.

Conformity with user expectations： the dialogue conforms with user expectations when it is consistent and corresponds to the user characteristics， such as task knowledge， education， experience， and to commonly accepted conventions.

Error tolerance： the dialogue is error tolerant if despite evident errors in input， the intended result may be achieved with either no or minimal action by the user.