Android Screen sizes
Supporting Multiple Screens ( ภาษาไทย ด้านล่าง )
Android runs on a variety of devices that offer different screen sizes and densities. For applications, the Android system provides a consistent development environment across devices and handles most of the work to adjust each application's user interface to the screen on which it is displayed. At the same time, the system provides APIs that allow you to control your application's UI for specific screen sizes and densities, in order to optimize your UI design for different screen configurations. For example, you might want a UI for tablets that's different from the UI for handsets.Although the system performs scaling and resizing to make your application work on different screens, you should make the effort to optimize your application for different screen sizes and densities. In doing so, you maximize the user experience for all devices and your users believe that your application was actually designed for their devices—rather than simply stretched to fit the screen on their devices.
By following the practices described in this document, you can create an application that displays properly and provides an optimized user experience on all supported screen configurations, using a single
.apk file.
แม้ว่าระบบจะทำการปรับขนาดเพื่อให้การทำงานของโปรแกรมประยุกต์ของคุณบนหน้าจอที่แตกต่างกัน แต่คุณควรปรับแต่งหน้าจอให้เหมาะสม กับแอพลิเคชันของคุณสำหรับขนาดหน้าจอที่แตกต่างกัน คุณควรจะทำให้ผู้ใช้เสมือนว่า คุณออกแบบหน้าจอให้เหมาะสมกับอุปกรณ์ของผู้ใช้จริงๆ -แทนที่จะใช้วิธียืด หรือขยายหน้าจอ เพื่อเพียงให้พอดีกับหน้าจอกับอุปกรณ์ของพวกเขา
ในเอกสารนี้ ได้แสดงวิธีที่คุณสามารถสร้างโปรแกรมประยุกต์ที่จะแสดงผลได้อย่างถูกต้อง สำหรับหน้าจอความละเอียดต่างๆ โดยใช้ไฟล์ .APK เพียงไฟล์เดียว
Overview of Screens Support
This section provides an overview of Android's support for multiple screens, including: an
introduction to the terms and concepts used in this document and in the API, a summary of the screen
configurations that the system supports, and an overview of the API and underlying
screen-compatibility features.Terms and concepts
- Screen size
- Actual physical size, measured as the screen's diagonal. For simplicity, Android groups all actual screen sizes into four generalized sizes: small, normal, large, and extra large.
- Screen density
- The quantity of pixels within a physical area of the screen; usually referred to as dpi (dots
per inch). For example, a "low" density screen has fewer pixels within a given physical area,
compared to a "normal" or "high" density screen.
For simplicity, Android groups all actual screen densities into four generalized densities:
low, medium, high, and extra high.
- Orientation
- The orientation of the screen from the user's point of view. This is either landscape or
portrait, meaning that the screen's aspect ratio is either wide or tall, respectively. Be aware
that not only do different devices operate in different orientations by default, but the
orientation can change at runtime when the user rotates the device.
- Resolution
- The total number of physical pixels on a screen. When adding support for multiple screens, applications do not work directly with resolution; applications should be concerned only with screen size and density, as specified by the generalized size and density groups.
- Density-independent pixel (dp)
- A virtual pixel unit that you should use when defining UI layout, to express layout dimensions
or position in a density-independent way.
The density-independent pixel is equivalent to one physical pixel on a 160 dpi screen, which is
the baseline density assumed by the system for a "medium" density screen. At runtime, the system
transparently handles any scaling of the dp units, as necessary, based on the actual density of the
screen in use. The conversion of dp units to screen pixels is simple:
px = dp * (dpi / 160)
Range of screens supported
Starting with Android 1.6 (API Level 4), Android provides support for multiple screen sizes and densities, reflecting the many different screen configurations that a device may have. You can use features of the Android system to optimize your application's user interface for each screen configuration and ensure that your application not only renders properly, but provides the best user experience possible on each screen.To simplify the way that you design your user interfaces for multiple screens, Android divides the range of actual screen sizes and densities into:
- A set of four generalized sizes: small, normal,
large,
and xlarge
Note: Beginning with Android 3.2 (API level 13), these size groups are deprecated in favor of a new technique for managing screen sizes based on the available screen width. If you're developing for Android 3.2 and greater, see Declaring Tablet Layouts for Android 3.2 for more information.
- A set of four generalized densities: ldpi (low), mdpi (medium), hdpi (high), and xhdpi (extra high)
Each generalized size and density spans a range of actual screen sizes and densities. For example, two devices that both report a screen size of normal might have actual screen sizes and aspect ratios that are slightly different when measured by hand. Similarly, two devices that report a screen density of hdpi might have real pixel densities that are slightly different. Android makes these differences abstract to applications, so you can provide UI designed for the generalized sizes and densities and let the system handle any final adjustments as necessary. Figure 1 illustrates how different sizes and densities are roughly categorized into the different size and density groups.
เพื่อความง่ายในออกแบบส่วนติดต่อผู้ใช้ของคุณสำหรับหลายหน้าจอ, Android แบ่งช่วงของขนาดหน้าจอที่เกิดขึ้นจริงและมีความหนาแน่นเป็นดังนี้:
- 4 ขนาดหน้าจอ: small, normal, large, and xlarge
- ความละเอียด : ldpi (ต่ำ), mdpi (ขนาดกลาง) hdpi (สูง), และ xhdpi (สูงพิเศษ)
รูปที่ 1 แสดงความแตกต่างกันของขนาดหน้าจอและความหนาแน่นมีการแบ่งประเภทเป็นขนาดและความหนาแน่นที่แตกต่างกัน
Figure 1.
Illustration of how Android roughly maps actual sizes and densities
to generalized sizes and densities (figures are not exact).
As you design your UI for different screen sizes, you'll discover that each design requires a
minimum amount of space. So, each generalized screen size above has an associated minimum
resolution that's defined by the system. These minimum sizes are in "dp" units—the same units
you should use when defining your layouts—which allows the system to avoid worrying about
changes in screen density.- xlarge screens are at least 960dp x 720dp
- large screens are at least 640dp x 480dp
- normal screens are at least 470dp x 320dp
- small screens are at least 426dp x 320dp
Note: These minimum screen sizes were not as well defined prior to
Android 3.0, so you may encounter some devices that are mis-classified between normal and large.
These are also based on the physical resolution of the screen, so may vary across devices—for
example a 1024x720 tablet with a system bar actually has a bit less space available to the
application due to it being used by the system bar.
To optimize your application's UI for the different screen sizes and densities, you can provide
alternative
resources for any of the generalized sizes and densities. Typically, you should
provide alternative layouts for some of the different screen sizes and alternative bitmap images for
different screen densities. At runtime, the system uses the appropriate resources
for your application, based on the generalized size or density of the current device screen.You do not need to provide alternative resources for every combination of screen size and density. The system provides robust compatibility features that can handle most of the work of rendering your application on any device screen, provided that you've implemented your UI using techniques that allow it to gracefully resize (as described in the Best Practices, below).
Note: The characteristics that define a device's generalized screen
size and density are independent from each other. For example, a WVGA high-density screen is
considered a normal size screen because its physical size is about the same as the T-Mobile G1
(Android's first device and baseline screen configuration). On the other hand, a WVGA medium-density
screen is considered a large size screen. Although it offers the same resolution (the same number of
pixels), the WVGA medium-density screen has a lower screen density, meaning that each pixel is
physically larger and, thus, the entire screen is larger than the baseline (normal size) screen.
Density independence
Your application achieves "density independence" when it preserves the physical size (from the user's point of view) of user interface elements when displayed on screens with different densities.Maintaining density independence is important because, without it, a UI element (such as a button) appears physically larger on a low density screen and smaller on a high density screen. Such density-related size changes can cause problems in your application layout and usability. Figures 2 and 3 show the difference between an application when it does not provide density independence and when it does, respectively.
Figure 2. Example application without support for
different densities, as shown on low, medium, and high density screens. 
Figure 3. Example application with good support for
different densities (it's density independent), as shown on low, medium, and high
density screens.
The Android system helps your application achieve density independence in two ways: - The system scales dp units as appropriate for the current screen density
- The system scales drawable resources to the appropriate size, based on the current screen density, if necessary
px
units), so the views are physically larger on a low density screen and smaller on a high density
screen. This is because although the actual screen sizes may be the same, the high density screen
has more pixels per inch (the same amount of pixels fit in a smaller area). In figure 3, the layout
dimensions are specified in density-independent pixels (dp units). Because the baseline for
density-independent pixels is a medium-density screen, the device with a medium-density screen looks
the same as it does in figure 2. For the low-density and high-density screens, however, the system
scales the density-independent pixel values down and up, respectively, to fit the screen as
appropriate.In most cases, you can ensure density independence in your application simply by specifying all layout dimension values in density-independent pixels (
dp units) or with "wrap_content", as appropriate. The system then scales bitmap drawables as appropriate in order to
display at the appropriate size, based on the appropriate scaling factor for the current screen's
density.However, bitmap scaling can result in blurry or pixelated bitmaps, which you might notice in the above screenshots. To avoid these artifacts, you should provide alternative bitmap resources for different densities. For example, you should provide higher-resolution bitmaps for high-density screens and the system will use those instead of resizing the bitmap designed for medium-density screens. The following section describes more about how to supply alternative resources for different screen configurations.
Android example code ตัวอย่าง Android Code
http://androidcodeexample.blogspot.com/Android Control ควบคุมอุปกรณ์ต่างๆ ด้วย Android
http://androidcontrol.blogspot.com
สอนเขียน Android สอนเขียนโปรแกรม Android
http://androidcontrol.blogspot.com/2012/01/beginning-android-training-android.html
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