They insert text data of an arbitrary language—and an arbitrary text direction—into localized messages. This mixing of directions often doesn't include a clear indication of where opposite-direction text starts and ends. These characteristics of app-generated text cause most of the problems. Although the system's default handling of bidirectional text usually renders text as expected, it's possible that text won't render properly when your app inserts it into a localized message.
The following situations present examples of cases where it's more likely that text won't appear correctly:. Because the app supports different UI locales, the message comes from a locale-specific resource and uses the RTL direction when an RTL locale is in use.
For a Hebrew UI, it should appear as follows:. The suggestion, however, might come from a database that doesn't include text in the locale's language. For example, if the address in question is for a place in California, it appears in the database using English text.
If you insert the address "15 Bay Street, Laurel, CA" into the RTL message without providing any hints regarding text direction, the result isn't expected or correct:. Note that the house number appears to the right of the address, not to the left as intended, and makes the house number look more like a strange postal code.
The problem in previous example occurs because the text formatter doesn't specify that "15" is part of the address, so the system cannot determine whether the "15" is part of the RTL text that comes before it or the LTR text that comes after it.
To solve this problem, use the unicodeWrap method, found in the BidiFormatter class, on every piece of text that you insert into a localized message. The only times when you shouldn't use unicodeWrap include the following:. The unicodeWrap method detects the direction of a string and wraps it in Unicode formatting characters that declare that direction. Because the "15" now appears inside text that is declared as LTR, it's displayed in the correct position:.
The following code snippet demonstrates how to use unicodeWrap :. Note: If your app targets Android 4. Otherwise, use the version of BidiFormatter found in the Support Library. Use format strings , not method calls, to convert numbers to strings in your app's logic:. This will format the numbers appropriately for your locale, which may include using a different set of digits. When you use String. This is because the number is formatted in the locale's digits, and these digits are invalid in SQL.
The locale argument should be Locale. Support layout mirroring People who use RTL scripts prefer an RTL user interface, which includes right-aligned menus, right-aligned text, and forward arrows pointing to the left.
When adding RTL support to your app, it's particularly important to keep the following points in mind:. Note: To view additional design guidelines related to layout mirroring, including a list of elements that you should and shouldn't mirror, see the Bidirectionality material design guidelines.
Modify your app module's build. In this case, RTL layout mirroring doesn't happen automatically in your app. Convert left and right to start and end , respectively, in each of your existing layout resource files. By doing this, you allow the framework to align your app's UI elements based on the user's language settings. Note: Before updating your resources, learn how to provide support for legacy apps , or apps that target Android 4.
To use the framework's RTL alignment capabilities, change the attributes in your layout files that appear in Table 1. Table 1. Attributes to use when your app supports multiple text directions. Table 2 shows how the system handles UI alignment attributes based on the target SDK version, whether left and right attributes are defined, and whether start and end attributes are defined. Table 2. UI element alignment behavior based on the target SDK version and defined attributes.
This step involves adding specific versions of your layout, drawables, and values resource files that contain customized values for different languages and text directions. In Android 4.
To maintain backward compatibility with loading existing resources, older versions of Android use a resource's language qualifiers to infer the correct text direction. Suppose that you want to add a specific layout file to support RTL scripts, such as the Hebrew, Arabic, and Persian languages.
If you want to add a specific version of the layout that is designed for only Arabic text, your directory structure becomes the following:. Note: Language-specific resources take precedence over layout-direction-specific resources, which take precedence over the default resources.
As of Android 4. If your app targets Android 4. Note: To avoid compatibility issues, use version On devices running Android 4. This section describes specific places in your app's logic that you should update when adapting your app for handling multiple text directions. To handle a change in any RTL-related property—such as layout direction, layout parameters, padding, text direction, text alignment, or drawable positioning—you can use the onRtlPropertiesChanged callback.
This callback allows you to get the current layout direction and update an activity's View objects accordingly. If you are creating a UI widget that is not directly part of an activity's view hierarchy, such as a dialog or a toast-like UI element, set the correct layout direction depending on the context. The following code snippet demonstrates how to complete this process:.
Several methods of the View class require additional consideration:. If you have a drawable that needs to be mirrored for an RTL layout, complete one of these steps based on the version of Android running on the device:. On Android 4. Note: The android:autoMirrored attribute only works for simple drawables whose bidirectional mirroring is simply a graphical mirroring of the entire drawable.
If your drawable contains multiple elements, or if reflecting your drawable would change its interpretation, you should perform the mirroring yourself. Whenever possible, check with a bidirectional expert to determine whether your mirrored drawables make sense to users.
If your app's code is using Gravity. LEFT or Gravity. END , respectively. This means that you can keep your existing code that handles left-aligned and right-aligned values, even if you are using start and end for your gravity values.
Note: When applying your gravity settings, use an overloaded version of Gravity. To support RTL scripts in your app, follow these best practices related to margin and padding values:. Content and code samples on this page are subject to the licenses described in the Content License. App Basics. Build your first app. App resources. Resource types. App manifest file. Device compatibility. Multiple APK support.
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Package visibility. Intents and intent filters. User interface. Add motion to your layout with MotionLayout. MotionLayout XML reference. Dart is an open-source programing language that powers the Flutter framework, which is getting a lot of traction these days because of its ability to deliver beautiful and performance app for the web, desktop, and mobile in lesser time.
The key selling point of dart is that it is designed by Google as a client-optimized language for fast apps on any platform. Dart mainly focuses on making UI development easier for developers with features such as hot-reload, which lets developers see changes instantly while working on the app. Dart is also known for its fast performance, it compiles to ARM and x64 machine code for mobile, desktop, and backend.
And to JavaScript for the web apps. Bonus: Corona- Corona is a software development kit that can be used for developing Android apps using Lua. It has two operational modes, namely Corona Simulator and Corona Native. The Corona Simulator is used to build apps directly while the Corona Native is used to integrate the Lua code with an Android Studio project to build an app using native features.
While Lua is a little limited as compared to Java, it is also much simpler and has an easier learning curve.
Moreover, there are build in monetization features as well as various assets and plugins that enrich the app development experience. Corona is mostly used to create graphics applications and games but is by no means limited to that. And always remember, whatever your choice, it will only expand your skill set and lead to your growth as an Android developer. Skip to content. Change Language. Related Articles. Table of Contents. Improve Article.
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