New in ADT 20

• A lot of bug fixes, particularly in the Lint area.
• Performance and memory fixes (loading SDK data should be 30% faster.)
• A few new lint rules:
• Detect usages of Toast.makeText() without calling show() on the result, as well as passing invalid duration parameters (e.g. a number instead of one of the two allowed constants.)
• Detect incorrect manifest registrations (where elements such as <uses-library>, <activity> etc are placed under the wrong parent.)
• Several security checks: Look for exported content providers without required permissions, look for creation of world readable files and preferences, look for calls to  android.webkit.WebSettings.setJavaScriptEnabled.
• New property sheet in the layout editor which offers:
• Highlighting (in bold) for important attributes.
• Inline preview of colors and images, as well as the corresponding resource name.
• Displays default values, when available.
• Completion of resource values and enum and flag constants.
• Support for showing and hiding "advanced" properties.
• Nested properties (and collapse all and expand all) for better categorization. For example, layout params are listed first as a single nested property.
• Tooltips over the attribute names, not values, so they never obscure the value column.
• Checkbox support for boolean values.
• Support for switching between alphabetical and natural sort orders.
• More details here.
• Support XML editor outlines for layout files.
• Switching back and forth between the text editor and graphical editor will alternate between the two outlines, and in particular the XML editor outline will keep up to date with edits in the editor, and selection will follow the mouse cursor etc.
• SDK Manager:
• Cache to avoid downloading repository definitions all the time.
• New "Tools > Manage Add-on Sites" option that allows deactivating 3rd party sites (e.g. if one or more are temporarily slow to load.)
• Fixes in Ant:
• Test projects now have access to the full classpath from the tested projects, including Library Projects and 3rd party jar
• Applications embedding tests can now be deployed and tested, including with code coverage, like test applications.
• NDK support (alpha):
• Initial support for building and debugging projects with C/C++ code.
• To enable this, install the NDK feature (depends on CDT), and then set the path to NDK in Android Preferences.
• Add NDK nature to an Android project by right clicking on the project and select "Android Tools -> Add Native Support".
• To debug an NDK project, create a new debug configuration of type "Android Native Application".
• New in Preview 2:
• New window management in the layout editor (more details)
• New configuration chooser in the layout editor (more details)
• Lint-on-Save for Java files (more details)
• Lint check ensuring that when you edit() a SharedPreference object you call commit()
• Asset Studio Wizard support for padding and turning off background shapes
• More bug fixes
• New in Preview 3:
• Eclipse 4.x support: Previous releases of ADT 20 did not work well on Eclipse 4.x. As of Preview 3, the known critical issues (such as cut/copy/paste being broken in XML editors) have been fixed. Please let us know of any remaining ADT-specific issues with Eclipse 4.2.
• Build System
• Automatic merging of library project manifest files into the including project's manifest. Enable with the manifestmerger.enabled property.
• Automatic ProGuard support for the aapt -G flag. This means that the build system will generate a temporary ProGuard keep-rules file containing classes to keep that are referenced from XML files (such as custom views) and pass this to ProGuard at shrink-time. This can make the resulting APK much smaller when using just a small portion of a large library project (such as the Android Support library), since we have also removed the catch-all rules to keep all custom views from the default ProGuard configuration file.
• Execution
• LogCat:  Allow users to set colors for different priorities
• Allow running on multiple devices with a single launch. The target tab in the launch configuration dialog adds a new option which allows launching on all connected devices, and a drop down allows the user to further narrow down the list to just physical devices or just emulators. (This applies only to Run configurations, not to Debug/JUnit tests.)
• Lint
• Tighter integration of lint with the layout editor (more details).
• New lint checks:
• Check to make sure that Fragment classes are instantiatable. If you accidentally make a fragment innerclass non-static, or forget to have a default constructor, you can hit runtime errors when the system attempts to reinstantiate your fragment after a configuration change.
• Look for handler leaks: This check makes sure that a handler inner class does not hold an implicit reference to its outer class.
• Duplicate Activity registrations in the manifest. This can lead to subtle errors that can be difficult to understand.
• NDK
• Custom GDB configuration tab
• Add support for debugging on MIPS targets
• Add NDK debug launch shortcut ("Debug as Android Native Application")
• Improve the way the device chooser dialog is handled (should be shown less often)
• XML Editing
• Go to Declaration now works for theme references (?android:attr, ?attr: etc,)
• Improvements to code completion in style definitions
• Completion of the minSdkVersion and targetSdkVersion attributes in manifest files now include version descriptions for each of the API levels
• As of Preview 2, code completion includes custom attributes for custom views. In Preview 3, this is further fixed such that edits to the style files result in the code completion picking up recent edits.
• Settings for the SDK Manager download cache (SDK Manager > Tools > Options)
• More bugfixes

Installation

Updating the SDK

Installing the ADT plugins