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Android development.md

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Android development

  • Use the Linkify class or any TextView's autoLink attribute to make links, email addresses and phone numbers clickable in your TextView.
  • Never change the class name or package name of your default Activity that is started by the launcher. It will break home screen shortcuts. If you really need to change your default Activity's class name or package name, add an alias with the old name for compatibility.
  • Always create one keystore per app for signing your APKs. Otherwise, when selling an app, you'll have to hand over the shared keystore.
  • The ratio for Android's density buckets from ldpi to *hdpi is 3:4:6:8:12:16.
  • Apart from the normal android:textColor, you can also set android:textColorHint, android:textColorLink and android:textColorHighlight for a TextView.
  • When using an ListView or GridView (or any other AbsListView) and the Adapter has items of varying height, you must set android:smoothScrollbar="false" on the View in XML. While the scrollbar will not run smoothly anymore, it will have a fixed height and doesn't change its size all the time anymore.
  • If you want to make the background of a View transparent, either for design or performance reasons, use android:background="@null" in XML or View.setBackgroundDrawable(null) in Java.
  • When adding new permissions into permission groups that have already been accepted by the user, Google Play will not require the user to review the new permissions. In the Android source code, you can look up which permissions belong to the same groups. Just search for the <permission android:name="<PERMISSION_NAME>" string and check the android:permissionGroup attribute.
  • If you want to find all URLs in your custom code, search for the regex :\/\/(?!schemas\.android\.com|www\.w3\.org|ns\.adobe.com).
  • In order to inspect a third-party (closed-source) APK, for example to see the required permissions, run <ANDROID_SDK_PATH>/build-tools/<VERSION>/aapt.exe l -a <APK_PATH>.apk and optionally pipe the results to grep, etc.

Keystores and APK signing

Requirements

  • Java Development Kit (JDK) with keytool
  • the command line interface

Guidelines

  • Use the RSA algorithm for the key algorithm (-keyalg)
  • Use 2048+ bits for the key size (-keysize)
  • Use 25+ years (convert to days) for the validity (-validity)
  • Use a unique keystore per app
  • Use strong passwords

How-to

  1. Open the command line interface
  2. Add the keytool location to your path or prepend it to the following command
  3. Run keytool -genkey -v -keystore <APP_NAME>.keystore -alias <APP_NAME> -dname "CN=<COMPANY_NAME>,OU=IT,O=<COMPANY_NAME>,L=Unknown,ST=Unknown,C=<COUNTRY_CODE>" -keyalg RSA -keysize 2048 -validity 13149 where you replace <APP_NAME> with the name of your app ([a-z]{1,8}), <COMPANY_NAME> with the name of your company and <COUNTRY_CODE> with your country code (ISO-3166 alpha-2)
  4. Enter your new store password ("outer password")
  5. Enter your new key password ("inner password")

Where do I find the keytool?

  • Windows: <PATH_TO_JDK>\bin\keytool.exe

Why do I need a secure key?

If a third party should manage to take your key without your knowledge or permission, that person could sign and distribute applications that maliciously replace your authentic applications or corrupt them. Such a person could also sign and distribute applications under your identity that attack other applications or the system itself, or corrupt or steal user data. Your reputation as a developer entity depends on your securing your private key properly, at all times, until the key is expired.

Source: http://developer.android.com/tools/publishing/app-signing.html

What if I lose the key?

Your private key is required for signing all future versions of your application. If you lose or misplace your key, you will not be able to publish updates to your existing application. You cannot regenerate a previously generated key.

Source: http://developer.android.com/tools/publishing/app-signing.html