Android 小手段

查看签名

很多开发者服务都需要绑定签名信息，用下面的命令可以查看签名：

 keytool -list -v -keystore release.jks
 

单例模式(懒汉式)的更好的写法

1.JDK1.5就引入volatile关键字，所以有了一种更好的双重校验锁写法：

 public class Singleton {
 private volatile static Singleton singleton;
 private Singleton (){}
 public static Singleton getSingleton() {
 if (singleton == null) {
 synchronized (Singleton.class) {
 if (singleton == null) {
 singleton = new Singleton();
 }
 }
 }
 return singleton;
 }
 }

注意，别忘记volatile关键字哦，否则就是10重，100重也可能还是会出问题。
2.另外一种静态内部类写法更推荐：

 publlic class Singleton {
 private Singleton() {}
 private static class SingletonLoader {
 private static final Singleton INSTANCE = new Singleton();
 }
 public static Singleton getInstance() {
 return SingletonLoader.INSTANCE;
 }
 }
 

ListView的局部刷新

有的列表可能notifyDataSetChanged()代价有点高，最好能局部刷新。局部刷新的重点是，找到要更新的那项的View，然后再根据业务逻辑更新数据即可。

 private void updateItem(int index) {
 int visiblePosition = listView.getFirstVisiblePosition();
 if (index - visiblePosition >= 0) {
 //得到要更新的item的view
 View view = listView.getChildAt(index - visiblePosition);
 // 更新界面（示例参考）
 // TextView nameView = ViewLess.$(view, R.id.name);
 // nameView.setText("update " + index);
 // 更新列表数据（示例参考）
 // list.get(index).setName("Update " + index);
 }
 }
 

系统内置的一些工具类

// 系统
 ./android/database/DatabaseUtils.java
 ./android/transition/TransitionUtils.java
 ./android/view/animation/AnimationUtils.java
 ./android/view/ViewAnimationUtils.java
 ./android/webkit/URLUtil.java
 ./android/bluetooth/le/BluetoothLeUtils.java
 ./android/gesture/GestureUtils.java
 ./android/text/TextUtils.java
 ./android/text/format/DateUtils.java
 ./android/os/FileUtils.java
 ./android/os/CommonTimeUtils.java
 ./android/net/NetworkUtils.java
 ./android/util/MathUtils.java
 ./android/util/TimeUtils.java
 ./android/util/ExceptionUtils.java
 ./android/util/DebugUtils.java
 ./android/drm/DrmUtils.java
 ./android/media/ThumbnailUtils.java
 ./android/media/ImageUtils.java
 ./android/media/Utils.java
 ./android/opengl/GLUtils.java
 ./android/opengl/ETC1Util.java
 ./android/telephony/PhoneNumberUtils.java
 // 设计和支持库
 ./design/src/android/support/design/widget/ViewGroupUtils.java
 ./design/src/android/support/design/widget/ThemeUtils.java
 ./design/src/android/support/design/widget/ViewUtils.java
 ./design/lollipop/android/support/design/widget/ViewUtilsLollipop.java
 ./design/base/android/support/design/widget/AnimationUtils.java
 ./design/base/android/support/design/widget/MathUtils.java
 ./design/honeycomb/android/support/design/widget/ViewGroupUtilsHoneycomb.java
 ./v7/recyclerview/src/android/support/v7/widget/helper/ItemTouchUIUtil.java
 ./v7/recyclerview/src/android/support/v7/widget/helper/ItemTouchUIUtilImpl.java
 ./v7/recyclerview/src/android/support/v7/util/MessageThreadUtil.java
 ./v7/recyclerview/src/android/support/v7/util/AsyncListUtil.java
 ./v7/recyclerview/src/android/support/v7/util/ThreadUtil.java
 ./v7/recyclerview/tests/src/android/support/v7/widget/AsyncListUtilLayoutTest.java
 ./v7/recyclerview/tests/src/android/support/v7/util/AsyncListUtilTest.java
 ./v7/recyclerview/tests/src/android/support/v7/util/ThreadUtilTest.java
 ./v7/appcompat/src/android/support/v7/graphics/drawable/DrawableUtils.java
 ./v7/appcompat/src/android/support/v7/widget/DrawableUtils.java
 ./v7/appcompat/src/android/support/v7/widget/ThemeUtils.java
 ./v7/appcompat/src/android/support/v7/widget/ViewUtils.java
 ./v4/tests/java/android/support/v4/graphics/ColorUtilsTest.java
 ./v4/jellybean-mr1/android/support/v4/text/TextUtilsCompatJellybeanMr1.java
 ./v4/jellybean/android/support/v4/app/BundleUtil.java
 ./v4/jellybean/android/support/v4/app/NavUtilsJB.java
 ./v4/java/android/support/v4/app/NavUtils.java
 ./v4/java/android/support/v4/database/DatabaseUtilsCompat.java
 ./v4/java/android/support/v4/graphics/ColorUtils.java
 ./v4/java/android/support/v4/text/TextUtilsCompat.java
 ./v4/java/android/support/v4/util/TimeUtils.java
 ./v4/java/android/support/v4/util/DebugUtils.java
 ./v4/java/android/support/v4/content/res/TypedArrayUtils.java
 

dpi文件夹的换算比例

之前的ldpi基本可以抛弃了，主流的dpi已经从很早之前的mdip转移到了xhdpi了，特别提醒。
PPI RESOLUTION DP PX
mdpi(160dp) 320P 1 1
hdpi(240dp) 480P 1 1.5
xhdpi(320dp) 720P 1 2
xxhdpi(480dpi) 1080P 1 3

Monkey参数

跑monkey的参数设置有一些要注意的地方，比如太快了不行不切实际，太慢了也不行等等，这里给出一个参考：

 adb shell monkey -p -s 1000 --ignore-crashes --ignore-timeouts --ignore-security-exceptions --pct-trackball 0 --pct-nav 0 --pct-majornav 0 --pct-anyevent 0 -v --throttle 300 1200000000
 

~20160523