单独用eclipse打开一个工程，出现SystemProperties.get()会出现SystemProperties cannot be resolved.错误
1. 引用SystemProperties.get()会出现SystemProperties cannot be resolved.
解决方法:
在当前工程属性(Properties) -> Java Build Path -> Libraries
点击Add External JARs...按钮， 选择layoutlib.jar文件，然后在项目源文件中增加import android.os.SystemProperties;
layoutlib.jar文件位于: android sdk/platforms/android-*.*/data目录下.
layoutlib.jar项目是从外部导入Eclipse中的，只要一编译，就会报错：Conversion to Dalvik format failed: Unable to execute dex: null , 同时Eclipse也变的很卡，好几次都挂掉了.
解决
1：设置内存
eclipse.exe的快捷方式——右键/属性 在 目标 里填写如下内容
"D:/eclipse/eclipse.exe" -vmargs -Xms128M -Xmx512M -XX:PermSize=64M -XX:MaxPermSize=128M
双引号内 为eclipse的安装路径。
如果1不行：
应该采用用户库的形式导入该库，具体步骤如下：
1. Right-click the project in Eclipse and select "Build Path -> Add Libraries...".
2. Select User Library from the list and click Next.
3. Click the "User Libraries..." button.
4. Click "New..." in the User Libraries dialog.
5. Give the user library a name and select the System library checkbox and click OK.
6. Highlight the newly added user library in the list and click the "Add JARs..." button and add the desired jar files.
7. Click OK on the User Libraries dialog.
8. Make sure the new user library is checked in the Add Library dialog and
用到我自己的项目上去。编译OK。
如果还是有红色叉叉，则选择java build path --》order and export把自己导入的包放到android的包前面即可