最近在树莓派上需要安装libgtk2.0-dev，执行如下命令：
$ sudo apt-get install libgtk2.0-dev
出错信息如下：
Reading package lists... Done
Building dependency tree
Reading state information... Done
Some packages could not be installed. This may mean that you have
requested an impossible situation or if you are using the unstable
distribution that some required packages have not yet been created
or been moved out of Incoming.
The following information may help to resolve the situation:
The following packages have unmet dependencies:
libgtk2.0-dev : Depends: libpango1.0-dev (>= 1.20) but it is not going to be installed
Depends: libcairo2-dev (>= 1.6.4-6.1) but it is not going to be installed
E: Unable to correct problems, you have held broken packages.
根据出错信息，明显是软件源中出现了安装包缺失的问题。这个现象是不应该出现的。网上查询了不少地方，最终找到解决方法：
$ sudo vim /etc/apt/sources.list.d/raspi.list
可以看到如下内容：
#deb http://archive.raspberrypi.org/debian/ stretch main ui staging # Uncomment line below then 'apt-get update' to enable 'apt-get source' #deb-src http://archive.raspberrypi.org/debian/ stretch main ui
默认里面的内容都是被注释掉的，我们需要做的就是把这个源打开即可。
也可以直接执行如下命令来开启：
#先备份配置文件 $ sudo cp /etc/apt/sources.list.d/raspi.list /etc/apt/sources.list.d/raspi.list.bak $ sudo sed -i "s/^\#deb/deb/g" /etc/apt/sources.list.d/raspi.list