通过包名判断是否有装某个APP

####在app判断手机里面某个app是否安装，调用此方法即可，前提是要知道要判断点app的包名，像微信这类应用，百度一下就知道包名了

    private boolean isAppInstalled(Context context, String packagename) {

    PackageManager pm = context.getPackageManager();

     boolean installed = false;

> try {

> pm.getPackageInfo(packagename, PackageManager.GET_ACTIVITIES);

> installed = true;

. } catch (PackageManager.NameNotFoundException e) {

> installed = false;

> }

> return installed;

>}