在app判断手机里面某个app是否安装，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;
}