When I have flashed a new ROM, I have to download all the apps I need in google play one by one, which is very inconvenient absolutely. Some of you may recommend "Titanium Backup", but it will lead to some errors with my device sometimes. So I want to download all my apps using google play in one time, instead of downloading my apps one by one. That is, I want google play to download and install all the apps in my previous ROM automatically after I have flashed a new ROM, Is that possible? Better if you have some more convenient methods. Thanks for any help!
You have two options.
Do a factory reset. Go to
Settings > Backup & reset > Factory data reset.
When you are asked to log-in your Google account, it will ask you if you want to download the apps you installed before. Usually, your paid apps will be installed (and possibly some of the free apps). You may have to manually install the others.
Or, you can always use Titanium Backup. Make sure to back-up only user apps, not system apps. Then, restore those user apps after you have flashed a new ROM.
Also, if the above doesn't work for you, or there are many apps that haven't been downloaded you can bulk install previously installed apps using the "My Apps" on the Play Store.
My Apps > All
Then press and hold on an app, and it will be selected. Apps that have already been installed onto your device will be greyed out.
You can then press on any other apps you want to install, then "Install" at the top right.