Android：使用目标SDK？

Question

I understand that the minimum SDK defines a minimum required OS level for your application to run and that target SDK tells the device the highest API version you used features from, assuming backwards compatibility has been implemented.

But that's what I don't understand. How do you implement backwards compatibility for entirely new API features?

For example:

I've been using the old Notification system during development of my current app, not Notification.Builder. If I choose to use Notification.Builder, will the OS or compiler automatically replace this with compatible code for platforms previous to when this was introduced? Or do I have to check the OS version and write separate code?

Answer 1

You have to account for the new methods yourself, for example by using,

if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.HONEYCOMB) {
    // Use methods introduced in API 11. (i.e. Notification.Builder)
} else {
    // Use old methods to ensure backwards compatibility.
}

A nice place to put these checks is in a utility class (ie CompatUtils.java ). So for example, you might create a static method that takes a Context argument and returns a new Notification :

public static buildNotification(Context ctx) {
    if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.HONEYCOMB) {
        // Create and return the Notification using Notification.Builder
    } else {
        // Create and return the Notification using pre-HoneyComb methods
    }
}

Then simply call CompatUtils.buildNotification(this) within your Activity to create the new Notification . Abstracting out these sorts of details keeps your Activity concise, and is easily changeable if you ever need to later on.

Of course, it might be a better idea to just use the old methods to create your Notification , since you need to implement them anyway and the Notification.Builder is mostly just for convenience. Nonetheless, this is definitely something that you should keep in mind in case you run into similar issues later on!

---

Edit:

Notification.Builder is also provided in the Android Support Package, so you should just use that in this case... however, for methods that are not provided in the compatibility package, you should use the design pattern described above.

Answer 2

google has its own compatability packages (in the support library) and there are also other third party solutions (like actionBarSherlock) , and the Lint tool can tell you when you're trying to use a too-new feature that won't work on the API range you've set.

one way to check the API is using the android.os.Build.VERSION.SDK_INT . another way is by using reflection , which sometimes google uses (yet i'm not sure why) .

in any case , google suggests in its videos to always set the targetSdk to the highest one that there is, in order to improve the optimization of the output APK.