反射对Android有用吗？

Question

I learnt a bit about reflection after reading about it in some tpics here. From what I understands, it is used to check the avaibility of a certain class/method/field at runtime. But is it really useful in Android ? Android provide us with the api version at runtime and we can know if a particular class/method or field is available by reading the Android doc (or with error message with Android Studio).

I understand how it can be useful with Java in general, but is there any meaning to use it in Android?

Answer 1

Reflection (in every languages) is very powerful.

In Android most of time reflection is not needed, because you can find Security Exceptions, problems. It depends on what You do.

If you use undocumented classes, libs, you can use it, and it's very useful.

Sometimes, to do particular things, like turn on/off 3g on old device, change device language, you need rooted device to use reflection.

Finally, depends always on what You do.

Answer 2

Sometimes it works , and some times it does't work .

ET work example : You can reflect the method to hang off a phone call (there are a lot example codes on Internet so I won't copy the code.).

Doesn't work example: If you want to switch data connect status , use reflection works on 4.4 but will not work on 5.0 because it's a binder connection, the BN will check Permission the app granted , but this permission only granted to system app . So if your app is a third part app,on 5.0 you can't use reflection to switch data connect status.

Hope that helps

Answer 3

This is a very general question, it really depends on what you're trying to do. Sometimes you have to use reflection, if the APIs are hidden, all depends on your use case, generally you should avoid reflection as it complicates your code more than its needs to be and its potentially unsafe for further versions of android.

Answer 4

In my opinion it's a good to way to do particular things. For example you can use the methods of PowerProfile class to do a simple power model for your phone.

By the method getAveragePower(POWER_WIFI_SCAN) you can take the average current in mA consumed by the subsystem (in this case: wi-fi during scan).

So to use PowerProfile's methods for get your battery capacity you you could use java reflection in this way:

private Object mPowerProfile_;
private static final String POWER_PROFILE_CLASS = "com.android.internal.os.PowerProfile";
private Double batteryCapacity = Double.valueOf(1);

public Double getBatteryCapacity(Context ctx) {

    try {
mPowerProfile_ = Class.forName(POWER_PROFILE_CLASS).getConstructor(Context.class).newInstance(this);
    } catch (InstantiationException e) {
        e.printStackTrace();
    } catch (IllegalAccessException e) {
        e.printStackTrace();
    } catch (InvocationTargetException e) {
        e.printStackTrace();
    } catch (NoSuchMethodException e) {
        e.printStackTrace();
    } catch (ClassNotFoundException e) {
        e.printStackTrace();
    }

try {
batteryCapacity = (Double) Class.forName(POWER_PROFILE_CLASS).getMethod("getAveragePower", String.class).invoke(mPowerProfile_, "battery.capacity");
            } catch (IllegalAccessException e) {
                e.printStackTrace();
            } catch (InvocationTargetException e) {
                e.printStackTrace();
            } catch (NoSuchMethodException e) {
                e.printStackTrace();
            } catch (ClassNotFoundException e) {
                e.printStackTrace();
            }
}