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@mdesoto
Forked from konmik/gist:6ac725fa7134402539c4
Created February 18, 2016 22:33
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Dagger 2 injection with inheritance
/**
* This class allows to inject into objects through a base class,
* so we don't have to repeat injection code everywhere.
*
* The performance drawback is about 0.013 ms per injection on a very slow device,
* which is negligible in most cases.
*
* Example:
* <pre>{@code
* Component {
* void inject(B b);
* }
*
* class A {
* void onCreate() {
* componentReflectionInjector.inject(this);
* }
* }
*
* class B extends A {
* @Inject MyDependency dependency;
* }
*
* new B().onCreate() // dependency will be injected at this point
*
* class C extends B {
*
* }
*
* new C().onCreate() // dependency will be injected at this point as well
* }</pre>
*
* @param <T> a type of dagger 2 component.
*/
public final class ComponentReflectionInjector<T> implements Injector {
private final Class<T> componentClass;
private final T component;
private final HashMap<Class<?>, Method> methods;
public ComponentReflectionInjector(Class<T> componentClass, T component) {
this.componentClass = componentClass;
this.component = component;
this.methods = getMethods(componentClass);
}
public T getComponent() {
return component;
}
@Override
public void inject(Object target) {
Class targetClass = target.getClass();
Method method = methods.get(targetClass);
while (method == null && targetClass != null) {
targetClass = targetClass.getSuperclass();
method = methods.get(targetClass);
}
if (method == null)
throw new RuntimeException(String.format("No %s injecting method exists in %s component", target.getClass(), componentClass));
try {
method.invoke(component, target);
}
catch (Exception e) {
throw new RuntimeException(e);
}
}
private static final ConcurrentHashMap<Class<?>, HashMap<Class<?>, Method>> cache = new ConcurrentHashMap<>();
private static HashMap<Class<?>, Method> getMethods(Class componentClass) {
HashMap<Class<?>, Method> methods = cache.get(componentClass);
if (methods == null) {
synchronized (cache) {
methods = cache.get(componentClass);
if (methods == null) {
methods = new HashMap<>();
for (Method method : componentClass.getMethods()) {
Class<?>[] params = method.getParameterTypes();
if (params.length == 1)
methods.put(params[0], method);
}
cache.put(componentClass, methods);
}
}
}
return methods;
}
}
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