安卓中級教程（2）：@InjectView中的對象inject

 package com.example.ele_me.util;

 import java.lang.annotation.Annotation;
 import java.lang.reflect.Field;

 import android.app.Activity;

 /**
  * Very lightweight form of injection, inspired by RoboGuice, for injecting common ui elements.
  * <p>
  * Usage is very simple. In your Activity, define some fields as follows:
  *
  * <pre class="code">
  * @InjectView(R.id.fetch_button)
  * private Button mFetchButton;
  * @InjectView(R.id.submit_button)
  * private Button mSubmitButton;
  * @InjectView(R.id.main_view)
  * private TextView mTextView;
  * </pre>
  * <p>
  * Then, inside your Activity's onCreate() method, perform the injection like this:
  *
  * <pre class="code">
  * setContentView(R.layout.main_layout);
  * Injector.get(this).inject();
  * </pre>
  * <p>
  * See the {@link #inject()} method for full details of how it works. Note that the fields are
  * fetched and assigned at the time you call {@link #inject()}, consequently you should not do this
  * until after you've called the setContentView() method.
  */
 public final class Injector {
     private final Activity mActivity;

     private Injector(Activity activity) {
         mActivity = activity;
     }
 //mActicity本身擁有獨立的變量，並賦值給class Injector，然而我們也可透過修改activity去改變mActivity。
     /**
      * Gets an {@link Injector} capable of injecting fields for the given Activity.
      */
     public static Injector get(Activity activity) {
         return new Injector(activity);
     }

     /**
      * Injects all fields that are marked with the {@link InjectView} annotation.
      * <p>
      * For each field marked with the InjectView annotation, a call to
      * {@link Activity#findViewById(int)} will be made, passing in the resource id stored in the
      * value() method of the InjectView annotation as the int parameter, and the result of this call
      * will be assigned to the field.
      *
      * @throws IllegalStateException if injection fails, common causes being that you have used an
      *             invalid id value, or you haven't called setContentView() on your Activity.
      */
     public void inject()
 //inject等待被另一個Java檔召喚。
  {
         for (Field field : mActivity.getClass().getDeclaredFields())
 //Field是一個對象類型，其作用等同於findViewById一樣，在於捕捉其對象。而下面的for迴圈則為了去捕捉對象所需要運用到的算式。
 {
             for (Annotation annotation : field.getAnnotations()) {
                 if (annotation.annotationType().equals(InjectView.class)) {
                     try {
                         Class<?> fieldType = field.getType();
                         int idValue = InjectView.class.cast(annotation).value();
                         field.setAccessible(true);
                         Object injectedValue = fieldType.cast(mActivity.findViewById(idValue));
                         if (injectedValue == null) {
                             throw new IllegalStateException("findViewById(" + idValue
                                     + ") gave null for " +
                                     field + ", can't inject");
                         }
                         field.set(mActivity, injectedValue);
                         field.setAccessible(false);
                     } catch (IllegalAccessException e) {
                         throw new IllegalStateException(e);
                     }
                 }
             }
         }
     }
 }

這是一個必須複製的編碼。我們必須重新開一個Java檔案去讓injectView運行，injectView本身並不會獨自地去尋找對象，而是透過injectView Inject()去運算，並且尋找對象。