安卓中級教程（2）：@InjectView中的對象inject

標籤：

 1 package com.example.ele_me.util; 2  3 import java.lang.annotation.Annotation; 4 import java.lang.reflect.Field; 5  6 import android.app.Activity; 7  8 /** 9  * Very lightweight form of injection, inspired by RoboGuice, for injecting common ui elements.10  * <p>11  * Usage is very simple. In your Activity, define some fields as follows:12  *13  * <pre class="code">14  * @InjectView(R.id.fetch_button)15  * private Button mFetchButton;16  * @InjectView(R.id.submit_button)17  * private Button mSubmitButton;18  * @InjectView(R.id.main_view)19  * private TextView mTextView;20  * </pre>21  * <p>22  * Then, inside your Activity‘s onCreate() method, perform the injection like this:23  *24  * <pre class="code">25  * setContentView(R.layout.main_layout);26  * Injector.get(this).inject();27  * </pre>28  * <p>29  * See the {@link #inject()} method for full details of how it works. Note that the fields are30  * fetched and assigned at the time you call {@link #inject()}, consequently you should not do this31  * until after you‘ve called the setContentView() method.32  */33 public final class Injector {34     private final Activity mActivity;35 36     private Injector(Activity activity) {37         mActivity = activity;38     }39 //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。40     /**41      * Gets an {@link Injector} capable of injecting fields for the given Activity.42      */43     public static Injector get(Activity activity) {44         return new Injector(activity);45     }46 47     /**48      * Injects all fields that are marked with the {@link InjectView} annotation.49      * <p>50      * For each field marked with the InjectView annotation, a call to51      * {@link Activity#findViewById(int)} will be made, passing in the resource id stored in the52      * value() method of the InjectView annotation as the int parameter, and the result of this call53      * will be assigned to the field.54      *55      * @throws IllegalStateException if injection fails, common causes being that you have used an56      *             invalid id value, or you haven‘t called setContentView() on your Activity.57      */58     public void inject()59 //inject等待被另一個Java檔召喚。60  {61         for (Field field : mActivity.getClass().getDeclaredFields()) 62 //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。63 {64             for (Annotation annotation : field.getAnnotations()) {65                 if (annotation.annotationType().equals(InjectView.class)) {66                     try {67                         Class<?> fieldType = field.getType();68                         int idValue = InjectView.class.cast(annotation).value();69                         field.setAccessible(true);70                         Object injectedValue = fieldType.cast(mActivity.findViewById(idValue));71                         if (injectedValue == null) {72                             throw new IllegalStateException("findViewById(" + idValue73                                     + ") gave null for " +74                                     field + ", can‘t inject");75                         }76                         field.set(mActivity, injectedValue);77                         field.setAccessible(false);78                     } catch (IllegalAccessException e) {79                         throw new IllegalStateException(e);80                     }81                 }82             }83         }84     }85 }

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。

安卓中級教程（2）：@InjectView中的對象inject