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      1 /*
      2  * Copyright (C) 2017 The Android Open Source Project
      3  *
      4  * Licensed under the Apache License, Version 2.0 (the "License");
      5  * you may not use this file except in compliance with the License.
      6  * You may obtain a copy of the License at
      7  *
      8  *      http://www.apache.org/licenses/LICENSE-2.0
      9  *
     10  * Unless required by applicable law or agreed to in writing, software
     11  * distributed under the License is distributed on an "AS IS" BASIS,
     12  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
     13  * See the License for the specific language governing permissions and
     14  * limitations under the License.
     15  */
     16 
     17 package com.android.setupwizardlib.items;
     18 
     19 import android.content.Context;
     20 import android.support.annotation.NonNull;
     21 import android.support.annotation.Nullable;
     22 import android.util.AttributeSet;
     23 import android.view.InflateException;
     24 
     25 import java.lang.reflect.Constructor;
     26 import java.util.HashMap;
     27 
     28 /**
     29  * An XML inflater that creates items by reading the tag as a class name, and constructs said class
     30  * by invoking the 2-argument constructor {@code Constructor(Context, AttributeSet)} via reflection.
     31  *
     32  * <p>Optionally a "default package" can be specified so that for unqualified tag names (i.e. names
     33  * that do not contain "."), the default package will be prefixed onto the tag.
     34  *
     35  * @param <T> The class where all instances (including child elements) belong to. If parent and
     36  *     child elements belong to different class hierarchies, it's OK to set this to {@link Object}.
     37  */
     38 public abstract class ReflectionInflater<T> extends SimpleInflater<T> {
     39 
     40     /* static section */
     41 
     42     private static final Class<?>[] CONSTRUCTOR_SIGNATURE =
     43             new Class<?>[] {Context.class, AttributeSet.class};
     44 
     45     private static final HashMap<String, Constructor<?>> sConstructorMap = new HashMap<>();
     46 
     47     /* non-static section */
     48 
     49     // Array used to contain the constructor arguments (Context, AttributeSet), to avoid allocating
     50     // a new array for creation of every item.
     51     private final Object[] mTempConstructorArgs = new Object[2];
     52 
     53     @Nullable
     54     private String mDefaultPackage;
     55 
     56     @NonNull
     57     private final Context mContext;
     58 
     59     /**
     60      * Create a new inflater instance associated with a particular Context.
     61      *
     62      * @param context The context used to resolve resource IDs. This context is also passed to the
     63      *     constructor of the items created as the first argument.
     64      */
     65     protected ReflectionInflater(@NonNull Context context) {
     66         super(context.getResources());
     67         mContext = context;
     68     }
     69 
     70     @NonNull
     71     public Context getContext() {
     72         return mContext;
     73     }
     74 
     75     /**
     76      * Instantiate the class by name. This attempts to instantiate class of the given {@code name}
     77      * found in this inflater's ClassLoader.
     78      *
     79      * @param tagName The full name of the class to be instantiated.
     80      * @param attrs The XML attributes supplied for this instance.
     81      *
     82      * @return The newly instantiated item.
     83      */
     84     @NonNull
     85     public final T createItem(String tagName, String prefix, AttributeSet attrs) {
     86         String qualifiedName = tagName;
     87         if (prefix != null && qualifiedName.indexOf('.') == -1) {
     88             qualifiedName = prefix.concat(qualifiedName);
     89         }
     90         @SuppressWarnings("unchecked") // qualifiedName should correspond to a subclass of T
     91         Constructor<? extends T> constructor =
     92                 (Constructor<? extends T>) sConstructorMap.get(qualifiedName);
     93 
     94         try {
     95             if (constructor == null) {
     96                 // Class not found in the cache, see if it's real, and try to add it
     97                 @SuppressWarnings("unchecked") // qualifiedName should correspond to a subclass of T
     98                 Class<? extends T> clazz =
     99                         (Class<? extends T>) mContext.getClassLoader().loadClass(qualifiedName);
    100                 constructor = clazz.getConstructor(CONSTRUCTOR_SIGNATURE);
    101                 constructor.setAccessible(true);
    102                 sConstructorMap.put(tagName, constructor);
    103             }
    104 
    105             mTempConstructorArgs[0] = mContext;
    106             mTempConstructorArgs[1] = attrs;
    107             final T item = constructor.newInstance(mTempConstructorArgs);
    108             mTempConstructorArgs[0] = null;
    109             mTempConstructorArgs[1] = null;
    110             return item;
    111         } catch (Exception e) {
    112             throw new InflateException(attrs.getPositionDescription()
    113                     + ": Error inflating class " + qualifiedName, e);
    114         }
    115     }
    116 
    117     @Override
    118     protected T onCreateItem(String tagName, AttributeSet attrs) {
    119         return createItem(tagName, mDefaultPackage, attrs);
    120     }
    121 
    122     /**
    123      * Sets the default package that will be searched for classes to construct for tag names that
    124      * have no explicit package.
    125      *
    126      * @param defaultPackage The default package. This will be prepended to the tag name, so it
    127      *     should end with a period.
    128      */
    129     public void setDefaultPackage(@Nullable String defaultPackage) {
    130         mDefaultPackage = defaultPackage;
    131     }
    132 
    133     /**
    134      * Returns the default package, or null if it is not set.
    135      *
    136      * @see #setDefaultPackage(String)
    137      * @return The default package.
    138      */
    139     @Nullable
    140     public String getDefaultPackage() {
    141         return mDefaultPackage;
    142     }
    143 }
    144