google加载资源的源码
ImageView里面的Src图片属性，最终都是通过下面这行代码去加载的：
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final TypedArray a = context.obtainStyledAttributes(
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attrs, R.styleable.ImageView, defStyleAttr, defStyleRes);
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final Drawable d = a.getDrawable(R.styleable.ImageView_src);//R.styleable.ImageView_src读取的就是我们在xml里面的ImageView下面设置的src属性
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if (d != null) {
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setImageDrawable(d);
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}
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public Drawable getDrawable(@StyleableRes int index) {
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if (mRecycled) {
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throw new RuntimeException("Cannot make calls to a recycled instance!");
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}
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final TypedValue value = mValue;
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if (getValueAt(index*AssetManager.STYLE_NUM_ENTRIES, value)) {
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if (value.type == TypedValue.TYPE_ATTRIBUTE) {
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throw new UnsupportedOperationException(
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"Failed to resolve attribute at index " + index + ": " + value);
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}
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return mResources.loadDrawable(value, value.resourceId, mTheme);//主要是这行代码去Load资源
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}
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return null;
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}
这个时候我们需要去找mResources的实例对象，我们平时在Activity中使用的getResources()，点进去发现是抽象类，最后在AndroidSDK源码下找到
ContextImpl.java
文件，再搜索getResources()方法。
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@Override
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public Resources getResources() {
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return mResources;
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}
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mResources = resources;
一路方法跟进去，最后在
ResourcesManager下面发现了这样的代码
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final Resources resources;
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if (activityToken != null) {
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resources = getOrCreateResourcesForActivityLocked(activityToken, classLoader,
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resourcesImpl);
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} else {
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resources = getOrCreateResourcesLocked(classLoader, resourcesImpl);
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}
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return resources;
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Resources resources = new Resources(classLoader);
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resources.setImpl(impl);
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activityResources.activityResources.add(new WeakReference<>(resources));
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if (DEBUG) {
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Slog.d(TAG, "- creating new ref=" + resources);
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Slog.d(TAG, "- setting ref=" + resources + " with impl=" + impl);
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}
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return resources;
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//Resources的另外一个构造方法，因为对类加载的机制不熟悉，虽然这个已经过时了，我们这里还是使用一下吧
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/**
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* Create a new Resources object on top of an existing set of assets in an
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* AssetManager.
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*
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* @deprecated Resources should not be constructed by apps.
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* See {@link android.content.Context#createConfigurationContext(Configuration)}.
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*
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* @param assets Previously created AssetManager.
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* @param metrics Current display metrics to consider when
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* selecting/computing resource values.
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* @param config Desired device configuration to consider when
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* selecting/computing resource values (optional).
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*/
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public Resources(AssetManager assets, DisplayMetrics metrics, Configuration config) {
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this(null);
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mResourcesImpl = new ResourcesImpl(assets, metrics, config, new DisplayAdjustments());
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}
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这边就已经得到我们想要的如何去创建Resources对象的代码了。
总结：既然资源的加载是通过Resource类，如果想要去获取另外一个Apk中的资源是不是可以自己去实例化一个呢？所以我们在阅读的过程中只需要去找到如何去实例化Resouces对象的代码就可以了，怎么new的对象
Resources resources = new Resources(new AssetManager(),new DiaplayMetrics(),new Configuration());-->
AssetManager其实是Resources的核心实例--->最终是通过AssetManager去获取。
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/**
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* Add an additional set of assets to the asset manager. This can be
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* either a directory or ZIP file. Not for use by applications. Returns
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* the cookie of the added asset, or 0 on failure.
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* {@hide}也可以是一个Apk文件或者是一个Zip文件
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*/
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public final int addAssetPath(String path) {
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return addAssetPathInternal(path, false);
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}