前言
Glide 是 Google 官方推荐的一款图片加载库,我们可以通过配置 GlideModule
来修改 Glide 的一些初始化配置。
其中一个常见的做法如下:
继承
GlideModule
接口并实现其对应的方法:public class MyGlideModule implements GlideModule { @Override public void applyOptions(Context context, GlideBuilder builder) { //.............. } @Override public void registerComponents(Context context, Glide glide) { //............ } }
第二步就是到
AndroidManifest
里面设置相关的meta-data
:<?xml version="1.0" encoding="utf-8"?> <manifest ......> ...... <application > <meta-data android:name="XXX.XXX.XXX.MyGlideModule" android:value="GlideModule" /> </application>
咦,好像有点不对,在 AndroidManifest
里面添加上面的 meta-data
节点, Glide 是怎么做到自动加载 MyGlideModule
来改变它的默认配置的?
解析 AndroidManifest 的方法
要做到这点,那就肯定是有方法在运行时获取 AndroidManifest
的数据,而这个方法就是通过 PackageManager
去获取 App 里面的各项信息,从而获取到你需要的信息。
具体的操作方法如下:
public class ManifestParser {
private static final String TAG = "ManifestParser";
public void parser(Context context) {
if (context == null) {
return;
}
PackageManager packageManager = context.getPackageManager();
try {
//flag配置需要获取的节点数据标签
PackageInfo packageInfo = packageManager.getPackageInfo(context.getPackageName(),
PackageManager.GET_ACTIVITIES | PackageManager.GET_SERVICES
| PackageManager.GET_RECEIVERS | PackageManager.GET_META_DATA);
//获取App全部的Activity信息
if (arrayNotEmpty(packageInfo.activities)) {
for (ActivityInfo activity : packageInfo.activities) {
Log.e(TAG, "Activity is " + activity.name);
}
}
//获取App全部的Service信息
if (arrayNotEmpty(packageInfo.services)) {
for (ServiceInfo service : packageInfo.services) {
Log.w(TAG, "Service is " + service.name);
}
}
//获取App全部的广播信息
if (arrayNotEmpty(packageInfo.receivers)) {
for (ActivityInfo receiver : packageInfo.receivers) {
Log.d(TAG, "Receiver is " + receiver.name);
}
}
//获取App全部的metaData节点数据
Bundle metaData = packageInfo.applicationInfo.metaData;
if (metaData != null && metaData.keySet() != null
&& metaData.keySet().size() > 0) {
for (String item : metaData.keySet()) {
Log.i(TAG, "metaData name is " + item);
Log.i(TAG, "metaData value is " + metaData.get(item));
}
}
} catch (PackageManager.NameNotFoundException e) {
e.printStackTrace();
}
}
//判断数组是否为null
private boolean arrayNotEmpty(Object[] array) {
return array != null && array.length > 0;
}
}
输出为:
E/ManifestParser: Activity is OneActivity
E/ManifestParser: Activity is TwoActivity
E/ManifestParser: Activity is ThreeActivity
E/ManifestParser: Activity is FourActivity
W/ManifestParser: Service is OneService
D/ManifestParser: Receiver is OneBroadcastReceiver
I/ManifestParser: metaData name is android.support.VERSION
I/ManifestParser: metaData value is 26.1.0
I/ManifestParser: metaData name is android.arch.lifecycle.VERSION
I/ManifestParser: metaData value is 27.0.0-SNAPSHOT
I/ManifestParser: metaData name is XXX.XXX.XXX.MyGlideModule
I/ManifestParser: metaData value is GlideModule
可以看到我们很简单就把 App 的相关信息打印出来了,在这里我们也拿到了 meta-data
的全部数据,这时应该有人也注意到了,我们已经把创建的 GlideModule
类的路径放到里 meta-data
里面,那么接下来就简单了。
我们可以通过指定的 value 值来筛选出我们需要的 meta-Data
节点来获取路径,然后通过反射来实例化对象,下面贴上部分 Glide 的源码:
public final class ManifestParser {
private static final String GLIDE_MODULE_VALUE = "GlideModule";
.......
public List<GlideModule> parse() {
.........
for (String key : appInfo.metaData.keySet()) {
//进行筛选
if (GLIDE_MODULE_VALUE.equals(appInfo.metaData.get(key))) {
//parseModule实例化对象
modules.add(parseModule(key));
if (Log.isLoggable(TAG, Log.DEBUG)) {
Log.d(TAG, "Loaded Glide module: " + key);
}
}
}
......
}
private static GlideModule parseModule(String className) {
Class<?> clazz;
try {
clazz = Class.forName(className);
} catch (ClassNotFoundException e) {
throw new IllegalArgumentException("Unable to find GlideModule implementation", e);
}
Object module = null;
try {
module = clazz.getDeclaredConstructor().newInstance();
} catch (InstantiationException e) {
throwInstantiateGlideModuleException(clazz, e);
} catch (IllegalAccessException e) {
throwInstantiateGlideModuleException(clazz, e);
} catch (NoSuchMethodException e) {
throwInstantiateGlideModuleException(clazz, e);
} catch (InvocationTargetException e) {
throwInstantiateGlideModuleException(clazz, e);
}
//如果生成对象不是需要就直接抛出异常
if (!(module instanceof GlideModule)) {
throw new RuntimeException("Expected instanceof GlideModule, but found: " + module);
}
//强转为 GlideModule
return (GlideModule) module;
}
............
}
可以看到,这种方法就用到一次反射,没有太多的其他东西,可以说是解耦得非常彻地,这一点很值得我们去学习。