动态代理+注解+反射实现View的点击事件绑定

Posted 2021-02-21 milovetingting

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动态代理+注解+反射实现View的点击事件绑定

代理模式是给对象提供一个代理对象，由代理对象来控制原对象的引用。代理模式分为静态代理和动态代理。

静态代理

定义接口

public interface Player {

    void play();

}

定义具体的实现类

public class PlayerImpl implements Player {

    @Override
    public void play() {
        System.out.println("PlayerImpl play...");
    }
}

定义代理类

public class ProxyImpl implements Player {

    private Player player;

    public ProxyImpl(Player player) {
        this.player = player;
    }

    @Override
    public void play() {
        player.play();
    }
}

可以看到，具体的实现类和代理类都会实现相同的接口类，在代理类的实现中，会引用具体的实现类。

动态代理

静态代理，在运行前定义。动态代理是在运行时创建代理和实例。JDK提供了Proxy类来创建动态代理

public static Object newProxyInstance(ClassLoader loader,
                                          Class<?>[] interfaces,
                                          InvocationHandler h)
        throws IllegalArgumentException
    {

    }

先看下具体的使用

Proxy.newProxyInstance(getClass().getClassLoader(), new Class[]{Player.class}, new InvocationHandler() {
            @Override
            public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
                return method.invoke(player, args);
            }
        });

newProxyInstance对应的三个参数：

• 类加载器

• 接口的class，Proxy会根据这个class来生成Proxy类

• InvocationHandler,方法的回调,代理的类的方法调用时都会回调到这来

动态代理类的完整代码

public class DynamicProxy {

    private Player player;

    public DynamicProxy(Player player) {
        this.player = player;
    }

    public void setPlayer(Player player) {
        this.player = player;
    }

    public Player getProxy() {
        return (Player) Proxy.newProxyInstance(getClass().getClassLoader(), new Class[]{Player.class}, new InvocationHandler() {
            @Override
            public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
                return method.invoke(player, args);
            }
        });
    }

}

Proxy.newProxyInstance方法最终是调用ProxyGenerator的generateProxyClass方法

public static byte[] generateProxyClass(final String var0, Class<?>[] var1, int var2) {
        ProxyGenerator var3 = new ProxyGenerator(var0, var1, var2);
        final byte[] var4 = var3.generateClassFile();
        if (saveGeneratedFiles) {
            AccessController.doPrivileged(new PrivilegedAction<Void>() {
                public Void run() {
                    try {
                        int var1 = var0.lastIndexOf(46);
                        Path var2;
                        if (var1 > 0) {
                            Path var3 = Paths.get(var0.substring(0, var1).replace(‘.‘, File.separatorChar));
                            Files.createDirectories(var3);
                            var2 = var3.resolve(var0.substring(var1 + 1, var0.length()) + ".class");
                        } else {
                            var2 = Paths.get(var0 + ".class");
                        }

                        Files.write(var2, var4, new OpenOption[0]);
                        return null;
                    } catch (IOException var4x) {
                        throw new InternalError("I/O exception saving generated file: " + var4x);
                    }
                }
            });
        }

        return var4;
    }

动态代理生成的代理类存在于内存中。

实现点击事件的绑定

下面基于动态代理+注解+反射，实现控件的点击事件绑定。

首先定义注解

@Target(ElementType.METHOD)
@Retention(RetentionPolicy.RUNTIME)
public @interface OnClick {
    @IdRes int[] value();
}

然后在Activity中定义点击事件,引用OnClick注解

@OnClick({R.id.btn1, R.id.btn2})
    public void click(Button view) {
        Toast.makeText(getApplicationContext(), view.getText(), Toast.LENGTH_SHORT).show();
    }

在Activity中绑定

@Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        InjectHelper.inject(this);
    }

InjectHelper的实现

public static void inject(final Activity target) {
        if (target == null) {
            return;
        }
        Class<? extends Activity> clz = target.getClass();
        Method[] declaredMethods = clz.getDeclaredMethods();
        for (final Method method : declaredMethods) {
            if (method.isAnnotationPresent(OnClick.class)) {
                OnClick annotation = method.getAnnotation(OnClick.class);
                int[] resIds = annotation.value();
                for (int resId : resIds) {
                    final View view = target.findViewById(resId);
                    final Object proxyInstance = Proxy.newProxyInstance(InjectHelper.class.getClassLoader(), new Class[]{View.OnClickListener.class}, new InvocationHandler() {
                        @Override
                        public Object invoke(Object proxy, Method m, Object[] args) throws Throwable {
                            return method.invoke(target, view);
                        }
                    });
                    view.setOnClickListener((View.OnClickListener) proxyInstance);
                }
            }
        }
    }