ButterKnife源码阅读

公司项目里用的是版本7.0.1。以下就以7.0.1为例

以ButterKnife在activity中绑定为例；

ButterKnife.bind(this)

bind(target, target, Finder.ACTIVITY);

Finder枚举

static void bind(Object target, Object source, Finder finder) {  Class<?> targetClass = target.getClass();  try {      if (debug) Log.d(TAG, "Looking up view binder for " + targetClass.getName());      ViewBinder<Object> viewBinder = findViewBinderForClass(targetClass);  if (viewBinder != null) {      viewBinder.bind(finder, target, source);  }  } catch (Exception e) {      throw new RuntimeException("Unable to bind views for " + targetClass.getName(), e);  }}

 private static ViewBinder<Object> findViewBinderForClass(Class<?> cls)      throws IllegalAccessException, InstantiationException {    ViewBinder<Object> viewBinder = BINDERS.get(cls);//根据Class查找viewBinder    if (viewBinder != null) {      if (debug) Log.d(TAG, "HIT: Cached in view binder map.");      return viewBinder;    }    String clsName = cls.getName();    if (clsName.startsWith(ANDROID_PREFIX) || clsName.startsWith(JAVA_PREFIX)) {//android.或者java.为开头包名的      if (debug) Log.d(TAG, "MISS: Reached framework class. Abandoning search.");      return NOP_VIEW_BINDER;    }    try {      Class<?> viewBindingClass = Class.forName(clsName + ButterKnifeProcessor.SUFFIX);//如xxx.MainActivity$$ViewBinder      //noinspection unchecked      viewBinder = (ViewBinder<Object>) viewBindingClass.newInstance();      if (debug) Log.d(TAG, "HIT: Loaded view binder class.");    } catch (ClassNotFoundException e) {      if (debug) Log.d(TAG, "Not found. Trying superclass " + cls.getSuperclass().getName());      viewBinder = findViewBinderForClass(cls.getSuperclass());    }    BINDERS.put(cls, viewBinder);//保存这个viewBinder到LinkedHashMap.    return viewBinder;  }

public <T> T findRequiredView(Object source, int id, String who) {      T view = findOptionalView(source, id, who);      if (view == null) {        String name = getContext(source).getResources().getResourceEntryName(id);        throw new IllegalStateException("Required view '"            + name            + "' with ID "            + id            + " for "            + who            + " was not found. If this view is optional add '@Nullable' annotation.");      }      return view;    }

 public <T> T findOptionalView(Object source, int id, String who) {      View view = findView(source, id);      return castView(view, id, who);    }

通过枚举类中的方法获取view：

 public enum Finder { .....        ACTIVITY {              @Override protected View findView(Object source, int id) {                return ((Activity) source).findViewById(id);           }}

通过泛型转化得到真正的view：

 public <T> T castView(View view, int id, String who) {      try {        return (T) view;      } catch (ClassCastException e) {        if (who == null) {          throw new AssertionError();        }        String name = view.getResources().getResourceEntryName(id);        throw new IllegalStateException("View '"            + name            + "' with ID "            + id            + " for "            + who            + " was of the wrong type. See cause for more info.", e);      }    }

    public <T> T findRequiredView(Object source, int id, String who) {      T view = findOptionalView(source, id, who);      if (view == null) {        String name = getContext(source).getResources().getResourceEntryName(id);        throw new IllegalStateException("Required view '"            + name            + "' with ID "            + id            + " for "            + who            + " was not found. If this view is optional add '@Nullable' annotation.");      }      return view;    }

解析注解生成的MainActivity$$ViewBinder.class内容：

public class MainActivity$$ViewBinder<T extends MainActivity>implements ButterKnife.ViewBinder<T> {    public void bind(ButterKnife.Finder finder, T target, Object source) {        View view = (View) finder.findRequiredView(source, 2131624181, "field 'llAlert' and method 'onClick'");        target.llAlert = ((LinearLayout) finder.castView(view, 2131624181, "field 'llAlert'"));        view.setOnClickListener(new MainActivity..ViewBinder .1 (this, target));        .....    }    public void unbind(T target) {        target.llAlert = null;        .....    }}

编译时注解处理基于annotation processing tool:
1、自定义类继承自 javax.annotation.processing.AbstractProcessor
2、重写其中的 process 函数
在编译时自动查找所有继承自 AbstractProcessor 的类，然后调用他们的 process 方法去处理。
ButterKnife中继承AbstractProcessor的是ButterKnifeProcessor类.