butterknife.md

ButterKnife源码分析

1. 编译器干了什么

   扫描注解，获取所有带有注解的文件， 生成一个className_ViewBinding.java的文件 ；例如MainActivity使用注解后生成

   MainActivity_ViewBinding.java

   public class MainActivity_ViewBinding implements Unbinder { private MainActivity target;

   @UiThread public MainActivity_ViewBinding(MainActivity target) { this(target, target.getWindow().getDecorView()); }

   @UiThread public MainActivity_ViewBinding(MainActivity target, View source) { this.target = target;

   target.btn_test = Utils.findRequiredViewAsType(source, R.id.btn_test, "field 'btn_test'", Button.class);
   

   }

   @Override @CallSuper public void unbind() { MainActivity target = this.target; if (target == null) throw new IllegalStateException("Bindings already cleared."); this.target = null;

   target.btn_test = null;
   

   } }

2. Butterknife.bind() 干了什么?

    @NonNull @UiThread
    public static Unbinder bind(@NonNull Object target, @NonNull Dialog source) {
      View sourceView = source.getWindow().getDecorView();
      return createBinding(target, sourceView);
    }
    
    private static Unbinder createBinding(@NonNull Object target, @NonNull View source) {
      Class<?> targetClass = target.getClass();
      if (debug) Log.d(TAG, "Looking up binding for " + targetClass.getName());
      Constructor<? extends Unbinder> constructor = findBindingConstructorForClass(targetClass);
    
      if (constructor == null) {
        return Unbinder.EMPTY;
      }
    
      //noinspection TryWithIdenticalCatches Resolves to API 19+ only type.
      try {
        return constructor.newInstance(target, source);
      } catch (IllegalAccessException e) {
        throw new RuntimeException("Unable to invoke " + constructor, e);
      } catch (InstantiationException e) {
        throw new RuntimeException("Unable to invoke " + constructor, e);
      } catch (InvocationTargetException e) {
        Throwable cause = e.getCause();
        if (cause instanceof RuntimeException) {
          throw (RuntimeException) cause;
        }
        if (cause instanceof Error) {
          throw (Error) cause;
        }
        throw new RuntimeException("Unable to create binding instance.", cause);
      }
    }
    
    @Nullable @CheckResult @UiThread
    private static Constructor<? extends Unbinder> findBindingConstructorForClass(Class<?> cls) {
      Constructor<? extends Unbinder> bindingCtor = BINDINGS.get(cls);
      if (bindingCtor != null) {
        if (debug) Log.d(TAG, "HIT: Cached in binding map.");
        return bindingCtor;
      }
      String clsName = cls.getName();
      if (clsName.startsWith("android.") || clsName.startsWith("java.")) {
        if (debug) Log.d(TAG, "MISS: Reached framework class. Abandoning search.");
        return null;
      }
      try {
        Class<?> bindingClass = cls.getClassLoader().loadClass(clsName + "_ViewBinding");
        //noinspection unchecked
        bindingCtor = (Constructor<? extends Unbinder>) bindingClass.getConstructor(cls, View.class);
        if (debug) Log.d(TAG, "HIT: Loaded binding class and constructor.");
      } catch (ClassNotFoundException e) {
        if (debug) Log.d(TAG, "Not found. Trying superclass " + cls.getSuperclass().getName());
        bindingCtor = findBindingConstructorForClass(cls.getSuperclass());
      } catch (NoSuchMethodException e) {
        throw new RuntimeException("Unable to find binding constructor for " + clsName, e);
      }
      BINDINGS.put(cls, bindingCtor);
      return bindingCtor;
    }
   

通过对象获取class，通过class查询缓存 看看有没有，如果没有，就用classLoder加载一个 clsName_ViewBinding类文件，这个就是刚刚生成，然后拿到构造方法，传入布局和对象，创建clsName_ViewBinding 对象，而clsName_ViewBinding的构造方法就是进行findViewById了