PropertyUtil.java

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// -*- mode: java; c-basic-offset: 2; -*-
// Copyright 2009-2011 Google, All Rights reserved
// Copyright 2011-2012 MIT, All rights reserved
// Released under the Apache License, Version 2.0
// http://www.apache.org/licenses/LICENSE-2.0
package com.google.appinventor.components.runtime.util;
 
import com.google.appinventor.components.annotations.SimpleProperty;
import com.google.appinventor.components.annotations.SimplePropertyCopier;
import com.google.appinventor.components.runtime.Component;
 
import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;
 
public class PropertyUtil {
 
  public static Component copyComponentProperties(Component source, Component target)
      throws Throwable {
    if (!source.getClass().equals(target.getClass())) {
      throw new IllegalArgumentException("Source and target classes must be identical");
    }
 
    final Class componentClass = source.getClass();
    final Method[] componentMethods = componentClass.getMethods();
    for (Method componentMethod : componentMethods) {
      // A SimpleProperty which takes a single argument is a property setter.
      if (componentMethod.isAnnotationPresent(SimpleProperty.class)
          && componentMethod.getParameterTypes().length == 1) {
        final Method propertySetterMethod = componentMethod;
        try {
          final String propertyName = propertySetterMethod.getName();
 
          // Look for a property copier method.
          final Method propertyCopierMethod =
              getPropertyCopierMethod("Copy" + propertyName, componentClass);
          if (propertyCopierMethod != null) {
            propertyCopierMethod.invoke(target, source);
            continue; // Don't return here because we still need to copy more properties.
          }
          // It's fine if there's no copy method.  We'll look for a getter.
 
          // The getter will have the same name as the setter
          final Method propertyGetterMethod = componentClass.getMethod(propertyName);
          final Class propertySetterParameterType = propertySetterMethod.getParameterTypes()[0];
          // The getter also needs to be a SimpleProperty and its return type needs to be
          // compatible with the setter's single argument type
          if (propertyGetterMethod.isAnnotationPresent(SimpleProperty.class) &&
              propertySetterParameterType.isAssignableFrom(propertyGetterMethod.getReturnType())) {
            final Object propertyValue = propertyGetterMethod.invoke(source);
            propertySetterMethod.invoke(target, propertyValue);
          }
        } catch (NoSuchMethodException e) {
          // It's fine if there's no getter method.  We just won't invoke the setter.
          continue;
        } catch (InvocationTargetException e2) {
          // This re-throws any Exceptions generated by the property getters or setters themselves.
          throw e2.getCause();
        }
      }
    }
    return target;
  }
 
  private static Method getPropertyCopierMethod(String copierMethodName, Class componentClass) {
    // If the copier method is declared in a superclass of componentClass, the parameter
    // would be the superclass also.
    // For example, componentClass might be Button. But the CopyWidth method is declared in
    // AndroidViewComponent and the paremeter is also AndroidViewComponent.
    // So, we may need to look up the superclass chain to
    do {
      try {
        Method propertyCopierMethod = componentClass.getMethod(copierMethodName, componentClass);
        if (propertyCopierMethod.isAnnotationPresent(SimplePropertyCopier.class)) {
          return propertyCopierMethod;
        }
      } catch (NoSuchMethodException e) {
        // It's fine if there's no copier method.  We'll try the superclass.
      }
      componentClass = componentClass.getSuperclass();
    } while (componentClass != null);
 
    // It's fine if we didn't find a copier method. Just return null;
    return null;
  }
}