该类就一个execute方法，execute方法先判断传入的参数对象是坐标值还是元素值，是元素值直接调用AndroidElement中的click方法，；是坐标的话，会调用UiDevice的click方法，它是uiautomator包中的类。appium在android api16以上使用uiautomator机制。再分析一个touchDown命令，如果传过来的命令后缀是touchDown，那么它会调用TouchDown对象的execute方法。

map.put("touchDown", new TouchDown());

TouchDown.java

package io.appium.android.bootstrap.handler;

import com.android.uiautomator.common.ReflectionUtils;
import com.android.uiautomator.core.UiObjectNotFoundException;
import io.appium.android.bootstrap.Logger;

import java.lang.reflect.Method;

/**
 * This handler is used to perform a touchDown event on an element in the
 * Android UI.
 * 
 */
public class TouchDown extends TouchEvent {

  @Override
  protected boolean executeTouchEvent() throws UiObjectNotFoundException {
    printEventDebugLine("TouchDown");
    try {
      final ReflectionUtils utils = new ReflectionUtils();
      final Method touchDown = utils.getControllerMethod("touchDown", int.class,
          int.class);
      return (Boolean) touchDown.invoke(utils.getController(), clickX, clickY);
    } catch (final Exception e) {
      Logger.debug("Problem invoking touchDown: " + e);
      return false;
    }
  }
}
该方法用到反射机制，调用uiautomator隐藏api执行操作