如何在Android中将方法作为参数传递

Question

This may be a really stupid question or not even possible.

I am not sure if this would be called as a method, but going with this. How can I pass getCountryName(); as parameter? like show below;

public static String Utils(Something something){
    Geocoder geoCoder = new Geocoder(context, Locale.getDefault());
    List<Address> address = null;

    if (geoCoder != null) {
        try {
            address = geoCoder.getFromLocation(lat, lng, 1);
        } catch (IOException e1) {
            e1.printStackTrace();
        }
        if (address.size() > 0) {
            return address.get(0).getCountryName(); // pass this as parameter (something)
        }
    }
    return null;
}

and then call it like so,

Utils(getCountryName());
Utils(getCountryCode());
etc.

Answer 1

This Answer helped me to do it. You can try it, too.

Methods aren't first-class objects in Java, so they can't be passed as parameters. You could use wrap your method call in an annoymous class that extends eg the Runnable interface.

Answer 2

You can use reflection.

eg

Method[] methods = Address.class.getMethods();
for (Method method : methods){
    if(method.getName().equals(param)){
        return (String) method.invoke(address.get(0));
    }
}

param would be of type String with value of the method you want to call.

EDIT: Full example, using getMethod(String)

public static String Utils(String param){
    Geocoder geoCoder = new Geocoder(context, Locale.getDefault());
    List<Address> address = null;

    if (geoCoder != null) {
        try { 
            address = geoCoder.getFromLocation(lat, lng, 1);
        } catch (IOException e1) {
            e1.printStackTrace();
        } 
        if (address.size() > 0) {
            Method method = Address.class.getMethod(param);
            if(method == null) return null;
            try{
                return (String) method.invoke(address.get(0));
            }catch(ReflectiveOperationException e){
                // Expected param maybe?
                return null;
            }
        } 
    } 
    return null; 
} 

Answer 3

In java that is the language that you are finally using. You can't pass a method or function as a parameter to a function. If you are able to use it, from Java 8 you have lambda expressions that are a kind of "anonymous" function. Try with that.

http://docs.oracle.com/javase/tutorial/java/javaOO/lambdaexpressions.html

In this SO answer you have a very detailed guide. Java Pass Method as Parameter

In that thread there are more info with some patterns if you can't use java8

Answer 4

try this;

First define an Interface with the method you want to pass as a parameter

public interface Callable {
  public void getCountryName();
  public void getCountryCode();
}

Implement a class with the method

class Method_passing implements Callable {
  public void getCountryName() {
     //do your task
  }

  public void getCountryCode() {
     //do your task
  }
}

Invoke like that

Callable cmd = new Method_passing();
//This allows you to pass cmd as parameter and invoke the method call defined in the interface

public invoke( Callable callable ) {
  cmd.getCountryName(); //return name etc..
  cmd.getCountryCode();
}

Answer 5

You could implement a getUtil function inside your adress class and then use identifiers to execute a function of your choice.

public class Address {
public static final int GET_COUNTRY_NAME = 1;
public static final int GET_COUNTRY_CODE = 2;

public String getUtil(int code){
    switch(code){
    case GET_COUNTRY_NAME: return this.getCountryName();
    case GET_COUNTRY_CODE: return this.getCountryCode();
    default: return null;
    }
}

private String getCountryName(){
    //do something
    return "";
}

private String getCountryCode(){
    //do something
    return "";
}}

and then define your function like

public static String Utils(int something){
Geocoder geoCoder = new Geocoder(context, Locale.getDefault());
List<Address> address = null;

if (geoCoder != null) {
    try {
        address = geoCoder.getFromLocation(lat, lng, 1);
    } catch (IOException e1) {
        e1.printStackTrace();
    }
    if (address.size() > 0) {
        return address.get(0).getUtil(something);
    }
}
return null; }}

which would be called using

Utils(Address.GET_COUNTRY_NAME);
Utils(Address.GET_COUNTRY_CODE);