安卓 如何从另一个文件访问一个类到MainActivity

Question

I created a separate java class called SetIP.java with just a simple print:

package com.myname.appname;

import android.util.Log;

public class SetIP {

    public void hello(){
        Log.d("System", "Hello World!");
    }
}

In the MainActivity I try to call it by:

public class MainActivity extends AppCompatActivity {

    SetIP setip = new SetIP();
    setip.hello();
   // OnCreate and Stuff
}

But the error said cannot resolve symbol 'Hello'. Please help. Thanks

Answer 1

You need to call it in onCreate method.

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);

    SetIP setip = new SetIP();
    setip.hello();
}

Answer 2

You shouldn't call a method of an object of any of the classes on the fly as you are calling now, As you told your // OnCreate and Stuff is below than your object's method call.

It has to be inside constructor or some methods, Like here

SetIP setip = new SetIP();
@Override
   public void onCreate(Bundle savedInstanceState) {
      super.onCreate(savedInstanceState);
      setip.hello();
   }

OR

@Override
   public void onCreate(Bundle savedInstanceState) {
      super.onCreate(savedInstanceState);
      SetIP setip = new SetIP();
      setip.hello();
   }

Answer 3

You can instantiate SetIP as global variable to MainActivity, but calling the function should still resides within a function of MainActivity. One example is to put this in onCreate activity as below

public class MainActivity extends AppCompatActivity {

    SetIP setip = new SetIP();

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        setip.hello();
    }

    // Other Stuff
}

Answer 4

public class MainActivity extends AppCompatActivity {

   @Override
   protected void onCreate(Bundle savedInstanceState) {
      super.onCreate(savedInstanceState);
      setContentView(R.layout.activity_main);

      SetIP setip = new SetIP();
      setip.hello();
   }

   // Other methods
} 

Answer 5

You need change only method is static like

public class SetIP {    
    public static void hello(){
        Log.d("System", "Hello World!");
    }
}

Try this work.