按下另一个活动中的按钮时更改按钮颜色

Question

I'm new in Android programming and I still have sometimes small problems. My problem currently is the following:

I have 2 activities with just one button in each. The button of the first activity is opening the second activity. But when I press the button in the second activity, the Text in the Button of the first activity should change to "Hello" and the color should be red.

I have managed to change the text but not the color. Could someone help me please?

My Code:

First activity:

package com.example.myapplication;

import androidx.appcompat.app.AppCompatActivity;

import android.content.Intent;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;

public class MainActivity extends AppCompatActivity {

Button placeHolder;
Intent intent;

public void button0(View v){

    intent = new Intent(getApplicationContext(), MainActivity2.class);
    startActivity(intent);
}

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    placeHolder = findViewById(R.id.button);

    placeHolder.setText(getIntent().getStringExtra("message"));
}
}

The code of second activity:

package com.example.myapplication;

import androidx.appcompat.app.AppCompatActivity;

import android.content.Intent;
import android.graphics.Color;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;

public class MainActivity2 extends AppCompatActivity {


public void buttonOnClick(View v){

    Intent intent=new Intent(MainActivity2.this, MainActivity.class);
    intent.putExtra("message", "Hello");
    startActivity(intent);
}

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main2);
}
}

Answer 1

Add this line of code in your first activity where you set your text to your button:

To change background color:

placeHolder.setBackgroundColor(Color.parseColor("#FF0000"));

To change text color:

placeHolder.setTextColor(Color.parseColor("#FF0000"));

package com.example.myapplication;

import androidx.appcompat.app.AppCompatActivity;

import android.content.Intent;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;

public class MainActivity extends AppCompatActivity {

Button placeHolder;
Intent intent;

public static final int REQUEST_CODE = 101;

public void button0(View v){

    intent = new Intent(getApplicationContext(), MainActivity2.class);
    startActivityForResult(intent, REQUEST_CODE);
}

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    placeHolder = findViewById(R.id.button);
}

    // Call Back method  to get the Message form other Activity  
    @Override  
    protected void onActivityResult(int requestCode, int resultCode, Intent data){  
    super.onActivityResult(requestCode, resultCode, data);  

    // check if the request code is same as what is passed
  
    if(requestCode == REQUEST_CODE) {  
       placeHolder.setText(data.getStringExtra("message"));
       placeHolder.setTextColor(Color.parseColor("#FF0000"));
    }  

}  

package com.example.myapplication;

import androidx.appcompat.app.AppCompatActivity;

import android.content.Intent;
import android.graphics.Color;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;

public class MainActivity2 extends AppCompatActivity {


public void buttonOnClick(View v){

    Intent intent=new Intent();
    intent.putExtra("message", "Hello");
    setResult(MainActivity2.REQUEST_CODE, intent);
    finish();
}

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main2);
}
}

Answer 2

you can use startActivityforResult() insted of startActivity() and then when you come back from second class to the first class then set red color tor your button onActivityResult() function thanks

Answer 3

You can use GreenRobot. Then you can do anything from other activities. Here is the link Event Bus

Answer 4

Second Activity:

Intent intent=new Intent(MainActivity2.this, MainActivity.class);
    intent.putExtra("message", "Hello");
    intent.putExtra("color", -65536); //-65536 is color RED int value
    startActivity(intent);

First Activity

placeHolder.setText(getIntent().getStringExtra("message"));
placeHolder.setBackgroundColor(getIntent().getStringExtra("color",0)); // 0 is default value