如何使用按钮更改所有活动的背景颜色？

Question

I made a code which is not complete and I wanted to change the background color for all activities. But it always crashes. Please help, I'm stuck. Thanks in advance!

package com.example.dk199.calculator;

import android.graphics.Color;
import android.support.constraint.ConstraintLayout;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.RadioButton;
import android.widget.RelativeLayout;

public class DisplayActivity extends AppCompatActivity {
Button b1, b2, b3, b4;
RelativeLayout Rd;
ConstraintLayout Cl;

@Overeride
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_display);

    b1 = (RadioButton) findViewById(R.id.green2);
    b4 = (RadioButton) findViewById(R.id.orange2);
    b3 = (RadioButton) findViewById(R.id.yellow2);
    b4 = (RadioButton) findViewById(R.id.white2);
    Rd = (RelativeLayout) findViewById(R.id.DisplayActivity);
    Cl = (ConstraintLayout) findViewById(R.id.MainActivity);

    b1.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            Rd.setBackgroundColor(Color.GREEN);
            Cl.setBackgroundColor(Color.GREEN);
        }
    });
  }
}

I was hoping to change the backrgound for this 2 activities but end of the result, I got crashes.

Answer 1

You can use custom theme of your own. At first, make a theme and then set the theme from application scope in Manifest.xml . Like -

<application
android:theme="@android:style/Theme.Holo"
android:theme="@style/MyTheme">

Or you can define your theme in every activity from Manifest.xml .

<activity
android:theme="@android:style/Theme.Holo"
android:theme="@style/MyTheme">

If you want to know more about android styling and themeing, read this post upto full playlist.