Calling a method from another class crashes the App

Question

I have a button in my MainActivity, which opens a PopupActivity with 5 Buttons. I want that these 5 buttons change the Background Image from another Button (bSay3) in my MainActivity.

But for some reason, my App crashes when i click on one of these 5 buttons.

Here is my MainActivity Code:

public void changeColors(View v) {
    startActivity(new Intent(MainActivity.this,PopupActivity.class));}


public void ChangeColor() {
    Button bSay3 = (Button) findViewById(R.id.bSay3);
    if (Farbe == "Purple") {
        bSay3.setBackgroundResource(R.drawable.purple_3button);}
    if (Farbe == "Blue") {
        bSay3.setBackgroundResource(R.drawable.blue_3button);}
    if (Farbe == "Green") {
        bSay3.setBackgroundResource(R.drawable.green_3button);}
    if (Farbe == "Orange") {
        bSay3.setBackgroundResource(R.drawable.orange_3button);}
    if (Farbe == "Red") {
        bSay3.setBackgroundResource(R.drawable.red_3button);}
}

and my PopupActivity:

public static String Farbe;

MainActivity ma = new MainActivity();

public void ColorPurple(View v){
    Farbe = ("Purple");
    ma.ChangeColor();
}
public void ColorBlue(View v){
    Farbe = ("Blue");
    ma.ChangeColor();
}
public void ColorGreen(View v){
    Farbe = ("Green");
    ma.ChangeColor();
}
public void ColorOrange(View v){
    Farbe = ("Orange");
    ma.ChangeColor();
}
public void ColorRed(View v){
    Farbe = ("Red");
    ma.ChangeColor();
}

stack trace

where is your stack trace? I think this is a useful read: http://stackoverflow.com/questions/23353173/unfortunately-myapp-has-stopped-how-can-i-solve-this — trooper, Apr 04 '17 at 18:05

score 0 · Answer 1 · answered Apr 04 '17 at 18:07

Your logic is not correct.The below piece of code does not take into consideration the instance of MainActivity ,Its basically creating another object of MainActivity.

public static String Farbe;

MainActivity ma = new MainActivity();

public void ColorPurple(View v){
    Farbe = ("Purple");
    ma.ChangeColor();
}
public void ColorBlue(View v){
    Farbe = ("Blue");
    ma.ChangeColor();
}
public void ColorGreen(View v){
    Farbe = ("Green");
    ma.ChangeColor();
}
public void ColorOrange(View v){
    Farbe = ("Orange");
    ma.ChangeColor();
}
public void ColorRed(View v){
    Farbe = ("Red");
    ma.ChangeColor();
}

In order to change the background pass the result as stated below

Intent i = new Intent(MainActivity.this,PopupActivity.class);
i.putExtra("bg_color","what ever color you want");
startActivity(i);

and in the PopUpActivity in onCreate() do as below

String bg_color = getIntent().getExtra("bg_color");

with bg_color variable now you can change the color of background.

Dude please read Intent and how to pass data from one activity to another .. You would automatically get to know what am I talking about. As to your piece of code it would never work — DRY Believer, Apr 05 '17 at 12:39

Calling a method from another class crashes the App

1 Answers1