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Press back button on main activity opens other activity

In my project i move from main activity to activity A and from activity A to activity B. From activity B using home menu on toolbar i jump back to main activity. Now when i press back button application should exit but it opens the activity A again.

You should make use of the launch flags to manage your activities in the back stack. As far as I understood your scenario, I think you need to use FLAG_ACTIVITY_CLEAR_TOP for starting your main/home activity.
Read more about launch flags: https://developer.android.com/reference/android/content/Intent#FLAG_ACTIVITY_CLEAR_TOP.
Also, take a look this for more details on managing activity back stack on Android: https://developer.android.com/guide/components/activities/tasks-and-back-stack#ManagingTasks

Call the finish() method before starting the next activity to have it removed from the activity. Find more details and options here.

For Kotlin write this in your MainActivity :
override fun onBackPressed() {
moveTaskToBack(true)
exitProcess(-1)
}
For Java write this in your MainActivity :
#Override
void onBackPressed() {
moveTaskToBack(true)
exitProcess(-1)
}
Hope to it will work for you as good as for me

hey i write some code for you
Variables:
boolean backactivity = true;
CODE:
public boolean onOptionsItemSelected(MenuItem item){
if(backactivity==true)
{
finishActivity(1);
backactivity=false;
}else
{
Intent homeIntent = new Intent(Intent.ACTION_MAIN);
homeIntent.addCategory( Intent.CATEGORY_HOME );
homeIntent.setFlags(Intent.FLAG_ACTIVITY_CLEAR_TOP);
startActivity(homeIntent);
}
return true;
}

Activity is destroyed when I start another activity without finishing the first activity

I'm struggling with this issue and I want to know if there is any option to know why an activity is being closed, I have checked if it was a low memory issue with Runtime.getRuntime().freeMemory(); but everything looks fine.
UPDATE
Here is how I call the activities and when suddenly all the background activities are closed. In all the way from MainActivity to SketchActivity I'm not calling the finish(); method but when I start the SketchActivity from BoulderProfileActivity, all the activies are destroyed, except SketchActivity :
MainActivity:
private void SendUserToFindBoulderActivity(){
Intent boulderFindIntent = new Intent(MainActivity.this, FindBouldersActivity.class);
startActivity(boulderFindIntent);
}
FindBouldersActivity:
holder.mView.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
Intent boulderProfileIntent = new
Intent(FindBouldersActivity.this,BoulderProfileActivity.class);
boulderProfileIntent.putExtra("BoulderKey", BoulderKey);
startActivity(boulderProfileIntent);
}
});
BoulderProfileActivity:
public void SendUserToSketchUpActivity(){
Intent sketchIntent = new Intent(BoulderProfileActivity.this, SketchActivity.class);
sketchIntent.addFlags(Intent.FLAG_ACTIVITY_NEW_TASK | Intent.FLAG_ACTIVITY_CLEAR_TASK);
if(sustituir==false) {
sketchIntent.putExtra("BoulderKey", BoulderKey);
sketchIntent.putExtra("Uri", ImageUri);
sketchIntent.putExtra("sustituir", sustituir);
}else{
sketchIntent.putExtra("BoulderKeyForSwitchFirstImage", BoulderKey);
sketchIntent.putExtra("Uri", ImageUri);
sketchIntent.putExtra("photoKey", photoKey);
sketchIntent.putExtra("sustituir", sustituir);
}
startActivity(sketchIntent);
}

When you start SketchActivity you are using flags
sketchIntent.addFlags(Intent.FLAG_ACTIVITY_NEW_TASK | Intent.FLAG_ACTIVITY_CLEAR_TASK);
and these flags close all previous activities and start the activity in a new task.
so to keep old previous activities please remove this line.
if you don't know what is a task, the task is the container for activities, so when you start new task this means that the activity is the first activity if you want to read more about tasks follow this link :
https://developer.android.com/guide/components/activities/tasks-and-back-stack
and you can find more information about intent flags here
https://developer.android.com/reference/android/content/Intent#FLAG_ACTIVITY_CLEAR_TASK

Any chance you enabled developer mode (System -> Developer options), and it is force-closing the Activity?
There's an option (Developer Options, under 'apps', I'm using a Pixel 3) called 'Don't keep Activities' which should be disabled.

How to display a screen only for some seconds Android Studio

I am new in Android Development. I have been trying to figure out how to display a screen in android studio only for 5 seconds and then get transfered into a new activity.
For example:
Activity A -> Activity B (Shown for 5 seconds) -> Activity C
Also I want to make sure that when a user clicks on the back button while he is in Activity B nothing happens (It doesnt go back to Activity A).
What is the easiest way to do that?
I know I have to use Intent.

try this. I have commented it out, but if you have any questions about it feel free to ask.
public class ClassB extends AppCompatActivity {
//Handler allows you to send and process Runnable Objects (Classes in this case)
private Handler mHandler = new Handler();
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_classb);
//postDelayed method, Causes the Runnable r (in this case Class B) to be added to the message queue, to be run
// after the specified amount of time elapses.
mHandler.postDelayed(new Runnable() {
#Override
public void run() {
//Create a new Intent to go from Class B to Class C and start the new Activity.
Intent intent = new Intent(ClassB.this, ClassC.class);
startActivity(intent);
finish()
}
//Here after the comma you specify the amount of time you want the screen to be delayed. 5000 is for 5 seconds.
}, 5000);
}
//Override onBackPressed method and give it no functionality. This way when the user clicks the back button he will not go back.
public void onBackPressed() {
} }

In Kotlin you can do:
Handler().postDelayed({
// Start activity
startActivity(Intent(this, YourTargetActivity::class.java))
// terminate this activity(optional)
finish()
}, 5000)

Changing background in other activities with a button

I have a problem. I have 3 activities (MainActivity, DetailsActivity, SettingsActivity) and in SettingsActivity I have a Togglebutton "Nightmode". What I want is, when the button is changed, change background of all three activities on gray color.
public class SettingsActivity extends AppCompatActivity {
//This is SettingsActivity(not Main one)
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_settings);
TextView SettingsTitle = (TextView) findViewById(R.id.SettingsTitle);
TextView NightText = (TextView) findViewById(R.id.NightmodeText);
ToggleButton toggleNightMode = (ToggleButton) findViewById(R.id.toggleNightmode);
final RelativeLayout NightBG = (RelativeLayout) findViewById(R.id.NightBG);
final LinearLayout DetailsBG = (LinearLayout) findViewById(R.id.mainBG);
final LinearLayout HomeBG = (LinearLayout) findViewById(R.id.HomeBG);
toggleNightMode.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
NightBG.setBackgroundColor(Color.parseColor("#545657"));
HomeBG.setBackgroundColor(Color.parseColor("#545657"));
DetailsBG.setBackgroundColor(Color.parseColor("#545657"));
}
});
NightBG is in the same activity as that java file (SettingsActivity). But HomeBG is in MainActivity and DetailsBG is in the DetailsActivity. Everytime I start the app, and press on that button, app craches. If I delete HomeBG and DetailsBG from this file, it works just fine with changing current layout's color to gray. Please help me.

One easy way to store little settings like this across multiple activities that may not be open/active at the time of the button click would be to use SharedPreferences.
It might be a little overkill for such a simple piece of code but you can always give it a try if you don't find anything else.
Your code could look something like this:
toggleNightMode.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
// Set the color of this activity
int color = Color.parseColor("#545657")
View view = SettingsActivity.this.getWindow().getDecorView();
view.setBackgroundColor(color);
// Save color preference
SharedPreferences sharedPref = SettingsActivity.this.getSharedPreferences("bgColorFile",Context.MODE_PRIVATE);
SharedPreferences.Editor editor = sharedPref.edit();
editor.putInt("color", color);
editor.apply();
}
});
And then when you open your activities you place something like this in the onStart() or onCreate() method of your activity:
// Get the color preference
SharedPreferences sharedPref = getSharedPreferences("bgColorFile",Context.MODE_PRIVATE);
int colorValue = sharedPref.getInt("color", 0);
View view = this.getWindow().getDecorView();
view.setBackgroundColor(colorValue);
So what you're actually doing is storing the background color as persistent data and fetching it once you reopen/open the activity that you want to have the color on. The benefit of this method is that whenever you close your app the preferred background color will be remembered. I hope this helps.

Change background for current activity in the same activity. Since DetailsActivity is not running, you can't do that, it gives you null pointer. Is kind of you are trying to eat 3 apples and you have just one. After current activity is started, change background.
Update:
You can do that in current activity and just in current activity:
findViewById(android.R.id.content).setBackground(getColor(R.color.your_color));
Don't try to call this in other activities that are not running.
setBackground()
or
setBackgroundColor()

If your other activities are open, you should send a message to the other activities by using an Intent.
How to send string from one activity to another?
When you receive the Intent you could then set the background of the activity.
If your other activities are not open yet, you will not be able to send an Intent to them. In this case you could have each Activity reference a static value in your main activity that could contain the current background color. You would want to reference that value on the other activities on create functions.
Here is an example on how to reference a variable from another activity.
How do I get a variable in another activity?
This might not be the most pretty way to handle it but it should work.

as Ay Rue said you have 2 options: use static variable for that button, and then in onResume of each activity, check the value of the static variable (true or false). or you can save a private variable nightMode and then pass this value in the intent when you need to move to the other two activities.
don't set the background color if you already set before and have an updated background color.

Avoid splash screen activity when pressing Back button

In my application, I have two activities. First is a splash screen, which simply shows the application name and few other info.
Upon clicking on the splash screen activity, I'm loading the main activity. My app works fine, but I'm facing a small issue. If I press back button from my main activity, control is going to splash screen activity. But I don't want to show the splash screen activity again, I want to avoid splash screen activity when pressing Back button.
Is it possible? If so how?

In your AndroidManifest.xml file, add android:noHistory="true" attribute in your splash screen <activity>.

As I understand, you want the splash activity to not show after changing activity. You should note activities save On Stack and with starting new activity push on it and with finish you pop on top stack. I think that if you the call finish() method your problem fix as in your splash screen activity where you call StartActivity insert finish() after
public void onClick(View v) {
Intent intent = new Intent(Main.this, Splash.class);
startActivity(intent);
finish();
}
Hope to be useful :)

You can just call
finish();
In your Splash screen when you jump to the second screen.

In addition to the above answers, you should note
that:
1: by calling the finish() method, the Splash activity
will close after execution, meaning that it will not be
available in the stack.
#Override
protected void onCreate(Bundle saveInstsnceState){
super.onCreate( saveInstanceState);
\\ do something here
Intent intentSplash = new Intent(SplashActivity.this, NextActivity.class);
StartActivity(intentSplash);
finish ();
}
You will achieve your aim using the method above
but...
2: If you want to prevent your users from force
exiting the app (pressing back button) while the
splash activity in still ongoing which is the best
practice in android, then you need to call the
onBackPressed () method.
Class NoBackSplash{
#Override
protected void onCreate(Bundle saveInstsnceState){
super.onCreate( saveInstanceState);
\\ do something here
Intent intentSplash = new Intent(SplashActivity.this, NextActivity.class);
StartActivity(intentSplash);
finish ();
}
#Override
public void OnBackPressed(){
};
}
With this OnBackPressed() method, your splash activity will not be force to exit no matter how hard the user try.

I understand, you want the splash activity to not show when you click on back button. First of all you should know that all the activities on android are in form of STACK. So what we need we just end the splash activity after it execute. we can do this by calling finish() method in android studio. here is the solution:
Intent intent = new Intent(MainActivity.this, home.class);
startActivity(intent);
finish();

public class Splash extends AppCompatActivity {
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_splash);
Handler hd = new Handler();
hd.postDelayed(new Runnable() {
#Override
public void run() {
Intent i = new Intent(Splash.this,MainActivity.class);
startActivity(i);
#by calling finish() method,splash activity will close after execution
finish();
}
},3000);
}}