I've spent 8 years programming and for 8 years I've been pretty happy, but after using Android Studio for two weeks I already want to

So here's the deal. I made 2 layouts. One is the default, named activity_main.xml, the other is named graph_layout.xml. They are both ConstraintLayouts (but the same issue occurred when I tried making graph_layout a LinearLayout or RelativeLayout, so we can rule that out as a factor).

In activity_main, there's a button with the ID, graph_button_1. When I click it, it prints to the console "AAAAAAAAAAAAAAAAAAAA" (but with more A's) and switches from activity_main layout to graph_layout. As it should, that's precisely what I designed it to do.

Now, here's the problem. I also have a button in graph_layout with the ID, calc_button_3. When I click this button, it's supposed to print to the console "AAAAAAAAAAAAAAAAAAAAA2" (but with more A's) and then switch from graph_layout to activity_main. It doesn't do that, though. It prints to the console a little message that, "yes, you did click the button, here are all the details of how you clicked that button" (I'm paraphrasing), but it does not print "AAAAAAAAAAAAAAAAAAAAAAA2" to the console, nor does it switch back to activity_main. (If you're wondering, the AAAAA message is just to see whether the setOnClickListener functions are actually executing).

Speaking of which, here's what the setOnClickListener does for calc_button_3:

//final Context context = this;
calcButton3.setOnClickListener(new View.OnClickListener() { //I know I can use lambda funcitons, but I wanted to play it safe
    @Override
    public void onClick(View v) {
        //Intent intent = new Intent(context, MainActivity.class); //This was one of the solutions I found online. It does not do anything.
        //startActivity(intent);
        System.out.println("AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA2");
        setContentView(R.layout.activity_main);
    }
});

To be fair, I'm a step in the right direction. Before, this function made my app crash. Now, it just does nothing. So...that's a little better, and I'd like to thank the LayoutInflater class for making that possible. I'd also like to point out that I'm willing to supply you with any code or extra information you might want to see. I'd send the whole MainActivity.java file if I could, but I know from experience the longer I make my question, the less likely people are to answer, and it is a VERY long file.

I've scoured the internet for a solution to this, and while I've found people with a similar problem, none of their solutions worked for me.

Your help is greatly appreciated. Thank you.

Below, I will attach any code or additional info anyone in the comments asks me to give them:

CodePudding user response：

You have to start a new activity using intent or if you want to use the same activity then use fragments. and replace fragment layout on button press. but you can not directly use setContentView();

CodePudding user response：

All setContentView(R.layout.activity_main) does is inflate that layout file into its hierarchy of View objects, and display that in the current Activity. You're still in the same Activity, you've just changed its contents.

When you say you're doing this:

In activity_main, there's a button with the ID, graph_button_1. When I click it, it prints to the console "AAAAAAAAAAAAAAAAAAAA" (but with more A's) and switches from activity_main layout to graph_layout.

does that mean you're "switching" by calling setContentView there too, instead of starting a different Activity that displays graph_layout?

If so, and all your code for both layouts is in the same Activity, then your problem is probably related to the fact you're replacing your Views with a new set of objects when you call setContentView. If you set up your buttons like this:

// a Button from your current view hierarchy gets assigned to this at some point 
val someButton: Button

// just use the lambda, it's literally the same as creating the object under the hood
someButton.setOnClickListener {
    // do a thing
}

And then later you call setContentView(R.layout.some_layout), then whatever Button object someButton is referencing is no longer on the screen. So you can't see it, you can't click it. If you just inflated the same layout as before (creating an entirely seperate set of View objects) then there's another button in the same place - but you haven't set a click listener on it, so it doesn't do anything.

So if you are going to go replacing the view hierarchy like this, then you need to perform your View setup (like assigning click listeners) when you create those new views. If you just set things up when the Activity starts, then it's only applied to the view hierarchy in use at that moment. As soon as you replace it with setContentView, that stuff is gone.

So you could write functions that "switch" to one layout or the other by calling setContentView and then applying the click listeners. Generally speaking though, this isn't how you normally do things in Android. The old way would be to create separate Activities for each screen, a more modern approach is using Fragments which can be swapped out manually or by using something like the Navigation library.

Either way, both those approaches involve configuring your Activity or Fragment once during setup, making buttons do this or that, and then you're done. Everything's neatly separated and self-contained, instead of you having to swap views out and rewire everything according to the state you want to display. That's just complicating things, and it'll get much worse if you start adding more screens you have to juggle!

I'd recommend at least taking a look at the Fragments guide, or the Navigation component if you have time. The latter has more to learn, but it also handles a lot of complexity for you. It would help to at least have an understanding of the usual way of doing things, anyway!