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How to get the context inside a mouse click listener

In Android Studio, developing in Java, I have the following (a somewhat minimized version of what I'm trying to do).
package com.example.japanesequiz;
import androidx.appcompat.app.AppCompatActivity;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.RadioButton;
import android.widget.RadioGroup;
import android.widget.TextView;
import java.util.Random;
public class MainActivity extends AppCompatActivity {
String[] hiragana = {"あ", "か"};
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
Button generate = findViewById(R.id.generate);
TextView questionText = findViewById(R.id.question_text);
RadioGroup radioGroup = new RadioGroup(this);
MainActivity ma_inst = this;
generate.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View view) {
Random rand = new Random();
int hir_index = rand.nextInt(2);
questionText.setText(hiragana[hir_index]);
RadioButton rb1 = new RadioButton(ma_inst);
rb1.setId(View.generateViewId());
rb1.setText("Ah");
radioGroup.addView(rb1);
RadioButton rb2 = new RadioButton(ma_inst);
rb2.setId(View.generateViewId());
rb2.setText("Ka");
radioGroup.addView(rb2);
}
});
}
}
The basic idea is that I want to have the main screen initially mostly blank, but with a button at the bottom. When tapped, it eventually show some text and a radio button group. (I haven't yet fully built out the rest, of course.)
But at this stage what I expect when I launch the app is to see the mostly blank screen, and maybe if I tap the button it will generate some text and options (that then do nothing, further implementation to come).
But the app never launches. Instead, Graddle finishes building, I get a terminal saying that it's launching the app, but it hangs and times out.
If I had to guess -- and this is a guess because I'm very new to Android development -- there is some issue with grabbing the this instance and then using it in the OnClickListener. I'm not certain what the issue is, but it's the only thing I see here that looks fishy. Also, I'm not sure how else one is supposed to add objects to the current activity from inside of the anonymous class passed into the OnClickListener since, there, a reference to this then refers to the anonymous inner class.
I know that it is possible to use a lambda instead, and that probably resolves the issue, but I want to really understand what's going on here, since it seems like it might be conceptually important for later development.
My question: If I have correctly understood this much, then how does a lambda get around this issue? If I've not correctly understood then I'd appreciate any insight, thanks!

There are many questions in one question. First, let me try to answer your title question: "How to get context inside a mouse click listener":
There are many ways, but you can consider this one (your click lisener's onClick has the signature void onClick(View view), hence you have access to view.
view.getContext()
Next, nothing wrong with these though you better migrate to view binding https://developer.android.com/topic/libraries/view-binding as butterknife is deprecated officially
Button generate = findViewById(R.id.generate);
TextView questionText = findViewById(R.id.question_text);
Next, you don't really need this trick in order to get activity in your lambda:
MainActivity ma_inst = this;
Instead and if really needed, you can always do Context context = MainActivity.this;
Lastly, I think the issue the app never launches roots into something else not related with title question you posted, unfortunately.

Crosswalk call Java method from JavaScript

I'm using crosswalk now. I need to call a Java method when a user clicks a button in the HTML, which may look like:
Start
I'm not sure if Crosswalk extension is what I wanted, which seems to be so heavy-weighted just for calling a Java function.
Is there a simpler way to do this? Or should I use Cordova with Crosswalk in this case?

Here is about how to call java function with js in the crosswalk XWalkView. How to use XWalkView refer this answer.
References:
crosswalk-calling-java-methods-with-javascript
XWalkView manual
Below is the process to call java from js, and notices.
add this to activity you XWalkView in
webSettings.setJavaScriptEnabled(true);
mXWalkView.addJavascriptInterface(new JsInterface(), "NativeInterface");
and this, you also make it a class
public class JsInterface {
public JsInterface() {
}
#JavascriptInterface
public void act() {
//do something
}
}
and in the html page
<button onclick="NativeInterface.act()">Call Java Here</button>
when you import JavascriptInterface, take care, make sure you imported the exact one.
import org.xwalk.core.JavascriptInterface;
Not this one, this is for webview
import android.webkit.JavascriptInterface;
If you import this one, this will cause no action when you operation on the page and below error in your android studio.
12-02 13:24:49.921 12376-12376/com.xxxxxx.app E/chromium:
[ERROR:xwalk_autofill_client.cc(121)] Not implemented reached in
virtual void xwalk::XWalkAutofillClient::OnFirstUserGestureObserved()
Usually when you import the JavascriptInterface, the first one is what we want just like below pic shows.
But sometime when you change from webview to XWalkView, you may forget to change the JavascriptInterface.

If you are only using XWalkView as an embedded view, the addJavascriptInterface is sufficient to inject Java object into XWalkView(JavaScript), which is just like the addJavascriptInterface in android.webkit.WebView:
https://crosswalk-project.org/apis/embeddingapidocs_v2/reference/org/xwalk/core/XWalkView.html
http://developer.android.com/guide/webapps/webview.html#BindingJavaScript

What is the difference between specifying a class in these two ways?

I can run this code in my computer:
getWindow().addFlags(WindowManager.LayoutParams.FLAG_KEEP_SCREEN_ON);
inside onResume(). I sent the code to someone else for testing. But they tell me that that this line shows an error in their SDK, and replacing it with
getWindow().addFlags(android.view.WindowManager.LayoutParams.FLAG_KEEP_SCREEN_ON);
works, while in my case, both the codes work. Why is this happening?
PS: My SDK version is the one with the zip file name adt-bundle-windows-x86-20130522. I am not sure the exact version they are using, but it is newer than mine.

WindowManager is a class in the Android SDK. Its fully qualified name is android.view.WindowManager. The WindowManager.LayoutParams is a nested class of WindowsManager and its fully qualified name is android.view.WindowManager.LayoutParams
You can either specify the fully qualified name when you want to use it.
getWindow().addFlags(android.view.WindowManager.LayoutParams.FLAG_KEEP_SCREEN_ON);
or you can import its outer class
import android.view.WindowManager;
and use it directly
getWindow().addFlags(WindowManager.LayoutParams.FLAG_KEEP_SCREEN_ON);

progressbar circle in SherlockActionBar using Fragments

I have a SherlockFragmentActivity using tabhost and viewpager. Calling
requestWindowFeature(Window.FEATURE_INDETERMINATE_PROGRESS);
in the fragmentactivity creates the spinner, and calling
setSupportProgressBarIndeterminateVisibility(false);
won't disable it. I also don't seem to be able to call getActivity().setSupportProgressBarIndeterminateVisibility(false);
from the fragments;
I get the error "The Method setSupportProgressBarIndeterminateVisibility(boolean) is undefined for the type FragmentActivity."
What am I doing wrong, can someone show me the way how to use it properly in fragments? I want to be able to create the progressbar in my asynctask pre execute and stop it in postexecute.
I'm using2.2 emulator and importing import com.actionbarsherlock.view.Window; instead of the android.view one.
[Edit] I just confirmed using setProgressBarIndeterminateVisibility works in the 4.1 emulator. Anyway, I need to get this work in 2.2

"I also don't seem to be able to call getActivity().setSupportProgressBarIndeterminateVisibility(false); from the fragments;"
You need to be calling getSherlockActivity() instead of getActivity().
"I'm using2.2 emulator and importing import com.actionbarsherlock.view.Window; instead of the android.view one."
Plus one for that, hadn't spotted that import and came across this post which fixed my bug - wasn't showing the progress indicator in Gingerbread before, many thanks :)

This works perfect for me:
getActivity().setProgressBarIndeterminate(true);
ProgressDialog progressDialog = new ProgressDialog(getActivity());
progressDialog.show(getActivity(), "This is", " a message...");
May you help ;)

Trying to make a Adapter class to choose .Java file depending on firmware version

What I did was create two .java files. One that can compile and run on a 1.5 phone (SDK3) and then one that works on 2.0(SDK5) So for this example i'll call the 1.5 file ExampleOld and the new one Example. I was wondering if i just made activity like this if it would work sort of like a "portal" and pick the activity to load depending on the SDK so there is no crash or compile errors. Are there any changes I should make to my code? Maybe anyone out there that's had to do this before. thanks!
package com.my.app;
import android.app.Activity;
import android.content.Intent;
import android.os.Build;
import android.os.Bundle;
public class ExamplePortal extends Activity {
int sdk=new Integer(Build.VERSION.SDK).intValue();
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
if (sdk<5) {
Intent v = new Intent(this, ExampleOld.class);
startActivity(v);
}
else {
Intent v = new Intent(this, Example.class);
startActivity(v);
}
}
}

What you're doing (correct me if I'm wrong) is trying to maintain backwards compatibility while making use of new APIs if the user is running a newer android version. The best way to do this is to follow the tutorial Google posted here. This avoids any verification issues and is really the best way to do stuff imho.

I would put this decision in a Factory Class to avoid having these if-else statements all over the codebase.