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The value of QR Code Scanner cannot show on new activity

I am trying to make a simple QR Code scanner and run well if the result shows in the MainActivity. But when I'm trying to generate new Activity as a result, it can't show. Would you like to help me with this problem? Thank you.
Here is the result of the scanner code in the scanner.java:
#Override
public void handleResult(Result rawResult) {
startActivity(new Intent(getApplicationContext(),ResultActivity.class));
ResultActivity.scanText2.setText(rawResult.getText());
onBackPressed();
}
And here is the code of my new Activity for showing the result:
public class ResultActivity extends AppCompatActivity {
public static TextView scanText2;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_patient);
scanText2 = (TextView) findViewById(R.id.scanText2);
}
}

There are a lot of issues with this:
You are launching PatientActivity, not ResultActivity in handleResult()
You are trying to set the value of a TextView in another Activity with this code:
ResultActivity.scanText2.setText(rawResult.getText());
This is an absolute no-no. Pass the data to ResultActivity as an Intent extra when you launch it. You cannot access the views of another Activity like that.
You expect that ResultActivity.scanText2 will contain a reference to a TextView, but at this point it will only contain null. The reason is that it takes some time for ResultActivity to actually start and call its onCreate(). You have not accounted for this timing in your code. To solve this problem, just see (2) above.
Also, you should have gotten a bunch of crashes with useful messages in your logcat. In the future please look there to solve problems and/or post the messages with stacktrace in your Stackoverflow questions.

How can I let another class know that a button was clicked (Android Studio)

Below is the code which I'm using to return a number which should be 1 when the button is clicked. However when I try to get that number from another class, it always stays 0.
As you might recognize, I tried to change the number in the onClickListener and returned it below.
I also tried to use the onPause command so that it will return the number onPause but it still doesn't work.
public class MainActivity extends Activity {
public int number;
Button btnAngled;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_my);
btnAngled = (Button) findViewById(R.id.btnAngled);
final Intent intent = new Intent(this, angledForeheadActivity.class);
btnAngled.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View view) {
number = 1;
startActivity(intent);
}
});
}
#Override
protected void onPause() {
super.onPause();
}
public int getNumber() {
return number;
}
}
I try to get the code in another class with:
MainActivity a = new MainActivity();
int number = a.getNumber();
Sorry for the noob question..

declare the variable as static variable. Then you can simply obtain the result you want since there is only one copy of that variable. If you want to pass the value using intent, you can call putExtra() of intent to carry information to another activity.
Intent reference page

What you actually want is getting the number from another Class. Don't mix the job with button click together. You should setup the concept of model to store data and seperate UI and data, UI just change/get the data.
I suggest you either of the two ways
Store the number in some global model, then you can get the number from another Class.
User Android Broadcast to transfer the data
Use static variable in Activity is not a good idea, it may cause memroy leak, though it can solve your problem.

Using buttons on android - newbie

I am a newbie to android development, trying to get buttons working. every time i use this code below, the error message "unfortunately the app has stopped". but when i remove the code the app runs but obviously the buttons do nothing. here is the code ive tried
public class MyActivity extends Activity {
/**
* Called when the activity is first created.
*/
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
Button button1 = (Button) findViewById(R.id.ExerciseButton);
button1.setOnClickListener (new View.OnClickListener(){
public void onClick(View v) {
setContentView(R.layout.exercises);
}
});
}
}
anybody able to help me out there? thanks

Don't try to load another View in the current activity. Navigate to a new ExercisesActivity.
Use:
public void onClick(View v) {
Intent intent = new Intent(ExercisesActivity.this, WcActivity.class);
startActivity(intent);
}

You can't call setContentView anymore after the view has loaded (which it obviously has to receive button clicks). Use a different approach, like showing and hiding views or using a ViewFlipper (see Calling setContentView() multiple times), using fragments (see Fragments) or starting a new activity.

Well, from your code, I see a couple of things:
I am usually familiar to using the onClickListener of the Button class if I want to use it for a button. Makes sense, doesn't it?
buttonOne.setOnClickListener(new Button.OnClickListener() {
public void onClick(View v) {
//Do stuff here
}
Second thing:
Start a new Activity (if that is what you want) by using an Intent:
Intent myIntent = new Intent(this, exercises.class);
startActivity(myIntent);

You CAN absolutaly call setContentView on any event, even after the view has loaded
I tried your code in a demo project and it is working fine. So, i think the error will be some where in your layout.(Let me know more if you need more help on this)

Opening Android system apps/utilities

I am learning Android. I learned to use my app to start another app I wrote. Using this code below:
public class MainActivity extends Activity {
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
Button appOpener = (Button) findViewById(R.id.button1);
appOpener.setOnClickListener(new View.OnClickListener(){
public void onClick(View v){
Intent i = new Intent(Intent.ACTION_MAIN);
PackageManager firstApp = getPackageManager();
i = firstApp.getLaunchIntentForPackage("com.assignment.projecttomiko");
}
});
}
It's pretty straight-forward and I am happy wit it. But now I want to start apps already on the Android platform itself, like browser, calender, calculator, etc. From the above, I see I just have to put in the package name of my other apps. I am assuming I can do the same thing to say start a calculator. Or maybe not. What is the best way to do this? If I can use package names, then what are the package names of these in-built apps. If there's a better way I would like someone to help me out.
I read this: Opening System Application Using Intent and realised there's an introduction of an extra LaunchComponent I don't know what that is but the main thing is I see on that thread that they are also putting in some package names to call system apps. What'll be your best way to get this done? :)
EDIT:
I searched for hours and tried this code but doesn't work :(
// activity name and package for stock calculator
private static final String CALCULATOR_PACKAGE_NAME = "com.android.calculator2";
private static final String CALCULATOR_CLASS_NAME = "com.android.calculator2.Calculator";
public void launchCalculator() {
Intent intent = new Intent();
intent.setAction(Intent.ACTION_MAIN);
intent.addCategory(Intent.CATEGORY_LAUNCHER);
intent.setComponent(new ComponentName(CALCULATOR_PACKAGE_NAME,
CALCULATOR_CLASS_NAME));
try {
this.startActivity(intent);
} catch (ActivityNotFoundException noSuchActivity) {
// handle exception where calculator intent filter is not registered
}
}

My Simple ListView app is leaking memory. What am I doing wrong?‏

First off, I did post this to the android google group first but its moderated and I'm not sure how long itll take to show up there so hoping someone here can help.
I created a simple app with a ListView following the ListActivity
examples I found on the net.
The app has 2 activities with the first having a button to create the
second. When i hit the close button on the second activity I would
like it to release its memory (or at least allow it to be garbage
collected). Currently it will never release.
I must be doing something wrong here because the MyListActivity never
gets released. Can anyone tell me if I am doing something wrong with
the way my activities are created/destroyed? or if my usage of the
ListView is wrong?
Thanks.
My App as a zip - http://www.mediafire.com/?l26o5hz2bmbwk6j
Screen Shot of Eclipse MAT showing the list activity never releasing
memory - www.mediafire.com/?qr6ga0k
public class MyListActivity extends ListActivity {
/** Called when the activity is first created. */
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.listlayout);
ListAdapter ada = new ArrayAdapter<String>(this,android.R.layout.simple_list_item_1, GENRES);
setListAdapter(ada);
}
#Override
public void onDestroy()
{
super.onDestroy();
System.gc();
}
public void ClickHandler(View target)
{
switch (target.getId())
{
case R.id.LL_Btn1:
finish();
break;
}
}
private static final String[] GENRES = new String[] {
"Action", "Adventure", "Animation", "Children", "Comedy", "Documentary", "Drama",
"Foreign", "History", "Independent", "Romance", "Sci-Fi", "Television", "Thriller"
};}
public class MainActivity extends Activity {
/** Called when the activity is first created. */
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
}
public void ClickHandler(View target)
{
switch (target.getId())
{
case R.id.M_Button01:
Intent intent = new Intent();
intent.setClassName(MyListActivity.class.getPackage().getName(), MyListActivity.class.getName());
startActivity(intent);
break;
}
}}

Have you tried getting rid of System.gc() and see what happens? Calling System.gc() is merely telling the VM to initiate garbage collection - there is no guarantee when it will be done.

Not sure if this will help, and its not generally recommended to do this, but the following will kill your process in onDestroy():
System.runFinalizersOnExit(true);
android.os.Process.killProcess(android.os.Process.myPid());
Put that in the onDestroy method. Now this may actually kill your main process if called from a child activity (havn't tested it).
WARNING: I generally don't recommend doing this as its a "hackly" way of doing it, but if you just need your app (or activity) to close upon exit then this will work. You still need to debug to find out why your app is staying open and eating memory.

Eclipse MAT was the cause. New Android Studio doesn't cause these problems.