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How to delete individual elements from textview on Android studio

I am doing this project, can anyone help me to delete individual elements from the text view?enter image description here
here's i implemented the 'button' to insert and 'button2' to delete, and here's the code down bellow
public class MainActivity extends Activity {
private EditText editText;
private Button button;
private TextView textView;
private static final String TAG = "MainActivity";
// To hold all data in different mode : Portrait and landscape
private final String text_context = "TX";
#Override
protected void onCreate(Bundle savedInstanceState) {
Log.d(TAG, "onCreate: in");
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
editText = (EditText)findViewById(R.id.editText);
button = (Button)findViewById(R.id.button);
textView = (TextView)findViewById((R.id.textView));
textView.setText(""); // make it no text at runtime, but text at view
textView.setMovementMethod(new ScrollingMovementMethod()); // make it scrolling
editText.setText("");
final View.OnClickListener onClickListener = new View.OnClickListener() {
#Override
public void onClick(View view) {
String result = editText.getText().toString();
result += "\n";
textView.append(result);
editText.setText(""); // text on EDITTEXT will disappear as soon as we click the button
}
};
final View.OnClickListener onClickListener1 = new View.OnClickListener() {
#Override
public void onClick(View view) {
}
};
if(editText != null)
button.setOnClickListener(onClickListener);
Log.d(TAG, "onCreate:out");
}
}
Please help me TO IMPLEMENT DELETE ACTION VIA BUTTON2....

Right now your onclick listeners are generically listening for clicks on any view.
button.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
// Handle button events
}
});
button2.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
// Handle button2 events
}
});
Or better yet implement View.OnClickListener() on your activity

Use regex
String input = editText.getText().toString();
String regex = "\\b" + input + "\\b";
String tvText = textView.getText().toString();
tvText = tvText.replaceAll(regex, "");
textView.setText(tvText);
Put this code in
final View.OnClickListener onClickListener1 = new View.OnClickListener() {
#Override
public void onClick(View view) {
//code goes here
}
};
if(editText != null)
// add this onclick to your button2
button2.setOnClickListener(onClickListener1);
Log.d(TAG, "onCreate:out");
}

Null pointer on not null index? [duplicate]

This question already has answers here:
What is a NullPointerException, and how do I fix it?
(12 answers)
Closed 5 years ago.
Like in subject. I got null pointer, how it is possible ?
java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.Button.setOnClickListener(android.view.View$OnClickListener)' on a null object reference
public class MainActivity extends AppCompatActivity {
Button button, button2;
TextView textView, textView2;
String abc;
public List list = new ArrayList<>();
int size;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
list.add("abc");
abc = (String) list.get(0);
button.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View view) {
textView.setText(abc);
}
});
button2.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View view) {
size = list.size();
textView2.setText(size);
}
});
}
}

You just forgot to do findViewById to your Controls in OnCreate()
button2 =(Button) findViewById(R.id.button2);
button = (Button) findViewById(R.id.btnID);
textView2 =(textView) findViewById(R.id.textView2);
Sample code
#Override
protected void onCreate( Bundle savedInstanceState ){
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
button = (Button) findViewById(R.id.mybtnID);
button2 = (Button) findViewById(R.id.button2);
textView2 = (textView) findViewById(R.id.textView2);
list.add("abc");
abc = (String) list.get(0);
button.setOnClickListener(new View.OnClickListener(){
#Override
public void onClick( View view ){
textView.setText(abc);
}
});
button2.setOnClickListener(new View.OnClickListener(){
#Override
public void onClick( View view ){
size = list.size();
textView2.setText(size);
}
});
}

You are missing
findViewById for all your widget
i.e.
Button button, button2;
TextView textView, textView2;
button = findViewById(R.id.id_of_button_1); // same for button2,textview,textview2

You can initialize with findById(R.id.myBtn) like everyone is saying. Or programatically like button = new Button(this);

Try this
You forgot to add findViewById
public class MainActivity extends AppCompatActivity {
Button button, button2;
TextView textView, textView2;
String abc;
public List list = new ArrayList<>();
int size;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
button=(Button)findViewById(R.id.button);
button2=(Button)findViewById(R.id.button2);
list.add("abc");
abc = (String) list.get(0);
button.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View view) {
textView.setText(abc);
}
});
button2.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View view) {
size = list.size();
textView2.setText(size);
}
});
}
}

Try this are missing findViewById for all your widget
button = (Button) findViewById(R.id.btnID);
button2 =(Button) findViewById(R.id.button2);
textView = =(textView) findViewById(R.id.textView);
textView2 =(textView) findViewById(R.id.textView2);
Sample Code
public class MainActivity extends AppCompatActivity {
Button button, button2;
TextView textView, textView2;
String abc;
public List list = new ArrayList<>();
int size;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
button = (Button) findViewById(R.id.btnID);
button2 =(Button) findViewById(R.id.button2);
textView = =(textView) findViewById(R.id.textView);
textView2 =(textView) findViewById(R.id.textView2);
list.add("abc");
abc = (String) list.get(0);
button.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View view) {
textView.setText(abc);
}
});
button2.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View view) {
size = list.size();
textView2.setText(size);
}
});
}
}

Multiple buttons in MainActivity Android studio

public class MainActivity extends AppCompatActivity implements View.OnClickListener {
EditText textmsg;
static final int READ_BLOCK_SIZE = 100;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
textmsg = (EditText) findViewById(R.id.editText1);
}
#Override
public void onClick(View v) {
Button noteBtn = (Button) findViewById(R.id.noteBtn);
Button resuBtn = (Button) findViewById(R.id.resuBtn);
Button agenBtn = (Button) findViewById(R.id.agenBtn);
noteBtn.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
Intent intent = new Intent(MainActivity.this, Notes.class);
}
});
resuBtn.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
Intent intent = new Intent(MainActivity.this, Results.class);
}
});
agenBtn.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
Intent intent = new Intent(MainActivity.this, Agenda.class);
}
});
When I run the application the buttons don't work. If I set the buttons as so..
public class MainActivity extends AppCompatActivity {
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
Button agenBtn = (Button) findViewById(R.id.agenBtn);
Button resuBtn= (Button) findViewById(R.id.resuBtn);
Button noteBtn = (Button) findViewById(R.id.noteBtn);
agenBtn.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
Intent intent = new Intent(MainActivity.this, Agenda.class);
startActivity(intent);
}
}); etc...
If I use this code above, the code works fine and the buttons work correctly. But other functionality with different classes/activities won't run. Could someone please show me a solution or explain how to solve this issue.

You should place:
this.noteBtn = (Button) findViewById(R.id.noteBtn);
this.notBtn.setOnClickListener(this);
this.resuBtn = (Button) findViewById(R.id.resuBtn);
this.resuBtn.setOnClickListener(this);
this.timeBtn = (Button) findViewById(R.id.timeBtn);
this.timeBtn.setOnClickListener(this);
in onCreate() instead of onClick(). Make the buttons belong to the class, so you can reference them in onClick(). You should not be setting new onClickListeners in onClick(), but should rather have a switch statement based on the clicked view's id to determine which button was pressed.

this code
#Override
public void onClick(View v) {
Button noteBtn = (Button) findViewById(R.id.noteBtn);
Button resuBtn = (Button) findViewById(R.id.resuBtn);
Button timeBtn = (Button) findViewById(R.id.timeBtn);
...
}
is not working because it's never going to get call, since none of your buttons is implementing it, worse yet they have not even been initialized because the onClick has not and will never be called.
the correct way to do it is like:
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
Button but1 = (Button) findViewById(R.id.but1);
Button resBtn = (Button) findViewById(R.id.resBtn);
Button noteBtn = (Button) findViewById(R.id.noteBtn);
agendaBtn.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View viewTimeTable) {
Intent intent = new Intent(MainActivity.this, Agenda.class);
startActivity(intent);
}
}); etc...
because you are first getting a reference to your buttons and assigning them the onClickListener to each one of it.
I will suggest reading more about the Android Activity life cycle you can find it
here

Button that Plays Sound in Android Studio not Playing

I am trying to make a simple button that plays a sound, but I am getting an error on (this, R.raw.shotgun). I have the raw folder and the sound file. I think the problem is with the this but I don't know why. Thanks.
public class MainActivity extends AppCompatActivity {
private Button button;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
Button button = (Button) findViewById(R.id.button);
button.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
MediaPlayer mp = MediaPlayer.create(this, R.raw.shotgun);
mp.start();
}
});
}
}

The first parameter of MediaPlayer.create is a Context. The usage of MediaPlayer.create(this, R.raw.shotgun) works when you are working in your Activitys scope, because Activity extends Context, therefore this in this case ends up being a Context as well.
However, you're working within View.OnClickListener scope, and this assumes this class' value, and not Context as required. To fix that, just set the Context variable to this while still in your Activity scope.
public class MainActivity extends AppCompatActivity {
private Button button;
Context context;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
context = this;
Button button = (Button) findViewById(R.id.button);
button.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
MediaPlayer mp = MediaPlayer.create(context, R.raw.shotgun);
mp.start();
}
});

Adding second onClick method in Android Studio?

I've just started to learn Java and I've been stumped on adding the code for a second button in an activity. I apologize for my (possible dumb question) and any wrong terminology.
Here is the MainActivity Java code:
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
Button btnGo = (Button) findViewById(R.id.btnGo);
btnGo.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
startActivity(new Intent(MainActivity.this, GoActivity.class));
}
});
}
}
How can I add to this code for btnEscape to go to EscapeActivity?

You just have to do exacly the same thing you do with btnGo - this is find your button by id, and then set clickListener to it. It could looks like that:
Button btnEscape = (Button) findViewById(R.id.btnEscape);
btnEscape.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
startActivity(new Intent(MainActivity.this, EscapeActivity.class));
}
});

The optimised way to do that is implement your class with View.OnClickListener and override the method onClick and inside it use switch cases to switch between views and apply on clicks like this:
public class SampleActivity extends AppCompatActivity implements View.OnClickListener{
Button btnGo,btnEscape;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
btnGo = (Button) findViewById(R.id.btnGo);
btnEscape= (Button) findViewById(R.id.btnEscape);
btnGo.setOnClickListener(this);
btnEscape.setOnClickListener(this);
}
#Override
public void onClick(View v) {
switch (v.getId()){
case R.id.btnGo:
startActivity(new Intent(MainActivity.this, GoActivity.class));
break;
case R.id.btnEscape:
startActivity(new Intent(MainActivity.this, EscapeActivity.class));
break;
default:
break;
}
}
}

In code, what the two comments by Shiram and Nik above are saying is to add the block below that begins Button btnEscape... after Button btnGo.setOnclick's block.
#Override
protected void onCreate(Bundle savedInstanceState) {
...
Button btnGo = (Button) findViewById(R.id.btnGo);
...
Button btnEscape = (Button) findViewById(R.id.<<name of button in xml>>);
btnEscape.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
... whatever ... }
});
}
In short, the following is a really good pattern to have at your fingertips:
Button btn___ = (Button) findViewById(R.id.<<name of button in xml>>);
btn___.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
... whatever ... }
});