Why is mainB_news allways null? (in the method onBackPressed())
In onCreate I set a value to the button!!! :(
PS: with findViewById() I get the same error...
public class MainActivity extends Activity {
private Button mainB_news;
/** Called when the activity is first created. */
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
mainB_news = (Button) findViewById(R.id.mainB_news);
mainB_news.setOnClickListener(new View.OnClickListener() {
public void onClick(View v) {
setContentView(R.layout.news);
}
});
}
#Override
public void onBackPressed() {
// check if page 2 is open
if (mainB_news != null && mainB_news.isShown()){
setContentView(R.layout.main); // open main view again
return;
}else
super.onBackPressed(); // allows standard use of backbutton for page 1
}
}
THANKS a lot!
Because you change contentView on button click. mainB_news doesn't exist after contentView changing. You shouldn't use setContentView() in this manner. Consider using another activity for showing news.
Because it is not defined in res/layout/main.xml ?
Related
for my android app, I use a button to go to the next Activity.
the problem is when I touch the button on the screen one instance of the activity is created but when
I use performClick() method to click the button programmatically, it creates two instances of the activity. ( performClick() is called from a callback method).
I used the CLEAR_TOP FLAG but it seems to break the back button.
Any idea how to solve this problem ?
this is what my code looks like:
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
Button btn = (Button)findViewById(R.id.btn);
btn.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(final View v) {
startActivity(new Intent(Activity1.this, Activity2.class));
}
});
}
private void A_callback_method(){
if (some_condition_to_launch_activity){
btn.performClick();
}
}
Just a simple trick. create function
private void function_name(){
startActivity(new Intent(Activity1.this, Activity2.class));
}
Then on the button onClickListener
btn.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(final View v) {
function_name();
}
});
and also inside A_callback_method
private void A_callback_method(){
if (some_condition_to_launch_activity){
function_name();
}
}
hope this will solve your problems.
I succesfully did a work around to solve this problem by adding a boolean variable intialise it to false in the onResume() method and then did the following:
private boolean clicked_btn;
private void A_callback_method(){
if ((some_condition_to_launch_activity)&&!clicked_btn){
clicked_btn=true;
btn.performClick();
}
}
I am new to Android Programming and I am making a simple browser in which I want to open my web activity by clicking the button but I am amazed to see that setOnClicklistener is not available in Android Studio 3.5 as I have just updated
You need to put the setOnClickListener in one of the activity callbacks. In your onCreate() method, move the button there and then setOnClickListener().
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.filters);
Button button = findViewById(R.id.google);
button.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
//TODO()
}
}
}
Access/init Your button inside onCreate() method.
private Button btn;
#Override
public void onCreate(#Nullable Bundle savedInstanceState, #Nullable PersistableBundle persistentState) {
super.onCreate(savedInstanceState, persistentState);
setContentView(R.layout.home_search_layout);
btn = findViewById(R.id.someId);
setClickListener();
}
private void setClickListener() {
btn.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
}
});
}
All the functional elements' code is to be initialized in the activity's onCreate() method. Since you want to make a button clickable, you need to add the setOnClickListener() in the onCreate() method, like so:
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_selectionactivity);
Button button = findViewById(R.id.google); //this id should be of a button not a view
button.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
//TODO do something
}
}
}
I highlighted some text because from the image, you can see that the 9th that you get from the code completion menu is the setOnClickListener but the parent is from the group android.view.View but not from android.widget.Button. Make sure, that R.id.google is a Button and also put the code inside onCreate()
I made one of the simplest programs that creates a login page, however, I cannot add an OnClickListener to my button, and I do not know why. I'm really new to Android Studio and have no idea what to do. When I hover over the error it says "In View cannot be applied".
I've tried these bits of code found on the internet, but the error doesn't leave, and the machine says that the #Override does not override what's above.
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_teacher_in_j);
regist1 = (Button)findViewById(R.id.btnregister1);
regist1.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View view) {
Intent teachtoregist = new Intent(TeacherInJ.this, TeacherRegisterInJ.class);
startActivity(teachtoregist);
}
});
etUsername = (EditText) findViewById(R.id.editText2);
etPassword = (EditText) findViewById(R.id.editText3);
bLogin = (Button) findViewById(R.id.btnlogin);
bLogin.setOnClickListener(this);
}
#Override
public void onClick(View v) {
switch (v.getId()) {
case R.id.btnlogin:
//Start activity one
break;
When I hover over the error it says "In View cannot be applied".
I've tried these bits of code found on the internet, but the error doesn't leave, and the machine says that the #override does not override what's above.
Both the above problems are because you didn't add the implements keyword to your Activity. You need to add it so the Activity can be regarded as OnClickListener interface by the button.
You need to do something like this (See the comments inside the code):
// see below the implements View.OnClickListener line that
// need to be added so the Activitiy can be regarded as the listener.
public class TeacherInJ extends AppCompatActivity implements View.OnClickListener {
...
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_teacher_in_j);
...
// now you can use this as the listener. It's because you have
// set the current Activity class as the View.OnClickListener
// this is refer to current Activity object.
bLogin.setOnClickListener(this);
}
// Now you can add the #Override to the onClick method from
// the View.OnClickListener.
#Override
public void onClick(View v) {
switch (v.getId()) {
case R.id.btnlogin:
//Start activity one
break;
}
}
}
I'm trying to learn android development with Android Studio but I can't seem to figure out why my clicks are not registering. Is there something I'm missing here?
I don't like the way Stack Overflow FORCES me to format things they way THEY want. Here is pastebin! :_
http://pastebin.com/hdzZpsud
call this changeText() method inside onCreate() method of your activity
your activity should look like this:
public class MyActivity extends Activity {
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_my);
changeText();
}
public void changeText(){
final Button button = (Button) findViewById(R.id.button1);
final TextView text = (TextView)findViewById(R.id.largetext);
button.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View view) {
button.setText("Button has been pressed");
text.setText("The large text has been changed");
}
});
}
}
In fact, you didn't set the listener. So you should add changeText() after setContentView(R.layout.activity_my);.
I am trying to create an Android app, and i want to create a on click listener, here is what I have so far.
public void amazonListener() {
amazonButton = (Button) findViewById(R.id.amazonButton);
}
As you see, i am in the very early stages, but where I first referenced amazonButton (before the = sign) button, it turns into red text and it says Cannot resolve symbol 'amazonButton'. Also, I have referenced this method in the onCreate method
This is how you'd go about creating a button and setting a click listener to it.
public class MainActivity extends YouTubeFailureRecoveryActivity {
Button amazonButton;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
amazonButton = (Button) findViewById(R.id.amazonButton);
amazonButton.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
//Define what should happen when the button is clicked.
}
});
}
}
You can also put the initializations in a single method and call that method, like you've tried :
public class MainActivity extends YouTubeFailureRecoveryActivity {
Button amazonButton;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
initializeViews();
}
private void initializeViews() {
//Make sure you've declared the buttons before you initialize them.
amazonButton = (Button) findViewById(R.id.amazonButton);
amazonButton.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
//Define what should happen when the button is clicked.
}
});
// Add more Views initialization here ...
....
}
}
You need to give the type of the variable when you declare it.
Button amazonButton = (Button) findViewById(R.id.amazonButton);
The alternative is to declare it (but not initialize it) outside of any method and then initialize it later.
Button amazonButton;
/* ... */
private void amazonListener() {
amazonButton = (Button) findViewById(R.id.amazonButton);
}