This question already has answers here:
Unfortunately MyApp has stopped. How can I solve this?
(23 answers)
Closed 2 years ago.
I am new to android programming and I can't figure out what i'm doing wrong.
My code:
Every time I run the code, the emulator works just fine, but when I try to open the app it show the error message.
Please help. Thanks.
first you must inflate your layout by setContentView method .
second in onCreate method , bind your view .
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.your_activity_layout);
TextView tf1 = (TextView) findViewById(R.id.tf0);
tf1.setText("Hello World!");
}
You must call setContentView before calling findViewById.
void onCreate() {
super.onCreate()
setContentView(R.layout.my_activity_layout)
TextView tf1 = findViewById(R.id.tf0)
tf1.setText("hello")
}
You need SetContentView(R.layout.your_layout) before calling findViewById.
For example:
super.onCreate(savedInstanceState);
setContentView(R.layout.your_layout);
tf1 = findViewById(R.id.tf0);
tf1.setText("text")
I suspect tf1 is null because the layout hasnt been inflated yet also setContentView(view) is required to be called in onCreate to inflate the view. Also at the point you are declaring the tf1 (outside onCreate) the reference will be null.
Try this
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
TextView tf1 = (TextView) findViewById(R.id.tf0);
tf1.setText("Hello World!");
}
Related
lately, I was working on a very small training project.
But there is one error in my code:
public class MainActivity extends AppCompatActivity {
TextView textView = (TextView) findViewById(R.id.textview);
#override
protected void onCreate (Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
textView.setText("Welcome");
}
}
but when I tried to cut the textview global variable and paste it inside the onCreate method, the error has gone. Why is this error occur although I already have inflated the textView in a global variable ?!
You need to call findViewById(...) after calling setContentView(...).
Fetching the view before inflating the layout isn’t possible since there is no view.
findViewById() should only be used after setContentView() in onCreate.
That's where your entire layout get inflated. Only then you can access views using findViewById().
This is what you want:
public class MainActivity extends AppCompatActivity {
TextView textView;
#override
protected void onCreate (Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
textView = (TextView) findViewById(R.id.textview);
textView.setText("Welcome");
}
}
This question already has answers here:
Can not find a View with findViewById()
(4 answers)
Closed 5 years ago.
public class MainActivity extends AppCompatActivity {
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
String test = "test";
TextView text = (TextView) findViewById(R.id.textView);
text.setText(test);
setContentView(R.layout.activity_main);
}
The problem started in a fragment, I tried all StackOverflow solutions to no avail so I made a fresh build and now I'm just trying to make it work in MainActivity. Can someone please explain why this code does not update the textView, and why it is caushing a crash.
Note: I have tried making my own setText() methods, i've tried using strings and char arrays from other safer locations, I've moved the code before and after setContentView(), and if its just another way of coding the above^ in a different way, I've probably tried it. Pretty much each thing I try leads to the same result. This leads me to believe the solution isn't just in the code above, but something else overlooked, and probably a simple fix. Thanks!
EDIT: Here is my xml, my freshman CS senses tingle seeing the android:text="" line.
<TextView
android:id="#+id/textView"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="TextView"
app:layout_constraintLeft_toLeftOf="parent"
Try this code You must call the setcontentView method before calling findViewById method
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
String test = "test";
TextView text = (TextView) findViewById(R.id.textView);
text.setText(test);
}
Closed. This question needs debugging details. It is not currently accepting answers.
Edit the question to include desired behavior, a specific problem or error, and the shortest code necessary to reproduce the problem. This will help others answer the question.
Closed 6 years ago.
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I do not get any errors but when I run the app it crashes:
public class MainActivity extends AppCompatActivity {
ImageButton Nr1 = (ImageButton) findViewById(R.id.ImageButton1);
public void machwas(View v) {
Nr1.setImageResource(R.drawable.x);
}
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
}
}
This here is wrong:
public class MainActivity extends AppCompatActivity {
ImageButton Nr1 = (ImageButton)findViewById(R.id.ImageButton1);
because findViewById() should be called INSIDE the onCreate method, the reason is that after that are layouts inflated and you are ready to get the views and initialize the widgets...
so what you are doing is initializing the ImageButton wrongly, probably will be null after that line and then this here
public void machwas(View v){
Nr1.setImageResource(R.drawable.x);
}
is going to explode with a NullPointer Exception...
but this is only an inference because you dont post the LogCat...
For more info please take a look to the Activity lifeCycle and the Official Android Documentation
findViewById() searches the view that is set by setContentView(). In your code findViewById() is called before onCreate() so there's no view set yet and due to that all finds will fail and you will always get null there.
BTW: consider using helpers like ButterKnife
You have to call findViewById after view created.
public class MainActivity extends AppCompatActivity {
ImageButton Nr1 ;
public void machwas(View v){
Nr1.setImageResource(R.drawable.x);
}
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
Nr1 = (ImageButton)findViewById(R.id.ImageButton1);
machwas(0);
}
}
I'm trying to execute more then one layout screens from single class using onClick() method
Here goes my code
Button bt1,bt2;
#Override
protected void onCreate(Bundle savedInstanceState){
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
bt1 = (Button)findViewById(R.id.button);
bt2 = (Button)findViewById(R.id.button1);
onClick(); //onClick(View) in MainActivity cannot be applied to ()
}
public void onClick(View v){
if(v.getId()==R.id.button){
setContentView(R.layout.next1);
}
else if(v.getId()==R.id.button){
setContentView(R.layout.next1);
}
}
Kindly help me out, Thank you
Fragment is what you have to use, in this case. Load either of the fragment based on button click.
If you go for setContentView in this scenario, then your code will be clumsy and it will be very tedious for you to keep track on view.
I am new to android dev, I created a new project with NavigationDrawer activity, I use Android Studio. The problem is when I add a button and create OnClickListener, the app crushes, but without it, it launches fine. Please look at my code below.
I tried adding setContentView(View) but doesn't help
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main); //comes by default
setContentView(R.layout.fragment_main); //added by me, but doesnt help
//referencing my button
btnTest = (Button)findViewById(R.id.btnTest);
mNavigationDrawerFragment = (NavigationDrawerFragment)
getSupportFragmentManager().findFragmentById(R.id.navigation_drawer);
mTitle = getTitle();
// Set up the drawer.
mNavigationDrawerFragment.setUp(
R.id.navigation_drawer,
(DrawerLayout) findViewById(R.id.drawer_layout));
//my event listeners
//when i highlight the below code everythin works..these block cause the crash
btnTest.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
}
});
}
I know others have had these issue and solved it, but I'm not able to solve mine, please help, Thank You
setContentView(R.layout.activity_main); //comes by default
setContentView(R.layout.fragment_main); //added by me, but doesnt help
Don't call setContentView twice. The one that "comes by default" is provided for your convenience when the IDE is generating the Activity class, if you don't need it, delete it.
Secondly, you are setting a fragment layout as View for your Activity. So unless R.id.btnTest is included in that layout, btnTest will be null, hence causing a NullPointerException when calling setOnClickListener.
delete this :
setContentView(R.layout.fragment_main);
and here
setContentView(R.layout.activity_main);
make sure you have a layout file for your Activity that is named activity_main.xml or replace that reference with the name of your layout file.
EDIT : I'm guessing you chose the option in AS to generate a placeholder in your Activity and a Fragment to be added to it. You need to handle the button in the Fragment class, and more importantly, you need to add the Fragment to your Activity.
In your Activity (in OnCreate, after the setup of the nav drawer) :
Fragment newFragment = new ExampleFragment(); // replace ExampleFragment by your Fragment's class name
FragmentTransaction ft = getFragmentManager().beginTransaction();
ft.add(CONTENT_VIEW_ID, newFragment).commit(); // CONTENT_VIEW_ID is the id of the View in your Activity that should contain the Fragment.
And then in your Fragment, move this to onActivityCreated :
btnTest.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
}
});
You will need to inflate R.layout.fragment_main in onCreateView in your Fragment, and get a reference to btnTest from the View you inflate.
Without Logcat I would say that your problem is one of the following:
btnTest is not defined in your ActivityLayout (activity_main). If this is the case check your XML.
Is your btnTest inside your Fragment? If so you should put the OnClickListener in your Fragment class instead of your Activity class.
BTW, the second setContentView doesnt make any sense you should use only one.
Hope it helps