I want to create layout programmatically in different class which is not an activity so i will call one function from Activity and all code for creating layout is in function. so please give me some idea to write code.
this is my Activity:
public class Main extends Activity {
/** Called when the activity is first created. */
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
TableLayout tl = (TableLayout) findViewById(R.id.table1);
testing t1 = new testing();
Main m = new Main();
t1.makelayout(tl,m);
}
}
And this is my class which has function that is generating layout programmatically:
public class testing {
public void makelayout(TableLayout tl,Main m1) {
// TODO Auto-generated method stub
//Main m = new Main();
TextView tv= new TextView(m1);
tv.setText("hello1");
tl.addView(tv);
}
}
can i do this or not please help me.
If your makelayout(TableLayout tl,Main m1) would be makelayout(Context c, TableLayout tl) and you call it by giving the Activity's context, then it would work.
For such "external" things, you always need to give over the appropriate context to allow creating the Views in it.
Related
I need to execute a method before initiating the layout in an activity. If I call the method I need to execute inside onCreate(), would it be executed before the layout is set?
The reason is because I need the method to return a piece of information that is displayed in the layout before initiating it. Would love some feedback on this.
You can do whatever you like before setContentView like so:
public class TestActivity extends Activity {
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
int i = 0;
setContentView(R.layout.main);
}
}
As long as you do not interact with views that have not been inflated yet
For example this is an error:
public class TestActivity extends Activity {
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
// ERROR, CAN'T TOUCH UI ELEMENTS
ImageView img = (ImageView)findViewById(R.id.img);
setContentView(R.layout.main);
}
}
Default activity created with Android Studio contains following code
#Override public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
//Here is code, that executed before layout inflated
setContentView(R.layout.example_activity); //This line inflates layout
}
BTW, you can even remove setContentView and inflate layout programmaticaly.
Do it in onCreate(), preferably before calling setContentView().
However, if the data you want to receive comes from the network, then it will be obtained on a separate Thread (as no network calls can be done on the main Thread). In this situation the layout will almost certainly display before the data is obtained.
A solution would be to obtain the piece of data before you start the Activity, pass it in the Intent as extra and then retrieve in onCreate() using getIntent().getStringExtra()
You are probably inflating your layout in Activity.onCreate() with setContentView(), so you need to put your function call in that method before the call to setContentView().
#Override
public void onCreate(Bundle savedInstanceState)
{
super.onCreate(savedInstanceState);
yourFunctionCallHere();
setContentView(R.layout.act_main);
}
I have my code defined the way below. There are two crucial activities. Activity (1) shows some images in a ViewFlipper. It uses methods to load desired image directly. The onOptionsItemSelected() method fetches data from a menu defined within linked XML layout R.layout.browse. The other method, displaySelectedFlag(), gets a tag parameter passed from a different activity, let's call it activity (2).
Activity (1):
public class BrowserActivity extends AppCompatActivity implements SimpleGestureListener, View.OnClickListener {
public ViewFlipper vFlipper;
(...)
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.browse);
vFlipper = (ViewFlipper) findViewById(R.id.viewFlipperBrowser);
(...)
} // onCreate() ends here
// this method below works fine:
#Override
public boolean onOptionsItemSelected(MenuItem item) {
vFlipper.setDisplayedChild(item.getOrder());
return true;
}
// and this one doesn't:
public void displaySelectedFlag(int orderTag) {
vFlipper.setDisplayedChild(orderTag); // crashes here
}
}
Activity (2):
public class ListActivity extends Activity implements View.OnClickListener {
private BrowserActivity browserActivity = new BrowserActivity();
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_list);
ImageButton imageA = (ImageButton) findViewById(R.id.img_a);
imageA.setOnClickListener(this);
ImageButton imageB = (ImageButton) findViewById(R.id.img_b);
imageB.setOnClickListener(this);
}
public void displayImageInfo(View view) {
String tagValue = (String) view.getTag();
int tagId = Integer.parseInt(tagValue);
Intent intent = new Intent(this, BrowserActivity.class);
startActivity(intent);
browserActivity.displaySelectedImage(imageId);
}
#Override
public void onClick(View view) {
displayImageInfo(view);
}
}
As I checked, the method onClick() called in activity (2) fetches an ID of an ImageButton and passes it to activity (1). Unfortunately, I get a NullPointerException when calling the ViewFlipper (the line is marked in the code above, activity (1)).
Any idea why it happens?
You cannot reference one Activity from another activity. You must let the Android OS create the Activity object via the call to "startActivity". Allocating a local variable as an instance of an Activity doesn't actually mean anything (like your instantiation of the BrowserActivity). Apoorv's comment links to a decent article on the subject.
If you want to pass data from one Activity to another, you need to pass extras within the Intent's bundle. This post goes into detail: https://stackoverflow.com/a/819427/504252
I'm new to android and I am making an app as part of an assignment, and can't get this function to return a value - the app closes and I get an error message: "Unfortunately, APP has stopped".
I have two classes, one is the MainActivity and one is a class that I am wanting to use to do arithmetic, and they are:
import com.calc.Calculation;
public class MainActivity extends Activity {
private Calculation util;
calculate = (Button) findViewById(R.id.btnCalc);
private TextView tvMultiply;
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
tvMultiply = (TextView) findViewById(R.id.tvMult);
}
btnCalc.setOnClickListener(new OnClickListener() {
#Override
public void onClick(View v) {
tvMiltiply.setText(String.valueOf(util.CalculateMult(4,6)));
}
});
}
and
package com.calc;
public class Calculation{
public int CalculateMult(int numOne, int numTwo)
{
return numOne * numTwo;
}
}
I've tried a few alternatives but to no avail. It's going to be something simple that I am not doing quite right.
Any help appreciated.
Thanks
You need to create instance to the class before acccessing the member.
private Calculation util = new Calculation()
Else make the method in the class as static and access without creating instance.
This would be done by defining the class as:
package com.calc;
public class Calculation{
public static int CalculateMult(int numOne, int numTwo)
{
return numOne * numTwo;
}
}
and calling the method as:
Calculation.CalculateMult(4,6)
You should move the line
calculate = (Button) findViewById(R.id.btnCalc);
to the onCreate() function after you have set the content view. You should also move the assignment of the onClickListener to your button to the onCreate() method.
Finally, you should initialize your Calculation object by using the new operator in onCreate(), i.e:
util = new Calculation();
I was trying out coding android layout on Java. Then, I noticed that following code is incorrect (as in not working):
public class MainActivity extends Activity {
LinearLayout topLayout = new LinearLayout(this);
Button button1 = new Button(this);
protected void onCreate(Bundle savedInstanceState){
super.onCreate(savedInstanceState);
... setText, layoutParam and etc ...
topLayout.addView(button1, layoutParam);
setContentView(topLayout);
}
}
while following code is correct (working):
public class MainActivity extends Activity {
protected void onCreate(Bundle savedInstanceState){
super.onCreate(savedInstanceState);
LinearLayout topLayout = new LinearLayout(this);
Button button = new Button(this);
... setText, layoutParm and etc ...
topLayout.addView(button1, layoutParam);
setContentView(topLayout);
}
}
Why is that?
The context of an Activity is created once onCreate() is called.
In the first case, you don't have context set.
The comment made by #Blundell explains it, but if you want to go a little bit deeper, you need to understand the object lifecycle and order of things.
An Activity is a Java Object in the end. And so it must go through the Java Object creation process.
public class MainActivity extends Activity {
LinearLayout topLayout = new LinearLayout(this);
Button button1 = new Button(this);
Member variables (or Fields) are created right after the constructor. If you don't have a constructor, one is created for you (even tho you don't see it) you can try to create one:
public class MainActivity extends Activity {
public MainActivity() {
super();
Log.d("MAINACTIVITY", "Constructor!");
}
Now add log to your onCreate()…
protected void onCreate(Bundle savedInstanceState){
super.onCreate(savedInstanceState);
Log.d("MAINACTIVITY", "onCreate!");
}
Start your Activity and look at the log.
You should see:
Constructor!
onCreate!
With that being said, Since an Activity implements a Context interface, you cannot use them until they are not constructed, something that can be considered done after the constructor is called and ends.
Field members which are initialized inline, must be initialized during object Construction too, because that's the idea of their initialization being there…
So in short, you're trying to initialize Field Members that require something (a context) that is not yet available because it hasn't been created (this).
;)
I do my android app , but I have a bug I don't know how to fix it.
My code is below :
This is my Main Activity :
public class MainActivity extends Activity {
private ImageView imgHot;
public final static String EXTRA_MESSAGE="com.cuonglm.KhoHinh.MESSAGE";
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
imgHot=(ImageView)findViewById(R.id.imageViewHot);
imgHot.setOnClickListener(toContentHot);
}
View.OnClickListener toContentHot=new View.OnClickListener() {
#Override
public void onClick(View v) {
// TODO Auto-generated method stub
Intent content=new Intent(MainActivity.this,ContentActivity.class);
String signal="1";
content.putExtra(EXTRA_MESSAGE,signal);
startActivity(content);
}
};
And this is my second Activity :
public class ContentActivity extends Activity {
private TextView viewMessage;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
Intent content=getIntent();
String messageReceive=content.getStringExtra(MainActivity.EXTRA_MESSAGE);
viewMessage=(TextView)findViewById(R.id.content_receive);
viewMessage.setText(messageReceive);
setContentView(R.layout.activity_content);
}
I want to click on the image on the Main Activity , string "1" or number "1" will send to the Second Activity via Intent and view on the TextView.
But my app will be close "Unfortunately..."
Thanks
Change to
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_content);
viewMessage=(TextView)findViewById(R.id.content_receive);
viewMessage.setText(messageReceive);
In your ContentActivity
findViewById looks for a view with the id for the current infalted layout. SO you need to set the content of your layout to the activity first and then initialize your views.
You are probably gettting NullPointerException coz your initialization fails.
You need to call setContentView() in your second Activity before trying to access any of the Views in that layout. Change it to
public class ContentActivity extends Activity {
private TextView viewMessage;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_content);
Intent content=getIntent();
String messageReceive=content.getStringExtra(MainActivity.EXTRA_MESSAGE);
viewMessage=(TextView)findViewById(R.id.content_receive);
viewMessage.setText(messageReceive);
}
If this doesn't fix your problem then please post your logcat so we can see the error. Also always post logcat in the future when your app crashes. They aren't always this easy to see.
Also, I'm not sure you understand how putExtra() works. It is a key, value pair so when you put EXTRA_MESSAGE as the key then that is what you would use to retrieve the value added in the second param. So the way you are doing it may work if the Activity gets destroyed but it looks really strange to me and probably not realy safe or efficient. I would change it to something like
content.putExtra("message",signal);
in your first Activity then get it with
String messageReceive = content.getStringExtra("message");
in your second Activity
You need to set the layout before trying to reference the Views associated with it.
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
Intent content=getIntent();
String messageReceive=content.getStringExtra(MainActivity.EXTRA_MESSAGE);
setContentView(R.layout.activity_content);
viewMessage=(TextView)findViewById(R.id.content_receive);
viewMessage.setText(messageReceive);
}