I'm new to Android (and surely I'm not an expert Java developer), so I'm sorry for the dumb question
I would like to "capture" the id of a textView and to set its text value dynamically,
here is how I'm trying to do this:
public class AndStringTestActivity extends Activity {
/** Called when the activity is first created. */
String abc = "abcabc";
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
TextView tv = (TextView)findViewById(R.id.test);
tv.setText(abc);
setContentView(R.layout.main);
}
}
and here is the Xml from which i'm reading the id of the textview i would like to write inside
// main.xml
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:orientation="vertical"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
>
<TextView
android:id="#+id/test"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
/>
</LinearLayout>
the error i receive is the usual Application stopped unexpectedly
Thanks.
Call setContentView before trying to find the TextView. The TextView does not exist before you have called setContentView (which will inflate your XML layout)
Call setContentView(R.layout.main) before you call findViewById().
Related
There are a number of questions like this but the solutions haven't worked for me.
Anyways, my main activity has a button that, in its onclick method, takes me to another activity, ViewPowerActivity. I have a layout xml file for it called power_view.xml. Inside that I have some layout:
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:layout_marginLeft="#dimen/screen_margin"
android:layout_marginRight="#dimen/screen_margin"
android:layout_marginTop="#dimen/screen_margin"
android:orientation="vertical" >
...
ViewPowerActivity has the basic onCreateMethod:
public class ViewPowerActivity extends Activity {
private final static Powers powers=new StubPowers();
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.power_view);
Power power=powers.getPowers().get(0);
View powerView = findViewById(R.layout.power_view);
...
}
...
}
The findViewById call above is returning null.
If I remove all the code after setContentView(...) and simply return there, it displays the empty layout just fine. I've setContentView, I've cleaned the project, I've tried setting the power view as the main activity, and all sorts of things. What else could it be?
From you code it is clear thar power_view is a layout ie. xml. So R.id.power_view is incorrect.
It seems you want to access the parent view of that layout. Then do the following.
You have to set an id to the parent LinearLayout.
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:id="#+id/parentLinear"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:layout_marginLeft="#dimen/screen_margin"
android:layout_marginRight="#dimen/screen_margin"
android:layout_marginTop="#dimen/screen_margin"
android:orientation="vertical" >
...
Then,
View powerView = findViewById(R.id.parentLinear);
If you want to take some other view in powerView, you should set id to that view in xml layout and initialize your that view to power_view by findViewById(R.id.your_view)
power_view.xml
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:id="#+id/layout"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:layout_marginLeft="#dimen/screen_margin"
android:layout_marginRight="#dimen/screen_margin"
android:layout_marginTop="#dimen/screen_margin"
android:orientation="vertical" >
public class ViewPowerActivity extends Activity {
private final static Powers powers=new StubPowers();
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.power_view);
Power power=powers.getPowers().get(0);
View powerView = (ViewGroup)findViewById(R.id.layout);
...
}
...
}
i have a xml layout main.xml like this
<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="wrap_content"
android:layout_height="fill_parent"
android:gravity="center" >
<EditText
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:text="text"
android:textColor="#000"
android:textSize="16dp"
android:id="#+id/edtxt"
android:gravity="center|top|left"/>
</RelativeLayout>
and i declare this in my activity like this
public class MyActivity extends Activity {
private TextView txt = null;
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
txt= (TextView)findViewById(R.id.edtxt);
}
}
but i have no problem in my activity. why?
see this link http://developer.android.com/reference/android/widget/EditText.html
and look here
you will find your answer
That would be because EditText is a subclass of TextView. You're casting an EditText to a TextView, which works because an EditText IS a TextView.
Check out the EditText's docs: http://developer.android.com/reference/android/widget/EditText.html
And here's a little something so that you can learn about inheritance, which is what is happening here: http://docs.oracle.com/javase/tutorial/java/IandI/subclasses.html
Answer is simple, it is so because EditText extends TextView.
My problem is communication between custom GameView (extends SurfaceView) and TextView: I want to set TextView's text from inside of the GameView.
In main activity i'm using this layout file, it should explain structure of my app:
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:orientation="vertical"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
>
<RelativeLayout
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:background="#00ff00"
>
<TextView
android:id="#+id/scoreTV"
android:layout_alignParentLeft="true"
android:layout_centerVertical="true"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="score: 0"
/>
<Button
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="back"
android:layout_alignParentRight="true" />
</RelativeLayout>
<org.gk.grApp.GameView
android:id="#+id/gameplayScreen"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
/>
</LinearLayout>
I can't change TextView's text in my GameView object, because it's impossible to touch UI thread from another.
Handler doesn't work too, because i can't give a handler's reference to GameView's constructor, that is performed after loading this xml file (a read about default constructor for xml files eg here How can I use GLSurfaceView in a LinearLayout together with other Views, such as TextView or Button?).
Do you have any idea what I should do now? Maybe my deduction is wrong, so please, tell me about this.
EDIT: I changed my xml file, instead of GameView I have now:
<LinearLayout
android:id="#+id/gameplayScreen"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
>
</LinearLayout>
Also I added an argument (third) into constructor's signature:
public GameView(Context context, AttributeSet as, Handler h) { ... }
and changed my onCreate in GameplayActivity:
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.gameplay);
LinearLayout ll = (LinearLayout)findViewById(R.id.gameplayScreen);
GV = new GameView(this, null, scoreHandler);
ll.addView(GV);
}
It works, now I can set TextView's text but after clicking on the back button another exception is thrown:
"Performing pause of activity that is not resumed: {org.gk.grApp/org.gk.grApp.MainMenuActivity}". I just started searching information about this.
First make a reference to the TextView on the activity level:
TextView txv;
In onCreate assign this reference:
txv = (TextView) findViewById(R.id.MyTextView);
Then make a method in your Activity after onCreate like this:
public void setTextView(final String txt){
MyActivity.this.runOnUiThread(new Runnable() {
public void run() {
txv.setText(txt);
}
});
}
Then you make a call from your custom view:
((MyActivity) getContext()).setTextView(str);
i hava a layout file like
test.xml
<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent" android:layout_height="match_parent">
<TextView android:layout_width="wrap_content"
android:layout_height="wrap_content" android:id="#+id/test_string" />
</RelativeLayout>
and java file like this.
test1.java
public class test1 extends Activity {
String temp="This is String"; //which change dynamically
TextView tempview;
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
tempview=(TextView)findViewById(R.id.test_string);
tempview.setText(temp);
setContentView(R.layout.test);
}
}
what i am trying to do is show the value of temp in activity as above code. but it throws an NullPointerException. so how to do. how to set the values of sting.xml???
thanks in advance..
setContentView(R.layout.test); should come before (TextView)findViewById(R.id.test_string);
I'm new to android platform , I'd like to settext using textviews , I tried to write set text into two textviews but its just draws one textview why?
I can't draw two textviews
TextView tv1;
TextView tv2;
#Override
public void onCreate(Bundle savedInstanceState)
{
super.onCreate(savedInstanceState);
layout = new LinearLayout(this);
tv1 = new TextView(this);
tv2 = new TextView(this);
tv1.setText("Hello");
tv2.setText("How are you?");
}
On Android, the user interface normally should be created using XML-files, instead of Java code. You should read up on the tutorials on android.com, especially:
http://developer.android.com/guide/topics/ui/declaring-layout.html
An example:
In your res/layout/main.xml, you define the text TextView's:
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:orientation="vertical"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
>
<TextView android:id="#+id/TextView1" android:layout_width="fill_parent" android:layout_height="wrap_content" android:text="TextView 1"/>
<TextView android:id="#+id/TextView2" android:layout_width="fill_parent" android:layout_height="wrap_content" android:text="TextView 2"/>
</LinearLayout>
Then if you use setContentView in the activity to display this, the app will show to TextView's:
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
this.setContentView(R.layout.main);
}
If you want to programmatically set the text in the Activity, just use findViewById():
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
this.setContentView(R.layout.main);
((TextView)this.findViewById(R.id.TextView1)).setText("Setting text of TextView1");
}
I definitely second TuomasR's suggestion to use XML layouts. However, if you're wanting to add new TextViews dynamically (i.e. you don't know how many you will need until runtime), you need to do a couple of other steps to what you are doing:
First, define your LinearLayout in main.xml (it's just easier that way than LayoutParams, IMO):
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout
xmlns:android="http://schemas.android.com/apk/res/android"
android:id="#+id/my_linear_layout"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
android:orientation="vertical"
/>
Now, you can go to your code, and try the following:
#Override
public void onCreate(Bundle savedInstanceState)
{
super.onCreate(savedInstanceState);
//This inflates your XML file to the view to be displayed.
//Nothing exists on-screen at this point
setContentView(R.layout.main);
//This finds the LinearLayout in main.xml that you gave an ID to
LinearLayout layout = (LinearLayout)findViewById(R.id.my_linear_layout);
TextView t1 = new TextView(this);
TextView t2 = new TextView(this);
t1.setText("Hello.");
t2.setText("How are you?");
//Here, you have to add these TextViews to the LinearLayout
layout.addView(t1);
layout.addView(t2);
//Both TextViews should display at this point
}
Again, if you know ahead of time how many views that you need, USE XML.