First of all: yes, I read all the other threads on this topic. And not only those from this site... (you see, I'm a little frustrated)
Most of them come with the advice to use android:id instead of just id in the XML file. I did.
From others, I learned, that View.findViewById works different than Activity.findViewById. I handled that, too.
In my location_layout.xml, I use:
<FrameLayout .... >
<some.package.MyCustomView ... />
<LinearLayout ... >
<TextView ...
android:id="#+id/txtLat" />
...
</LinearLayout>
</FrameLayout>
In my Activity I do:
...
setContentView( R.layout.location_layout );
and in my custom view class:
...
TextView tv = (TextView) findViewById( R.id.txtLat );
which returns null. Doing this, my Activity works fine. So maybe it's because of the Activity.findViewById and View.findViewById differences. So I stored the context passed to the customs view constructor locally and tried:
...
TextView tv = (TextView) ((Activity) context).findViewById( R.id.txtLat );
which also returned null.
Then, I changed my custom view to extend ViewGroup instead View and changed the location_layout.xml to let the TextView be a direct child of my custom view, so that the View.findViewById should work as supposed. Suprise: it didn't solve anything.
So what the heck am I doing wrong?
I'll appreciate any comments.
which returns null
Possibly because you are calling it too early. Wait until onFinishInflate(). Here is a sample project demonstrating a custom View accessing its contents.
Possibly, you are calling findViewById before calling setContentView?
If that's the case, try calling findViewById AFTER calling setContentView
Make sure you don't have multiple versions of your layout for different screen densities. I ran into this problem once when adding a new id to an existing layout but forgot to update the hdpi version. If you forget to update all versions of the layout file it will work for some screen densities but not others.
FindViewById can be null if you call the wrong super constructor in a custom view. The ID tag is part of attrs, so if you ignore attrs, you delete the ID.
This would be wrong
public CameraSurfaceView(Context context, AttributeSet attrs) {
super(context);
}
This is correct
public CameraSurfaceView(Context context, AttributeSet attrs) {
super(context,attrs);
}
Alongside the classic causes, mentioned elsewhere:
Make sure you've called setContentView() before findViewById()
Make sure that the id you want is in the view or layout you've given to setContentView()
Make sure that the id isn't accidentally duplicated in different layouts
There is one I have found for custom views in standard layouts, which goes against the documentation:
In theory you can create a custom view and add it to a layout (see here). However, I have found that in such situations, sometimes the id attribute works for all the views in the layout except the custom ones. The solution I use is:
Replace each custom view with a FrameLayout with the same layout properties as you would like the custom view to have. Give it an appropriate id, say frame_for_custom_view.
In onCreate:
setContentView(R.layout.my_layout);
FrameView fv = findViewById(R.id.frame_for_custom_layout);
MyCustomView cv = new MyCustomView(context);
fv.addView(cv);
which puts the custom view in the frame.
In my case, I had 2 activites in my project, main.xml and main2.xml. From the beginning, main2 was a copy of main, and everything worked well, until I added new TextView to main2, so the R.id.textview1 became available for the rest of app. Then I tried to fetch it by standard calling:
TextView tv = (TextView) findViewById( R.id.textview1 );
and it was always null. It turned out, that in onCreate constructor I was instantiating not main2, but the other one. I had:
setContentView(R.layout.main);
instead of
setContentView(R.layout.main2);
I noticed this after I arrived here, on the site.
#Override
protected void onStart() {
// use findViewById() here instead of in onCreate()
}
A answer for those using ExpandableListView and run into this question based on it's title.
I had this error attempting to work with TextViews in my child and group views as part of an ExpandableListView implementation.
You can use something like the following in your implementations of the getChildView() and getGroupView() methods.
if (convertView == null) {
LayoutInflater inflater = (LayoutInflater) myContext.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
convertView = inflater.inflate(R.layout.child_layout, null);
}
I found this here.
FWIW, I don't see that anyone solved this in quite the same way as I needed to. No complaints at compile time, but I was getting a null view at runtime, and calling things in the proper order. That is,
findViewById()
after
setContentView().
The problem turned out that my view is defined in content_main.xml, but in my activity_main.xml, I lacked this one statement:
<include layout="#layout/content_main" />
When I added that to activity_main.xml, no more NullPointer.
I'm pretty new to Android/Eclipse, by mistake I added the UI stuff to activity_main.xml instead of fragment_main.xml. Took me some hours to figure that out...
I had this same problem. I was using a third-party library that allows you to override their adapter for a GridView and to specify your own layout for each GridView cell.
I finally realized what was happening. Eclipse was still using the library's layout xml file for each cell in the GridView, even though it gave no indication of this. In my custom adapter, it indicated that it was using the xml resource from my own project even though at runtime, it wasn't.
So what I did was to make sure my custom xml layouts and ids were different from those still sitting in the library, cleaned the project and then it started reading the correct custom layouts that were in my project.
In short, be careful if you're overriding a third-party library's adapter and specifying your own layout xml for the adapter to use. If your layout inside your project has the same file name as that in the library, you might encounter a really difficult-to-find bug!
In my particular case, I was trying to add a footer to a ListView. The following call in onCreate() was returning null.
TextView footerView = (TextView) placesListView.findViewById(R.id.footer);
Changing this to inflate the footer view instead of finding it by ID solved this issue.
View footerView = ((LayoutInflater) getSystemService(Context.LAYOUT_INFLATER_SERVICE)).inflate(R.layout.footer_view, null, false);
Just wanted to throw my specific case in here. Might help someone down the line.
I was using the directive in my Android UI XML like this:
Parent view:
<FrameLayout
xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:tag="home_phone"
android:background="#color/colorPrimary">
...
<include
layout="#layout/retry_button"
android:visibility="gone" />
Child view (retry_button):
<com.foo.RetryButton
xmlns:android="http://schemas.android.com/apk/res/android"
android:id="#+id/retry"
android:layout_gravity="center"
android:orientation="vertical"
android:layout_width="100dp"
android:layout_height="140dp">
.findViewById(R.id.retry) would always return null. But, if I moved the ID from the child view into the include tag, it started working.
Fixed parent:
<FrameLayout
xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:tag="home_phone"
android:background="#color/colorPrimary">
...
<include
layout="#layout/retry_button"
android:id="#+id/retry"
android:visibility="gone" />
Fixed child:
<com.foo.RetryButton
xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_gravity="center"
android:orientation="vertical"
android:layout_width="100dp"
android:layout_height="140dp">
In my case, I was using ExpandableListView and I had set android:transcriptMode="normal". This was causing few children in expandable group to disappear and I used to get NULL exception when ever I used scroll the list.
For me I had two xml layouts for the same activity - one in portrait mode and one in landscape. Of course I had changed the id of an object in the landscape xml but had forgotten to make the same change in the portrait version. Make sure if you change one you do the same to the other xml or you will not get an error until you run/debug it and it can't find the id you didn't change. Oh dumb mistakes, why must you punish me so?
Set the activity content from a layout resource.
ie.,setContentView(R.layout.basicXml);
In addition of the above solutions you make sure the
tools:context=".TakeMultipleImages"
in the layout is same value in the mainfest.xml file :
android:name=".TakeMultipleImages" for the same activity element.
it is occur when use copy and paste to create new activity
I have the same problem, but I think its worth sharing with you guys.
If you have to findViewById in custom layout, for example:
public class MiniPlayerControllBar extends LinearLayout {
//code
}
you cannot get the view in constructor.
You should call findViewById after view has inflated.
Their is a method you can override onFinishInflate
My case is none like above, no solutions worked. I assume my view was too deep into layout hierarchy. I moved it one level up and it was not null anymore.
INFLATE THE LAYOUT !! (which contains the id)
In my case findViewById() returned null, because the layout in which the element was written, was not inflated...
Eg.
fragment_layout.xml
<ListView
android:id="#+id/listview">
findViewById(R.id.listview) returned null, because I had not done
inflater.inflate(R.layout.fragment_layout, ..., ...);
before it.
Hope this answer helps some of y'all.
In my case I had inflated the layout but the child views were returning null. Originally I had this:
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_history);
footerView = ((LayoutInflater) getApplicationContext().getSystemService(Context.LAYOUT_INFLATER_SERVICE)).inflate(R.layout.listview_footer, null, false);
pbSpinner = (ProgressBar) findViewById(R.id.pbListviewFooter);
tvText = (TextView) findViewById(R.id.tvListviewFooter);
...
}
However, when I changed it to the following it worked:
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_history);
footerView = ((LayoutInflater) getApplicationContext().getSystemService(Context.LAYOUT_INFLATER_SERVICE)).inflate(R.layout.listview_footer, null, false);
pbSpinner = (ProgressBar) footerView.findViewById(R.id.pbListviewFooter);
tvText = (TextView) footerView.findViewById(R.id.tvListviewFooter);
...
}
The key was to specifically reference the already inflated layout in order to get the child views. That is, to add footerView:
footerView.findViewById...
It crashed for me because one of fields in my activity id was matching with id in an other activity. I fixed it by giving a unique id.
In my loginActivity.xml password field id was "password". In my registration activity I just fixed it by giving id r_password, then it returned not null object:
password = (EditText)findViewById(R.id.r_password);
In my experience, it seems that this can also happen when your code is called after OnDestroyView (when the fragment is on the back stack.) If you are updating the UI on input from a BroadCastReceiver, you ought to check if this is the case.
findViewById also can return null if you're inside a Fragment. As described here: findViewById in Fragment
You should call getView() to return the top level View inside a Fragment. Then you can find the layout items (buttons, textviews, etc)
In my case, findViewById returned null when I moved the call from a parent object into an adapter object instantiated by the parent. After trying tricks listed here without success, I moved the findViewById back into the parent object and passed the result as a parameter during instantiation of the adapter object.
For example, I did this in parent object:
Spinner hdSpinner = (Spinner)view.findViewById(R.id.accountsSpinner);
Then I passed the hdSpinner as a parameter during creation of the adapter object:
mTransactionAdapter = new TransactionAdapter(getActivity(),
R.layout.transactions_list_item, null, from, to, 0, hdSpinner);
I was facing a similar problem when I was trying to do a custom view for a ListView.
I solved it simply by doing this:
public View getView(int i, View view, ViewGroup viewGroup) {
// Gets the inflater
LayoutInflater inflater = LayoutInflater.from(this.contexto);
// Inflates the layout
ConstraintLayout cl2 = (ConstraintLayout)
inflater.inflate(R.layout.custom_list_view, viewGroup, false);
//Insted of calling just findViewById, I call de cl2.findViewById method. cl2 is the layout I have just inflated.
TextView tv1 = (TextView)cl2.findViewById(cl2);
Ways to debug and find the issue:
Comment out all findViewById in your activity.
Comment out everything except onCreate and setContentView
Run the project and see if any layout is set
In my case, I was using activity_main.xml in both my app module and also my library module. So when I performed the above steps, instead of the layout which I designed in the library, the layout inside app module was inflated.
So I changed the activity_main.xml file name to activity_main_lib.xml.
So make sure you do not have any duplicate layout names in your whole project.
The issue for me was that I had two layouts with the same file name activity_main.xml. (The layouts were in different libraries but in the same app) The issue was solved by renaming one of them to a unique name.
For me it returned null because the given control was (programmatically) hidden. When I put a condition to call findViewByID(id) only when the control is visible, it started working again.
For me it was only null when using Evaluate Expression or the Debug Watch View of the IDE.
So the Negative and Positive buttons of my AlertDialog are greyed-out, but they shouldn't be.
greyed-out text screen
I suspect it has something to do with Context, becouse once i had identical problem with my ListView. I have repaired that by changing argument in ArrayAdapter's reference from getApplicationContext() to getBaseContext(). Can someone explain it to me? I don't really understand the 'Context'
This is my code
AlertDialog.Builder builder = new AlertDialog.Builder(MainActivity.this);
builder.setTitle("What do you want to do with " + getArrayList("ListOfRecipes").get(position) );
builder.setPositiveButton("Delete", new DialogInterface.OnClickListener() {
#Override
public void onClick(DialogInterface dialog, int which) {
List<String> list = new ArrayList<>(getArrayList("ListOfRecipes"));
Toast.makeText(getBaseContext(), list.get(position) + "has been removed", Toast.LENGTH_SHORT).show();
list.remove(position);
saveList(list, "ListOfRecipes");
}
});
builder.setNegativeButton("Modify", new DialogInterface.OnClickListener() {
#Override
public void onClick(DialogInterface dialog, int which) {
List<String> list = new ArrayList<>(getArrayList("ListOfRecipes"));
SharedPreferences sp = getSharedPreferences("Recip", MODE_PRIVATE);
SharedPreferences.Editor editor = sp.edit();
editor.putString("Recip", list.get(position));
editor.apply();
startActivity(new Intent(getBaseContext(), ManageRecipeActivity.class));
}
});
AlertDialog alertDialog = builder.create();
alertDialog.show();
First of all, if that piece of code is inside an activity, you can simply declare context with "this" (which is what you have done by passing MainActivity.this) to the dialog builder.
What I'm suspecting is that it may be that your MainActivity is getting a theme for the AlertDialog that is making the buttons look gray. You could check that out in your styles.xml (if there is a style defined for the dialog) and in the AndroidManifest file for the theme you are passing to your MainActivity.
If you don't find anything wrong/don't want to change the theme, I can think of two ways to solve that problem.
First way - Changing the button color (less work, but less flexible)
The first is actually changing the dialog button color as it's done in this post to whatever color you want.
Second way - inflating a custom view that meets your needs (more work, but more flexible)
The second way would be to inflate a view and pass it to the dialog. Actually, you don't really have to use the standard dialog style at all, you can inflate your own view inside it to fit your needs.
To do that, you must:
1) Inflate a chosen view
As an example:
LayoutInflater factory = LayoutInflater.from(this);
final View view = factory.inflate(R.layout.image_dialog_layout, null);
2) Pass the inflated view to your dialog builder:
final AlertDialog dialog = new AlertDialog.Builder(this);
dialog.setView(view);
//Additional code to set click listeners, i.e.
dialog.create().show();
}
That way, you'll be inflating whatever layout you want, so you can just put the buttons you want inside it (with the color, size, font type you want).
It is important to notice that, even after inflating a view to it, you can still use methods setPositiveButton and setNegativeButton, they will appear below your inflated layout in the dialog. So, beware inflating buttons AND using those methods, because the buttons will appear duplicated.
Since, in this case, you don't want them to be gray, you want to put buttons inside your layout, with whatever style you want, and inflate them (and reference them in your code through findViewById).
The biggest advantage of the second way is that you can inflate whatever you want, with the styles you want. You can even put images inside it, if you wish.
Hope it helps, let me know if it worked for you.
Context is an interesting topic in android. And one thing to understand is Application Context and Activity Context are different. You should make sure that any thing that is related to UI, you should be using Activity Context.
This can be things like
Showing a dialog
Starting another activity
Inflating a new layout
This is because Activity is the only Context on which the themes defined in your manifest are actually attached.
I also recommend Context, What Context article to get a complete picture.
Happy Coding :)
I want to create a animation between two Activities with a image as shared element, see Customize Activity Transitions
My problem: In the source activity the image is drawn on a canvas of a custom view :-(
Is there a way to use this image as a shared element or do I have to add a real ImageView?
You can't share the image only, but you can share the entire custom view. This means that the entire custom View would disappear from the calling Activity when the shared element is transferred to the launched Activity. If your custom View only has the image, that would be fine, but if it paints other things, that would be disastrous.
If you want to share only the image, you'll have to create a View (e.g. ImageView) and move the image to it and then share it. That way, when the shared element is transferred, it hides properly from the calling activity.
The shared elements don't actually move Views between Activities, they just share a 'snapshot' of the view as a bitmap and the position of the view. In the launched activity, the view with the given transition name will be laid out in that position. You can use the snapshot or not, depending on your needs. By default, the snapshot is not used.
So you'll need some code like this:
public void launchActivity(final Intent intent, final CustomView view) {
final Bitmap bitmap = view.getSharedImage();
ImageView imageView = new ImageView(view.getContext());
imageView.setBitmap(bitmap);
LayoutParams layoutParams = view.createSharedImageLayoutParams();
final ViewGroup parent = (ViewGroup)view.getParent();
parent.addView(imageView, layoutParams);
parent.getViewTreeObserver().addOnPreDrawListener(new OnPreDrawListener() {
#Override
public boolean onPreDraw() {
parent.getViewTreeObserver().removeOnPreDrawListener(this);
customView.hideSharedImage();
ActivityOptions activityOptions = ActivityOptions.
makeSceneTransitionAnimation(this, imageView, "destName");
startActivity(intent, activityOptions.toBundle();
}
});
setExitSharedElementCallback(new SharedElementCallback() {
#Override
public void onSharedElementsArrived(List<String> sharedElementNames,
List<View> sharedElements, OnSharedElementsReadyListener listener) {
super.onSharedElementsArrived(sharedElementNames, sharedElements,
listener);
parent.removeView(imageView);
customView.showSharedImage();
}
});
}
I haven't specifically tried the above, but that's the essence of it. If you don't want to use the newer onSharedElementsArrived, you can create a custom ImageView that listens for onVisibilityChanged. If you have an exit transition, you can also listen for the end of it as well. You just need some trigger that will tell you to reset the state so that the ImageView is removed and your custom View should draw the image again.
In the example above, I placed the ImageView in the same parent as the custom View. You may get more flexibility by putting it into the DecorView, but you'll have to figure out what the global position is and it will also overlay everything on the screen. Alternatively, since I added the ImageView to the parent, that won't work for all parents (e.g. ListView, LinearLayout). You know your View hierarchy and you'll have to choose the best place to put it.
Or, you could change your custom View to be a custom ViewGroup and contain the sharable image as an ImageView! Sounds easier to me.