Develop Reference

Views are not reflecting any changes whatsoever, when done programmatically

The basic view hierarchy is this:
secondActivity
linearLayout(LinearLayout)
constLayout(ConstraintLayout)
textbox(TextView)
image(ImageView)
image2
image3
...
The textbox TextView has visibility GONE, and goal is to make it VISIBLE on clicking other visible siblings, change some colors and text, and when clicked again it must be invisible again and reverse all changes.
Cant understand whatever it is that am missing. I have checked many older projects in which I did the same thing and cant find any visible differences as to why this code is not working now.
secondActivity.java
public class secondActivity extends Activity {
public boolean isTextBoxHidden;
public ConstraintLayout constLayout;
public TextView textbox;
#Override protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_second);
constLayout = findViewById(R.id.constLayout);
textbox = findViewById(R.id.textbox);
isTextBoxHidden = false;
// SETTING UP LISTENER
View.OnClickListener clickListener = new View.OnClickListener() {
#Override
public void onClick(View v) {
if(!isTextBoxHidden) {
constLayout.setBackgroundColor(Color.BLACK); //setting color on previously
v.setBackgroundColor(Color.BLACK); //setting color on visible view
textbox.setText("whatever");
textbox.setVisibility(View.VISIBLE); //was gone
isTextBoxHidden = true;
}
else {
textbox.setVisibility(View.GONE); //hide again
constLayout.setBackgroundColor(Color.WHITE);
v.setBackgroundColor(Color.WHITE);
isTextBoxHidden = false;
}
}
};
// INSERTING LISTENERS into all children
for(int i=0; i<constLayout.getChildCount(); i++) {
constLayout.getChildAt(i).setOnClickListener(clickListener);
}
}
}
activity_second.xml
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
xmlns:tools="http://schemas.android.com/tools"
android:id="#+id/linearLayout"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical"
tools:context=".secondActivity">
<android.support.constraint.ConstraintLayout
android:id="#+id/constLayout"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:background="#android:color/white">
<TextView
android:id="#+id/textbox"
android:layout_width="0dp"
android:layout_height="wrap_content"
android:gravity="center"
android:text="example"
android:visibility="gone"
app:layout_constraintLeft_toLeftOf="parent"
app:layout_constraintRight_toRightOf="parent"
app:layout_constraintTop_toTopOf="parent"/>
<ImageButton
android:id="#+id/image"
android:layout_width="0dp"
android:layout_height="wrap_content"
android:adjustViewBounds="true"
android:scaleType="fitXY"
android:src="#drawable/example"
android:clickable="true"
app:layout_constraintBottom_toBottomOf="parent"
app:layout_constraintRight_toRightOf="parent"
app:layout_constraintLeft_toLeftOf="parent"/>
<!--few more clones of the first imageButton-->
</android.support.constraint.ConstraintLayout>
</LinearLayout>

I can't see where you're setting textbox reference, so maybe that's a clue.
Edit:
Did compiled that example you have provided and everything works correctly, but i assume that [...] gone again for good meant you probably want this to be one shot action so instead of boolean just use Boolean and compare it to null.
Edit:
On the second thought you can just remove isTextBoxHidden = false; in else branch

How can i access fragment layout in parent activity?

I have got a tabpager and fragments. And a frament has got a "GridView". I am using a basedapter innerclass in the fragment parent activity.
But when i want to set adapter to my gridview i m getting nullpointerexception. Because GridView variable is always null.how can solve this issue?
Fragment Parent MainActivity OnCreate Method;
GridView gv = (GridView)findViewById(R.id.gridview); // debugging and always null
gv.setAdapter(new AdapterB(this,WallPaperList));
Fragment xml
<!-- TODO: Update blank fragment layout -->
<GridView xmlns:android="http://schemas.android.com/apk/res/android"
android:id="#+id/gridview"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
android:numColumns="auto_fit"
android:verticalSpacing="10dp"
android:horizontalSpacing="10dp"
android:columnWidth="90dp"
android:stretchMode="columnWidth"
android:gravity="center"
/>
MyGrid.xml (For populate with adapter)
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:orientation="vertical">
<ImageView
android:id="#+id/imagepart"
android:layout_width="fill_parent"
android:layout_height="wrap_content"/>
<CheckBox
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="Seç"
android:id="#+id/checkBox" />
</LinearLayout>

You cant acces fragment views like that, becouse they could be not yet in the activity view hierarchy.
You have to add some method to your fragment, like
myCustomFragment.setGridAdapter(MyCustomGridViewAdapter adapter)
and in this method in your custom fragment:
public void setGridAdapter(){
this.myCustomGridAdapter = adapter;
GridView gv = (GridView)findViewById(R.id.gridview);
if(gv != null)
gv.setAdapter(this.myCustomGridAdapter);
}

This code:
GridView gv = (GridView)findViewById(R.id.gridview); // debugging and always null
gv.setAdapter(new AdapterB(this,WallPaperList));
should be inside of your fragment's onCreateView. You should create fragments that are independent from the activity they're attached to.
If you absolutely need to access the fragment's layout from your activity you need to delay the findViewById because the fragment's layout is not yet inflated when you call it:
new Handler().postDelayed(new Runnable() {
#Override
public void run() {
GridView gv = (GridView)findViewById(R.id.gridview);
gv.setAdapter(new AdapterB(this, WallPaperList));
}
}, 1000);
Although this code would work, I highly discourage you from using it!

How do I hide or show layout elements when an Android Activity goes out of focus?

I am trying to hide certain elements in a layout when Android goes out of focus, such that when viewed in the "View recent applications" display, the layout elements will not be visible. Upon selecting the application and going into focus, these elements will be visible again.
My implementation below attempts to show the "content" layout when the application is in focus, and show the "overlay" layout when out of focus, via onWindowFocusChanged().
activity_main.xml
<FrameLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:id="#+id/container"
android:layout_width="match_parent"
android:layout_height="match_parent"
tools:context=".MainActivity">
<RelativeLayout
android:id="#+id/content"
android:layout_width="match_parent"
android:layout_height="match_parent">
<TextView
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:text="This is the content page"/>
</RelativeLayout>
<RelativeLayout
android:id="#+id/overlay"
android:layout_width="match_parent"
android:layout_height="match_parent">
<TextView
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:text="This is the overlay"/>
</RelativeLayout>
</FrameLayout>
MainActivity.java
public class MainActivity extends ActionBarActivity {
FrameLayout layoutContainer;
RelativeLayout layoutContent;
RelativeLayout layoutOverlay;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
layoutContainer = (FrameLayout) findViewById(R.id.container);
layoutContent = (RelativeLayout) findViewById(R.id.content);
layoutOverlay = (RelativeLayout) findViewById(R.id.overlay);
}
#Override
public void onWindowFocusChanged(boolean hasFocus) {
if (hasFocus) {
layoutContent.setVisibility(View.VISIBLE);
layoutOverlay.setVisibility(View.GONE);
} else {
layoutOverlay.setVisibility(View.VISIBLE);
layoutContent.setVisibility(View.GONE);
}
}
}
enter code here
However, my implementation does not work. Anyone with any suggestion as to solve this? Thanks!

If you want to hide views in your layout in recent apps try like this
getWindow().setFlags(WindowManager.LayoutParams.FLAG_SECURE,WindowManager.LayoutParams.FLAG_SECURE);

Android: null exception when call findviewbyid

I have a problem, when I call findViewById in a TextView throws NullPointerException, but not for the others elements. I've tried anything (change identifiers, call on OnCreateView, Clean and Build the project) and I don't Know what to do.
This is my Activity
public class RoutesActivity extends Activity {
ListView routesList;
EditText searchTxt;
TextView noneRouteTxt;
long uuid;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_routes);
noneRouteTxt = (TextView)this.findViewById(R.id.notroute_txt);
getControls();
Bundle extra = this.getIntent().getExtras();
getRoutesList(extra);
}
and this is my layout: activity_routes.xml
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
tools:context="com.geochild.app.com.geochild.app.activitities.RoutesActivity">
<RelativeLayout
android:layout_width="match_parent"
android:layout_height="325dp"
android:background="#drawable/app_background_waves"
android:layout_above="#+id/linearLayout"
android:layout_below="#+id/header_layout">
<ListView
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:id="#+id/routes_listview"
android:visibility="invisible">
</ListView>
<TextView
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="#string/no_routes"
android:id="#+id/notroute_txt"
android:visibility="invisible"
android:layout_centerVertical="true"
android:layout_centerHorizontal="true" />
</RelativeLayout>
Can you help me? Thanks

The NPE will be obviously thrown in the following line. But you should also present the first lines of the stack trace.
noneRouteTxt = (TextView)this.findViewById(R.id.notroute_txt);
And the NPE is thrown because, the layout the application is using when calling your onCreate() method is another one and not the 'activity_routes', where the id notroute_txt does not exist.
How many layouts are you using or do you have copied in your res folder?

onClick on an imageview within a listview within a dialog

I can't seem to get an onClick event on an imageview from a class that extends Fragment. What am i doing wrong here? I'm relatively new to developing for android..
Currently, this code gives me a null pointer exception - when i add the onClickListener code
Here is my code:
ImageView mImageView = (ImageView) v.findViewById(R.id.option_icon);
mImageView.setOnClickListener(new OnClickListener() {
#Override
public void onClick(View arg0) {
}
});
these icons are placed in a listview which is placed on a Dialog:
Dialog's list view and button:
<?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">
<ListView android:id="#+id/preset_list_view"
android:layout_height="wrap_content"
android:layout_width="fill_parent"/>
<Button
android:id="#+id/dialogButtonOK"
android:layout_width="300dp"
android:layout_height="wrap_content"
android:text="#string/ok"
android:layout_marginTop="5dp"
android:layout_marginRight="5dp"
android:layout_below="#+id/image"/>
</LinearLayout>
items within the list view (imageview and textview):
<?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" >
<ImageView
android:id="#+id/option_icon"
android:clickable="true"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_alignParentRight="true"
android:layout_alignParentTop="true"
android:src="#drawable/ic_launcher"
/>
<TextView
android:id="#+id/option_text"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_toLeftOf="#+id/image"
android:layout_alignParentLeft="true"
android:layout_alignParentTop="true"
android:textSize="20dp" />
</RelativeLayout>

It must be that the ImageView you're trying to find it outside the scope of whatever v refers to.
If the image view is inside a list view then you should add the onClickListener from within the adapter

The imageView that you are trying to find is not accessible from v. If the imageView is in the main layout then use findViewById without using v else first inflate the view and then use view.findViewById.