Develop Reference

Dynamically Creating Multiple TextViews in LinearLayout

I want to create multiple TextViews inside a LinearLayout.The following code builds successfully but gives a NullPointerException at the line root.addView(t[i]);
public class MainActivity extends ActionBarActivity {
TextView t[];
LinearLayout root;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
root=(LinearLayout)findViewById(R.id.master);
t=new TextView[10];
LinearLayout.LayoutParams dim=new LinearLayout.LayoutParams(LinearLayout.LayoutParams.WRAP_CONTENT, LinearLayout.LayoutParams.WRAP_CONTENT);
for(int i=0;i<10;i++)
{
t[i]=new TextView(this);
t[i].setLayoutParams(dim);
t[i].setText("YOHOHO: "+i);
root.addView(t[i]);
}
setContentView(root);
}
This really has no aim Iam just trying to learn things!

It's giving NPE because you are not setting your activity layout properly.
Do this
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.whereLinearLayoutMasterIs); // Add your layout here
root=(LinearLayout)findViewById(R.id.master);
t=new TextView[10];
LinearLayout.LayoutParams dim=new LinearLayout.LayoutParams(LinearLayout.LayoutParams.WRAP_CONTENT, LinearLayout.LayoutParams.WRAP_CONTENT);
for(int i=0;i<10;i++)
{
t[i]=new TextView(this);
t[i].setLayoutParams(dim);
t[i].setText("YOHOHO: "+i);
root.addView(t[i]);
}
}
NOTER.layout.whereLinearLayoutMasterIs is indicative, use your layout in which R.id.master is

The problem is that root is null - this is because you've not yet set your Activity's content view via setContentView.
You need to do something like this:
super.onCreate(...);
setContentView(R.layout.yourLayoutName);
root=(LinearLayout)findViewById(R.id.master);

Dynamically add element to layout

I am quite new to developing apps. Still I would have thought that this is a basic action, so if there is already a solved thread I would be OK with the link. But since I am searching for over 2 hours for this I am asking anyway:
I want to dynamically add an element to my layout every time the user clicks a button.
By now I have this:
XML (R.layout.game.xml)
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
android:orientation="vertical">
<Button
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="#string/submit_choice"
android:onClick="submitChoice"/>
</LinearLayout>
Java
public void submitChoice(View view)
{
TextView textView = new TextView(this);
textView.setTextSize(40);
textView.setText("text");
LinearLayout ll = new LinearLayout(this);
ll.addView(View.inflate(ll.getContext(), R.layout.game, null));
ll.addView(textView);
setContentView(ll);
}
Since the XML file does not change, it only works once.
So how can I add a second text when the user clicks the button a second time (without changing the XML file)? Examples are appreciated.

The problem comes from this line, that recreate the whole layout every time:
LinearLayout ll = new LinearLayout(this);
You should define it and setContentView(ll) outside the submitChoice function. Then on click only create and add the textView , then call ll.invalidate(); to see the changes.
Something like:
LinearLayout ll;
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.game);
ll = (LinearLayout) findViewById(R.id.ll_game);
}
// More code...
public void submitChoice(View view) {
TextView textView = new TextView(this);
textView.setTextSize(40);
textView.setText("text");
ll.addView(textView);
ll.invalidate();
}
where ll_game is the id you have to set in xml for your LinearLayout.

Android app Crash

Why is this:
public class HelpTab extends Activity
{
LinearLayout helpLayout; //was changed to LinearLayout helpLayout = new LinearLayout(this);
TextView helpText = new TextView(this);
Button tips = new Button(this);
Button walkThrough = new Button(this);
public void onCreate(Bundle savedInstanceState)
{
super.onCreate(savedInstanceState);
buttonCreator();
setContentView(helpLayout);
}
public void buttonCreator()
{
//Button featuress defined in here (setText("") and adding them to the layout, addView();)
}
Causing my program to crash?
I have looked at the code extensively and I can't put my finger on it, and the debugger also says source not found when it opens the new page tab thing to tell me what is happening.

Try calling setContentView(helpLayout); first and then buttonCreator();
public void onCreate(Bundle savedInstanceState)
{
super.onCreate(savedInstanceState);
setContentView(helpLayout);
buttonCreator();
}
Assuming that you are trying to initialize your button inside buttonCreater() with respect to a button you have declared in your helplayout, you might run into Null Pointer Exception.

If a toggle button is checked or not

Well I am trying to see if a checkbox is checked or not, but I get errors.
Defining the checkbox code:
public class Preferences extends PreferenceActivity {
CheckBoxPreference togglePref;
...
}
CheckBox Code:
public void checkNotify() {
if (togglePref.isChecked()==(true)) {
...
}
}
OnCreate code:
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
//SharedPreferences settings = getSharedPreferences("EasySettingsPreferences", MODE_PRIVATE);
//boolean notify = settings.getBoolean("notify", false);
checkNotify();
rootView = new LinearLayout(this);
rootView.setLayoutParams(new LayoutParams(LayoutParams.FILL_PARENT, LayoutParams.FILL_PARENT));
rootView.setOrientation(LinearLayout.VERTICAL);
togglePref = new CheckBoxPreference(this);
textView = new TextView(this);
textView.setText(R.string.app_name);
titleView = new LinearLayout(this);
titleView.setLayoutParams(new LayoutParams(LayoutParams.FILL_PARENT, 26));
titleView.setBackgroundResource(R.drawable.pattern_carbon_fiber_dark);
titleView.addView(textView);
preferenceView = new ListView(this);
preferenceView.setLayoutParams(new LayoutParams(LayoutParams.FILL_PARENT, LayoutParams.FILL_PARENT));
preferenceView.setId(android.R.id.list);
PreferenceScreen screen = createPreferenceHierarchy();
screen.bind(preferenceView);
preferenceView.setAdapter(screen.getRootAdapter());
rootView.addView(titleView);
rootView.addView(preferenceView);
this.setContentView(rootView);
setPreferenceScreen(screen);
}
Logcat Picture:
logcat pic http://img710.imageshack.us/img710/8529/unledxq.png
Debugger Picture
debugger pic http://img847.imageshack.us/img847/1192/unled1rn.png
Please help me if you can. Thanks!

I guess that you never initialise togglePref. To be sure we need to see the onCreate(). (I will update my answer if my guess was wrong...)
edit
I was right. You call checkNotify() before your even initialized the togglePref variable. Check your logic if it really makes sense to call that method before everything else or if it is fine if you call it later.
A tip: You can simplify your if statement:
// yours:
if (togglePref.isChecked()==(true)) {
// simplified:
if (togglePref.isChecked()) {

In your onCreate() method, you're calling checkNotify() before togglePref has been initialized. You want to move that initialization up (or move checkNotify() down.)

Android ContextMenu starts in the onCreate method?

is it possible to start a context menu on the onCreate method? I know its probably bad design ethics but I have my resons!! I've tried the:
registerForContextMenu(this.getCurrentFocus());
But its not working.. So does anyone have any better ideas?
Many thanks in advance!
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
LinearLayout layout = new LinearLayout(this);
layout.setLayoutParams(new
LayoutParams(LayoutParams.WRAP_CONTENT, LayoutParams.WRAP_CONTENT));
//Button button = new Button(this);
//button.setLayoutParams(new
//LayoutParams(LayoutParams.WRAP_CONTENT, LayoutParams.WRAP_CONTENT));
//button.setText("my button");
TextView text = new TextView(this);
text.setLayoutParams(new
LayoutParams(LayoutParams.WRAP_CONTENT, LayoutParams.WRAP_CONTENT));
layout.addView(text);
setContentView(layout);
registerForContextMenu(text);
openContextMenu(layout);

You need to do registerForContextMenu() for some widget, then use openContextMenu(). However, I agree with your conclusion that this is a bad design.