Develop Reference

Android Add Items One By One Into a LinearLayout

I'm new to Android and I'm trying to find out how to do that:
- I have an activity with a ScrollView and inside it I have a LinearLayout (R.id.my_layout)
- I nedd to add TextView programmatically so I'm doing this:
I load the main XML layout via seContentView, I refer to my LinearLayout inside the ScrollView as "mLayout" and so on.
I load a list of names from a file and with a function called populateList()I do:
private void populateList() {
try {
for (final String team : mTeams) {
rCount++;
addRow(team);
}
}
The addRow() method just create a new LinearLayout (mRow), a TextView, 2 Button, add the TextView and the 2 Buttons to the LinearLayout, and then I use addView to add the new mRow to the mLayout.
Everything is working fine, but the ScrollView is shown only when i finished creating the list (so when the populateList() ends). What I would like to do is to show the rows one by one in sequence to give the activty a better look and a bit of animation.
Is there a way to do this?
I hope i was able to explain it :-)
Thank you

new Thread(new Runnable() { // i am creating the new thread
#Override
public void run() {
// so call populateList() function here
}
}).start();
and for your addRow(String string) method the place you call View.addView(); edit it this way and place the following code in your addRow(String string) method
View.post(new new Runnable() {// view here is mlayout the scrollView.
#Override
public void run() {
mlayout.addView(yourview); // note yourview should be final,
//eclipse might help you with that
}
});
remember to declare mlayout globally, so you do not have to attach final

how to add onClickListener to buttons inside CardLayout

I am using Gabrielemariotti's Cardslib library to implement card layout in my android application. I am using a custom layout for my cards. Below is the code for creating custom cards:
Card card = new Card(getActivity().getApplicationContext(), R.layout.status_card);
card.setTitle("sample title");
I have three buttons at the bottom of my card (like buttons in Facebook android app). I want to set onClickListener for these buttons. But I am not sure how to do that.
Please help me here.
Thanks,

You have to define your layout.
Then create a Card with this layout, and override the setupInnerViewElements method.
Inside this method you can define your OnClickListener on your buttons, and you can access to all card's values.
public class CustomCard extends Card {
/**
* Constructor with a custom inner layout
*
* #param context
*/
public CustomCard(Context context) {
super(context, R.layout.carddemo_mycard_inner_content);
}
#Override
public void setupInnerViewElements(ViewGroup parent, View view) {
//Retrieve button
Button myButton = (Button) view.findViewById(R.id.myButton);
if (myButton != null) {
myButton.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
Toast.makeText(getContext(), "Click Listener card=" + getId(),
Toast.LENGTH_LONG).show();
}
});
}
}
}

I have an easy solution for this.
So another way to add onClick listeners, which is a bit easier, is through the XML.
In the xml for the button, you add this line:
android:onClick="methodName"
Where 'methodName' is obviously the name of a method. This will call the method whenever the button is clicked. The next step is obvious - just go into your java activity and create the method that you want called, making sure to take the View as a parameter. So you'd have something like this in your activity class:
public void methodName(View view) {
Log.v("appTag","BUTTON WAS PRESSED");
//whatever you want to do here
}
This is a shortcut to creating a whole onClickListener.
Hope that helps. Good luck :)
EDIT:
Remember, you're passing in a view here, so you can get whatever you want off of that view. Since you commented that you need to get the text off of your card, I'll show you how to do that.
Here is your method for this case:
public void methodName(View view) {
Log.v("appTag","BUTTON WAS PRESSED");
TextView textFromCard = view.findViewById(R.id.THE_ID_YOU_GAVE_YOUR_TEXTVIEW_IN_THE_XML);
String textFromTextView = textFromCard.getText().toString();
//do whatever you want with the string here
}

Auto-scrolling textview in Android

I've tried a lot of different ways, most of the suggestions found here, but none of them seems to work. What I'm trying to achieve is at chat area below my game area, a SurfaceView. It is supposed to scroll upwards as new lines are added to the textview.
At first, it looks like a really simple task, but having tried all kinds of suggestions, like a TextView in a ScrollView, like a TextView in a TableRow in a TableLayout in a ScrollView, and so on...I've still not made it happen. Of course this must be something easily achieved in Android, right??
The task is to display like 6 lines of text in the bottom of the screen, and as a new message is added last it should scroll the rest upwards, like a terminal window. The important thing is that it should add the latest message after the other and, when reached the bottom line, scroll the text upwards and add the new line(s) at the end.
Any kind of help or suggestions would be highly appreciated!!

I needed the same behavior in one of my apps and I achieved in just with one command:
view.setGravity(Gravity.BOTTOM);
Or, analogously, setting this attribute in your layout:
android:gravity="bottom"
Then simply add your lines using:
your_text_view.append(newLine);

Suppose, you declared your ScrollView as follows...
private ScrollView mScrollView;
you initialized it as...
mScrollView = (ScrollView) findViewById(R.id.scroll_view_chat_window);
Now, create a method to perform scroll down when you call the method. Inside the method implement a thread which will do the scroll down independently. And call the method after every chat message update thats will do the auto-srcoll functionality.
private void scrollDown() {
mScrollView.post(new Runnable() {
#Override
public void run() {
mScrollView.smoothScrollTo(mScrollView.getScrollY(), mScrollView.getScrollY()
+ mScrollView.getHeight());
}
});
}

I've achieved this (crudely!) by maintaining my own list, deleting the lowest element then adding at the end each time. Here i've just got a 3 line window:
public class MessageWindow {
private ArrayList <String> msgs;
private Activity parentActivity;
public MessageWindow(Activity act, int allMsgsMax) {
this.parentActivity = act;
msgs = new ArrayList <String> ();
// create empty list elements for initial display
for (int i = 0; i < allMsgsMax; i++){
msgs.add("");
}
}
//
public void put (String msg){
msgs.remove(0);
msgs.add(msg);
// get a handle to the textview 'messages', a 3-line box
TextView t2v = (TextView) parentActivity.findViewById(R.id.messages);
// crappy but you get the idea:
t2v.setText(msgs.get(0) + "\n" + msgs.get(1) + "\n" + msgs.get(2) );
}
then in the activity:
protected MessageWindow messageWindow;
// setup splash screen
messageWindow = new MessageWindow(this, 3);
// write some stuff - row1 will disappear off the top of the box
messageWindow.put ("row1")
messageWindow.put ("row2")
messageWindow.put ("row3")
messageWindow.put ("row4")

Adding items to ListView, maintaining scroll position and NOT seeing a scroll jump

I'm building an interface similar to the Google Hangouts chat interface. New messages are added to the bottom of the list. Scrolling up to the top of the list will trigger a load of previous message history. When the history comes in from the network, those messages are added to the top of the list and should not trigger any kind of scroll from the position the user had stopped when the load was triggered. In other words, a "loading indicator" is shown at the top of the list:
Which is then replaced in-situ with any loaded history.
I have all of this working... except one thing that I've had to resort to reflection to accomplish. There are plenty of questions and answers involving merely saving and restoring a scroll position when adding items to the adapter attached to a ListView. My problem is that when I do something like the following (simplified but should be self-explanatory):
public void addNewItems(List<Item> items) {
final int positionToSave = listView.getFirstVisiblePosition();
adapter.addAll(items);
listView.post(new Runnable() {
#Override
public void run() {
listView.setSelection(positionToSave);
}
});
}
Then what the user will see is a quick flash to the top of the ListView, then a quick flash back to the right location. The problem is fairly obvious and discovered by many people: setSelection() is unhappy until after notifyDataSetChanged() and a redraw of ListView. So we have to post() to the view to give it a chance to draw. But that looks terrible.
I've "fixed" it by using reflection. I hate it. At its core, what I want to accomplish is reset the first position of the ListView without going through the rigamarole of the draw cycle until after I've set the position. To do that, there's a helpful field of ListView: mFirstPosition. By gawd, that's exactly what I need to adjust! Unfortunately, it's package-private. Also unfortunately, there doesn't appear to be any way to set it programmatically or influence it in any way that doesn't involve an invalidate cycle... yielding the ugly behavior.
So, reflection with a fallback on failure:
try {
Field field = AdapterView.class.getDeclaredField("mFirstPosition");
field.setAccessible(true);
field.setInt(listView, positionToSave);
}
catch (Exception e) { // CATCH ALL THE EXCEPTIONS </meme>
e.printStackTrace();
listView.post(new Runnable() {
#Override
public void run() {
listView.setSelection(positionToSave);
}
});
}
}
Does it work? Yes. Is it hideous? Yes. Will it work in the future? Who knows? Is there a better way? That's my question.
How do I accomplish this without reflection?
An answer might be "write your own ListView that can handle this." I'll merely ask whether you've seen the code for ListView.
EDIT: Working solution with no reflection based on Luksprog's comment/answer.
Luksprog recommended an OnPreDrawListener(). Fascinating! I've messed with ViewTreeObservers before, but never one of these. After some messing around, the following type of thing appears to work quite perfectly.
public void addNewItems(List<Item> items) {
final int positionToSave = listView.getFirstVisiblePosition();
adapter.addAll(items);
listView.post(new Runnable() {
#Override
public void run() {
listView.setSelection(positionToSave);
}
});
listView.getViewTreeObserver().addOnPreDrawListener(new OnPreDrawListener() {
#Override
public boolean onPreDraw() {
if(listView.getFirstVisiblePosition() == positionToSave) {
listView.getViewTreeObserver().removeOnPreDrawListener(this);
return true;
}
else {
return false;
}
}
});
}
Very cool.

As I said in my comment, a OnPreDrawlistener could be another option to solve the problem. The idea of using the listener is to skip showing the ListView between the two states(after adding the data and after setting the selection to the right position). In the OnPreDrawListener(set with listViewReference.getViewTreeObserver().addOnPreDrawListener(listener);) you'll check the current visible position of the ListView and test it against the position which the ListView should show. If those don't match then make the listener's method return false to skip the frame and set the selection on the ListView to the right position. Setting the proper selection will trigger the draw listener again, this time the positions will match, in which case you'd unregister the OnPreDrawlistener and return true.

I was breaking up my head until I found a solution similar to this.
Before adding a set of items you have to save top distance of the firstVisible item and after adding the items do setSelectionFromTop().
Here is the code:
// save index and top position
int index = mList.getFirstVisiblePosition();
View v = mList.getChildAt(0);
int top = (v == null) ? 0 : v.getTop();
// for (Item item : items){
mListAdapter.add(item);
}
// restore index and top position
mList.setSelectionFromTop(index, top);
It works without any jump for me with a list of about 500 items :)
I took this code from this SO post: Retaining position in ListView after calling notifyDataSetChanged

The code suggested by the question author works, but it's dangerous.
For instance, this condition:
listView.getFirstVisiblePosition() == positionToSave
may always be true if no items were changed.
I had some problems with this aproach in a situation where any number of elements were added both above and below the current element. So I came up with a sligtly improved version:
/* This listener will block any listView redraws utils unlock() is called */
private class ListViewPredrawListener implements OnPreDrawListener {
private View view;
private boolean locked;
private ListViewPredrawListener(View view) {
this.view = view;
}
public void lock() {
if (!locked) {
locked = true;
view.getViewTreeObserver().addOnPreDrawListener(this);
}
}
public void unlock() {
if (locked) {
locked = false;
view.getViewTreeObserver().removeOnPreDrawListener(this);
}
}
#Override
public boolean onPreDraw() {
return false;
}
}
/* Method inside our BaseAdapter */
private updateList(List<Item> newItems) {
int pos = listView.getFirstVisiblePosition();
View cell = listView.getChildAt(pos);
String savedId = adapter.getItemId(pos); // item the user is currently looking at
savedPositionOffset = cell == null ? 0 : cell.getTop(); // current item top offset
// Now we block listView drawing until after setSelectionFromTop() is called
final ListViewPredrawListener predrawListener = new ListViewPredrawListener(listView);
predrawListener.lock();
// We have no idea what changed between items and newItems, the only assumption
// that we make is that item with savedId is still in the newItems list
items = newItems;
notifyDataSetChanged();
// or for ArrayAdapter:
//clear();
//addAll(newItems);
listView.post(new Runnable() {
#Override
public void run() {
// Now we can finally unlock listView drawing
// Note that this code will always be executed
predrawListener.unlock();
int newPosition = ...; // Calculate new position based on the savedId
listView.setSelectionFromTop(newPosition, savedPositionOffset);
}
});
}

Updating LinearLayout from other class in Android

I have a class which uses other classes to build up a FrameLayout. One is for Navigation through a building, the other for displaying schematics with sensors of it, and the other one to display sensordata. I build up the whole frame one time, and want to make the sensordata visible in the sensorview part of the frame. Lets say I have 5 sensors, and when I click on one the sensorview shows up the sensordata. I could just make 5 sensorviewframes on top of each other, initiating them invisible, and just make the one visible which was selected via a click on a sensor.
I wanted to ask, is it possible to change the LinearLayout containing the TextViews in a different class with an update method?
I already tried it, but with my code it doesn't work at the moment.
public static SensorBar Create_SensorBar_Layout(Context myContext, ObjectStructure objStruct, ObjectView objView, List<SensorDevice> listofCurrentSensordevices)
{
// Init
LinearLayout SensorBarLinearLayout = new LinearLayout(myContext);
LinearLayout.LayoutParams layoutParamsSensorBar = new LinearLayout.LayoutParams(
200, 653);
layoutParamsSensorBar.setMargins(5, 5, 5, 5);
SensorBarLinearLayout.setOrientation(LinearLayout.VERTICAL);
SensorBarLinearLayout.setLayoutParams(layoutParamsSensorBar);
SensorBarLinearLayout.setBackgroundResource(R.drawable.window_frame);
SensorBarLinearLayout.setPadding(4,4,4,4);
LinearLayout SensorBarData = new LinearLayout(myContext);
LinearLayout.LayoutParams layoutParamsSensorBarData = new LinearLayout.LayoutParams(
LayoutParams.MATCH_PARENT, LayoutParams.MATCH_PARENT);
SensorBarData.setOrientation(LinearLayout.VERTICAL);
SensorBarData.setLayoutParams(layoutParamsSensorBarData);
//--- Button Headline ---
Button buttonNavBarHeadline = new Button(myContext);
buttonNavBarHeadline.setText("Sensordata");
buttonNavBarHeadline.setTextColor(Color.BLACK);
buttonNavBarHeadline.setBackgroundResource(R.layout.mainview_window_headline);
buttonNavBarHeadline.setTextAppearance(myContext, R.style.headline3);
//Layout buildup
SensorBarLinearLayout.addView(buttonNavBarHeadline);
SensorBarLinearLayout.addView(SensorBarData);
return new SensorBar(SensorBarLinearLayout, SensorBarData);
}
This is the Sensorbar, and I want to have the LinearLayout SensorBarData to be dynamically swapped out by clicking on the sensorbuttons.
public void updateSensorBar(Context myContext, ObjectStructure objStruct, List<SensorDevice> listofCurrentSensordevices, int activeSensor)
{
LinearLayout linearlayoutSensorvalueTextviews = new LinearLayout(myContext);
... (additional Textviews for Sensordata, which get added with addview())
setSensorBarData(linearlayoutSensorvalueTextviews);
}
This is used by an OnClick event.
public void setSensorBarData(LinearLayout SensorBarData) { this.dataSensorBar = SensorBarData; }
This is used by the updateSensorBar to update the LinearLayout.
I would be glad for any help.

Define an interface and use a callback to let the activity know that a sensor has been updated.
public Interface SensorUpdatedListener {
void onSensorUpdated();
}
In your SensorBar class.
ArrayList<SensorUpdatedListener > listeners = new ArrayList<SensorUpdatedListener >();
...
public void setSensorUpdatedListener(SensorUpdatedListener listener){
listeners.add(listener);
}
In your sensor bar update method:
for (SensorUpdatedListener listener:listeners){
listener.onSensorUpdated();
}
In your Activity:
public class Test extends Activity implements SensorUpdatedListener {
...
#Override
public void onCreate(Bundle savedInstanceState)
{
...
sensorBar.setSensorUpdatedListener(this);
...
}
public void onSensorUpdated(){
// do whatever you need to do
}
You could improve the SensorBar class by adding removeSensorUpdatedListener and checking that you do not add the same listener twice in setSensorUpdatedListener.