I have a Listview with fullscreen pictures. (Like a vertical gallery). My problem is that I want to override the listviews onTouchEvent so that it only changes one picture at a time and so that after scrolling (When no fling occurs), the selected picure centers itself.
My problem is that when i call getChildAt(getFirstVisiblePosition()), it returns null. I allready checked and getFirstVisiblePosition() is returning a view that is vissible at the moment.
I'm using smoothScrollToPosition to center the pictures.
My code is verry long, but the important part is here: (when recieving a MotionEvent.ACTION_UP).
case MotionEvent.ACTION_UP: { try { //Calculetes the velocity if the movement int initialVelocity = (int)ModifiedVelocityTracker.getYVelocity();*/ if (mVelocityTracker == null) { mVelocityTracker = VelocityTracker.obtain(); } final VelocityTracker ModifiedVelocityTracker = mVelocityTracker; ModifiedVelocityTracker.computeCurrentVelocity(1000); int initialVelocity = (int)ModifiedVelocityTracker.getYVelocity(); //Detects if the motion is a fling if ((Math.abs(initialVelocity) > ViewConfiguration.get(mContext).getScaledMinimumFlingVelocity()) && (getChildCount() > 0)) // TODO FLing { super.onTouchEvent(getEventWithACTION_MOVE(ev)); //Send the events to cancel the superclass fling //MotionEvent me[] = mVelocityTracker.getTrickEvents(); MotionEvent me[] = getTrickEvents(ev); for(int i=0;i<me.length;i++) super.onTouchEvent(me[i]); int firstVisiblePosition = getFirstVisiblePosition(); // Pint y=0 is located on the bottom, so a negative speed means //the finger moved up and the picture to come is the one under if(initialVelocity < 0) //EventUp-GoDown { if(firstVisiblePosition != getCount() - 1) //Can Move { //smoothScrollToPosition(firstVisiblePosition + 1); View currentTopView = getChildAt(firstVisiblePosition); int botom = currentTopView.getBottom(); botom = botom - firstVisiblePosition * getHeight(); smoothScrollBy(-botom, 500); } else { smoothScrollToPosition(firstVisiblePosition); } } else //EventDown-GoUp { smoothScrollToPosition(firstVisiblePosition); } } else // TODO Stay in the picture that has a bigger area shown { onTouchEvent = super.onTouchEvent(ev); //Center The View after the parent stops moving it /* * FIREST VIEW |****| / SECOND VIEW | | * * CASE 1 Bottom over center - Set second view the main one * |****| * |****| Bottom of Top View at First visible Position * | | * |----| center line * | | * | | * | | * * CASE 2 Bottom under center - Set first view the main one * |****| * |****| * |****| * |----| center line * |****| * |****| Bottom of Top View at First visible Position * | | * */ int firstVisiblePosition = getFirstVisiblePosition(); View currentTopView = getChildAt(firstVisiblePosition); int botom; if(currentTopView != null) { botom = currentTopView.getBottom(); }else{ currentTopView = getSelectedView(); if(firstVisiblePosition == getPositionForView(currentTopView)) { botom = currentTopView.getBottom(); } else { botom = currentTopView.getTop(); } } int center = getHeight()/2; botom = botom - firstVisiblePosition * getHeight(); if(botom < center) //Case 1 - Scroll Down { //Checks if the top view is the last one. //Shouldn't happen, but just in case. if(firstVisiblePosition != getCount() - 1) //Can Move { smoothScrollToPosition(firstVisiblePosition + 1); } else { smoothScrollToPosition(firstVisiblePosition); } } else //Case 2 { smoothScrollToPosition(firstVisiblePosition); } } onTouchEvent = true; } catch(NullPointerException e) { e.printStackTrace(); } } Tank you in advance.
Because of the comment.
import android.content.Context; import android.os.SystemClock; import android.util.Log; import android.view.MotionEvent; import android.view.VelocityTracker; import android.view.View; import android.view.ViewConfiguration; import android.widget.ListView; public class FixedListView extends ListView{ final static String LOGTAG = "TEST"; private Context mContext; VelocityTracker mVelocityTracker; public FixedListView(Context context) { super(context); mContext = context; setDivider(null); // TODO Auto-generated constructor stub } @Override public boolean onTouchEvent(MotionEvent ev) { boolean onTouchEvent = true; final int action = ev.getAction(); //Add the event to the ModifiedVelocityTracker used for detect if if the motion is a fling (also creates it) Log.d(LOGTAG, "Before add to Traker: " + SystemClock.uptimeMillis()); /*if (mVelocityTracker == null) { mVelocityTracker = ModifiedVelocityTracker.obtain(); } mVelocityTracker.addMovement(ev);*/ Log.d(LOGTAG, "After add to Traker: " + SystemClock.uptimeMillis()); //Detect the event action type switch (action) { case MotionEvent.ACTION_DOWN: case MotionEvent.ACTION_MOVE: { Log.d(LOGTAG, "After eval action Traker: " + SystemClock.uptimeMillis()); onTouchEvent = super.onTouchEvent(ev); Log.d(LOGTAG, "After super Y = " + ev.getY() +": " + SystemClock.uptimeMillis()); break; } case MotionEvent.ACTION_UP: { try { //Calculetes the velocity if the movement //NOTE: I'm using my own VelocityTraker because the Android.Utils //one can only be used once at a time and the superclass uses it. /*final ModifiedVelocityTracker ModifiedVelocityTracker = mVelocityTracker; ModifiedVelocityTracker.computeCurrentVelocity(1000); int initialVelocity = (int)ModifiedVelocityTracker.getYVelocity();*/ if (mVelocityTracker == null) { mVelocityTracker = VelocityTracker.obtain(); } final VelocityTracker ModifiedVelocityTracker = mVelocityTracker; ModifiedVelocityTracker.computeCurrentVelocity(1000); int initialVelocity = (int)ModifiedVelocityTracker.getYVelocity(); //Detects if the motion is a fling if ((Math.abs(initialVelocity) > ViewConfiguration.get(mContext).getScaledMinimumFlingVelocity()) && (getChildCount() > 0)) // TODO FLing { super.onTouchEvent(getEventWithACTION_MOVE(ev)); //Send the events to cancel the superclass fling //MotionEvent me[] = mVelocityTracker.getTrickEvents(); MotionEvent me[] = getTrickEvents(ev); for(int i=0;i<me.length;i++) super.onTouchEvent(me[i]); int firstVisiblePosition = getFirstVisiblePosition(); // Pint y=0 is located on the bottom, so a negative speed means //the finger moved up and the picture to come is the one under if(initialVelocity < 0) //EventUp-GoDown { if(firstVisiblePosition != getCount() - 1) //Can Move { //smoothScrollToPosition(firstVisiblePosition + 1); View currentTopView = getChildAt(firstVisiblePosition); int botom = currentTopView.getBottom(); botom = botom - firstVisiblePosition * getHeight(); smoothScrollBy(-botom, 500); } else { smoothScrollToPosition(firstVisiblePosition); } } else //EventDown-GoUp { smoothScrollToPosition(firstVisiblePosition); } } else // TODO Stay in the picture that has a bigger area shown { onTouchEvent = super.onTouchEvent(ev); //Center The View after the parent stops moving it /* * FIREST VIEW |****| / SECOND VIEW | | * * CASE 1 Bottom over center - Set second view the main one * |****| * |****| Bottom of Top View at First visible Position * | | * |----| center line * | | * | | * | | * * CASE 2 Bottom under center - Set first view the main one * |****| * |****| * |****| * |----| center line * |****| * |****| Bottom of Top View at First visible Position * | | * */ int firstVisiblePosition = getFirstVisiblePosition(); View currentTopView = getChildAt(firstVisiblePosition); int botom; if(currentTopView != null) { botom = currentTopView.getBottom(); }else{ currentTopView = getSelectedView(); if(firstVisiblePosition == getPositionForView(currentTopView)) { botom = currentTopView.getBottom(); } else { botom = currentTopView.getTop(); } } int center = getHeight()/2; botom = botom - firstVisiblePosition * getHeight(); if(botom < center) //Case 1 - Scroll Down { //Checks if the top view is the last one. //Shouldn't happen, but just in case. if(firstVisiblePosition != getCount() - 1) //Can Move { smoothScrollToPosition(firstVisiblePosition + 1); } else { smoothScrollToPosition(firstVisiblePosition); } } else //Case 2 { smoothScrollToPosition(firstVisiblePosition); } } onTouchEvent = true; } catch(NullPointerException e) { e.printStackTrace(); } if(mVelocityTracker != null) mVelocityTracker.recycle(); break; } case MotionEvent.ACTION_CANCEL: { try { onTouchEvent = super.onTouchEvent(ev); //Center The View after the parent stops moving it /* * FIREST VIEW |****| / SECOND VIEW | | * * CASE 1 Bottom over center - Set second view the main one * |****| * |****| Bottom of Top View at First visible Position * | | * |----| center line * | | * | | * | | * * CASE 2 Bottom under center - Set first view the main one * |****| * |****| * |****| * |----| center line * |****| * |****| Bottom of Top View at First visible Position * | | * */ int firstVisiblePosition = getFirstVisiblePosition(); View currentTopView = getChildAt(firstVisiblePosition); int center = getHeight()/2; if(currentTopView.getBottom() < center) //Case 1 - Scroll Down { //Checks if the top view is the last one. //Shouldn't happen, but just in case. if(firstVisiblePosition != getCount() - 1) //Can Move { smoothScrollToPosition(firstVisiblePosition + 1); } else { smoothScrollToPosition(firstVisiblePosition); } } else //Case 2 { if(firstVisiblePosition != 0) //Can Move { smoothScrollToPosition(firstVisiblePosition - 1); } else { smoothScrollToPosition(firstVisiblePosition); } } onTouchEvent = true; } catch(NullPointerException e) { e.printStackTrace(); } if(mVelocityTracker != null) { mVelocityTracker.recycle(); mVelocityTracker = null; } } } // TODO Auto-generated method stub return onTouchEvent; } @Override public boolean onInterceptTouchEvent(MotionEvent ev) { // TODO Auto-generated method stub return super.onInterceptTouchEvent(ev); } public MotionEvent[] getTrickEvents(MotionEvent ev) { //Detect the last touched position final float requiredX = ev.getX(); final float requiredY = ev.getY(); //Get a time value that is longer than the last added event value by a bigger //number than the LONGEST_PAST_TIME accepted by the VelocityTraker //NOTE: If GOOGLE changes the LONGEST_PAST_TIME, we will have to change it too, //I wasn't able to retrieve the original VelocityTracker LONGEST_PAST_TIME directly from it. final long requiredPastTime = ev.getEventTime() + 201; //Create the MotionEvents (Simulating no movement in y). MotionEvent m1 = null; if(requiredX == 0) //If at the left border, move one pixel to the right. { m1 = MotionEvent.obtain(requiredPastTime, requiredPastTime, MotionEvent.ACTION_MOVE, requiredX + 1, requiredY, 0); } else //If not at the left border, move one pixel to the left { m1 = MotionEvent.obtain(requiredPastTime, requiredPastTime, MotionEvent.ACTION_MOVE, requiredX - 1, requiredY, 0); } //Return to the original position after 100 time units MotionEvent m2 = MotionEvent.obtain(requiredPastTime + 100, requiredPastTime + 100, MotionEvent.ACTION_UP, requiredX, requiredY, 0); MotionEvent motEvents[] = {m1,m2}; return motEvents; } public MotionEvent getEventWithACTION_MOVE(MotionEvent ev) { //Detect the last touched position final float requiredX = ev.getX(); final float requiredY = ev.getY(); //Get a time value that is longer than the last added event value by a bigger //number than the LONGEST_PAST_TIME accepted by the VelocityTraker //NOTE: If GOOGLE changes the LONGEST_PAST_TIME, we will have to change it too, //I wasn't able to retrieve the original VelocityTracker LONGEST_PAST_TIME directly from it. final long Time = ev.getEventTime(); //Create the MotionEvent MotionEvent m1 = MotionEvent.obtain(Time, Time, MotionEvent.ACTION_MOVE, requiredX , requiredY, 0); return m1; } } And the adapter
public class FixedListAdapter extends BaseAdapter { int pictures[]; public FixedListAdapter(int pictures[]) { this.pictures = pictures; } public int getCount() { return pictures.length; } public Object getItem(int position) { return pictures[position]; } public long getItemId(int position) { return pictures[position]; } public View getView(int position, View convertView, ViewGroup parent) { LinearLayout l = new LinearLayout(GalleryTest.this); l.setLayoutParams(new ListView.LayoutParams( ListView.LayoutParams.MATCH_PARENT, ListView.LayoutParams.MATCH_PARENT)); l.setGravity(Gravity.CENTER); l.setPadding(0,0,0,0); l.setBackgroundColor(Color.BLACK); ImageView i = new ImageView(GalleryTest.this); i.setLayoutParams(new LinearLayout.LayoutParams(width, height)); i.setScaleType(ImageView.ScaleType.FIT_CENTER); i.setImageResource(pictures[position]); l.addView(i); return l; } } NOTE: The picture changes on the device and the getFirstVisiblePosition() gives me the index of the first picture being shown. The problem is that getChildAt returns null with a view that is actually on screen.