Develop Reference

Android doubletap zoom in and out listview

I am using custom listview to zoom in and out, this is listview:
public class CustomListView extends ListView {
private static final int INVALID_POINTER_ID = -1;
private int mActivePointerId = INVALID_POINTER_ID;
private ScaleGestureDetector mScaleDetector;
private float mScaleFactor = 1.f;
private float maxWidth = 0.0f;
private float maxHeight = 0.0f;
private float mLastTouchX;
private float mLastTouchY;
private float mPosX;
private float mPosY;
private float width;
private float height;
public CustomListView(Context context) {
super(context);
mScaleDetector = new ScaleGestureDetector(getContext(),
new ScaleListener());
}
public CustomListView(Context context, AttributeSet attrs) {
super(context, attrs);
mScaleDetector = new ScaleGestureDetector(getContext(),
new ScaleListener());
}
public CustomListView(Context context, AttributeSet attrs, int defStyleAttr) {
super(context, attrs, defStyleAttr);
mScaleDetector = new ScaleGestureDetector(getContext(),
new ScaleListener());
}
#Override
protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
width = MeasureSpec.getSize(widthMeasureSpec);
height = MeasureSpec.getSize(heightMeasureSpec);
super.onMeasure(widthMeasureSpec, heightMeasureSpec);
}
#Override
public boolean onTouchEvent(#NonNull MotionEvent ev) {
super.onTouchEvent(ev);
final int action = ev.getAction();
mScaleDetector.onTouchEvent(ev);
switch (action & MotionEvent.ACTION_MASK) {
case MotionEvent.ACTION_DOWN: {
final float x = ev.getX();
final float y = ev.getY();
mLastTouchX = x;
mLastTouchY = y;
mActivePointerId = ev.getPointerId(0);
break;
}
case MotionEvent.ACTION_MOVE: {
final int pointerIndex = ev.findPointerIndex(mActivePointerId);
final float x = ev.getX(pointerIndex);
final float y = ev.getY(pointerIndex);
final float dx = x - mLastTouchX;
final float dy = y - mLastTouchY;
mPosX += dx;
mPosY += dy;
if (mPosX > 0.0f)
mPosX = 0.0f;
else if (mPosX < maxWidth)
mPosX = maxWidth;
if (mPosY > 0.0f)
mPosY = 0.0f;
else if (mPosY < maxHeight)
mPosY = maxHeight;
mLastTouchX = x;
mLastTouchY = y;
invalidate();
break;
}
case MotionEvent.ACTION_UP: {
mActivePointerId = INVALID_POINTER_ID;
break;
}
case MotionEvent.ACTION_CANCEL: {
mActivePointerId = INVALID_POINTER_ID;
break;
}
case MotionEvent.ACTION_POINTER_UP: {
final int pointerIndex = (action & MotionEvent.ACTION_POINTER_INDEX_MASK) >> MotionEvent.ACTION_POINTER_INDEX_SHIFT;
final int pointerId = ev.getPointerId(pointerIndex);
if (pointerId == mActivePointerId) {
final int newPointerIndex = pointerIndex == 0 ? 1 : 0;
mLastTouchX = ev.getX(newPointerIndex);
mLastTouchY = ev.getY(newPointerIndex);
mActivePointerId = ev.getPointerId(newPointerIndex);
}
break;
}
}
return true;
}
#Override
public void onDraw(Canvas canvas) {
super.onDraw(canvas);
canvas.save(Canvas.MATRIX_SAVE_FLAG);
canvas.translate(mPosX, mPosY);
canvas.scale(mScaleFactor, mScaleFactor);
canvas.restore();
}
#Override
protected void dispatchDraw(#NonNull Canvas canvas) {
canvas.save(Canvas.MATRIX_SAVE_FLAG);
if (mScaleFactor == 1.0f) {
mPosX = 0.0f;
mPosY = 0.0f;
}
canvas.translate(mPosX, mPosY);
canvas.scale(mScaleFactor, mScaleFactor);
super.dispatchDraw(canvas);
canvas.restore();
invalidate();
}
private class ScaleListener extends
ScaleGestureDetector.SimpleOnScaleGestureListener {
#Override
public boolean onScale(ScaleGestureDetector detector) {
mScaleFactor *= detector.getScaleFactor();
mScaleFactor = Math.max(1.0f, Math.min(mScaleFactor, 4.0f));
maxWidth = width - (width * mScaleFactor);
maxHeight = height - (height * mScaleFactor);
invalidate();
return true;
}
}
With this, listview can pinch to zoom in and out.
and I want one more thing, double tap to zoom in and double tap again to zoom out listview.
How to do it?

How to make Zoom on whole content in RecyclerView?

I need zoom in/out on whole content in RecyclerView.
In fact I need to resize all child views by width, and text inside each item.
public class ViewHolder {
Button btn;
...
}
When User make zoom in, the text of Button should be decrease down to 8sp and disappear if user continue zoom in.
So, now I have dilemma : what I need to do? Resize items in Adapter, or resize them in LayoutManager, and update whole adapter.
Both of scenarios seems affect an performance of visual effect, so I need help. Maybe you give me a better solution.
For state of 21/11/2016 I can't found any box-solution for this case.
So I decide write my own view and do remeasurement of visible views in each zoom scale factor change.

Which adapter do you use?
I've tried Horizontal LinearLayoutManager and do resize items inside adapter:
#Override
public void onBindViewHolder(RecyclerView.ViewHolder holder, int position) {
...
final ViewGroup.LayoutParams layoutParams = viewHolder.rootView.getLayoutParams();
layoutParams.width = getItemWidth(position); //width calculation using current zoom level
layoutParams.height = mItemLayoutHeight;
viewHolder.rootView.setLayoutParams(layoutParams);
...
and setZoom(..) method of the activity/fragment looks like:
public void setZoom(float newValue) {
int dScroll = (int) ((ADAPTER_ZOOM - newValue) * getResources().getDisplayMetrics().widthPixels/2f); //assume you Recycler view uses whole display
ADAPTER_ZOOM = newValue;
resetBoundaries();
//
epgAdapter.notifyDataSetChanged();
//
epgRecyclerView.scrollBy(dScroll, 0);
}
But with my custom LayoutManager performance is bad, seems there is a list of optimisations inside the LinearLayoutManager

for complete implementation refer to :
github.com/mosayeb-masoumi/zoom_whole_recyclerview

user this code. it's working fine for zooming all content of recyclerview.
import android.content.Context;
import android.graphics.Canvas;
import android.support.annotation.NonNull;
import android.support.v7.widget.RecyclerView;
import android.util.AttributeSet;
import android.view.MotionEvent;
import android.view.ScaleGestureDetector;
/**
#author yogesh
* */
public class PinchRecyclerView extends RecyclerView {
private static final int INVALID_POINTER_ID = -1;
private int mActivePointerId = INVALID_POINTER_ID;
private ScaleGestureDetector mScaleDetector;
private float mScaleFactor = 1.f;
private float maxWidth = 0.0f;
private float maxHeight = 0.0f;
private float mLastTouchX;
private float mLastTouchY;
private float mPosX;
private float mPosY;
private float width;
private float height;
public PinchRecyclerView(Context context) {
super(context);
if (!isInEditMode())
mScaleDetector = new ScaleGestureDetector(getContext(), new ScaleListener());
}
public PinchRecyclerView(Context context, AttributeSet attrs) {
super(context, attrs);
if (!isInEditMode())
mScaleDetector = new ScaleGestureDetector(getContext(), new ScaleListener());
}
public PinchRecyclerView(Context context, AttributeSet attrs, int defStyleAttr) {
super(context, attrs, defStyleAttr);
if (!isInEditMode())
mScaleDetector = new ScaleGestureDetector(getContext(), new ScaleListener());
}
#Override
protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
width = MeasureSpec.getSize(widthMeasureSpec);
height = MeasureSpec.getSize(heightMeasureSpec);
super.onMeasure(widthMeasureSpec, heightMeasureSpec);
}
#Override
public boolean onInterceptTouchEvent(MotionEvent ev) {
try {
return super.onInterceptTouchEvent(ev);
} catch (IllegalArgumentException ex) {
ex.printStackTrace();
}
return false;
}
#Override
public boolean onTouchEvent(#NonNull MotionEvent ev) {
super.onTouchEvent(ev);
final int action = ev.getAction();
mScaleDetector.onTouchEvent(ev);
switch (action & MotionEvent.ACTION_MASK) {
case MotionEvent.ACTION_DOWN: {
final float x = ev.getX();
final float y = ev.getY();
mLastTouchX = x;
mLastTouchY = y;
mActivePointerId = ev.getPointerId(0);
break;
}
case MotionEvent.ACTION_MOVE: {
/* this line is replaced because here came below isssue
java.lang.IllegalArgumentException: pointerIndex out of range
ref http://stackoverflow.com/questions/6919292/pointerindex-out-of-range-android-multitouch
*/
//final int pointerIndex = ev.findPointerIndex(mActivePointerId);
final int pointerIndex = (action & MotionEvent.ACTION_POINTER_INDEX_MASK)
>> MotionEvent.ACTION_POINTER_INDEX_SHIFT;
final float x = ev.getX(pointerIndex);
final float y = ev.getY(pointerIndex);
final float dx = x - mLastTouchX;
final float dy = y - mLastTouchY;
mPosX += dx;
mPosY += dy;
if (mPosX > 0.0f)
mPosX = 0.0f;
else if (mPosX < maxWidth)
mPosX = maxWidth;
if (mPosY > 0.0f)
mPosY = 0.0f;
else if (mPosY < maxHeight)
mPosY = maxHeight;
mLastTouchX = x;
mLastTouchY = y;
invalidate();
break;
}
case MotionEvent.ACTION_UP: {
mActivePointerId = INVALID_POINTER_ID;
break;
}
case MotionEvent.ACTION_CANCEL: {
mActivePointerId = INVALID_POINTER_ID;
break;
}
case MotionEvent.ACTION_POINTER_UP: {
final int pointerIndex = (action & MotionEvent.ACTION_POINTER_INDEX_MASK) >> MotionEvent.ACTION_POINTER_INDEX_SHIFT;
final int pointerId = ev.getPointerId(pointerIndex);
if (pointerId == mActivePointerId) {
final int newPointerIndex = pointerIndex == 0 ? 1 : 0;
mLastTouchX = ev.getX(newPointerIndex);
mLastTouchY = ev.getY(newPointerIndex);
mActivePointerId = ev.getPointerId(newPointerIndex);
}
break;
}
}
return true;
}
#Override
public void onDraw(Canvas canvas) {
super.onDraw(canvas);
canvas.save(Canvas.MATRIX_SAVE_FLAG);
canvas.translate(mPosX, mPosY);
canvas.scale(mScaleFactor, mScaleFactor);
canvas.restore();
}
#Override
protected void dispatchDraw(#NonNull Canvas canvas) {
canvas.save(Canvas.MATRIX_SAVE_FLAG);
if (mScaleFactor == 1.0f) {
mPosX = 0.0f;
mPosY = 0.0f;
}
canvas.translate(mPosX, mPosY);
canvas.scale(mScaleFactor, mScaleFactor);
super.dispatchDraw(canvas);
canvas.restore();
invalidate();
}
private class ScaleListener extends ScaleGestureDetector.SimpleOnScaleGestureListener {
#Override
public boolean onScale(ScaleGestureDetector detector) {
mScaleFactor *= detector.getScaleFactor();
mScaleFactor = Math.max(1.0f, Math.min(mScaleFactor, 3.0f));
maxWidth = width - (width * mScaleFactor);
maxHeight = height - (height * mScaleFactor);
invalidate();
return true;
}
}
}
Code taken from this StackOverflow answer: Android change recycler view column no. on pinch zoom

Pinch zoom not working properly in HorizontalScrollView in android

I am arranging my views inside HorizontalScrollView and my each view(DrawView.java) contains rectangle. When the activity only contain this view, pinch zoom functionality is working fine(See Code 1 and respective image 1) but when I am arranging multiple of these views in HorizontalScrollView, it's not working properly because touch events of this view are messing up with touch events of HorizontalScrollView(Code 2 and Image 2).
Someone please help me to fix this bug.
This is a code for activity in which pinch zoom is working fine.
public class MainActivity extends Activity {
DrawView drawView;
public class DrawView extends View {
Paint paint = new Paint();
public int recog=-1; // this variable will tell if onDraw is called for first time or is called by listener usinf invalidate()
boolean listener=false;
int data[] = new int[] {200,200,200,200,200,200,200,200,200,200,200,200};
private float MIN_ZOOM = 0.1f;
private float MAX_ZOOM = 10f;
private float mPosX;
private float mPosY;
boolean zoom=false;
private ScaleGestureDetector detector;
float width=200;
private float mLastTouchX;
private float mLastTouchY;
private ScaleGestureDetector mScaleDetector;
private float mScaleFactor = 1.f;
private static final int INVALID_POINTER_ID = -1;
// The ‘active pointer’ is the one currently moving our object.
private int mActivePointerId = INVALID_POINTER_ID;
public DrawView(Context context) {
this(context, null);
}
public DrawView(Context context, AttributeSet attrs) {
this(context, attrs, 0);
}
public DrawView(Context context, AttributeSet attrs, int defStyle) {
super(context, attrs, defStyle);
mScaleDetector = new ScaleGestureDetector(context, new ScaleListener());
}
#Override
public void onDraw(Canvas canvas) {
paint.setColor(Color.GREEN);
canvas.save();
if(listener ==true)
mScaleFactor+=0.4;
Log.e("Ronak","Listener"+listener);
Log.e("Ronak","ScaleFactor"+mScaleFactor);
canvas.scale(mScaleFactor, 1);
canvas.drawRect(0.0f, 0.0f, 300.0f, 100.0f, paint);
makeLinesinRange(0,100,300,100,200, 5, canvas,100);
width=mScaleFactor*300;
canvas.restore();
requestLayout();
}
public boolean onTouchEvent(MotionEvent ev) {
// Let the ScaleGestureDetector inspect all events.
mScaleDetector.onTouchEvent(ev);
final int action = ev.getAction();
switch (action & MotionEvent.ACTION_MASK) {
case MotionEvent.ACTION_DOWN: {
final float x = ev.getX();
final float y = ev.getY();
mLastTouchX = x;
mLastTouchY = y;
mActivePointerId = ev.getPointerId(0);
break;
}
case MotionEvent.ACTION_MOVE: {
final int pointerIndex = ev.findPointerIndex(mActivePointerId);
final float x = ev.getX(pointerIndex);
final float y = ev.getY(pointerIndex);
// Only move if the ScaleGestureDetector isn't processing a gesture.
if (!mScaleDetector.isInProgress()) {
final float dx = x - mLastTouchX;
final float dy = y - mLastTouchY;
mPosX += dx;
mPosY += dy;
invalidate();
}
mLastTouchX = x;
mLastTouchY = y;
break;
}
case MotionEvent.ACTION_UP: {
mActivePointerId = INVALID_POINTER_ID;
break;
}
case MotionEvent.ACTION_CANCEL: {
mActivePointerId = INVALID_POINTER_ID;
break;
}
case MotionEvent.ACTION_POINTER_UP: {
final int pointerIndex = (ev.getAction() & MotionEvent.ACTION_POINTER_INDEX_MASK)
>> MotionEvent.ACTION_POINTER_INDEX_SHIFT;
final int pointerId = ev.getPointerId(pointerIndex);
if (pointerId == mActivePointerId) {
// This was our active pointer going up. Choose a new
// active pointer and adjust accordingly.
final int newPointerIndex = pointerIndex == 0 ? 1 : 0;
mLastTouchX = ev.getX(newPointerIndex);
mLastTouchY = ev.getY(newPointerIndex);
mActivePointerId = ev.getPointerId(newPointerIndex);
}
break;
}
}
return true;
}
#Override protected void onMeasure(int widthMeasureSpec,
int heightMeasureSpec) {
// int width = MeasureSpec.getSize(widthMeasureSpec);
//int height = (int)(width * 0.5f);
setMeasuredDimension((int)width, 350);
}
private void makeLinesinRange(int x1, int y1, int x2, int y2, int size, int divisions, Canvas canvas,int width)
{
paint.setStrokeWidth(6);
paint.setColor(Color.DKGRAY);
float kk=(x2-x1)/(divisions-1);
for(int i=0;i<divisions;i++)
{
canvas.drawLine(x1+i*kk, y1, x1+i*kk, y2+size, paint);
}
}
private class ScaleListener extends ScaleGestureDetector.SimpleOnScaleGestureListener {
#Override
public boolean onScale(ScaleGestureDetector detector) {
mScaleFactor *= detector.getScaleFactor();
Log.e("Ronak","scale "+mScaleFactor);
// Don't let the object get too small or too large.
mScaleFactor = Math.max(0.3f, Math.min(mScaleFactor, 5.0f));
invalidate();
return true;
}
}
}
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
drawView = new DrawView(this);
drawView.setBackgroundColor(Color.WHITE);
setContentView(drawView);
}
}
DrawView.java. This is a code of single view. I am arranging multiple of these views in HorizontalScrollView
public class DrawView extends View {
Paint paint = new Paint();
public int recog=-1; // this variable will tell if onDraw is called for first time or is called by listener usinf invalidate()
boolean listener=false;
int view_number=0;
int data[] = new int[] {200,200,200,200,200,200,200,200,200,200,200,200};
int lines[] = new int[] {4,5,7,8,2,6,6,3,2,1,1,6};
String[] type=new String[]{"Song","Music","Magazine","Audible","Videos","Apps","Other"};
private static float MIN_ZOOM = 0.1f;
private static float MAX_ZOOM = 10f;
private float mPosX;
private float mPosY;
boolean zoom=false;
private ScaleGestureDetector detector;
float width=700;
float height=500;
private float mLastTouchX;
private float mLastTouchY;
private ScaleGestureDetector mScaleDetector;
private float mScaleFactor = 1.f;
private static final int INVALID_POINTER_ID = -1;
// The ‘active pointer’ is the one currently moving our object.
private int mActivePointerId = INVALID_POINTER_ID;
public DrawView(Context context) {
this(context, null);
}
public DrawView(Context context, AttributeSet attrs) {
this(context, attrs, 0);
}
public DrawView(Context context, AttributeSet attrs, int defStyle) {
super(context, attrs, defStyle);
mScaleDetector = new ScaleGestureDetector(context, new ScaleListener());
}
#Override
public void onDraw(Canvas canvas) {
paint.setColor(Color.BLUE);
canvas.save();
if(listener ==true)
mScaleFactor+=0.4;
Log.e("Ronak","Listener"+listener);
Log.e("Ronak","ScaleFactor"+mScaleFactor);
canvas.scale(mScaleFactor, 1);
canvas.drawRect(0.0f, 0.0f, 300.0f, 70.0f, paint);
makeLinesinRange(0,70,300,70,200, lines[view_number], canvas,100);
width=mScaleFactor*300;
height=mScaleFactor*100;
/*int start=0;
int temp=(int)width/lines[view_number];
for(int i=0;i<lines[view_number];i++)
{
canvas.drawText(type[i], 50, 100, paint);
start=temp;
temp+=temp;
}*/
canvas.restore();
requestLayout();
}
public boolean onTouchEvent(MotionEvent ev) {
// Let the ScaleGestureDetector inspect all events.
mScaleDetector.onTouchEvent(ev);
final int action = ev.getAction();
switch (action & MotionEvent.ACTION_MASK) {
case MotionEvent.ACTION_DOWN: {
final float x = ev.getX();
final float y = ev.getY();
mLastTouchX = x;
mLastTouchY = y;
mActivePointerId = ev.getPointerId(0);
break;
}
case MotionEvent.ACTION_MOVE: {
final int pointerIndex = ev.findPointerIndex(mActivePointerId);
final float x = ev.getX(pointerIndex);
final float y = ev.getY(pointerIndex);
// Only move if the ScaleGestureDetector isn't processing a gesture.
if (!mScaleDetector.isInProgress()) {
final float dx = x - mLastTouchX;
final float dy = y - mLastTouchY;
mPosX += dx;
mPosY += dy;
// invalidate();
}
mLastTouchX = x;
mLastTouchY = y;
break;
}
case MotionEvent.ACTION_UP: {
mActivePointerId = INVALID_POINTER_ID;
break;
}
case MotionEvent.ACTION_CANCEL: {
mActivePointerId = INVALID_POINTER_ID;
break;
}
case MotionEvent.ACTION_POINTER_UP: {
final int pointerIndex = (ev.getAction() & MotionEvent.ACTION_POINTER_INDEX_MASK)
>> MotionEvent.ACTION_POINTER_INDEX_SHIFT;
final int pointerId = ev.getPointerId(pointerIndex);
if (pointerId == mActivePointerId) {
// This was our active pointer going up. Choose a new
// active pointer and adjust accordingly.
final int newPointerIndex = pointerIndex == 0 ? 1 : 0;
mLastTouchX = ev.getX(newPointerIndex);
mLastTouchY = ev.getY(newPointerIndex);
mActivePointerId = ev.getPointerId(newPointerIndex);
}
break;
}
}
return true;
}
public boolean onInterceptTouchEvent(MotionEvent event) {
/* switch (event.getAction()) {
case MotionEvent.ACTION_DOWN:
break;
case MotionEvent.ACTION_CANCEL:
case MotionEvent.ACTION_UP:
mIsBeingDragged = false;
break;
case MotionEvent.ACTION_MOVE:
float x = event.getX();
float y = event.getY();
float xDelta = Math.abs(x - mLastX);
float yDelta = Math.abs(y - mLastY);
float yDeltaTotal = y - mStartY;
if (yDelta > xDelta && Math.abs(yDeltaTotal) > mTouchSlop) {
mIsBeingDragged = true;
mStartY = y;
return true;
}
break;
}*/
Log.e("Ronak","Here");
return false;
}
#Override protected void onMeasure(int widthMeasureSpec,
int heightMeasureSpec) {
// int width = MeasureSpec.getSize(widthMeasureSpec);
//int height = (int)(width * 0.5f);
setMeasuredDimension((int)width, 350);
}
private void makeLinesinRange(int x1, int y1, int x2, int y2, int size, int total_events, Canvas canvas,int width)
{
paint.setStrokeWidth(6);
paint.setColor(Color.MAGENTA);
if(total_events<1)
{
return;
}
if(total_events==1)
{
canvas.drawLine(((x1+x2)/2), y1, (x1+x2)/2, y2+size, paint);
}
else if(total_events==2)
{
canvas.drawLine(((x1+x2)/3), y1, (x1+x2)/3, y2+size, paint);
canvas.drawLine((2*(x1+x2)/3), y1, 2*(x1+x2)/3, y2+size, paint);
}
else
{
paint.setStrokeWidth(6);
paint.setColor(Color.MAGENTA);
float kk=(x2-x1)/(total_events-1);
for(int i=0;i<total_events;i++)
{
canvas.drawLine(x1+i*kk, y1, x1+i*kk, y2+size, paint);
}
}
}
private class ScaleListener extends ScaleGestureDetector.SimpleOnScaleGestureListener {
#Override
public boolean onScale(ScaleGestureDetector detector) {
mScaleFactor *= detector.getScaleFactor();
Log.e("Ronak","scale "+mScaleFactor);
// Don't let the object get too small or too large.
mScaleFactor = Math.max(0.1f, Math.min(mScaleFactor, 5.0f));
invalidate();
return true;
}
}
}
I also have a class which is extending HorizontalScrollView and is calling the above class(DrawView.java) for fitting multiple of these view in horizontal scrolling. Is there ant need to override the onTouch function of this class?

First: YIKES! Don't call requestLayout() from onDraw() -- or you'll get 100% load, all it's ever going to do is relayout and redraw itself.
Second: Remove onInterceptTouchEvent() from DrawView. Since it extends View -- and Views don't have this method -- it'll not get called as part of the touch dispatch process anyway.
Third: which one's not working -- scrolling or scaling?
Read this thread, it's got some insights on how to handle multiple gesture-consuming components

Canvas view crash the application on touch events

I'm trying a simple CustomView with canvas. This custom view simply change the position of an icon picture on the screen randomly when is invoked updatePosition(), and in my intention should move the image on drag, scale on pinch... and when I touch a position in the screen should appear in the clicked position.
My try is the follow
public class CustomView extends View {
Bitmap mBmp;
Random mRnd;
Paint mPaint;
private static final int INVALID_POINTER_ID = -1;
private float mPosX;
private float mPosY;
private float mLastTouchX;
private float mLastTouchY;
private int mActivePointerId = INVALID_POINTER_ID;
private ScaleGestureDetector mScaleDetector;
private float mScaleFactor = 1.f;
int w, h, bw, bh;
int px = -1, py = -1;
public CustomView(Context context) {
this(context, null, 0);
mBmp = BitmapFactory.decodeResource(context.getResources(),
R.drawable.icon);
}
public CustomView(Context context, AttributeSet attrs, int defStyle) {
super(context, attrs, defStyle);
mScaleDetector = new ScaleGestureDetector(context, new ScaleListener());
}
public CustomView(Context context, AttributeSet attrs) {
super(context, attrs, 0);
mBmp = BitmapFactory.decodeResource(context.getResources(),
R.drawable.icon);
bw = mBmp.getWidth();
bh = mBmp.getHeight();
mPaint = new Paint();
mPaint.setColor(Color.CYAN);
mPaint.setAntiAlias(true);
mRnd = new Random();
}
#Override
protected void onDraw(Canvas canvas) {
super.onDraw(canvas);
canvas.save();
Log.d("DEBUG", "X: " + mPosX + " Y: " + mPosY);
canvas.translate(mPosX, mPosY);
canvas.scale(mScaleFactor, mScaleFactor);
if (px == -1 && py == -1) {
px = w / 2 - bw / 2;
py = h / 2 - bh / 2;
}
canvas.drawCircle(px + (bw / 2), py + (bh / 2), 70, mPaint);
canvas.drawBitmap(mBmp, px, py, null);
canvas.restore();
}
public void updatePosition() {
px = mRnd.nextInt(w - bw);
py = mRnd.nextInt(h - bh);
invalidate();
}
#Override
protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
w = MeasureSpec.getSize(widthMeasureSpec);
h = MeasureSpec.getSize(heightMeasureSpec);
setMeasuredDimension(w, h);
}
#Override
public boolean onTouchEvent(MotionEvent ev) {
mScaleDetector.onTouchEvent(ev);
final int action = ev.getAction();
switch (action & MotionEvent.ACTION_MASK) {
case MotionEvent.ACTION_DOWN: {
final float x = ev.getX();
final float y = ev.getY();
mLastTouchX = x;
mLastTouchY = y;
mActivePointerId = ev.getPointerId(0);
break;
}
case MotionEvent.ACTION_MOVE: {
final int pointerIndex = ev.findPointerIndex(mActivePointerId);
final float x = ev.getX(pointerIndex);
final float y = ev.getY(pointerIndex);
if (!mScaleDetector.isInProgress()) {
final float dx = x - mLastTouchX;
final float dy = y - mLastTouchY;
mPosX += dx;
mPosY += dy;
invalidate();
}
mLastTouchX = x;
mLastTouchY = y;
break;
}
case MotionEvent.ACTION_UP: {
mActivePointerId = INVALID_POINTER_ID;
break;
}
case MotionEvent.ACTION_CANCEL: {
mActivePointerId = INVALID_POINTER_ID;
break;
}
case MotionEvent.ACTION_POINTER_UP: {
final int pointerIndex = (ev.getAction() & MotionEvent.ACTION_POINTER_INDEX_MASK) >> MotionEvent.ACTION_POINTER_INDEX_SHIFT;
final int pointerId = ev.getPointerId(pointerIndex);
if (pointerId == mActivePointerId) {
final int newPointerIndex = pointerIndex == 0 ? 1 : 0;
mLastTouchX = ev.getX(newPointerIndex);
mLastTouchY = ev.getY(newPointerIndex);
mActivePointerId = ev.getPointerId(newPointerIndex);
}
break;
}
}
return true;
}
private class ScaleListener extends
ScaleGestureDetector.SimpleOnScaleGestureListener {
#Override
public boolean onScale(ScaleGestureDetector detector) {
mScaleFactor *= detector.getScaleFactor();
// Don't let the object get too small or too large.
mScaleFactor = Math.max(0.1f, Math.min(mScaleFactor, 10.0f));
invalidate();
return true;
}
}
}
updatePosition() listener works while onTouchListener cause crash of the application with a NullPointerException if I try to drag the image or touch any position of the screen
Could someone help me? Thanks

It looks like mScaleDetector is only initialized in one of the constructor. It should be initialized in all constructors. A common pattern is to create an init() method and place all you initializing in there then call that method from all constructors.
Note: It's always helpful to post a StackTrace... You should be able to see which constructor got called.

Teleport the image in the touched position in canvas

I have tried t create a simple canvas but the image does't appear in the touched position moves only when I drag, I want also that teleports in the touched position if the user clicks a point of the screen
My code
public class CustomView extends View {
Bitmap mBmp;
Random mRnd;
Paint mPaint;
private static final int INVALID_POINTER_ID = -1;
private float mPosX;
private float mPosY;
private float mLastTouchX;
private float mLastTouchY;
private int mActivePointerId = INVALID_POINTER_ID;
private ScaleGestureDetector mScaleDetector;
private float mScaleFactor = 1.f;
int w, h, bw, bh;
int px = -1, py = -1;
public CustomView(Context context) {
this(context, null, 0);
mBmp = BitmapFactory.decodeResource(context.getResources(),
R.drawable.icon);
mScaleDetector = new ScaleGestureDetector(context, new ScaleListener());
}
public CustomView(Context context, AttributeSet attrs, int defStyle) {
super(context, attrs, defStyle);
mScaleDetector = new ScaleGestureDetector(context, new ScaleListener());
}
public CustomView(Context context, AttributeSet attrs) {
super(context, attrs, 0);
mScaleDetector = new ScaleGestureDetector(context, new ScaleListener());
mBmp = BitmapFactory.decodeResource(context.getResources(),
R.drawable.icon);
bw = mBmp.getWidth();
bh = mBmp.getHeight();
mPaint = new Paint();
mPaint.setColor(Color.CYAN);
mPaint.setAntiAlias(true);
mRnd = new Random();
}
#Override
protected void onDraw(Canvas canvas) {
super.onDraw(canvas);
canvas.save();
Log.d("DEBUG", "X: " + mPosX + " Y: " + mPosY);
canvas.translate(mPosX, mPosY);
canvas.scale(mScaleFactor, mScaleFactor);
if (px == -1 && py == -1) {
px = w / 2 - bw / 2;
py = h / 2 - bh / 2;
}
canvas.drawCircle(px + (bw / 2), py + (bh / 2), 70, mPaint);
canvas.drawBitmap(mBmp, px, py, null);
canvas.restore();
}
public void updatePosition() {
px = mRnd.nextInt(w - bw);
py = mRnd.nextInt(h - bh);
invalidate();
}
#Override
protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
w = MeasureSpec.getSize(widthMeasureSpec);
h = MeasureSpec.getSize(heightMeasureSpec);
setMeasuredDimension(w, h);
}
#Override
public boolean onTouchEvent(MotionEvent ev) {
mScaleDetector.onTouchEvent(ev);
final int action = ev.getAction();
switch (action & MotionEvent.ACTION_MASK) {
case MotionEvent.ACTION_DOWN: {
final float x = ev.getX();
final float y = ev.getY();
mLastTouchX = x;
mLastTouchY = y;
mActivePointerId = ev.getPointerId(0);
break;
}
case MotionEvent.ACTION_MOVE: {
final int pointerIndex = ev.findPointerIndex(mActivePointerId);
final float x = ev.getX(pointerIndex);
final float y = ev.getY(pointerIndex);
if (!mScaleDetector.isInProgress()) {
final float dx = x - mLastTouchX;
final float dy = y - mLastTouchY;
mPosX += dx;
mPosY += dy;
invalidate();
}
mLastTouchX = x;
mLastTouchY = y;
break;
}
case MotionEvent.ACTION_UP: {
mActivePointerId = INVALID_POINTER_ID;
break;
}
case MotionEvent.ACTION_CANCEL: {
mActivePointerId = INVALID_POINTER_ID;
break;
}
case MotionEvent.ACTION_POINTER_UP: {
final int pointerIndex = (ev.getAction() & MotionEvent.ACTION_POINTER_INDEX_MASK) >> MotionEvent.ACTION_POINTER_INDEX_SHIFT;
final int pointerId = ev.getPointerId(pointerIndex);
if (pointerId == mActivePointerId) {
final int newPointerIndex = pointerIndex == 0 ? 1 : 0;
mLastTouchX = ev.getX(newPointerIndex);
mLastTouchY = ev.getY(newPointerIndex);
mActivePointerId = ev.getPointerId(newPointerIndex);
}
break;
}
}
return true;
}
private class ScaleListener extends
ScaleGestureDetector.SimpleOnScaleGestureListener {
#Override
public boolean onScale(ScaleGestureDetector detector) {
mScaleFactor *= detector.getScaleFactor();
// Don't let the object get too small or too large.
mScaleFactor = Math.max(0.1f, Math.min(mScaleFactor, 10.0f));
invalidate();
return true;
}
}
}
Could someone help me? Thanks

Don't forget to call invalidate(); so your canvas redraws in your ACTION_DOWN case statement. Also it looks like you should be setting the following in ACTION_DOWN.
mPosX = mLastTouchX;
mPosY = mLastTouchY;