Android UI How to - Handle custom Gesture
The following code shows how to Handle custom Gesture.
Code revised from
Android Recipes:A Problem-Solution Approach
http://www.apress.com/9781430234135
ISBN13: 978-1-4302-3413-5
Example
package com.java2s.myapplication3.app; /*w ww .j a va 2 s . c om*/ import android.content.Context; import android.util.AttributeSet; import android.view.GestureDetector; import android.view.GestureDetector.SimpleOnGestureListener; import android.view.MotionEvent; import android.view.View; import android.view.ViewConfiguration; import android.widget.FrameLayout; import android.widget.Scroller; import android.app.Activity; import android.os.Bundle; import android.widget.ImageButton; import android.widget.ImageView; import android.widget.LinearLayout; public class MainActivity extends Activity { @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); PanGestureScrollView scrollView = new PanGestureScrollView(this); LinearLayout layout = new LinearLayout(this); layout.setOrientation(LinearLayout.VERTICAL); for(int i=0; i < 5; i++) { ImageView iv = new ImageButton(this); iv.setImageResource(R.drawable.ic_launcher); layout.addView(iv, new LinearLayout.LayoutParams(1000, 500)); } scrollView.addView(layout); setContentView(scrollView); } } class PanGestureScrollView extends FrameLayout { private GestureDetector mDetector; private Scroller mScroller; /* Positions of the last motion event */ private float mInitialX, mInitialY; /* Drag threshold */ private int mTouchSlop; public PanGestureScrollView(Context context) { super(context); init(context); } public PanGestureScrollView(Context context, AttributeSet attrs) { super(context, attrs); init(context); } public PanGestureScrollView(Context context, AttributeSet attrs, int defStyle) { super(context, attrs, defStyle); init(context); } private void init(Context context) { mDetector = new GestureDetector(context, mListener); mScroller = new Scroller(context); // Get system constants for touch thresholds mTouchSlop = ViewConfiguration.get(context).getScaledTouchSlop(); } /* * Override the measureChild... implementations to guarantee that the child * view gets measured to be as large as it wants to be. The default * implementation will force some children to be only as large as this view. */ @Override protected void measureChild(View child, int parentWidthMeasureSpec, int parentHeightMeasureSpec) { int childWidthMeasureSpec; int childHeightMeasureSpec; childWidthMeasureSpec = MeasureSpec.makeMeasureSpec(0, MeasureSpec.UNSPECIFIED); childHeightMeasureSpec = MeasureSpec.makeMeasureSpec(0, MeasureSpec.UNSPECIFIED); child.measure(childWidthMeasureSpec, childHeightMeasureSpec); } @Override protected void measureChildWithMargins(View child, int parentWidthMeasureSpec, int widthUsed, int parentHeightMeasureSpec, int heightUsed) { final MarginLayoutParams lp = (MarginLayoutParams) child .getLayoutParams(); final int childWidthMeasureSpec = MeasureSpec.makeMeasureSpec( lp.leftMargin + lp.rightMargin, MeasureSpec.UNSPECIFIED); final int childHeightMeasureSpec = MeasureSpec.makeMeasureSpec( lp.topMargin + lp.bottomMargin, MeasureSpec.UNSPECIFIED); child.measure(childWidthMeasureSpec, childHeightMeasureSpec); } // Listener to handle all the touch events private SimpleOnGestureListener mListener = new SimpleOnGestureListener() { public boolean onDown(MotionEvent e) { // Cancel any current fling if (!mScroller.isFinished()) { mScroller.abortAnimation(); } return true; } public boolean onFling(MotionEvent e1, MotionEvent e2, float velocityX, float velocityY) { // Call a helper method to start the scroller animation fling((int) -velocityX / 3, (int) -velocityY / 3); return true; } public boolean onScroll(MotionEvent e1, MotionEvent e2, float distanceX, float distanceY) { // Any view can be scrolled by simply calling its scrollBy() method scrollBy((int) distanceX, (int) distanceY); return true; } }; @Override public void computeScroll() { if (mScroller.computeScrollOffset()) { // This is called at drawing time by ViewGroup. We use // this method to keep the fling animation going through // to completion. int oldX = getScrollX(); int oldY = getScrollY(); int x = mScroller.getCurrX(); int y = mScroller.getCurrY(); if (getChildCount() > 0) { View child = getChildAt(0); x = clamp(x, getWidth() - getPaddingRight() - getPaddingLeft(), child.getWidth()); y = clamp(y, getHeight() - getPaddingBottom() - getPaddingTop(), child.getHeight()); if (x != oldX || y != oldY) { scrollTo(x, y); } } // Keep on drawing until the animation has finished. postInvalidate(); } } // Override scrollTo to do bounds checks on any scrolling request @Override public void scrollTo(int x, int y) { // we rely on the fact the View.scrollBy calls scrollTo. if (getChildCount() > 0) { View child = getChildAt(0); x = clamp(x, getWidth() - getPaddingRight() - getPaddingLeft(), child.getWidth()); y = clamp(y, getHeight() - getPaddingBottom() - getPaddingTop(), child.getHeight()); if (x != getScrollX() || y != getScrollY()) { super.scrollTo(x, y); } } } /* * Monitor touch events passed down to the children and intercept as soon as * it is determined we are dragging */ @Override public boolean onInterceptTouchEvent(MotionEvent event) { switch (event.getAction()) { case MotionEvent.ACTION_DOWN: mInitialX = event.getX(); mInitialY = event.getY(); // Feed the down event to the detector so it has // context when/if dragging begins mDetector.onTouchEvent(event); break; case MotionEvent.ACTION_MOVE: final float x = event.getX(); final float y = event.getY(); final int yDiff = (int) Math.abs(y - mInitialY); final int xDiff = (int) Math.abs(x - mInitialX); // Verify that either difference is enough to be a drag if (yDiff > mTouchSlop || xDiff > mTouchSlop) { // Start capturing events return true; } break; } return super.onInterceptTouchEvent(event); } /* * Feed all touch events we receive to the detector for processing. */ @Override public boolean onTouchEvent(MotionEvent event) { return mDetector.onTouchEvent(event); } /* * Utility method to initialize the Scroller and start redrawing */ public void fling(int velocityX, int velocityY) { if (getChildCount() > 0) { int height = getHeight() - getPaddingBottom() - getPaddingTop(); int width = getWidth() - getPaddingLeft() - getPaddingRight(); int bottom = getChildAt(0).getHeight(); int right = getChildAt(0).getWidth(); mScroller.fling(getScrollX(), getScrollY(), velocityX, velocityY, 0, Math.max(0, right - width), 0, Math.max(0, bottom - height)); invalidate(); } } /* * Utility method to assist in doing bounds checking */ private int clamp(int n, int my, int child) { if (my >= child || n < 0) { /* * my >= child is this case: |--------------- me ---------------| * |------ child ------| or |--------------- me ---------------| * |------ child ------| or |--------------- me ---------------| * |------ child ------| * * n < 0 is this case: |------ me ------| |-------- child --------| * |-- mScrollX --| */ return 0; } if ((my + n) > child) { /* * this case: |------ me ------| |------ child ------| |-- mScrollX * --| */ return child - my; } return n; } }
