Android Drag and Zoom pictures

Android Drag and Zoom pictures

May 9, 2014

We use apps that often require a view of the image. For example, in which. After clicking on the image, you can zoom in on the image.

This blog describes how to drag and zoom pictures. This is the first thing to know about the touch mechanism in Android, where the finger is pressed, the finger is lifted, the finger is moved, and the touch of a finger moves.

We want to achieve the drag and zoom of the image is to be based on these actions for logical processing.

The drag and drop of the image is mainly to calculate the position of the finger starting with the position of the current finger, to translate, in detail to see the code.

The scaling of the image involves calculating the distance between two points to get the zoom ratio, and call the matrix method to achieve the scaling effect.

Demo Sample code: http://download.csdn.net/detail/wwj_748/7324363

Package Com.wwj.dragscale;import Android.app.activity;import Android.graphics.matrix;import Android.graphics.pointf;import Android.os.bundle;import Android.util.floatmath;import android.view.MotionEvent;  Import Android.view.view;import android.view.view.ontouchlistener;import android.widget.imageview;/** * Drag and zoom the image * * @author WWJ * */public class Mainactivity extends Activity {private ImageView ImageView; @Overrideprotected void Oncreat E (Bundle savedinstancestate) {super.oncreate (savedinstancestate); Setcontentview (R.layout.activity_main); ImageView = (ImageView) Findviewbyid (R.id.imageview); Imageview.setontouchlistener (new Touchlistener ());} Private class Touchlistener implements Ontouchlistener {private PointF startPoint = new PointF ();p rivate matrix matrix = n EW matrix ();p rivate matrix CURRENTMARITX = new Matrix ();p rivate int mode = 0; Used to mark the mode private static final int DRAG = 1; Drag private static final int ZOOM = 2; Enlarge private Float Startdis = 0;private PointF midpoint; Center Point @oVerridepublic boolean OnTouch (View V, motionevent event) {switch (Event.getaction () & Motionevent.action_mask) {case MotionEvent.ACTION_DOWN:mode = DRAG; Drag Currentmaritx.set (Imageview.getimagematrix ()); Record ImageView Current moving position startpoint.set (Event.getx (), event.gety ()); Start point break;case motionevent.action_move://Move Event if (mode = = DRAG) {//Picture drag event Float dx = event.getx ()-startpoint.x;//X-axis Moving distance float dy = event.gety ()-Startpoint.y;matrix.set (CURRENTMARITX); Move the matrix.posttranslate (dx, DY) based on the current position;} else if (mode = = Zoom) {//Picture magnification event float Enddis = distance (event);//End Distance if (Enddis > 10f) {float scale = Enddis/star TDis; Magnification Matrix.set (CURRENTMARITX); Matrix.postscale (scale, scaled, midpoint.x, MIDPOINT.Y);}} Break;case MotionEvent.ACTION_UP:mode = 0;break;//has a finger to leave the screen, but the screen also has a contact point (finger) case MotionEvent.ACTION_POINTER_UP:mode = 0; break;//when there is already a touch point (finger) on the screen, and then a finger presses down on the screen case MotionEvent.ACTION_POINTER_DOWN:mode = Zoom;startdis = Distance (event); if ( Startdis > 10f) {//Avoid two midpoint on fingers = mID (event); Currentmaritx.set (Imageview.getimagematrix ()); Record the current zoom multiplier}break;} Show scaled picture Imageview.setimagematrix (matrix); return true;}} /** * Calculates the distance between two points * * @param event * @return */public static float distance (Motionevent event) {Float dx = event.getx (1)- Event.getx (0); float dy = event.gety (1)-event.gety (0); return floatmath.sqrt (DX * dx + dy * dy);} /** * Calculates the middle point between two points * * @param event * @return */public static PointF Mid (Motionevent event) {Float Midx = (event.getx (1) + Event.getx (0))/2;float Midy = (event.gety (1) + event.gety (0))/2;return new PointF (Midx, Midy);}}

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Android Drag and Zoom pictures