概述：通过自定义ImageView控件，在xml布局里面调用自定的组件实现图片的缩放。

/*** 自定义的ImageView控制，可对图片进行多点触控缩放和拖动* * @author qiuwanyong*/public class MyImageView extends ImageView {/*** 初始化状态常量*/public static final int STATUS_INIT = 1;/*** 图片放大状态常量*/public static final int STATUS_ZOOM_OUT = 2;/*** 图片缩小状态常量*/public static final int STATUS_ZOOM_IN = 3;/*** 图片拖动状态常量*/public static final int STATUS_MOVE = 4;/*** 用于对图片进行移动和缩放变换的矩阵*/private Matrix matrix = new Matrix();/*** 待展示的Bitmap对象*/private Bitmap sourceBitmap;/*** 记录当前操作的状态，可选值为STATUS_INIT、STATUS_ZOOM_OUT、STATUS_ZOOM_IN和STATUS_MOVE*/private int currentStatus;/*** ZoomImageView控件的宽度*/private int width;/*** ZoomImageView控件的高度*/private int height;/*** 记录两指同时放在屏幕上时，中心点的横坐标值*/private float centerPointX;/*** 记录两指同时放在屏幕上时，中心点的纵坐标值*/private float centerPointY;/*** 记录当前图片的宽度，图片被缩放时，这个值会一起变动*/private float currentBitmapWidth;/*** 记录当前图片的高度，图片被缩放时，这个值会一起变动*/private float currentBitmapHeight;/*** 记录上次手指移动时的横坐标*/private float lastXMove = -1;/*** 记录上次手指移动时的纵坐标*/private float lastYMove = -1;/*** 记录手指在横坐标方向上的移动距离*/private float movedDistanceX;/*** 记录手指在纵坐标方向上的移动距离*/private float movedDistanceY;/*** 记录图片在矩阵上的横向偏移值*/private float totalTranslateX;/*** 记录图片在矩阵上的纵向偏移值*/private float totalTranslateY;/*** 记录图片在矩阵上的总缩放比例*/private float totalRatio;/*** 记录手指移动的距离所造成的缩放比例*/private float scaledRatio;/*** 记录图片初始化时的缩放比例*/private float initRatio;/*** 记录上次两指之间的距离*/private double lastFingerDis;/*** ZoomImageView构造函数，将当前操作状态设为STATUS_INIT。* * @param context* @param attrs*/public MyImageView(Context context, AttributeSet attrs) {super(context, attrs);currentStatus = STATUS_INIT;}/*** 将待展示的图片设置进来。* * @param bitmap* 待展示的Bitmap对象*/public void setImageBitmap(Bitmap bitmap) {sourceBitmap = bitmap;invalidate();}@Overrideprotected void onLayout(boolean changed, int left, int top, int right,int bottom) {super.onLayout(changed, left, top, right, bottom);if (changed) {// 分别获取到ZoomImageView的宽度和高度width = getWidth();height = getHeight();}}@SuppressLint("NewApi") @Overridepublic boolean onTouchEvent(MotionEvent event) {if (initRatio == totalRatio) {getParent().requestDisallowInterceptTouchEvent(false);} else {getParent().requestDisallowInterceptTouchEvent(true);}switch (event.getActionMasked()) {case MotionEvent.ACTION_POINTER_DOWN:if (event.getPointerCount() == 2) {// 当有两个手指按在屏幕上时，计算两指之间的距离lastFingerDis = distanceBetweenFingers(event);}break;case MotionEvent.ACTION_CANCEL:case MotionEvent.ACTION_MOVE:if (event.getPointerCount() == 1) {// 只有单指按在屏幕上移动时，为拖动状态float xMove = event.getX();float yMove = event.getY();if (lastXMove == -1 && lastYMove == -1) {lastXMove = xMove;lastYMove = yMove;}currentStatus = STATUS_MOVE;movedDistanceX = xMove - lastXMove;movedDistanceY = yMove - lastYMove;// 进行边界检查，不允许将图片拖出边界if (totalTranslateX + movedDistanceX > 0) {movedDistanceX = 0;} else if (width - (totalTranslateX + movedDistanceX) > currentBitmapWidth) {movedDistanceX = 0;}if (totalTranslateY + movedDistanceY > 0) {movedDistanceY = 0;} else if (height - (totalTranslateY + movedDistanceY) > currentBitmapHeight) {movedDistanceY = 0;}// 调用onDraw()方法绘制图片invalidate();lastXMove = xMove;lastYMove = yMove;} else if (event.getPointerCount() == 2) {// 有两个手指按在屏幕上移动时，为缩放状态centerPointBetweenFingers(event);double fingerDis = distanceBetweenFingers(event);if (fingerDis > lastFingerDis) {currentStatus = STATUS_ZOOM_OUT;} else {currentStatus = STATUS_ZOOM_IN;}// 进行缩放倍数检查，最大只允许将图片放大4倍，最小可以缩小到初始化比例if ((currentStatus == STATUS_ZOOM_OUT && totalRatio < 4 * initRatio)|| (currentStatus == STATUS_ZOOM_IN && totalRatio > initRatio)) {scaledRatio = (float) (fingerDis / lastFingerDis);totalRatio = totalRatio * scaledRatio;if (totalRatio > 4 * initRatio) {totalRatio = 4 * initRatio;} else if (totalRatio < initRatio) {totalRatio = initRatio;}// 调用onDraw()方法绘制图片invalidate();lastFingerDis = fingerDis;}}break;case MotionEvent.ACTION_POINTER_UP:if (event.getPointerCount() == 2) {// 手指离开屏幕时将临时值还原lastXMove = -1;lastYMove = -1;}break;case MotionEvent.ACTION_UP:// 手指离开屏幕时将临时值还原lastXMove = -1;lastYMove = -1;break;default:break;}return true;}/*** 根据currentStatus的值来决定对图片进行什么样的绘制操作。*/@Overrideprotected void onDraw(Canvas canvas) {super.onDraw(canvas);switch (currentStatus) {case STATUS_ZOOM_OUT:case STATUS_ZOOM_IN:zoom(canvas);break;case STATUS_MOVE:move(canvas);break;case STATUS_INIT:initBitmap(canvas);default:if (sourceBitmap != null) {canvas.drawBitmap(sourceBitmap, matrix, null);}break;}}/*** 对图片进行缩放处理。* * @param canvas*/private void zoom(Canvas canvas) {matrix.reset();// 将图片按总缩放比例进行缩放matrix.postScale(totalRatio, totalRatio);float scaledWidth = sourceBitmap.getWidth() * totalRatio;float scaledHeight = sourceBitmap.getHeight() * totalRatio;float translateX = 0f;float translateY = 0f;// 如果当前图片宽度小于屏幕宽度，则按屏幕中心的横坐标进行水平缩放。否则按两指的中心点的横坐标进行水平缩放if (currentBitmapWidth < width) {translateX = (width - scaledWidth) / 2f;} else {translateX = totalTranslateX * scaledRatio + centerPointX* (1 - scaledRatio);// 进行边界检查，保证图片缩放后在水平方向上不会偏移出屏幕if (translateX > 0) {translateX = 0;} else if (width - translateX > scaledWidth) {translateX = width - scaledWidth;}}// 如果当前图片高度小于屏幕高度，则按屏幕中心的纵坐标进行垂直缩放。否则按两指的中心点的纵坐标进行垂直缩放if (currentBitmapHeight < height) {translateY = (height - scaledHeight) / 2f;} else {translateY = totalTranslateY * scaledRatio + centerPointY* (1 - scaledRatio);// 进行边界检查，保证图片缩放后在垂直方向上不会偏移出屏幕if (translateY > 0) {translateY = 0;} else if (height - translateY > scaledHeight) {translateY = height - scaledHeight;}}// 缩放后对图片进行偏移，以保证缩放后中心点位置不变matrix.postTranslate(translateX, translateY);totalTranslateX = translateX;totalTranslateY = translateY;currentBitmapWidth = scaledWidth;currentBitmapHeight = scaledHeight;canvas.drawBitmap(sourceBitmap, matrix, null);}/*** 对图片进行平移处理* * @param canvas*/private void move(Canvas canvas) {matrix.reset();// 根据手指移动的距离计算出总偏移值float translateX = totalTranslateX + movedDistanceX;float translateY = totalTranslateY + movedDistanceY;// 先按照已有的缩放比例对图片进行缩放matrix.postScale(totalRatio, totalRatio);// 再根据移动距离进行偏移matrix.postTranslate(translateX, translateY);totalTranslateX = translateX;totalTranslateY = translateY;canvas.drawBitmap(sourceBitmap, matrix, null);}/*** 对图片进行初始化操作，包括让图片居中，以及当图片大于屏幕宽高时对图片进行压缩。* * @param canvas*/private void initBitmap(Canvas canvas) {if (sourceBitmap != null) {matrix.reset();int bitmapWidth = sourceBitmap.getWidth();int bitmapHeight = sourceBitmap.getHeight();if (bitmapWidth > width || bitmapHeight > height) {if (bitmapWidth - width > bitmapHeight - height) {// 当图片宽度大于屏幕宽度时，将图片等比例压缩，使它可以完全显示出来float ratio = width / (bitmapWidth * 1.0f);matrix.postScale(ratio, ratio);float translateY = (height - (bitmapHeight * ratio)) / 2f;// 在纵坐标方向上进行偏移，以保证图片居中显示matrix.postTranslate(0, translateY);totalTranslateY = translateY;totalRatio = initRatio = ratio;} else {// 当图片高度大于屏幕高度时，将图片等比例压缩，使它可以完全显示出来float ratio = height / (bitmapHeight * 1.0f);matrix.postScale(ratio, ratio);float translateX = (width - (bitmapWidth * ratio)) / 2f;// 在横坐标方向上进行偏移，以保证图片居中显示matrix.postTranslate(translateX, 0);totalTranslateX = translateX;totalRatio = initRatio = ratio;}currentBitmapWidth = bitmapWidth * initRatio;currentBitmapHeight = bitmapHeight * initRatio;} else {// 当图片的宽高都小于屏幕宽高时，直接让图片居中显示float translateX = (width - sourceBitmap.getWidth()) / 2f;float translateY = (height - sourceBitmap.getHeight()) / 2f;matrix.postTranslate(translateX, translateY);totalTranslateX = translateX;totalTranslateY = translateY;totalRatio = initRatio = 1f;currentBitmapWidth = bitmapWidth;currentBitmapHeight = bitmapHeight;}canvas.drawBitmap(sourceBitmap, matrix, null);}}/*** 计算两个手指之间的距离。* * @param event* @return 两个手指之间的距离*/@SuppressLint("NewApi") private double distanceBetweenFingers(MotionEvent event) {float disX = Math.abs(event.getX(0) - event.getX(1));float disY = Math.abs(event.getY(0) - event.getY(1));return Math.sqrt(disX * disX + disY * disY);}/*** 计算两个手指之间中心点的坐标。* * @param event*/@SuppressLint("NewApi") private void centerPointBetweenFingers(MotionEvent event) {float xPoint0 = event.getX(0);float yPoint0 = event.getY(0);float xPoint1 = event.getX(1);float yPoint1 = event.getY(1);centerPointX = (xPoint0 + xPoint1) / 2;centerPointY = (yPoint0 + yPoint1) / 2;}}

布局中调用

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