ViewPager图片预览之图片的放大缩小，移动，切换（第三课）连载

第三课（第三步）：支持以手指触控的任意点为中心开始缩放

关键部分是在缩放的时候不断进行边界检测，防止放大后缩小后出现白边：

/** * 在缩放的时候进行边界控制范围位置控制 */private void checkBorderAndCenterWhenScale() {// TODO Auto-generated method stubRectF rect = getMatrixRectF();float deltaX = 0;float deltaY = 0;float width = getWidth();float height = getHeight();//缩放时进行边界检测，放在出现白边if(rect.width() >= width){if(rect.left > 0){//处理左边的空白deltaX = -rect.left;}if(rect.right < width){//处理右边的空白deltaX = (int) (width - rect.right);}}if(rect.height() >= height){if(rect.top > 0){deltaY = -rect.top;}if(rect.bottom < height){deltaY = height - rect.bottom;}}//如果宽度或高度小于控件的宽或高，则让其居中if(rect.width() < width){deltaX = width/2f -rect.right + rect.width()/2f;}if(rect.height() < height){deltaY = height /2f -rect.bottom + rect.height()/2f;}mScaleMatrix.postTranslate(deltaX, deltaY);}

全部代码：

package com.example.viewpagerimage;import android.content.Context;import android.graphics.Matrix;import android.graphics.RectF;import android.graphics.drawable.Drawable;import android.util.AttributeSet;import android.view.MotionEvent;import android.view.ScaleGestureDetector;import android.view.ScaleGestureDetector.OnScaleGestureListener;import android.view.View;import android.view.View.OnTouchListener;import android.view.ViewTreeObserver.OnGlobalLayoutListener;import android.widget.ImageView;//实现监听器OnGlobalLayoutListener，监听图片是否加载完成public class MyImageView extends ImageView implements OnGlobalLayoutListener, OnScaleGestureListener,OnTouchListener{private boolean mOnce;//判断是否初始化private float mInitScale;//初始化时缩放的值private float mMidScale;//双击放大到达的值private float mMaxScale;//放大的最大值private ScaleGestureDetector mScaleGestureDetector;//捕获用户多指触控缩放的比例private Matrix mScaleMatrix;public MyImageView(Context context, AttributeSet attrs, int defStyleAttr) {super(context, attrs, defStyleAttr);//initmScaleMatrix = new Matrix();setScaleType(ScaleType.MATRIX);mScaleGestureDetector = new ScaleGestureDetector(context, this);setOnTouchListener(this);//当图片加载时，图片可能很大，也可能很小，需要让图片自适应屏幕大小，当图片太大时自动缩小到屏幕大小，当图片太小时放大到屏幕大小。}public MyImageView(Context context, AttributeSet attrs) {this(context, attrs,0);// TODO Auto-generated constructor stub}public MyImageView(Context context) {this(context,null);// TODO Auto-generated constructor stub}@Overrideprotected void onAttachedToWindow() {// TODO Auto-generated method stubsuper.onAttachedToWindow();//当View 显示在屏幕上时调用getViewTreeObserver().addOnGlobalLayoutListener(this);//注册接口}@SuppressWarnings("deprecation")@Overrideprotected void onDetachedFromWindow() {// TODO Auto-generated method stubsuper.onDetachedFromWindow();//当View从屏幕上移除时调用getViewTreeObserver().removeGlobalOnLayoutListener(this);//移除接口}/** * 获取ImageView加载完成的图片 */@Overridepublic void onGlobalLayout() {// 全局的布局完成后调用if(!mOnce){//得到控件的宽和高int width = getWidth();int height = getHeight();//得到我们的图片以及宽和高Drawable d = getDrawable();if(d == null)return;int dw = d.getIntrinsicWidth();int dh = d.getIntrinsicHeight();float scale = 1.0f;//缩放值//如果图片的宽度大于控件高度，但是宽度小于控件的宽度，将其缩小if(dw > width && dh < height){scale = width*1.0f/dw;}else if(dh > height && dw < width){scale = height*1.0f /dh;}else if(dw > width && dh > height){scale = Math.min(width*1.0f/dw, height*1.0f/dh);}else if(dw < width && dh < height){scale = Math.min(width *1.0f/dw, height*1.0f/dh);}/* * 得到初始化时缩放的比例 * */mInitScale = scale;mMaxScale = mInitScale * 4;mMidScale = mInitScale * 2;//将图片移动到当前控件的中心int dx = getWidth()/2 - dw /2;int dy = getHeight()/2 - dh/2;mScaleMatrix.postTranslate(dx, dy);//平移mScaleMatrix.postScale(mInitScale, mInitScale,width/2,height/2);//缩放,后面两个参数是缩放的中心点setImageMatrix(mScaleMatrix);mOnce = true;}}/** * 获取当前图片的缩放值 * @return */public float getScale(){float[] values = new float[9];mScaleMatrix.getValues(values);return values[Matrix.MSCALE_X];}//缩放的区间，initScale maxScale@Overridepublic boolean onScale(ScaleGestureDetector detector) {// TODO Auto-generated method stubfloat scale = getScale();float scaleFactor = detector.getScaleFactor();//得到缩放的值if(getDrawable() == null){return true;}//缩放范围的控制if((scale < mMaxScale && scaleFactor > 1.0f) || (scale > mInitScale && scaleFactor < 1.0f)){if(scale * scaleFactor < mInitScale){scaleFactor = mInitScale / scale;//当手指缩放小于最小值时 ，默认显示最小的比例}if(scale * scaleFactor > mMaxScale){//当手指缩放大于于最大值时 ，默认显示最大的比例scale = mMaxScale/scale;}//缩放,缩放中心是手指触控的地方mScaleMatrix.postScale(scaleFactor, scaleFactor, detector.getFocusX(),detector.getFocusY());checkBorderAndCenterWhenScale();setImageMatrix(mScaleMatrix);}return true;//设置完成返回true保证事件能够进行}/** * 获得图片放大缩小以后的宽和高以及l r t b * @return */private RectF getMatrixRectF(){Matrix matrix = mScaleMatrix;RectF recF = new RectF();Drawable d = getDrawable();if(d != null){recF.set(0, 0, d.getIntrinsicWidth(), d.getIntrinsicHeight());matrix.mapRect(recF);}return recF;}/** * 在缩放的时候进行边界控制范围位置控制 */private void checkBorderAndCenterWhenScale() {// TODO Auto-generated method stubRectF rect = getMatrixRectF();float deltaX = 0;float deltaY = 0;float width = getWidth();float height = getHeight();//缩放时进行边界检测，放在出现白边if(rect.width() >= width){if(rect.left > 0){//处理左边的空白deltaX = -rect.left;}if(rect.right < width){//处理右边的空白deltaX = (int) (width - rect.right);}}if(rect.height() >= height){if(rect.top > 0){deltaY = -rect.top;}if(rect.bottom < height){deltaY = height - rect.bottom;}}//如果宽度或高度小于控件的宽或高，则让其居中if(rect.width() < width){deltaX = width/2f -rect.right + rect.width()/2f;}if(rect.height() < height){deltaY = height /2f -rect.bottom + rect.height()/2f;}mScaleMatrix.postTranslate(deltaX, deltaY);}@Overridepublic boolean onScaleBegin(ScaleGestureDetector detector) {// TODO Auto-generated method stubreturn true;//必须返回true}@Overridepublic void onScaleEnd(ScaleGestureDetector detector) {// TODO Auto-generated method stub}@Overridepublic boolean onTouch(View v, MotionEvent event) {// TODO Auto-generated method stubmScaleGestureDetector.onTouchEvent(event);//把event传递给mscaleGestureDetector处理return true;//必须返true}}

效果图：左边是原图，右边是放大右上角的图