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Android实现图片在屏幕内缩放和移动效果

通常我们遇到的图片缩放需求，都是图片基于屏幕自适应后，进行缩放和移动，且图片最小只能是自适应的大小。最近遇到一个需求，要求图片只能在屏幕内缩放和移动，不能超出屏幕。

一、需求

在屏幕中加载一张图片，图片可以手势缩放移动。但是图片最大只能缩放到屏幕大小，也只允许在屏幕内移动。可以从系统中读取图片（通过绝对路径），也可以从资源文件中读取图片。

二、自定义ZoomImageView

屏幕内手势缩放图片与普通的图片缩放相比，比较麻烦的是，需要计算图片的精确位置。不同于普通缩放的图片充满屏幕，屏内缩放的图片只占据屏幕的一部分，我们需要判断手指是否点在图片内，才能进行各种操作。

/**
 * 判断手指是否点在图片内(单指)
 */
 private void isClickInImage(){
 if (translationX <= mFirstX && mFirstX <= (translationX + currentW)
  && translationY <= mFirstY && mFirstY <= (translationY + currentH)){
  isClickInImage = true;
 }else {
  isClickInImage = false;
 }
 }
 
 /**
 * 判断手指是否点在图片内(双指)
 * 只要有一只手指在图片内就为true
 * @param event
 */
 private void isClickInImage(MotionEvent event){
 if (translationX <= event.getX(0) && event.getX(0) <= (translationX + currentW)
  && translationY <= event.getY(0) && event.getY(0) <= (translationY + currentH)){
  isClickInImage = true;
 }else if (translationX <= event.getX(1) && event.getX(1) <= (translationX + currentW)
  && translationY <= event.getY(1) && event.getY(1) <= (translationY + currentH)){
  isClickInImage = true;
 }else {
  isClickInImage = false;
 }
 }

其他的各种操作，之于缩放，移动，边界检查等，和普通的图片缩放没有太多区别。完整代码如下：

package com.uni.myapplication;
 
import android.content.Context;
import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.graphics.Canvas;
import android.graphics.Matrix;
import android.graphics.Paint;
import android.support.annotation.Nullable;
import android.util.AttributeSet;
import android.view.MotionEvent;
import android.view.View;
 
import java.io.File;
 
/**
 * Created by newcboy on 2018/3/9.
 */
 
public class ZoomImageView extends View {
 
 public static final int IMAGE_MAX_SIZE = 1000;//加载图片允许的最大size，单位kb
 private float minimal = 100.0f;
 
 private float screenW;//屏幕宽度
 private float screenH;//屏幕高度
 
 //单指按下的坐标
 private float mFirstX = 0.0f;
 private float mFirstY = 0.0f;
 
 //单指离开的坐标
 private float lastMoveX =-1f;
 private float lastMoveY =-1f;
 
 //两指的中点坐标
 private float centPointX;
 private float centPointY;
 
 //图片的绘制坐标
 private float translationX = 0.0f;
 private float translationY = 0.0f;
 
 //图片的原始宽高
 private float primaryW;
 private float primaryH;
 
 //图片当前宽高
 private float currentW;
 private float currentH;
 
 private float scale = 1.0f;
 private float maxScale, minScale;
 private Bitmap bitmap;
 private Matrix matrix;
 
 private int mLocker = 0;
 private float fingerDistance = 0.0f;
 
 private boolean isLoaded = false;
 private boolean isClickInImage = false;
 
 public ZoomImageView(Context context, @Nullable AttributeSet attrs) {
 super(context, attrs);
 }
 
 
 /**
 * 从资源文件中读取图片
 * @param context
 * @param imageId
 */
 public void setResourceBitmap(Context context, int imageId){
 bitmap = BitmapFactory.decodeResource(context.getResources(), imageId);
 isLoaded = true;
 primaryW = bitmap.getWidth();
 primaryH = bitmap.getHeight();
 matrix = new Matrix();
 }
 
 /**
 * 根据路径添加图片
 * @param path
 * @param scale
 */
 public void setImagePathBitmap(String path, float scale){
 this.scale = scale;
 setImageBitmap(path);
 }
 
 private void setImageBitmap(String path){
 File file = new File(path);
 if (file.exists()){
  isLoaded = true;
  bitmap = ImageLoadUtils.getImageLoadBitmap(path, IMAGE_MAX_SIZE);
  primaryW = bitmap.getWidth();
  primaryH = bitmap.getHeight();
  matrix = new Matrix();
 }else {
  isLoaded = false;
 }
 }
 
 @Override
 protected void onLayout(boolean changed, int left, int top, int right, int bottom) {
 super.onLayout(changed, left, top, right, bottom);
 if (changed){
  screenW = getWidth();
  screenH = getHeight();
  translationX = (screenW - bitmap.getWidth() * scale)/ 2;
  translationY = (screenH - bitmap.getHeight() * scale) / 2;
  setMaxMinScale();
 }
 }
 
 /**
 *
 */
 private void setMaxMinScale(){
 float xScale, yScale;
 
 xScale = minimal / primaryW;
 yScale = minimal / primaryH;
 minScale = xScale > yScale ? xScale : yScale;
 
 xScale = primaryW / screenW;
 yScale = primaryH / screenH;
 if (xScale > 1 || yScale > 1 ) {
  if (xScale > yScale) {
  maxScale = 1/xScale;
  }else {
  maxScale = 1/yScale;
  }
 }else {
  if (xScale > yScale) {
  maxScale = 1/xScale;
  }else {
  maxScale = 1/yScale;
  }
 }
 if (isScaleError()){
  restoreAction();
 }
 }
 
 @Override
 public boolean onTouchEvent(MotionEvent event) {
 if (!isLoaded){
  return true;
 }
 switch (event.getActionMasked()){
  case MotionEvent.ACTION_DOWN:
  mFirstX = event.getX();
  mFirstY = event.getY();
  isClickInImage();
  break;
  case MotionEvent.ACTION_POINTER_DOWN:
  fingerDistance = getFingerDistance(event);
  isClickInImage(event);
  break;
  case MotionEvent.ACTION_MOVE:
  float fingerNum = event.getPointerCount();
  if (fingerNum == 1 && mLocker == 0 && isClickInImage){
   movingAction(event);
  }else if (fingerNum == 2 && isClickInImage){
   zoomAction(event);
  }
  break;
  case MotionEvent.ACTION_POINTER_UP:
  mLocker = 1;
  if (isScaleError()){
   translationX = (event.getX(1) + event.getX(0)) / 2;
   translationY = (event.getY(1) + event.getY(0)) / 2;
  }
  break;
  case MotionEvent.ACTION_UP:
  lastMoveX = -1;
  lastMoveY = -1;
  mLocker = 0;
  if (isScaleError()){
   restoreAction();
  }
  break;
 }
 return true;
 }
 
 
 /**
 * 移动操作
 * @param event
 */
 private void movingAction(MotionEvent event){
 float moveX = event.getX();
 float moveY = event.getY();
 if (lastMoveX == -1 || lastMoveY == -1) {
  lastMoveX = moveX;
  lastMoveY = moveY;
 }
 float moveDistanceX = moveX - lastMoveX;
 float moveDistanceY = moveY - lastMoveY;
 translationX = translationX + moveDistanceX;
 translationY = translationY + moveDistanceY;
 lastMoveX = moveX;
 lastMoveY = moveY;
 invalidate();
 }
 
 /**
 * 缩放操作
 * @param event
 */
 private void zoomAction(MotionEvent event){
 midPoint(event);
 float currentDistance = getFingerDistance(event);
 if (Math.abs(currentDistance - fingerDistance) > 1f) {
  float moveScale = currentDistance / fingerDistance;
  scale = scale * moveScale;
  translationX = translationX * moveScale + centPointX * (1-moveScale);
  translationY = translationY * moveScale + centPointY * (1-moveScale);
  fingerDistance = currentDistance;
  invalidate();
 }
 }
 
 /**
 * 图片恢复到指定大小
 */
 private void restoreAction(){
 if (scale < minScale){
  scale = minScale;
 }else if (scale > maxScale){
  scale = maxScale;
 }
 translationX = translationX - bitmap.getWidth()*scale / 2;
 translationY = translationY - bitmap.getHeight()*scale / 2;
 invalidate();
 }
 
 
 /**
 * 判断手指是否点在图片内(单指)
 */
 private void isClickInImage(){
 if (translationX <= mFirstX && mFirstX <= (translationX + currentW)
  && translationY <= mFirstY && mFirstY <= (translationY + currentH)){
  isClickInImage = true;
 }else {
  isClickInImage = false;
 }
 }
 
 /**
 * 判断手指是否点在图片内(双指)
 * 只要有一只手指在图片内就为true
 * @param event
 */
 private void isClickInImage(MotionEvent event){
 if (translationX <= event.getX(0) && event.getX(0) <= (translationX + currentW)
  && translationY <= event.getY(0) && event.getY(0) <= (translationY + currentH)){
  isClickInImage = true;
 }else if (translationX <= event.getX(1) && event.getX(1) <= (translationX + currentW)
  && translationY <= event.getY(1) && event.getY(1) <= (translationY + currentH)){
  isClickInImage = true;
 }else {
  isClickInImage = false;
 }
 }
 
 
 /**
 * 获取两指间的距离
 * @param event
 * @return
 */
 private float getFingerDistance(MotionEvent event){
 float x = event.getX(1) - event.getX(0);
 float y = event.getY(1) - event.getY(0);
 return (float) Math.sqrt(x * x + y * y);
 }
 
 /**
 * 判断图片大小是否符合要求
 * @return
 */
 private boolean isScaleError(){
 if (scale > maxScale
  || scale < minScale){
  return true;
 }
 return false;
 }
 
 
 /**
 * 获取两指间的中点坐标
 * @param event
 */
 private void midPoint(MotionEvent event){
 centPointX = (event.getX(1) + event.getX(0))/2;
 centPointY = (event.getY(1) + event.getY(0))/2;
 }
 
 @Override
 protected void onDraw(Canvas canvas) {
 super.onDraw(canvas);
 if (isLoaded){
  imageZoomView(canvas);
 }
 }
 
 private void imageZoomView(Canvas canvas){
 currentW = primaryW * scale;
 currentH = primaryH * scale;
 matrix.reset();
 matrix.postScale(scale, scale);//x轴y轴缩放
 peripheryJudge();
 matrix.postTranslate(translationX, translationY);//中点坐标移动
 canvas.drawBitmap(bitmap, matrix, null);
 }
 
 /**
 * 图片边界检查
 * (只在屏幕内)
 */
 private void peripheryJudge(){
 if (translationX < 0){
  translationX = 0;
 }
 if (translationY < 0){
  translationY = 0;
 }
 if ((translationX + currentW) > screenW){
  translationX = screenW - currentW;
 }
 if ((translationY + currentH) > screenH){
  translationY = screenH - currentH;
 }
 }
 
}

实际上，用Bitmap绘制图片时，可以通过Paint设置图片透明度。

Paint paint = new Paint();
paint.setStyle( Paint.Style.STROKE);
paint.setAlpha(150);

在setAlpha()中传入一个0~255的整数。数字越大，透明度越低。

然后在绘制图片时

canvas.drawBitmap(bitmap, matrix, paint);

三、ImageLoadUtils图片加载类

这个类是对传入的图片进行压缩处理的类，在应用从系统中读取图片时用到。在写这个类时，发现一些和网上说法不一样的地方。

options.inSampleSize这个属性，网上的说法是必须是2的幂次方，但实际上，我的验证结果是所有的整数都可以。

这里采用的压缩方法是，获取系统剩余内存和图片大小，然后将图片压缩到合适的大小。

package com.uni.myapplication;
 
import android.app.ActivityManager;
import android.content.Context;
import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.graphics.BitmapFactory.Options;
import android.net.Uri;
 
import java.io.File;
import java.io.FileInputStream;
 
/**
 * 图片加载工具类
 *
 * Created by newcboy on 2018/1/25.
 */
 
public class ImageLoadUtils {
 
 /**
 * 原图加载，根据传入的指定图片大小。
 * @param imagePath
 * @param maxSize
 * @return
 */
 public static Bitmap getImageLoadBitmap(String imagePath, int maxSize){
 int fileSize = 1;
 Bitmap bitmap = null;
 int simpleSize = 1;
 File file = new File(imagePath);
 if (file.exists()) {
  Uri imageUri = Uri.parse(imagePath);
  try {
  fileSize = (int) (getFileSize(file) / 1024);
  } catch (Exception e) {
  e.printStackTrace();
  }
  Options options = new Options();
  if (fileSize > maxSize){
  for (simpleSize = 2; fileSize>= maxSize; simpleSize++){
   fileSize = fileSize / simpleSize;
  }
  }
  options.inSampleSize = simpleSize;
  bitmap = BitmapFactory.decodeFile(imageUri.getPath(), options);
 }
 return bitmap;
 }
 
 
 /**
 * 获取指定文件的大小
 * @param file
 * @return
 * @throws Exception
 */
 public static long getFileSize(File file) throws Exception{
 if(file == null) {
  return 0;
 }
 long size = 0;
 if(file.exists()) {
  FileInputStream mInputStream = new FileInputStream(file);
  size = mInputStream.available();
 }
 return size;
 }
 
 
 /**
 * 获取手机运行内存
 * @param context
 * @return
 */
 public static long getTotalMemorySize(Context context){
 long size = 0;
 ActivityManager activityManager = (ActivityManager) context.getSystemService(context.ACTIVITY_SERVICE);
 ActivityManager.MemoryInfo outInfo = new ActivityManager.MemoryInfo();//outInfo对象里面包含了内存相关的信息
 activityManager.getMemoryInfo(outInfo);//把内存相关的信息传递到outInfo里面C++思想
 //size = outInfo.totalMem; //总内存
 size = outInfo.availMem; //剩余内存
 return (size/1024/1024);
 }
 
}

四、调用

使用方法和通常的控件差不多，只是多了一个设置图片的方法。

1.在布局文件中添加布局。

<com.uni.myapplication.ZoomImageView
 android:id="@+id/zoom_image_view"
 android:layout_width="wrap_content"
 android:layout_height="wrap_content" />

2.在代码中调用

zoomImageView = (ZoomImageView) findViewById(R.id.zoom_image_view);
zoomImageView.setImagePathBitmap(MainActivity.this, imagePath, 1.0f);
zoomImageView.setResourceBitmap(MainActivity.this, R.mipmap.ic_launcher);

其中setImagePathBitmap()是从系统中读取图片加载的方法，setResourceBitmap()是从资源文件中读取图片的方法。
当然，从系统读取图片需要添加读写权限，这个不能忘了。而且6.0以上的系统需要动态获取权限。动态获取权限的方法这里就不介绍了，网上有很详细的说明。

五、最终效果

以上就是本文的全部内容，希望对大家的学习有所帮助，也希望大家多多支持鸟哥教程(niaoge.com)。

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