Android implements code for zooming and dragging pictures through custom ImageView controls

/**
* 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();
}
@Override
protected 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") @Override
public 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。
*/
@Override
protected 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;
}
}