在实际项目中，常常要制作一个简易的图像裁剪功能，即获取一张图片。并用一个遮罩层选择目标范围并截取保存的功能。例如以下图所看到的：
在此分享下该自己定义视图的制作过程。
需求说明
整一个视图包括一个透明的遮罩层，一个透明带白色边框的矩形。要实现的功能是：
- 点击矩形框外围：无不论什么响应
- 点击矩形框内部：可随手指移动而移动
- 点击矩形框的4个顶点：可进行对角顶点坐标不变的情况下的矩形的缩放，同一时候边框变色
以下是实现该功能的完整源代码
/**
* Created by Farble on 2015/3/10.
*/
public class PhotoCropView extends View {
private static final String TAG = "PhotoCropView"; private onLocationListener locationListener;/*listen to the Rect */
private onChangeLocationlistener changeLocationlistener;/*listening position changed */ private int MODE;
private static final int MODE_OUTSIDE = 0x000000aa;/*170*/
private static final int MODE_INSIDE = 0x000000bb;/*187*/
private static final int MODE_POINT = 0X000000cc;/*204*/
private static final int MODE_ILLEGAL = 0X000000dd;/*221*/ private static final int minWidth = 100;/*the minimum width of the rectangle*/
private static final int minHeight = 200;/*the minimum height of the rectangle*/ private static final int START_X = 200;
private static final int START_Y = 200; private static final float EDGE_WIDTH = 1.8f;
private static final int ACCURACY= 15;/*touch accuracy*/ private int pointPosition;/*vertex of a rectangle*/ private int sX;/*start X location*/
private int sY;/*start Y location*/
private int eX;/*end X location*/
private int eY;/*end Y location*/ private int pressX;/*X coordinate values while finger press*/
private int pressY;/*Y coordinate values while finger press*/ private int memonyX;/*the last time the coordinate values of X*/
private int memonyY;/*the last time the coordinate values of Y*/ private int coverWidth = 300;/*width of selection box*/
private int coverHeight = 400;/*height of selection box*/ private Paint mPaint;
private Paint mPaintLine;
private Bitmap mBitmapCover;
private Bitmap mBitmapRectBlack;
private PorterDuffXfermode xfermode;/*paint mode*/ public PhotoCropView(Context context) {
super(context);
init();
} public PhotoCropView(Context context, AttributeSet attrs) {
super(context, attrs);
init();
} public PhotoCropView(Context context, AttributeSet attrs, int defStyleAttr) {
super(context, attrs, defStyleAttr);
init();
} @SuppressWarnings("deprecation")
private void init() {
sX = START_X;
sY = START_Y;
WindowManager manager = (WindowManager) getContext().getSystemService(Context.WINDOW_SERVICE);
int width = manager.getDefaultDisplay().getWidth();
int height = manager.getDefaultDisplay().getHeight();
mBitmapCover = makeBitmap(width, height, 0x5A000000, 0, 0);
mBitmapRectBlack = makeBitmap(coverWidth, coverHeight, 0xff000000, coverWidth, coverHeight); eX = sX + coverWidth;
eY = sY + coverHeight;
pressX = 0;
pressY = 0; xfermode = new PorterDuffXfermode(PorterDuff.Mode.SRC_IN); mPaint = new Paint();
mPaint.setAntiAlias(true); mPaintLine = new Paint();
mPaintLine.setColor(Color.WHITE);
mPaintLine.setStrokeWidth(2.0f);
} /*生成bitmap*/
private Bitmap makeBitmap(int mwidth, int mheight, int resource, int staX, int staY) {
Bitmap bm = Bitmap.createBitmap(mwidth, mheight, Bitmap.Config.ARGB_8888);
Canvas c = new Canvas(bm);
Paint p = new Paint(Paint.ANTI_ALIAS_FLAG); p.setColor(resource);
c.drawRect(staX, staY, mwidth, mheight, p);
return bm;
} @Override
protected void onDraw(Canvas canvas) {
super.onDraw(canvas);
mPaint.setFilterBitmap(false);
int sc = canvas.saveLayer(0, 0, canvas.getWidth(), canvas.getHeight(), null,
Canvas.MATRIX_SAVE_FLAG |
Canvas.CLIP_SAVE_FLAG |
Canvas.HAS_ALPHA_LAYER_SAVE_FLAG |
Canvas.FULL_COLOR_LAYER_SAVE_FLAG |
Canvas.CLIP_TO_LAYER_SAVE_FLAG); canvas.drawBitmap(mBitmapCover, 0, 0, mPaint);
mPaint.setXfermode(xfermode);
canvas.drawBitmap(mBitmapRectBlack, sX, sY, mPaint);
if (locationListener != null) {
locationListener.locationRect(sX, sY, eX, eY);
}
mPaint.setXfermode(null);
canvas.restoreToCount(sc);
canvas.drawLine((float) sX - EDGE_WIDTH, (float) sY - EDGE_WIDTH, (float) eX + EDGE_WIDTH, (float) sY - EDGE_WIDTH, mPaintLine);/*up -*/
canvas.drawLine((float) sX - EDGE_WIDTH, (float) eY + EDGE_WIDTH, (float) eX + EDGE_WIDTH, (float) eY + EDGE_WIDTH, mPaintLine);/*down -*/
canvas.drawLine((float) sX - EDGE_WIDTH, (float) sY - EDGE_WIDTH, (float) sX - EDGE_WIDTH, (float) eY + EDGE_WIDTH, mPaintLine);/*left |*/
canvas.drawLine((float) eX + EDGE_WIDTH, (float) sY - EDGE_WIDTH, (float) eX + EDGE_WIDTH, (float) eY + EDGE_WIDTH, mPaintLine);/*righ |*/ } @SuppressWarnings("NullableProblems")
@Override
public boolean onTouchEvent(MotionEvent event) {
switch (event.getAction()) {
case MotionEvent.ACTION_DOWN:
if (changeLocationlistener != null) {
changeLocationlistener.locationChange("change self");
} else {
changeLocationlistener = null;
} memonyX = (int) event.getX();
memonyY = (int) event.getY();
checkMode(memonyX, memonyY);
break;
case MotionEvent.ACTION_MOVE: {
switch (MODE) {
case MODE_ILLEGAL:
pressX = (int) event.getX();
pressY = (int) event.getY();
recoverFromIllegal(pressX, pressY);
postInvalidate();
break;
case MODE_OUTSIDE:
//do nothing;
break;
case MODE_INSIDE:
pressX = (int) event.getX();
pressY = (int) event.getY();
moveByTouch(pressX, pressY);
postInvalidate();
break;
default:
/*MODE_POINT*/
pressX = (int) event.getX();
pressY = (int) event.getY();
mPaintLine.setColor(getContext().getResources().getColor(R.color.orange));
moveByPoint(pressX, pressY);
postInvalidate();
break;
}
}
break;
case MotionEvent.ACTION_UP:
mPaintLine.setColor(Color.WHITE);
postInvalidate();
break;
default:
break;
}
return true;
} /*从非法状态恢复，这里处理的是达到最小值后能拉伸放大*/
private void recoverFromIllegal(int rx, int ry) {
if ((rx > sX && ry > sY) && (rx < eX && ry < eY)) {
MODE = MODE_ILLEGAL;
} else {
MODE = MODE_POINT;
}
} private void checkMode(int cx, int cy) {
if (cx > sX && cx < eX && cy > sY && cy < eY) {
MODE = MODE_INSIDE;
} else if (nearbyPoint(cx, cy) < 4) {
MODE = MODE_POINT;
} else {
MODE = MODE_OUTSIDE;
}
} /*推断点(inX,inY)是否靠近矩形的4个顶点*/
private int nearbyPoint(int inX, int inY) {
if ((Math.abs(sX - inX) <= ACCURACY && (Math.abs(inY - sY) <= ACCURACY))) {/*left-up angle*/
pointPosition = 0;
return 0;
}
if ((Math.abs(eX - inX) <= ACCURACY && (Math.abs(inY - sY) <= ACCURACY))) {/*right-up angle*/
pointPosition = 1;
return 1;
}
if ((Math.abs(sX - inX) <= ACCURACY && (Math.abs(inY - eY) <= ACCURACY))) {/*left-down angle*/
pointPosition = 2;
return 2;
}
if ((Math.abs(eX - inX) <= ACCURACY && (Math.abs(inY - eY) <= ACCURACY))) {/*right-down angle*/
pointPosition = 3;
return 3;
}
pointPosition = 100;
return 100;
} /*刷新矩形的坐标*/
private void refreshLocation(int isx, int isy, int iex, int iey) {
this.sX = isx;
this.sY = isy;
this.eX = iex;
this.eY = iey;
} /*矩形随手指移动*/
private void moveByTouch(int mx, int my) {/*move center point*/
int dX = mx - memonyX;
int dY = my - memonyY; sX += dX;
sY += dY; eX = sX + coverWidth;
eY = sY + coverHeight; memonyX = mx;
memonyY = my; } /*检測矩形是否达到最小值*/
private boolean checkLegalRect(int cHeight, int cWidth) {
return (cHeight > minHeight && cWidth > minWidth);
} /*点击顶点附近时的缩放处理*/
@SuppressWarnings("SuspiciousNameCombination")
private void moveByPoint(int bx, int by) {
switch (pointPosition) {
case 0:/*left-up*/
coverWidth = Math.abs(eX - bx);
coverHeight = Math.abs(eY - by);
//noinspection SuspiciousNameCombination
if (!checkLegalRect(coverWidth, coverHeight)) {
MODE = MODE_ILLEGAL;
} else {
mBitmapRectBlack = null;
mBitmapRectBlack = makeBitmap(coverWidth, coverHeight, 0xff000000, coverWidth, coverHeight);
refreshLocation(bx, by, eX, eY);
}
break;
case 1:/*right-up*/
coverWidth = Math.abs(bx - sX);
coverHeight = Math.abs(eY - by);
if (!checkLegalRect(coverWidth, coverHeight)) {
MODE = MODE_ILLEGAL;
} else {
mBitmapRectBlack = null;
mBitmapRectBlack = makeBitmap(coverWidth, coverHeight, 0xff000000, coverWidth, coverHeight);
refreshLocation(sX, by, bx, eY);
}
break;
case 2:/*left-down*/
coverWidth = Math.abs(eX - bx);
coverHeight = Math.abs(by - sY);
if (!checkLegalRect(coverWidth, coverHeight)) {
MODE = MODE_ILLEGAL;
} else {
mBitmapRectBlack = null;
mBitmapRectBlack = makeBitmap(coverWidth, coverHeight, 0xff000000, coverWidth, coverHeight);
refreshLocation(bx, sY, eX, by);
}
break;
case 3:/*right-down*/
coverWidth = Math.abs(bx - sX);
coverHeight = Math.abs(by - sY);
if (!checkLegalRect(coverWidth, coverHeight)) {
MODE = MODE_ILLEGAL;
} else {
mBitmapRectBlack = null;
mBitmapRectBlack = makeBitmap(coverWidth, coverHeight, 0xff000000, coverWidth, coverHeight);
refreshLocation(sX, sY, bx, by);
}
break;
default:
break;
}
} public void setLocationListener(onLocationListener locationListener) {
this.locationListener = locationListener;
} public interface onLocationListener {
public void locationRect(int startX, int startY, int endX, int endY);
} public interface onChangeLocationlistener {
@SuppressWarnings("SameParameterValue")
public void locationChange(String msg);
}
}
简要说明
1.可移动的透明矩形框通过PorterDuffXfermode（在还有一篇博文中有介绍，可点击这里查看）来实现
2.矩形边框的移动。缩放主要由onTouch事件做处理
3.onLocationListener 用于侦听矩形的坐标（终于可通过实现内部方法确定图像须要截取的位置）
3.onLocationListener 用于侦听矩形的坐标（终于可通过实现内部方法确定图像须要截取的位置）
怎样使用PhotoCropView
在布局文件里导入
<com.xxx.PhotoCropView
android:id="@+id/test"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:layout_marginLeft="20dp"
android:layout_marginRight="20dp"/>
绑定并设置侦听器：
mCropView = (PhotoCropView)mActivity.findViewById(R.id.photo_crop_photocrop);
mCropView .setLocationListener(this);
获取坐标信息：
@Override
public void locationRect(int startX, int startY, int endX, int endY) {
Log.d("[ "+startX+"--"+startY+"--"+endX+"--"+endY+" ]");
}
扩展该视图
在此基础上可进行进一步的扩展，如：
1.进一步改动边框的色值做警示之用
2.舍弃边框改为添加4个边角
等等，可自行在onDraw()方法及外部方法中进行扩展如：
@Override
protected void onDraw(Canvas canvas) {
super.onDraw(canvas);
mPaint.setFilterBitmap(false);
int sc = canvas.saveLayer(0, 0, canvas.getWidth(), canvas.getHeight(), null,
Canvas.MATRIX_SAVE_FLAG |
Canvas.CLIP_SAVE_FLAG |
Canvas.HAS_ALPHA_LAYER_SAVE_FLAG |
Canvas.FULL_COLOR_LAYER_SAVE_FLAG |
Canvas.CLIP_TO_LAYER_SAVE_FLAG); canvas.drawBitmap(mBitmapCover, 0, 0, mPaint);
mPaint.setXfermode(xfermode);
canvas.drawBitmap(mBitmapRectBlack, sX, sY, mPaint);
if (locationListener != null) {
locationListener.locationRect(sX, sY, eX, eY);
}
mPaint.setXfermode(null);
canvas.restoreToCount(sc);
/*在此加入4个边角...*/
}
致读者
首先感谢您阅读此文，因为本人能力有限。不免出现一些疏漏，错误。假设您有发现不论什么错误。不妥，或有更好的实现方式，可私信我。
Thanks advanced！
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