需求：像相册中的图片跟随手指拖动，双指的放大和缩小，相册中拖出范围之后有弹回的动画，感觉上很圆润，很舒服，我写的例子中并没有加动画
思路：1.自定义DragImageView.java
2.自定义中先画图片，图片大于屏幕就把图片缩小后显示，图片小于屏幕就直接显示，显示之前要计算显示图片的Rect，Rect是其实就是四个坐标，用来控制显示图片的范 围，这个Rect是根据图片的长宽比例计算而来，显示在屏幕中间。
3.跟随手指移动：在touchEvent事件中处理好单双指的各种事件之后，跟随手指就是不断的改变Rect的坐标，然后不断的invalidate()(该方法是重新强制绘制View);
4.双指缩放：双指缩放的时候从图片Rect的中心缩放的，没有实现相册那种从手指中心缩放的那种。
5.单指和双指的事件在touc事件中已近处理好了
event.getPointerCount()==2的情况就是双指部分
float X0,Y0,X1,Y1双指的四个坐标
在双指移动的时候计算一个双指的距离出来m1,在MOVE执行的时候重新计算一个新的距离m2，去判断m1和m2大小来判断双指是张开还是捏合，并且执行相应事件，判断之后把m2复制给m1，这时的MOVE事件会有新的m2出来，所以就一直判断就ok了。放大和缩小就是按照一定的比例去改变Rect的值。
DragImageView.java
public class DragImageView extends View {
private Paint mPaint;
private Drawable mDrawable;
private Rect mDrawableRect = new Rect();
// private Rect mDrawableOffsetRect = new Rect();
private Context mContext;
private float mRation_WH = 0;
private float mOldX = 0;
private float mOldY = 0;
private float mOldX0, mOldY0, mOldX1, mOldY1, mOldK, mOldB, mOldHandsX,
mOldHandsY;
private double mD1;
private boolean isFirst = true;
private int SINGALDOWN = 1;// 单点按下
private int MUTILDOWM = 2;// 双点按下
private int MUTILMOVE = 3;// 双点拖拽
private int mStatus = 0;
enum STATUS {
SINGAL, MUTILDOWN, MUTILMOVE;
}
public DragImageView(Context context) {
super(context);
this.mContext = context;
mPaint = new Paint();
mPaint.setAntiAlias(true);
mPaint.setColor(Color.BLACK);
mPaint.setStyle(Style.FILL);
mPaint.setTextSize(35.0f);
}
@SuppressLint("DrawAllocation")
@Override
protected void onDraw(Canvas canvas) {
// TODO Auto-generated method stub
super.onDraw(canvas);
if (mDrawable == null || mDrawable.getIntrinsicHeight() == 0
|| mDrawable.getIntrinsicWidth() == 0) {
return;
}
setBounds();
mDrawable.draw(canvas);
// Log.i("draw", "draw+++++++++++++++++++++++++++++++++++++++");
}
@SuppressLint("ClickableViewAccessibility")
@Override
public boolean onTouchEvent(MotionEvent event) {
// TODO Auto-generated method stub
switch (event.getPointerCount()) {
case 1:
switch (event.getAction()) {
case MotionEvent.ACTION_DOWN:
mStatus = SINGALDOWN;
mOldX = event.getX();
mOldY = event.getY();
// Log.i("x_y_down", event.getX() + "__" + event.getY());
break;
case MotionEvent.ACTION_UP:
checkBounds();
// Log.i("x_y_up", event.getX() + "__" + event.getY());
break;
case MotionEvent.ACTION_MOVE:
// Log.i("x_y_move", event.getX() + "__" + event.getY());
if (mStatus == SINGALDOWN) {
int offsetWidth = (int) (event.getX() - mOldX);
int offsetHeight = (int) (event.getY() - mOldY);
// Log.i("x_y_offset", offsetWidth + "__" + offsetHeight);
mOldX = event.getX();
mOldY = event.getY();
mDrawableRect.offset(offsetWidth, offsetHeight);
invalidate();
}
break;
default:
break;
}
break;
default:
/*
* mStatus = MUTILDOWM; if (mStatus == MUTILDOWM) { mOldX0 =
* event.getX(0); mOldY0 = event.getY(0); mOldX1 = event.getX(1);
* mOldY1 = event.getY(1); mOldK = (mOldY1 - mOldY0) / (mOldX1 -
* mOldX0); mOldB = (mOldY0 * mOldX1 - mOldY1 * mOldX0) / (mOldX1 -
* mOldX0); mOldHandsX = (mOldX0 + mOldX1) / 2; mOldHandsY =
* mOldHandsX * mOldK + mOldB; mD1 = Math.sqrt(Math.pow(mOldX0 -
* mOldX1, 2) + Math.pow(mOldY0 - mOldY1, 2)); Log.i("mD1", mD1 +
* "________________"); }
*/
switch (event.getAction()) {
case MotionEvent.ACTION_POINTER_DOWN:
Log.i("DOUBLETOWDOWN", "true");
break;
case MotionEvent.ACTION_MOVE:
// Log.i("x_y_move", event.getX(0) + "__" + event.getY(0) +
// "___"
// + event.getX(1) + "__" + event.getY(1));
mStatus = MUTILMOVE;
float X0 = event.getX(0);
float Y0 = event.getY(0);
float X1 = event.getX(1);
float Y1 = event.getY(1);
float k = (Y1 - Y0) / (X1 - X0);
float b = (Y0 * X1 - Y1 * X0) / (X1 - X0);
int RectCenterX = mDrawableRect.centerX();
int RectCenterY = mDrawableRect.centerY();
float mHandsX = (X0 + X1) / 2;
float mHandsY = mHandsX * k + b;
double mD2 = Math.sqrt(Math.pow(X0 - X1, 2)
+ Math.pow(Y0 - Y1, 2));
Log.i("GCM", mD2 + "________________X:" + mHandsX + "___Y:"
+ mHandsY);
if (mD1 < mD2) {
// double mMultiple = mD2 / mD1;
// int newWidth = (int) (mDrawableRect.width() * mMultiple);
// int newHeight = (int) (newWidth / mRation_WH);
//
// int newleft = mDrawableRect.left / 2;
// int newtop = mDrawableRect.top / 2;
// int newright = mDrawableRect.right * (3 / 2);
// int newbotto = mDrawableRect.bottom * (3 / 2);
// // mDrawableRect.set(newleft, newtop, newright,
// newbotto);
//
// mDrawableRect.set(RectCenterX - newWidth / 2, RectCenterY
// - newHeight / 2, RectCenterX + newWidth / 2,
// RectCenterY + newHeight / 2);
// invalidate();
if (mDrawableRect.width() < mContext.getResources()
.getDisplayMetrics().widthPixels * 2) {
int offsetwidth = 10;
int offsettop = (int) (offsetwidth / mRation_WH);
mDrawableRect.set(mDrawableRect.left - offsetwidth,
mDrawableRect.top - offsettop,
mDrawableRect.right + offsetwidth,
mDrawableRect.bottom + offsettop);
Log.i("GCM", "aaaaaaaaaaaaaaa");
invalidate();
}
// mDrawableRect.offset((int) mHandsX, (int) mHandsY);
} else {
if (mDrawableRect.width() > mContext.getResources()
.getDisplayMetrics().widthPixels / 3) {
int offsetwidth = 10;
int offsettop = (int) (offsetwidth / mRation_WH);
mDrawableRect.set(mDrawableRect.left + offsetwidth,
mDrawableRect.top + offsettop,
mDrawableRect.right - offsetwidth,
mDrawableRect.bottom - offsettop);
invalidate();
Log.i("GCM", "bbbbbbbbbbbbbbb");
}
}
mD1 = mD2;
if (mHandsX < RectCenterX) {
if (mHandsY < RectCenterY) {
Log.i("PPPPPPP", "1");
} else {
Log.i("PPPPPPP", "3");
}
} else {
if (mHandsY < RectCenterY) {
Log.i("PPPPPPP", "2");
} else {
Log.i("PPPPPPP", "4");
}
}
//
break;
case MotionEvent.ACTION_UP:
Log.i("mStatus", "mutildouble_up");
mStatus = 0;
break;
default:
break;
}
break;
}
return true;
}
public void setBounds() {
if (isFirst) {
mRation_WH = (float) mDrawable.getIntrinsicWidth()
/ (float) mDrawable.getIntrinsicHeight();
int px_w = Math.min(getWidth(),
dip2px(mContext, mDrawable.getIntrinsicWidth()));
int px_h = (int) (px_w / mRation_WH);
int left = (getWidth() - px_w) / 2;
int top = (getHeight() - px_h) / 2;
int right = px_w + left;
int bottom = px_h + top;
mDrawableRect.set(left, top, right, bottom);
// mDrawableOffsetRect.set(mDrawableRect);
isFirst = false;
Log.i("rect1______", mDrawableRect.left + "," + mDrawableRect.top
+ "," + mDrawableRect.right + "," + mDrawableRect.bottom);
}
mDrawable.setBounds(mDrawableRect);
Log.i("rect2______", mDrawableRect.left + "," + mDrawableRect.top + ","
+ mDrawableRect.right + "," + mDrawableRect.bottom);
Log.i("center_______",
mDrawableRect.centerX() + "," + mDrawableRect.centerY());
}
public void checkBounds() {
int newLeft = mDrawableRect.left;
int newTop = mDrawableRect.top;
boolean isChange = false;
if (newLeft < -mDrawableRect.width()) {
newLeft = -mDrawableRect.width();
isChange = true;
}
if (newTop < -mDrawableRect.height()) {
newTop = -mDrawableRect.height();
isChange = true;
}
if (newLeft > getWidth()) {
newLeft = getWidth();
isChange = true;
}
if (newTop > getHeight()) {
newTop = getHeight();
isChange = true;
}
if (isChange) {
mDrawableRect.offsetTo(newLeft, newTop);
invalidate();
}
}
public Drawable getmDrawable() {
return mDrawable;
}
public void setmDrawable(Drawable mDrawable) {
this.mDrawable = mDrawable;
}
public int dip2px(Context context, int value) {
final float scale = context.getResources().getDisplayMetrics().density;
return (int) (value * scale + 0.5f);
}
}
public class MainActivity extends Activity {
Context mContext;
@Override
protected void onCreate(Bundle savedInstanceState) {
// TODO Auto-generated method stub
super.onCreate(savedInstanceState);
this.mContext = getApplicationContext();
requestWindowFeature(Window.FEATURE_NO_TITLE);
DragImageView mView = new DragImageView(mContext);
mView.setmDrawable(mContext.getResources().getDrawable(R.drawable.bbb));
setContentView(mView);
}
}效果
