Android 对图片的缩放，拖地，跟系统图库的效果一样

本文转自：http://blog.csdn.net/xiaanming/article/details/8827257

这里只是将原文页面上的代码移植到自定义控件中，便于以后使用，暂时没做功能性扩展，要看讲解可以直接去原文看，直接上代码：

package com.home.view;

import android.app.Activity;
import android.content.Context;
import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.graphics.Matrix;
import android.graphics.PointF;
import android.graphics.RectF;
import android.graphics.drawable.BitmapDrawable;
import android.util.AttributeSet;
import android.util.DisplayMetrics;
import android.util.FloatMath;
import android.view.MotionEvent;
import android.view.View;
import android.view.View.OnTouchListener;
import android.widget.ImageView;

public class PhotoView extends ImageView implements OnTouchListener {

/** 最小缩放比例 */
private float minScaleR = 1.0f;
/** 最大缩放比例 */
private static final float MAX_SCALE = 10f;

/** 初始状态 */
private static final int NONE = 0;
/** 拖动 */
private static final int DRAG = 1;
/** 缩放 */
private static final int ZOOM = 2;

/** 当前模式 */
private int mode = NONE;

private PointF prev = new PointF();
private PointF mid = new PointF();
private float dist = 1f;

private Bitmap bitmap;

Matrix matrix = new Matrix();
Matrix savedMatrix = new Matrix();

private Context context;

private int screenWidth;
private int screenHeight;

public PhotoView(Context context, AttributeSet attrs) {
this(context, attrs, -1);
}

public PhotoView(Context context) {
this(context, null);
}

public PhotoView(Context context, AttributeSet attrs, int defStyle) {
super(context, attrs, defStyle);
this.context = context;
// 获取图片资源
bitmap = ((BitmapDrawable)getDrawable()).getBitmap();
setOnTouchListener(this);
DisplayMetrics dm = new DisplayMetrics();
((Activity) context).getWindowManager().getDefaultDisplay()
.getMetrics(dm);// 获取分辨率
screenWidth = dm.widthPixels;
screenHeight = dm.heightPixels;
center();
setImageMatrix(matrix);
setScaleType(ScaleType.MATRIX);
}

public void setImageBitmap(Bitmap bitmap) {
super.setImageBitmap(bitmap);
this.bitmap = bitmap;
}

public void setImageResource(int resId) {
super.setImageResource(resId);
this.bitmap = BitmapFactory.decodeResource(context.getResources(),
resId);
}

/**
* 限制最大最小缩放比例，自动居中
*/
private void CheckView() {
float p[] = new float[9];
matrix.getValues(p);
if (mode == ZOOM) {
if (p[0] < minScaleR) {
// Log.d("", "当前缩放级别:"+p[0]+",最小缩放级别:"+minScaleR);
matrix.setScale(minScaleR, minScaleR);
}
if (p[0] > MAX_SCALE) {
// Log.d("", "当前缩放级别:"+p[0]+",最大缩放级别:"+MAX_SCALE);
matrix.set(savedMatrix);
}
}
center();
}

private void center() {
center(true, true);
}

/**
* 横向、纵向居中
*/
protected void center(boolean horizontal, boolean vertical) {

Matrix m = new Matrix();
m.set(matrix);
RectF rect = new RectF(0, 0, bitmap.getWidth(), bitmap.getHeight());
m.mapRect(rect);

float height = rect.height();
float width = rect.width();

float deltaX = 0, deltaY = 0;

if (vertical) {
// 图片小于屏幕大小，则居中显示。大于屏幕，上方留空则往上移，下方留空则往下移
if (height < screenHeight) {
deltaY = (screenHeight - height) / 2 - rect.top;
} else if (rect.top > 0) {
deltaY = -rect.top;
} else if (rect.bottom < screenHeight) {
deltaY = getHeight() - rect.bottom;
}
}

if (horizontal) {
if (width < screenWidth) {
deltaX = (screenWidth - width) / 2 - rect.left;
} else if (rect.left > 0) {
deltaX = -rect.left;
} else if (rect.right < screenWidth) {
deltaX = screenWidth - rect.right;
}
}
matrix.postTranslate(deltaX, deltaY);
}

/**
* 两点的距离
*
* @param event
* @return
*/
public static float getSpacing(MotionEvent event) {
float x = event.getX(0) - event.getX(1);
float y = event.getY(0) - event.getY(1);
return FloatMath.sqrt(x * x + y * y);
}

/**
* 获取两点之间的中点
*
* @param event
* @return
*/
public static void setMiddlePoint(PointF point, MotionEvent event) {
float x = event.getX(0) + event.getX(1);
float y = event.getY(0) + event.getY(1);
point.set(x / 2, y / 2);
}

@Override
public boolean onTouch(View v, MotionEvent event) {
switch (event.getAction() & MotionEvent.ACTION_MASK) {
// 主点按下
case MotionEvent.ACTION_DOWN:
savedMatrix.set(matrix);
prev.set(event.getX(), event.getY());
mode = DRAG;
break;
// 副点按下
case MotionEvent.ACTION_POINTER_DOWN:
dist = getSpacing(event);
// 如果连续两点距离大于10，则判定为多点模式
if (getSpacing(event) > 10f) {
savedMatrix.set(matrix);
setMiddlePoint(mid, event);
mode = ZOOM;
}
break;
case MotionEvent.ACTION_UP:
case MotionEvent.ACTION_POINTER_UP:
mode = NONE;
// savedMatrix.set(matrix);
break;
case MotionEvent.ACTION_MOVE:
if (mode == DRAG) {
matrix.set(savedMatrix);
matrix.postTranslate(event.getX() - prev.x, event.getY()
- prev.y);
} else if (mode == ZOOM) {
float newDist = getSpacing(event);
if (newDist > 10f) {
matrix.set(savedMatrix);
float tScale = newDist / dist;
matrix.postScale(tScale, tScale, mid.x, mid.y);
}
}
break;
}
setImageMatrix(matrix);
CheckView();
return true;
}

}