自定义ImageView

package com.example.myimageview;

import android.content.Context;
import android.graphics.Bitmap;
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.widget.ImageView;

public class MyImageView extends ImageView{
        Matrix matrix = new Matrix();  
        Matrix savedMatrix = new Matrix();  
        /**位图对象*/  
        private Bitmap bitmap = null;  
        /** 屏幕的分辨率*/  
        private DisplayMetrics dm;  
      
        /** 最小缩放比例*/  
        float minScaleR = 1.0f;  
          
        /** 最大缩放比例*/  
        static final float MAX_SCALE = 15f;  
        /** 初始状态*/  
        static final int NONE = 0;  
        /** 拖动*/  
        static final int DRAG = 1;  
        /** 缩放*/  
        static final int ZOOM = 2;  
        /** 当前模式*/  
        int mode = NONE;  
        /** 存储float类型的x，y值，就是你点下的坐标的X和Y*/  
        PointF prev = new PointF();  
        PointF mid = new PointF();  
        float dist = 1f;  
        public MyImageView(Context context) {  
            super(context);  
            setupView();  
        }  
          
        public MyImageView(Context context, AttributeSet attrs) {  
            super(context, attrs);  
            setupView();  
        }  
          
          
        public void setupView(){  
            Context context = getContext();  
            //获取屏幕分辨率,需要根据分辨率来使用图片居中  
            dm = context.getResources().getDisplayMetrics();  
              
            //根据MyImageView来获取bitmap对象  
            BitmapDrawable bd = (BitmapDrawable)this.getDrawable();  
            if(bd != null){  
                bitmap = bd.getBitmap();  
            }  
    
            //设置ScaleType为ScaleType.MATRIX，这一步很重要  
            this.setScaleType(ScaleType.MATRIX);  
            this.setImageBitmap(bitmap);  
              
            //bitmap为空就不调用center函数  
            if(bitmap != null){  
                center(true, true);  
            }  
            this.setImageMatrix(matrix);  
            this.setOnTouchListener(new OnTouchListener() {  
                @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 = spacing(event);  
                            // 如果连续两点距离大于10，则判定为多点模式  
                            if (spacing(event) > 10f) {  
                                savedMatrix.set(matrix);  
                                midPoint(mid, event);  
                                mode = ZOOM;  
                            }  
                            break;  
                        case MotionEvent.ACTION_UP:{  
                            break;  
                        }  
                        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 = spacing(event);  
                                if (newDist > 10f) {  
                                    matrix.set(savedMatrix);  
                                    float tScale = newDist / dist;  
                                    matrix.postScale(tScale, tScale, mid.x, mid.y);  
                                }  
                            }  
                            break;  
                        }  
                        MyImageView.this.setImageMatrix(matrix);  
                        CheckView();  
                        return 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  
                int screenHeight = dm.heightPixels;  
                if (height < screenHeight) {  
                    deltaY = (screenHeight - height) / 2 - rect.top;  
                } else if (rect.top > 0) {  
                    deltaY = -rect.top;  
                } else if (rect.bottom < screenHeight) {  
                    deltaY = this.getHeight() - rect.bottom;  
                }  
            }  
      
            if (horizontal) {  
                int screenWidth = dm.widthPixels;  
                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);  
        }  
          
        /**
         * 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(true, true);  
        }  
          
        /**
         * 两点的距离
         */  
        private float spacing(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);  
        }  
        /**
         * 两点的中点
         */  
        private void midPoint(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);  
        }  
    }