Android编程实现图片的浏览、缩放、拖动和自动居中效果

本文实例讲述了android编程实现图片的浏览、缩放、拖动和自动居中效果的方法。分享给大家供大家参考，具体如下：

touch.java

/**
 * 图片浏览、缩放、拖动、自动居中
 */
public class touch extends activity implements ontouchlistener {
 matrix matrix = new matrix();
 matrix savedmatrix = new matrix();
 displaymetrics dm;
 imageview imgview;
 bitmap bitmap;
 float minscaler;// 最小缩放比例
 static final float max_scale = 4f;// 最大缩放比例
 static final int none = 0;// 初始状态
 static final int drag = 1;// 拖动
 static final int zoom = 2;// 缩放
 int mode = none;
 pointf prev = new pointf();
 pointf mid = new pointf();
 float dist = 1f;
 @override
 public void oncreate(bundle savedinstancestate) {
  super.oncreate(savedinstancestate);
  setcontentview(r.layout.scale);
  imgview = (imageview) findviewbyid(r.id.imag);// 获取控件
  bitmap = bitmapfactory.decoderesource(getresources(), this.getintent()
    .getextras().getint("img"));// 获取图片资源
  imgview.setimagebitmap(bitmap);// 填充控件
  imgview.setontouchlistener(this);// 设置触屏监听
  dm = new displaymetrics();
  getwindowmanager().getdefaultdisplay().getmetrics(dm);// 获取分辨率
  minzoom();
  center();
  imgview.setimagematrix(matrix);
 }
 /**
  * 触屏监听
  */
 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:
  case motionevent.action_pointer_up:
   mode = none;
   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;
  }
  imgview.setimagematrix(matrix);
  checkview();
  return true;
 }
 /**
  * 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) {
    matrix.setscale(minscaler, minscaler);
   }
   if (p[0] > max_scale) {
    matrix.set(savedmatrix);
   }
  }
  center();
 }
 /**
  * 最小缩放比例，最大为100%
  */
 private void minzoom() {
  minscaler = math.min(
    (float) dm.widthpixels / (float) bitmap.getwidth(),
    (float) dm.heightpixels / (float) bitmap.getheight());
  if (minscaler < 1.0) {
   matrix.postscale(minscaler, minscaler);
  }
 }
 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
   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 = imgview.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);
 }
 /**
  * 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);
 }
}

scale.xml

<?xml version="1.0" encoding="utf-8"?>
<framelayout xmlns:android="http://schemas.android.com/apk/res/android"
 android:layout_width="fill_parent"
 android:layout_height="fill_parent"
 android:layout_gravity="center" >
 <imageview
  android:id="@+id/imag"
  android:layout_width="fill_parent"
  android:layout_height="fill_parent"
  android:layout_gravity="center"
  android:scaletype="matrix" >
 </imageview>
</framelayout>

希望本文所述对大家android程序设计有所帮助。