Android-实现图片的拖动和缩放

从现在开始做学习博客，记录自己的Android学习历程。

最近一直做Android图片方面的研究，今天遇到了图片的拖拽和缩放问题，百度n多资料，自己边想边摸索，终于解决。现将源码贴下，我在真机上测试很流畅。

主要类：

import android.content.Context;
import android.graphics.Matrix;
import android.graphics.PointF;
import android.util.AttributeSet;
import android.util.FloatMath;
import android.view.MotionEvent;
import android.widget.ImageView;

public class FlexibleImageView extends ImageView {
	
	private int mode;
	private final int drag = 0;
	private final int zoom = 1;
	private final int none = 3;
	private float startDis;
	private Matrix matrix;
	private PointF startF;
	private PointF midPoint;
	
	public FlexibleImageView(Context context) {
		super(context);
		init();
	}
	
	public FlexibleImageView(Context context, AttributeSet attrs) {
		super(context, attrs, 0);
		init();
    }
	
	private void init(){
		matrix = this.getImageMatrix();
		startF = new PointF();
	}
	
	@Override
	public boolean onTouchEvent(MotionEvent event) {
		
		switch (event.getActionMasked()) {
		case MotionEvent.ACTION_DOWN:

			mode = drag;
			startF.set(event.getX(), event.getY());

			break;
		case MotionEvent.ACTION_UP:

			mode = none;
			break;
		case MotionEvent.ACTION_POINTER_DOWN:

			mode = zoom;

			startDis = getDis(event);

			break;
		case MotionEvent.ACTION_POINTER_UP:

			mode = none;

			break;
		case MotionEvent.ACTION_MOVE:

			// 这里做动作的处理
			switch (mode) {
			case drag:
				// 移动
				float x = event.getX() - startF.x;
				float y = event.getY() - startF.y;

				if (Math.abs(x) > 10 || Math.abs(y) > 10) {
					matrix.postTranslate(x, y);
				}
				//关键代码
				startF.set(event.getX(), event.getY());
				break;
			case zoom:
				// 放大
				float endDis = getDis(event);
				float scale = endDis / startDis;
				midPoint = getMidPoint(event);
				
				//将缩放的比例控制在2.0到0.5之间
				scale = scale > 1.8f ? 1.8f : scale;
				scale = scale < 0.7f ? 0.7f : scale;
				
				//怎么控制缩放的过程能够平缓
				matrix.postScale(scale, scale, midPoint.x,
						midPoint.y);
				//关键代码
				startDis = endDis;
				
				 break;
			}

			this.setImageMatrix(matrix);

			break;
		}
		
		return true;
	}
	
	/**
	 * 获取放大的参照中点
	 * 
	 * @param event
	 * @return
	 */
	private PointF getMidPoint(MotionEvent event) {
		PointF point = new PointF();

		float x = event.getX(0) + event.getX(1);
		float y = event.getY(0) + event.getY(1);

		point.set(x / 2, y / 2);

		return point;
	}
	
	/**
	 * 计算两点之间的距离
	 * 
	 * @param event
	 * @return
	 */
	private float getDis(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);
	}
}

顺便将我测试的Demo贴上，这里面还有关于大图片的加载相关工具类