手势缩放字体大小

使用装饰者模式，讲一个普通的TextView 包装成一个可放大缩小的View

关于多点触控还是要进一步学习啊。。。

package src.youer.text;

import android.util.FloatMath;
import android.view.MotionEvent;
import android.view.View;
import android.view.View.OnTouchListener;

/**
 * view缩放
 * 
 * @author Administrator
 * 
 * @param <V>
 */
public abstract class ZoomView<V extends View>
{

	protected V view;

	// -----------------------------------------------
	private static final int NONE = 0;// 空
	private static final int DRAG = 1;// 按下第一个点
	private static final int ZOOM = 2;// 按下第二个点

	/** 屏幕上点的数量 */
	private int mode = NONE;

	/** 记录按下第二个点距第一个点的距离 */
	float oldDist;

	public ZoomView(V view)
	{
		this.view = view;
		setTouchListener();
	}

	private void setTouchListener()
	{
		view.setOnTouchListener(new OnTouchListener()
		{
			@Override
			public boolean onTouch(View v, MotionEvent event)
			{
				switch (event.getAction() & MotionEvent.ACTION_MASK)
				{
				case MotionEvent.ACTION_DOWN:
					mode = DRAG;
					break;
				case MotionEvent.ACTION_UP:
				case MotionEvent.ACTION_POINTER_UP:
					mode = NONE;
					break;
				case MotionEvent.ACTION_POINTER_DOWN:
					oldDist = spacing(event);
					if (oldDist > 10f)
					{
						mode = ZOOM;
					}
					break;
				case MotionEvent.ACTION_MOVE:
					if (mode == ZOOM)
					{
						// 正在移动的点距初始点的距离
						float newDist = spacing(event);

						if (newDist > oldDist)
						{
							zoomOut();
						}
						if (newDist < oldDist)
						{
							zoomIn();
						}

					}
					break;
				}
				return true;
			}

			/**
			 * 求出2个触点间的 距离
			 * 
			 * @param event
			 * @return
			 */
			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);
			}
		});
	}

	protected abstract void zoomIn();

	protected abstract void zoomOut();
}

package src.youer.text;

import android.widget.TextView;

public class ZoomTextView extends ZoomView<TextView>
{
	/**最小字体*/
	public static final float MIN_TEXT_SIZE = 10f;
	
	/**最大子图*/
	public static final float MAX_TEXT_SIZE = 100.0f;

	/** 缩放比例 */
	float scale;

	/** 设置字体大小 */
	float textSize;

	public ZoomTextView(TextView view, float scale)
	{
		super(view);
		this.scale = scale;
		textSize = view.getTextSize();
	}

	/**
	 * 放大
	 */
	protected void zoomOut()
	{
		textSize += scale;
		if (textSize > MAX_TEXT_SIZE)
		{
			textSize = MAX_TEXT_SIZE;
		}
		view.setTextSize(textSize);
	}

	/**
	 * 缩小
	 */
	protected void zoomIn()
	{
		textSize -= scale;
		if (textSize < MIN_TEXT_SIZE)
		{
			textSize = MIN_TEXT_SIZE;
		}
		view.setTextSize(textSize);
	}

}

package src.youer.text;

import java.io.InputStream;

import android.app.Activity;
import android.os.Bundle;
import android.widget.TextView;

public class MultiTouchTestActivity extends Activity
{
	@Override
	public void onCreate(Bundle savedInstanceState)
	{
		super.onCreate(savedInstanceState);
		setContentView(R.layout.main);
		TextView textView = (TextView) this.findViewById(R.id.text_view);
		try
		{
			textView.setText(readText());
		}
		catch (Exception e)
		{
			// TODO Auto-generated catch block
			e.printStackTrace();
		}
		float zoomScale = 0.5f;// 缩放比例
		//装饰
		new ZoomTextView(textView, zoomScale);
	}

	/**
	 * 读取txt
	 * 
	 * @param str
	 * @return
	 * @throws Exception
	 */
	public String readText() throws Exception
	{
		InputStream is = this.getClass()
				.getResourceAsStream("/assets/text.txt");
		int index = is.available();
		byte data[] = new byte[index];
		is.read(data);
		return new String(data, "UTF-8");
	}
}