使用手势缩放文本

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思路：为呈现文本的组件注册setOnTouchListener监听，然后判断缩放来改变字体大小。

MainActivity：

package com.home.mutitouch;import java.io.InputStream;import android.app.Activity;import android.os.Bundle;import android.widget.TextView;public class MainActivity extends Activity {@Overridepublic void onCreate(Bundle savedInstanceState) {super.onCreate(savedInstanceState);setContentView(R.layout.main);TextView textView = (TextView) this.findViewById(R.id.main_tv);try {textView.setText(readText());} catch (Exception e) {e.printStackTrace();}float zoomScale = 0.5f;// 缩放比例new ZoomTextView(textView, zoomScale);}/** * 读取txt文本内容 *  * @param str * @return 文本内容 * @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");}}

ZoomTextView：

package com.home.mutitouch;import android.widget.TextView;public class ZoomTextView extends ZoomView<TextView> {/** 最小字体尺寸 */public static final float MIN_TEXT_SIZE = 10f;/** 最大字体尺寸 */public static final float MAX_TEXT_SIZE = 80.0f;/** 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();}/** * 放大字体 */protected void zoomOut() {textSize += scale;if (textSize > MAX_TEXT_SIZE) {textSize = MAX_TEXT_SIZE;}view.setTextSize(textSize);}/** * 缩小字体 */protected void zoomIn() {textSize -= scale;if (textSize < MIN_TEXT_SIZE) {textSize = MIN_TEXT_SIZE;}view.setTextSize(textSize);}}

ZoomView：

package com.home.mutitouch;import android.util.FloatMath;import android.view.MotionEvent;import android.view.View;import android.view.View.OnTouchListener;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() {/** * 缩放监听器 */view.setOnTouchListener(new OnTouchListener() {@Overridepublic 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();}

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