10_多点触摸交互处理

　　多点触摸，对图像进行缩放的实例。

package com.example.multitouch;

import android.app.Activity;
import android.os.Bundle;
import android.view.MotionEvent;
import android.view.View;
import android.view.WindowManager;
import android.widget.FrameLayout;
import android.widget.FrameLayout.LayoutParams;
import android.widget.ImageView;

public class MainActivity extends Activity {

    private FrameLayout root;
    private ImageView iv;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        root = (FrameLayout) findViewById(R.id.container);
        iv = (ImageView) findViewById(R.id.iv);

        root.setOnTouchListener(new View.OnTouchListener() {

            float currentDistance;
            float lastDistance = -1;

            FrameLayout.LayoutParams lp = (LayoutParams) iv.getLayoutParams();

            @Override
            public boolean onTouch(View v, MotionEvent event) {

                switch (event.getAction()) {
                case MotionEvent.ACTION_DOWN:
                    System.out.println("action_down");
                    break;
                case MotionEvent.ACTION_MOVE:
                    System.out.println("action_move");

                    if (event.getPointerCount() >= 2) {

                        float offsetX = event.getX(0) - event.getX(1);
                        float offsetY = event.getY(0) - event.getY(1);
                        currentDistance = (float) Math.sqrt(offsetX * offsetX
                                + offsetY * offsetY);

                        if (lastDistance < 0) {
                            lastDistance = currentDistance;
                        } else {
                            if (currentDistance - lastDistance > 5) {
                                System.out.println("放大");

                                lp.width = (int) (1.1f * iv.getWidth());
                                lp.height = (int) (1.1f * iv.getHeight());

                                iv.setLayoutParams(lp);

                                lastDistance = currentDistance;
                            } else if (lastDistance - currentDistance > 5) {
                                System.out.println("缩小");
                                lp.width = (int) (0.9f * iv.getWidth());
                                lp.height = (int) (0.9f * iv.getHeight());
                                iv.setLayoutParams(lp);
                                lastDistance = currentDistance;
                            }
                        }
                    }

                    // 获取到多个触摸点
                    // System.out.println("pointer count : " +
                    // event.getPointerCount() );
                    // System.out.println(String.format("x1:%f y1:%f",
                    // event.getX(0),event.getY(0)));

                    // FrameLayout.LayoutParams lp = (LayoutParams)
                    // iv.getLayoutParams();
                    // lp.leftMargin = (int) event.getX();
                    // lp.topMargin = (int) event.getY();
                    //
                    // iv.setLayoutParams(lp);
                    //
                    // System.out.println(String.format("x:%f,y:%f",
                    // event.getX(), event.getY() ));
                    break;
                case MotionEvent.ACTION_UP:
                    System.out.println("action_up");
                    break;
                }

                // 返回true的话，事件才会继续被触发。
                return true;
            }
        });
    }
}

<FrameLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:id="@+id/container"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context="com.example.multitouch.MainActivity"
    tools:ignore="MergeRootFrame" >

    <ImageView
        android:id="@+id/iv"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:src="@drawable/ic_launcher" />

</FrameLayout>

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="com.example.multitouch"
    android:versionCode="1"
    android:versionName="1.0" >

    <uses-sdk
        android:minSdkVersion="14"
        android:targetSdkVersion="19" />

    <application
        android:allowBackup="true"
        android:icon="@drawable/ic_launcher"
        android:label="@string/app_name"
        android:theme="@style/AppTheme" >
        <activity
            android:name="com.example.multitouch.MainActivity"
            android:label="@string/app_name" >
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />

                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
        </activity>
    </application>

</manifest>