通过手势实现Android自定义View的缩放

这里使用了一个自定义View–TouchImageView来实现图片的缩放，代码如下：

TouchImageView：

package com.example.test;

/**
 * Created by agint_bin on 2016/7/20.
 */

import android.content.Context;
import android.graphics.Matrix;
import android.graphics.PointF;
import android.graphics.drawable.Drawable;
import android.util.AttributeSet;
import android.util.Log;
import android.view.MotionEvent;
import android.view.ScaleGestureDetector;
import android.view.View;
import android.widget.ImageView;

public class TouchImageView extends ImageView {

    Matrix matrix;

    // We can be in one of these 3 states
    static final int NONE = 0;  //初始
    static final int DRAG = 1;  //拖动
    static final int ZOOM = 2;  //放大
    int mode = NONE;

    // Remember some things for zooming
    PointF last = new PointF();
    PointF start = new PointF();
    float minScale = 1f;
    float maxScale = 3f;
    float[] m;


    int viewWidth, viewHeight;
    static final int CLICK = 3;
    float saveScale = 1f;
    protected float origWidth, origHeight;
    int oldMeasuredWidth, oldMeasuredHeight;


    ScaleGestureDetector mScaleDetector;

    Context context;
    //默认构造函数
    public TouchImageView(Context context) {
        super(context);
        sharedConstructing(context);
    }

    public TouchImageView(Context context, AttributeSet attrs) {
        super(context, attrs);
        sharedConstructing(context);
    }

    private void sharedConstructing(Context context) {
        super.setClickable(true);
        this.context = context;
        mScaleDetector = new ScaleGestureDetector(context, new ScaleListener());
        matrix = new Matrix();
        m = new float[9];
        setImageMatrix(matrix);
        setScaleType(ScaleType.MATRIX);

        setOnTouchListener(new OnTouchListener() {

            @Override
            public boolean onTouch(View v, MotionEvent event) {
                mScaleDetector.onTouchEvent(event);
                PointF curr = new PointF(event.getX(), event.getY());

                switch (event.getAction()) {
                    case MotionEvent.ACTION_DOWN:
                        last.set(curr);  //当前位置
                        start.set(last);  //开始点
                        mode = DRAG;
                        break;

                    case MotionEvent.ACTION_MOVE:    //移动事件
                        if (mode == DRAG) {
                            float deltaX = curr.x - last.x;
                            float deltaY = curr.y - last.y;
                            float fixTransX = getFixDragTrans(deltaX, viewWidth, origWidth * saveScale);
                            float fixTransY = getFixDragTrans(deltaY, viewHeight, origHeight * saveScale);
                            matrix.postTranslate(fixTransX, fixTransY);
                            fixTrans();
                            last.set(curr.x, curr.y);
                        }
                        break;

                    case MotionEvent.ACTION_UP:
                        mode = NONE;
                        int xDiff = (int) Math.abs(curr.x - start.x);
                        int yDiff = (int) Math.abs(curr.y - start.y);
                        if (xDiff < CLICK && yDiff < CLICK)
                            performClick();
                        break;
                    //有手指离开屏幕，但屏幕还有触点(手指) 
                    case MotionEvent.ACTION_POINTER_UP:
                        mode = NONE;
                        break;
                }

                setImageMatrix(matrix);
                invalidate();
                return true; // indicate event was handled
            }

        });
    }

    public void setMaxZoom(float x) {
        maxScale = x;
    }

    private class ScaleListener extends ScaleGestureDetector.SimpleOnScaleGestureListener {
        @Override
        public boolean onScaleBegin(ScaleGestureDetector detector) {
            mode = ZOOM;
            return true;
        }

        @Override
        public boolean onScale(ScaleGestureDetector detector) {
            float mScaleFactor = detector.getScaleFactor();
            float origScale = saveScale;
            saveScale *= mScaleFactor;
            if (saveScale > maxScale) {
                saveScale = maxScale;
                mScaleFactor = maxScale / origScale;
            } else if (saveScale < minScale) {
                saveScale = minScale;
                mScaleFactor = minScale / origScale;
            }

            if (origWidth * saveScale <= viewWidth || origHeight * saveScale <= viewHeight)
                matrix.postScale(mScaleFactor, mScaleFactor, viewWidth / 2, viewHeight / 2);
            else
                matrix.postScale(mScaleFactor, mScaleFactor, detector.getFocusX(), detector.getFocusY());

            fixTrans();
            return true;
        }
    }

    void fixTrans() {
        matrix.getValues(m);
        float transX = m[Matrix.MTRANS_X];
        float transY = m[Matrix.MTRANS_Y];

        float fixTransX = getFixTrans(transX, viewWidth, origWidth * saveScale);
        float fixTransY = getFixTrans(transY, viewHeight, origHeight * saveScale);

        if (fixTransX != 0 || fixTransY != 0)
            matrix.postTranslate(fixTransX, fixTransY);
    }

    float getFixTrans(float trans, float viewSize, float contentSize) {
        float minTrans, maxTrans;

        if (contentSize <= viewSize) {
            minTrans = 0;
            maxTrans = viewSize - contentSize;
        } else {
            minTrans = viewSize - contentSize;
            maxTrans = 0;
        }

        if (trans < minTrans)
            return -trans + minTrans;
        if (trans > maxTrans)
            return -trans + maxTrans;
        return 0;
    }

    float getFixDragTrans(float delta, float viewSize, float contentSize) {
        if (contentSize <= viewSize) {
            return 0;
        }
        return delta;
    }

    @Override
    protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
        super.onMeasure(widthMeasureSpec, heightMeasureSpec);
        viewWidth = MeasureSpec.getSize(widthMeasureSpec);
        viewHeight = MeasureSpec.getSize(heightMeasureSpec);

        //
        // Rescales image on rotation
        //
        if (oldMeasuredHeight == viewWidth && oldMeasuredHeight == viewHeight
                || viewWidth == 0 || viewHeight == 0)
            return;
        oldMeasuredHeight = viewHeight;
        oldMeasuredWidth = viewWidth;

        if (saveScale == 1) {
            //Fit to screen.
            float scale;

            Drawable drawable = getDrawable();
            if (drawable == null || drawable.getIntrinsicWidth() == 0 || drawable.getIntrinsicHeight() == 0)
                return;
            int bmWidth = drawable.getIntrinsicWidth();
            int bmHeight = drawable.getIntrinsicHeight();

            Log.d("bmSize", "bmWidth: " + bmWidth + " bmHeight : " + bmHeight);

            float scaleX = (float) viewWidth / (float) bmWidth;
            float scaleY = (float) viewHeight / (float) bmHeight;
            scale = Math.min(scaleX, scaleY);
            matrix.setScale(scale, scale);

            // Center the image
            float redundantYSpace = (float) viewHeight - (scale * (float) bmHeight);
            float redundantXSpace = (float) viewWidth - (scale * (float) bmWidth);
            redundantYSpace /= (float) 2;
            redundantXSpace /= (float) 2;

            matrix.postTranslate(redundantXSpace, redundantYSpace);

            origWidth = viewWidth - 2 * redundantXSpace;
            origHeight = viewHeight - 2 * redundantYSpace;
            setImageMatrix(matrix);
        }
        fixTrans();
    }
}

MainActivity:

package com.example.test;

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

public class MainActivity extends Activity {

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

        TouchImageView img = (TouchImageView) findViewById(R.id.image);
        img.setImageResource(R.drawable.modern);
        img.setMaxZoom(4f);
    }
}

main.xml:

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:orientation="vertical"
    android:layout_width="match_parent"
    android:layout_height="match_parent">

    <LinearLayout
        android:id="@+id/root"
        android:orientation="vertical"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:background="@drawable/gridding">

    <com.example.test.TouchImageView   
    --这里特别注意，使用TouchImageViewz就要这样写-->

        android:id="@+id/image"
        android:layout_height="match_parent"
        android:layout_width="wrap_content" />
    LinearLayout>
   LinearLayout>