android多点触控自由对图片缩放

在系统的相册中,观看相片就可以用多个手指进行缩放.

要实现这个功能,只需要这几步:

1.新建项目,在项目中新建一个ZoomImage.java

public class ZoomImageView extends View {

    //初始化状态常量

    public static final int STATUS_INIT=1;

    //图片放大状态常量

    public static final int STATUS_ZOOM_OUT=2;

    //图片缩小状态常量

    public static final int STATUS_ZOOM_IN=3;

    //图片拖动状态的常量

    public static final int STATUS_MOVE=4;

    //对图片进行移动和缩放的矩阵

    private Matrix matrix=new Matrix();

    //需要处理的Bitmap对象

    private Bitmap sourceBitmap;

    //记录当前的操作状态

    private int currentStatus;

    

    //ZoomImageView的宽度

    private int width;

    //ZoomImageView的高度

    private int height;

    

    

    //记录两指同时放在屏幕上时,中心点的横坐标

    private float centerPointX;

    //记录两指同时放在屏幕上时,中心点的纵坐标

    private float centerPointY;

    

    //记录当前图片的宽度

    private float currentBitmapWidth;

    //记录当前图片的高度

    private float currentBitmapHeight;

    

    //记录上次手指移动时的横坐标

    private float lastXMove=-1;

    //记录上次手指移动时的纵坐标

    private float lastYMove=-1;

    

    //记录手指在横坐标上的距离

    private float moveDistanceX;

    //记录手指在纵坐标上的距离

    private float moveDistanceY;

    

    //记录图片在矩阵上横向偏移值

    private float totalTranslateX;

    //记录图片在矩阵上纵向偏移值

    private float totalTranslateY;

    

    //记录图片在矩阵上总缩放比例

    private float totalRatio;

    

    //记录手指移动的距离造成的缩放比例

    private float scaledRatio;

    

    //记录图片初始化时的缩放比例

    private float initRatio;

    

    //记录上次手指之间的距离

    private double lastFingerDis;

    

    //初始状态  设置当前操作状态为STATUS_INIT

    public ZoomImageView(Context context, AttributeSet attrs) {

        super(context, attrs);

        currentStatus=STATUS_INIT;

    }

    //将待展示的图片设置进来

    public void setImageBitmap(Bitmap bitmap){

        sourceBitmap=bitmap;

        invalidate();

    }

    @Override

    protected void onLayout(boolean changed, int left, int top, int right,

            int bottom) {

        super.onLayout(changed, left, top, right, bottom);

        if(changed){

            width=getWidth();

            height=getHeight();

        }

    }

    

    @Override

    public boolean onTouchEvent(MotionEvent event) {

        switch (event.getActionMasked()) {

        case MotionEvent.ACTION_POINTER_DOWN:

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

                lastFingerDis=distanceBetweenFingers(event);  //两指间按下的距离

            }

            break;

        case MotionEvent.ACTION_MOVE:

            if(event.getPointerCount()==1){  //如果只有一个手指在屏幕上 则为拖动模式

                float xMove=event.getX();

                float yMove=event.getY();

                if(lastXMove==-1&&lastYMove==-1){

                    lastXMove=xMove;

                    lastYMove=yMove;

                }

                currentStatus=STATUS_MOVE;

                moveDistanceX=xMove-lastXMove;

                moveDistanceY=yMove-lastYMove;

                //进行边界检查 不允许拖出边界

                if(totalTranslateX+moveDistanceX>0){

                    moveDistanceX=0;

                }

                else if(width-(totalTranslateX+moveDistanceX)>currentBitmapWidth){

                    moveDistanceX=0;

                }

                if(totalTranslateY+moveDistanceY>0){

                    moveDistanceY=0;

                }

                else if(height-(totalTranslateY+moveDistanceY)>currentBitmapHeight){

                    moveDistanceY=0;

                }

                

                //调用onDraw()方法绘制图片

                invalidate();

                lastXMove=xMove;

                lastYMove=yMove;

            }

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

                //有两个手指在屏幕上移动  为缩放状态

                centerPointBetweenFingers(event);

                double fingerDis=distanceBetweenFingers(event);

                if(fingerDis>lastFingerDis){

                    currentStatus=STATUS_ZOOM_OUT;

                }

                else{

                    currentStatus=STATUS_ZOOM_IN;

                }

                //进行缩放倍数检查

                if((currentStatus==STATUS_ZOOM_OUT&&totalRatio<4*initRatio)||(currentStatus==STATUS_ZOOM_IN&&totalRatio>initRatio)){

                    scaledRatio=(float) (fingerDis/lastFingerDis);  //需要缩放的比例

                    totalRatio=totalRatio*scaledRatio;

                    if(totalRatio>4*initRatio){

                        totalRatio=4*initRatio;

                    }

                    else if(totalRatio<initRatio){

                        totalRatio=initRatio;

                    }

                    //调用onDraw

                    invalidate();

                    lastFingerDis=fingerDis;

                }

            }

            break;

        case MotionEvent.ACTION_POINTER_UP:

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

                lastXMove=-1;

                lastYMove=-1;

            }

            break;

        case MotionEvent.ACTION_UP:

            lastXMove=-1;

            lastYMove=-1;

            break;

        default:

            break;

        }

        return true;

    }

    

    @Override

    protected void onDraw(Canvas canvas) {

        super.onDraw(canvas);

        switch (currentStatus) {

        case STATUS_ZOOM_OUT:

        case STATUS_ZOOM_IN:

            zoom(canvas);

            break;

        case STATUS_MOVE:

            move(canvas);

            break;

        case STATUS_INIT:

            initBitmap(canvas);

            break;

        default:

            canvas.drawBitmap(sourceBitmap, matrix, null);

            break;

        }

    }

    

    //初始化显示图片

    private void initBitmap(Canvas canvas){

        if(sourceBitmap!=null){

            matrix.reset();

            int bitmapWidth=sourceBitmap.getWidth();

            int bitmapHeight=sourceBitmap.getHeight();

            if(bitmapWidth>width||bitmapHeight>height){//如果图片的宽度或高度有大于屏幕宽高

                if(bitmapWidth-width>bitmapHeight-height){    //判断这张图片 是宽度长  还是高度长  如果是宽度长,则按宽度的那边进行压缩  高度也等比例压缩

                    float radio=width/(bitmapWidth*1.0f);     //需要压缩的比例  

                    matrix.postScale(radio,radio);             //缩放矩阵比例

                    float translateY=(height-(bitmapHeight*radio))/2f;   //因为是按宽度进行压缩  所以宽度应该是占满全屏  这时候还应该将图片Y轴向下移动

                    //在纵坐标上进行偏移 以保证图片居中显示

                    matrix.postTranslate(0, translateY);

                    totalTranslateY=translateY;

                    totalRatio=initRatio=radio;

                }

                else{

                    //当图片高度大于屏幕高度时

                    float radio=height/(bitmapHeight*1.0f);

                    matrix.postScale(radio, radio);

                    float translateX=(width-(bitmapWidth*radio))/2f;

                    //在横坐标上进行偏移 

                    matrix.postTranslate(translateX, 0);//平移

                    totalTranslateX=translateX;

                    totalRatio=initRatio=radio;

                }

            }

            else{

                //当图片的宽度与高度都小于屏幕宽高时,让图片居中显示

                float translateX=(width-sourceBitmap.getWidth())/2f;

                float translateY=(height-sourceBitmap.getHeight())/2f;

                matrix.postTranslate(translateX, translateY);

                totalTranslateX=translateX;

                totalTranslateY=translateY;

                totalRatio=initRatio=1f;

                currentBitmapHeight=bitmapHeight;

                currentBitmapWidth=bitmapWidth;

            }

            canvas.drawBitmap(sourceBitmap, matrix, null);

        }

    }

    

    //对图片进行缩放处理

    private void zoom(Canvas canvas){

        matrix.reset();

        //将图片按照比例缩放

        matrix.postScale(totalRatio, totalRatio);

        float scaledWidth=sourceBitmap.getWidth()*totalRatio;

        float scaledHeight=sourceBitmap.getHeight()*totalRatio;

        

        float translateX=0f;

        float translateY=0f;

        

        //如果当前图片宽度小于屏幕宽度  则按屏幕中心点 进行水平缩放,否则按两指中线点的横坐标进行缩放

        if(currentBitmapWidth<width){

            translateX=(width-scaledWidth)/2f;

        }

        else{

            translateX=totalTranslateX*scaledRatio+centerPointX*(1-scaledRatio);

            

            //进入边界检查 ,保证图片缩放后水平方向不会偏移屏幕

            if(translateX>0){

                translateX=0;

            }

            else if(width-translateX>scaledWidth){

                translateX=width-scaledWidth;

            }

        }

        if(currentBitmapHeight<height){

            translateY=(height-scaledHeight)/2f;

        }

        else{

            translateY=totalTranslateY*scaledRatio+centerPointY*(1-scaledRatio);

            //进行边界检查

            if(translateY>0){

                translateY=0;

            }

            else if(height-translateY>scaledHeight){

                translateY=height-scaledHeight;

            }

        }

        //缩放后对图片进行偏移 保证缩放后中心点位置不变

        matrix.postTranslate(translateX, translateY);

        totalTranslateX=translateX;

        totalTranslateY=translateY;

        currentBitmapWidth=scaledWidth;

        currentBitmapHeight=scaledHeight;

        canvas.drawBitmap(sourceBitmap, matrix, null);

    }

    

    //对图片进行平移处理

    private void move(Canvas canvas){

        matrix.reset();

        //根据手指移动的距离计算总偏移量

        float translateX=totalTranslateX+moveDistanceX;

        float translateY=totalTranslateY+moveDistanceY;

        //按照已有的缩放比例对图片缩放

        matrix.postScale(totalRatio, totalRatio);

        //根据移动距离进行偏移

        matrix.postTranslate(translateX, translateY);

        totalTranslateX=translateX;

        totalTranslateY=translateY;

        canvas.drawBitmap(sourceBitmap, matrix, null);

    }

    

    //计算两个手指的距离

    private double distanceBetweenFingers(MotionEvent event){

        float disX=Math.abs(event.getX(0)-event.getX(1));

        float disY=Math.abs(event.getY(0)-event.getY(1));

        return Math.sqrt(disX*disX+disY*disY);   

    }

    //计算两个手指之间中心点的坐标

    private void centerPointBetweenFingers(MotionEvent event){

        float xPoint0=event.getX(0);

        float yPoint0=event.getY(0);

        float xPoint1=event.getX(1);

        float yPoint1=event.getY(1);

        centerPointX=(xPoint0+xPoint1)/2;

        centerPointY=(yPoint0+yPoint1)/2;

    }

}

2.打开activity_main.xml

<com.example.bitmaptest.ZoomImageView xmlns:android="http://schemas.android.com/apk/res/android"

    xmlns:tools="http://schemas.android.com/tools"

    android:layout_width="match_parent"

    android:layout_height="match_parent"

    android:id="@+id/zoom_image"

    tools:context="com.example.bitmaptest.MainActivity" >

    

</com.example.bitmaptest.ZoomImageView>  

3.打开MainActivity.java

public class MainActivity extends ActionBarActivity {

    private Bitmap bitmap;

    @Override

    protected void onCreate(Bundle savedInstanceState) {

        super.onCreate(savedInstanceState);

        setContentView(R.layout.activity_main);

        ZoomImageView zoomImage=(ZoomImageView) findViewById(R.id.zoom_image);

        bitmap=BitmapFactory.decodeResource(getResources(), R.drawable.ic_launcher);

        if(bitmap!=null){

            zoomImage.setImageBitmap(bitmap);

        }

    }

}  

来自为知笔记(Wiz)