Android:ImageView图片缩放、居中

几个重要知识点：

1、布局文件中android:scaleType="matrix" 设置图片动态缩放

2、matrix.postTranslate(dx,dy); 平移图片 matrix.postScale(sx,sy,p.x,p.y); 缩放图片

3、两点的中点、距离计算方式，限制缩放范围函数，在指定区域内移动图片方法

(以下代码网上很多地方有类似的，仅供参考)

[java]
public class Main extends Activity
{
    private static final int NONE = 0;
    private static final int DRAG = 1;
    private static final int ZOOM = 2;

    private int mode = NONE;
    private float oldDist;
    private Matrix matrix = new Matrix();
    private Matrix savedMatrix = new Matrix();
    private PointF start = new PointF();
    private PointF mid = new PointF();

    ImageView view;
    Bitmap bitmap;
    DisplayMetrics dm;
    float minScaleR=0.1f; //最少缩放比例
    static final float MAX_SCALE = 4f; //最大缩放比例
    float dist = 1f;

    @Override
    public void onCreate(Bundle savedInstanceState)
    {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);
        view = (ImageView) findViewById(R.id.image_view);
        bitmap = BitmapFactory.decodeResource(getResources(), R.drawable.test);

        dm = new DisplayMetrics();
        getWindowManager().getDefaultDisplay().getMetrics(dm); //获取分辨率


        matrix.setScale(minScaleR, minScaleR); //开始先缩小
        matrix.postTranslate(120, 120);     //图片的位置相对于imageview的左上角往右往下各偏移120个像素
        view.setImageMatrix(matrix);

        view.setOnTouchListener(new OnTouchListener()
        {
            @Override
            public boolean onTouch(View v, MotionEvent event)
            {
                ImageView view = (ImageView) v;
                switch (event.getAction() & MotionEvent.ACTION_MASK)
                {
                case MotionEvent.ACTION_DOWN: //单点
                    Toast.makeText(Main.this, bitmap.getWidth()+"*"+bitmap.getHeight(), Toast.LENGTH_LONG).show();
                    savedMatrix.set(matrix);
                    start.set(event.getX(), event.getY());
                    mode = DRAG;
                    break;
                case MotionEvent.ACTION_UP: //单点弹起
                case MotionEvent.ACTION_POINTER_UP: //多点弹起
                    mode = NONE;
                    break;
                case MotionEvent.ACTION_POINTER_DOWN: //多点
                    oldDist = spacing(event);
                    if (oldDist > 10f)
                    {
                        savedMatrix.set(matrix);
                        midPoint(mid, event);
                        mode = ZOOM;
                    }
                    break;
                case MotionEvent.ACTION_MOVE: //按下且在拖动
                    if (mode == DRAG)
                    {
                        matrix.set(savedMatrix);
                        matrix.postTranslate(event.getX() - start.x,event.getY() - start.y); //xy方向都可以拖动
                        //matrix.postTranslate(event.getX() - start.x,0); //只在x轴方向拖动即左右拖动上下不动
                        //matrix.postTranslate(0,event.getY() - start.y); //只在y轴方向拖动即上下拖动左右不动
         &n

补充：移动开发 , Android ,