安卓 imageview放大,配合scroll

要实现ImageView的放大效果，可以结合ScrollView和GestureDetector实现。以下是一个简单的示例代码：

public class MainActivity extends AppCompatActivity implements GestureDetector.OnGestureListener, GestureDetector.OnDoubleTapListener {

    private ImageView imageView;
    private ScrollView scrollView;
    private GestureDetector gestureDetector;
    private Matrix matrix = new Matrix();
    private float scale = 1f;

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

        imageView = findViewById(R.id.image_view);
        scrollView = findViewById(R.id.scroll_view);

        gestureDetector = new GestureDetector(this, this);
        gestureDetector.setOnDoubleTapListener(this);

        imageView.setOnTouchListener(new View.OnTouchListener() {
            @Override
            public boolean onTouch(View v, MotionEvent event) {
                gestureDetector.onTouchEvent(event);
                return true;
            }
        });
    }

    @Override
    public boolean onDown(MotionEvent e) {
        return false;
    }

    @Override
    public void onShowPress(MotionEvent e) {

    }

    @Override
    public boolean onSingleTapUp(MotionEvent e) {
        return false;
    }

    @Override
    public boolean onScroll(MotionEvent e1, MotionEvent e2, float distanceX, float distanceY) {
        float deltaX = e2.getX() - e1.getX();
        float deltaY = e2.getY() - e1.getY();

        matrix.postTranslate(-deltaX, -deltaY);
        imageView.setImageMatrix(matrix);

        return true;
    }

    @Override
    public void onLongPress(MotionEvent e) {

    }

    @Override
    public boolean onFling(MotionEvent e1, MotionEvent e2, float velocityX, float velocityY) {
        return false;
    }

    @Override
    public boolean onSingleTapConfirmed(MotionEvent e) {
        return false;
    }

    @Override
    public boolean onDoubleTap(MotionEvent e) {
        if (scale == 1f) {
            scale = 2f;
        } else {
            scale = 1f;
        }

        matrix.setScale(scale, scale);
        imageView.setImageMatrix(matrix);

        return true;
    }

    @Override
    public boolean onDoubleTapEvent(MotionEvent e) {
        return false;
    }
}

在XML布局文件中，需要使用ScrollView包裹ImageView：

<ScrollView
    android:id="@+id/scroll_view"
    android:layout_width="match_parent"
    android:layout_height="match_parent">

    <ImageView
        android:id="@+id/image_view"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:src="@drawable/image" />

</ScrollView>

这里使用GestureDetector来监听手势事件，onDoubleTap方法用于处理双击事件，将图片的缩放比例设置为2倍或1倍；onScroll方法用于处理滑动事件，根据手指移动的距离计算出偏移量，然后调用Matrix的postTranslate方法进行平移操作。最后再将Matrix设置给ImageView即可。