Android Zoom Control with ScaleGestureDetector

In Android, you can achieve control scaling of components by using the ScaleGestureDetector class. Here is a simple example code:

1. Firstly, add a control in the layout file that needs to be scaled, such as ImageView.

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

1. In Activity or Fragment, utilize the ScaleGestureDetector class to enable zooming functionality.

public class MainActivity extends AppCompatActivity {

    private ImageView imageView;
    private ScaleGestureDetector scaleGestureDetector;
    private float scaleFactor = 1.0f;

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

        imageView = findViewById(R.id.imageView);

        scaleGestureDetector = new ScaleGestureDetector(this, new ScaleGestureListener());
        imageView.setOnTouchListener(new View.OnTouchListener() {
            @Override
            public boolean onTouch(View v, MotionEvent event) {
                scaleGestureDetector.onTouchEvent(event);
                return true;
            }
        });
    }

    private class ScaleGestureListener extends ScaleGestureDetector.SimpleOnScaleGestureListener {
        @Override
        public boolean onScale(ScaleGestureDetector detector) {
            scaleFactor *= detector.getScaleFactor();
            scaleFactor = Math.max(0.1f, Math.min(scaleFactor, 5.0f)); // 设置缩放范围
            imageView.setScaleX(scaleFactor);
            imageView.setScaleY(scaleFactor);
            return true;
        }
    }
}

In the ScaleGestureListener class, we override the onScale method, which is called when the user performs a zoom gesture. Within this method, we retrieve the current scaling factor and adjust the scale of the control based on this factor.

It is worth noting that when setting the scale ratio, we use the setScaleX and setScaleY methods, which are used to set the scale ratio of the control on the X and Y axes, respectively.

With that, we have successfully implemented the zoom feature for controls in Android.