ZoomGestureDetector

Artifact: androidx.camera.viewfinder:viewfinder-core

Added in 1.5.0

Kotlin |Java

public final class ZoomGestureDetector

Detector that interprets MotionEvents and notify users when a zooming gesture has occurred.

To use this class to do pinch-to-zoom on the viewfinder:

In the OnZoomGestureListener.onZoomEvent, when receiving ZoomEvent.Move, get the ZoomEvent.Move.incrementalScaleFactor and use the value with CameraControl.setZoomRatio if the factor is in the range of ZoomState.getMinZoomRatio and ZoomState.getMaxZoomRatio. Then create an instance of the ZoomGestureDetector with the OnZoomGestureListener.
In the View.onTouchEvent, call onTouchEvent and pass the MotionEvents to the ZoomGestureDetector.

import androidx.camera.viewfinder.core.ZoomGestureDetector
import androidx.camera.viewfinder.core.ZoomGestureDetector.ZoomEvent

val zoomGestureDetector =
    ZoomGestureDetector(context) { zoomEvent ->
        when (zoomEvent) {
            is ZoomEvent.Move -> {
                val zoomState = camera.cameraInfo.zoomState.value!!
                val ratio = zoomState.zoomRatio * zoomEvent.incrementalScaleFactor
                val minRatio = zoomState.minZoomRatio
                val maxRatio = zoomState.maxZoomRatio
                val clampedRatio = min(max(ratio, minRatio), maxRatio)
                camera.cameraControl.setZoomRatio(clampedRatio)
            }
            is ZoomEvent.Begin -> {
                // Handle the begin event. For example, determine whether this gesture
                // should be processed further.
            }
            is ZoomEvent.End -> {
                // Handle the end event. For example, show a UI indicator.
            }
        }
        true
    }

return zoomGestureDetector.onTouchEvent(event)

Summary

Nested types
`public fun interface ZoomGestureDetector.OnZoomGestureListener` The listener for receiving notifications when gestures occur.
`public abstract class ZoomGestureDetector.ZoomEvent` The zoom event that contains extended info about event state.
`public final class ZoomGestureDetector.ZoomEvent.Begin extends ZoomGestureDetector.ZoomEvent` The beginning of a zoom gesture.
`public final class ZoomGestureDetector.ZoomEvent.End extends ZoomGestureDetector.ZoomEvent` The end of a zoom gesture.
`public final class ZoomGestureDetector.ZoomEvent.Move extends ZoomGestureDetector.ZoomEvent` The moving events of a gesture in progress.

Public constructors
`ZoomGestureDetector( @NonNull Context context, @Px int spanSlop, @Px int minSpan, @NonNull ZoomGestureDetector.OnZoomGestureListener listener )` Creates a ZoomGestureDetector for detecting zooming gesture.

Public methods
`final long`	`getTimeDelta()` Returns the time difference in milliseconds between the previous accepted zooming event and the current zooming event.
`final boolean`	`isQuickZoomEnabled()` Whether the quick zoom gesture, in which the user performs a double tap followed by a swipe, should perform zooming.
`final boolean`	`isStylusZoomEnabled()` Whether the stylus zoom gesture, in which the user uses a stylus and presses the button, should perform zooming.
`final boolean`	`@UiThread onTouchEvent(@NonNull MotionEvent event)` Accepts `MotionEvent`s and dispatches events to a `OnZoomGestureListener` when appropriate.
`final void`	`setQuickZoomEnabled(boolean value)` Whether the quick zoom gesture, in which the user performs a double tap followed by a swipe, should perform zooming.
`final void`	`setStylusZoomEnabled(boolean value)` Whether the stylus zoom gesture, in which the user uses a stylus and presses the button, should perform zooming.

Public constructors

ZoomGestureDetector

Added in 1.5.0

public ZoomGestureDetector(
    @NonNull Context context,
    @Px int spanSlop,
    @Px int minSpan,
    @NonNull ZoomGestureDetector.OnZoomGestureListener listener
)

Creates a ZoomGestureDetector for detecting zooming gesture.

Parameters
`@NonNull Context context`	The application context.
`@Px int spanSlop`	The distance in pixels touches can wander before a gesture to be interpreted as zooming.
`@Px int minSpan`	The distance in pixels between touches that must be reached for a gesture to be interpreted as zooming.
`@NonNull ZoomGestureDetector.OnZoomGestureListener listener`	The listener to receive the callback.

Public methods

getTimeDelta

Added in 1.5.0

public final long getTimeDelta()

Returns the time difference in milliseconds between the previous accepted zooming event and the current zooming event.

Returns
`long`	Time difference since the last zooming event in milliseconds.

isQuickZoomEnabled

Added in 1.5.0

public final boolean isQuickZoomEnabled()

Whether the quick zoom gesture, in which the user performs a double tap followed by a swipe, should perform zooming.

If not set, this is enabled by default.

isStylusZoomEnabled

Added in 1.5.0

public final boolean isStylusZoomEnabled()

Whether the stylus zoom gesture, in which the user uses a stylus and presses the button, should perform zooming.

If not set, this is enabled by default.

onTouchEvent

Added in 1.5.0

@UiThread
public final boolean onTouchEvent(@NonNull MotionEvent event)

Accepts MotionEvents and dispatches events to a OnZoomGestureListener when appropriate.

Applications should pass a complete and consistent event stream to this method.

A complete and consistent event stream involves all MotionEvents from the initial MotionEvent.ACTION_DOWN to the final MotionEvent.ACTION_UP or MotionEvent.ACTION_CANCEL.

Parameters
`@NonNull MotionEvent event`	The event to process.

Returns
`boolean`	`true` if the event was processed and the detector wants to receive the rest of the `MotionEvent`s in this event stream. Return it in the `View.onTouchEvent` for a normal use case.

setQuickZoomEnabled

Added in 1.5.0

public final void setQuickZoomEnabled(boolean value)

Whether the quick zoom gesture, in which the user performs a double tap followed by a swipe, should perform zooming.

If not set, this is enabled by default.

setStylusZoomEnabled

Added in 1.5.0

public final void setStylusZoomEnabled(boolean value)

Whether the stylus zoom gesture, in which the user uses a stylus and presses the button, should perform zooming.

If not set, this is enabled by default.

ZoomGestureDetector

Summary

Nested types

Public constructors

Public methods

Public constructors

ZoomGestureDetector

Public methods

getTimeDelta

isQuickZoomEnabled

isStylusZoomEnabled

onTouchEvent

setQuickZoomEnabled

setStylusZoomEnabled