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PreviewView

public class PreviewView
extends FrameLayout

java.lang.Object
   ↳ android.view.View
     ↳ android.view.ViewGroup
       ↳ android.widget.FrameLayout
         ↳ androidx.camera.view.PreviewView


Custom View that displays the camera feed for CameraX's Preview use case.

This class manages the Surface lifecycle, as well as the preview aspect ratio and orientation. Internally, it uses either a TextureView or SurfaceView to display the camera feed.

If PreviewView uses a SurfaceView to display the preview stream, be careful when overlapping a View that's initially not visible (either View.INVISIBLE or View.GONE) on top of it. When the SurfaceView is attached to the display window, it calls ViewParent.requestTransparentRegion(View) which requests a computation of the transparent regions on the display. At this point, the View isn't visible, causing the overlapped region between the SurfaceView and the View to be considered transparent. Later if the View becomes visible, it will not be displayed on top of SurfaceView. A way around this is to call ViewParent.requestTransparentRegion(View) right after making the View visible, or initially hiding the View by setting its opacity to 0, then setting it to 1.0F to show it.

Summary

Nested classes

enum PreviewView.ImplementationMode

The implementation mode of a PreviewView

enum PreviewView.ScaleType

Options for scaling the preview vis-à-vis its container PreviewView

enum PreviewView.StreamState

Definitions for current preview stream state. 

Inherited constants

Inherited fields

Public constructors

PreviewView(Context context)
PreviewView(Context context, AttributeSet attrs)
PreviewView(Context context, AttributeSet attrs, int defStyleAttr)
PreviewView(Context context, AttributeSet attrs, int defStyleAttr, int defStyleRes)

Public methods

Bitmap getBitmap()

Returns a Bitmap representation of the content displayed on the preview Surface, or null if the camera preview hasn't started yet.

PreviewView.ImplementationMode getImplementationMode()

Returns the PreviewView.ImplementationMode.

MeteringPointFactory getMeteringPointFactory()

Gets the MeteringPointFactory for the Camera currently connected to the PreviewView.

LiveData<PreviewView.StreamState> getPreviewStreamState()

Gets the LiveData of current preview PreviewView.StreamState.

PreviewView.ScaleType getScaleType()

Returns the PreviewView.ScaleType currently applied to the preview.

Preview.SurfaceProvider getSurfaceProvider()

Gets the Preview.SurfaceProvider to be used with Preview.setSurfaceProvider(Executor, Preview.SurfaceProvider).

ViewPort getViewPort()

Gets a ViewPort based on the current status of PreviewView.

ViewPort getViewPort(int targetRotation)

Gets a ViewPort with custom target rotation.

boolean onTouchEvent(MotionEvent event)
void setImplementationMode(PreviewView.ImplementationMode implementationMode)

Sets the PreviewView.ImplementationMode for the PreviewView.

void setScaleType(PreviewView.ScaleType scaleType)

Applies a PreviewView.ScaleType to the preview.

Protected methods

void onAttachedToWindow()
void onDetachedFromWindow()

Inherited methods

Public constructors

PreviewView

public PreviewView (Context context)

Parameters
context Context

PreviewView

public PreviewView (Context context, 
                AttributeSet attrs)

Parameters
context Context

attrs AttributeSet

PreviewView

public PreviewView (Context context, 
                AttributeSet attrs, 
                int defStyleAttr)

Parameters
context Context

attrs AttributeSet

defStyleAttr int

PreviewView

public PreviewView (Context context, 
                AttributeSet attrs, 
                int defStyleAttr, 
                int defStyleRes)

Parameters
context Context

attrs AttributeSet

defStyleAttr int

defStyleRes int

Public methods

getBitmap

public Bitmap getBitmap ()

Returns a Bitmap representation of the content displayed on the preview Surface, or null if the camera preview hasn't started yet.

The returned Bitmap uses the Bitmap.Config.ARGB_8888 pixel format, and its dimensions depend on the PreviewView's PreviewView.ScaleType. When the PreviewView.ScaleType is PreviewView.ScaleType.FILL_START, PreviewView.ScaleType.FILL_CENTER or PreviewView.ScaleType.FILL_END, the returned Bitmap has the same size as the PreviewView. However, when the PreviewView.ScaleType is PreviewView.ScaleType.FIT_START, PreviewView.ScaleType.FIT_CENTER or PreviewView.ScaleType.FIT_END, the returned Bitmap might be smaller than the PreviewView, since it doesn't also include its background.

Do not invoke this method from a drawing method (View.onDraw(Canvas) for instance).

If an error occurs during the copy, an empty Bitmap will be returned.

Returns
Bitmap A Bitmap.Config.ARGB_8888 Bitmap representing the content displayed on the preview Surface, or null if the camera preview hasn't started yet.

getMeteringPointFactory

public MeteringPointFactory getMeteringPointFactory ()

Gets the MeteringPointFactory for the Camera currently connected to the PreviewView.

The returned MeteringPointFactory is capable of creating MeteringPoints from (x, y) coordinates in the PreviewView. This conversion takes into account its PreviewView.ScaleType.

When the PreviewView has a width and/or height equal to zero, or when a preview Surface is not yet requested, the returned factory will always create invalid MeteringPoints which could lead to the failure of CameraControl.startFocusAndMetering(FocusMeteringAction) but it won't cause any crash.

Returns
MeteringPointFactory a MeteringPointFactory

getPreviewStreamState

public LiveData<PreviewView.StreamState> getPreviewStreamState ()

Gets the LiveData of current preview PreviewView.StreamState.

There are two states, PreviewView.StreamState.IDLE and PreviewView.StreamState.STREAMING. PreviewView.StreamState.IDLE represents the preview is currently not visible and streaming is stopped. PreviewView.StreamState.STREAMING means the preview is streaming.

When PreviewView is in a PreviewView.StreamState.STREAMING state, it guarantees preview is visible only when implementationMode is PreviewView.ImplementationMode.COMPATIBLE. When in PreviewView.ImplementationMode.PERFORMANCE mode, it is possible that preview becomes visible slightly after state changes to PreviewView.StreamState.STREAMING. For apps relying on the preview visible signal to be working correctly, please set PreviewView.ImplementationMode.COMPATIBLE mode in setImplementationMode(PreviewView.ImplementationMode).

Returns
LiveData<PreviewView.StreamState> A LiveData containing the PreviewView.StreamState. Apps can either get current value by LiveData.getValue() or register a observer by LiveData.observe(LifecycleOwner, Observer) .

getScaleType

public PreviewView.ScaleType getScaleType ()

Returns the PreviewView.ScaleType currently applied to the preview.

By default, PreviewView.ScaleType.FILL_CENTER is applied to the preview.

Returns
PreviewView.ScaleType The PreviewView.ScaleType currently applied to the preview.

getSurfaceProvider

public Preview.SurfaceProvider getSurfaceProvider ()

Gets the Preview.SurfaceProvider to be used with Preview.setSurfaceProvider(Executor, Preview.SurfaceProvider).

The returned Preview.SurfaceProvider will provide a preview Surface to the camera that's either managed by a TextureView or SurfaceView depending on the PreviewView.ImplementationMode.

Returns
Preview.SurfaceProvider A Preview.SurfaceProvider used to start the camera preview.

getViewPort

public ViewPort getViewPort ()

Gets a ViewPort based on the current status of PreviewView.

Returns a ViewPort instance based on the PreviewView's current width, height, layout direction, scale type and display rotation. By using the ViewPort, all the UseCases in the UseCaseGroup will have the same output image that also matches the aspect ratio of the PreviewView.

Returns
ViewPort

getViewPort

public ViewPort getViewPort (int targetRotation)

Gets a ViewPort with custom target rotation.

Returns a ViewPort instance based on the PreviewView's current width, height, layout direction, scale type and the given target rotation.

Use this method if Preview's desired rotation is not the default display rotation. For example, when remote display is in use and the desired rotation for the remote display is based on the accelerometer reading. In that case, use OrientationEventListener to obtain the target rotation and create ViewPort as following:

OrientationEventListener.ORIENTATION_UNKNOWN: orientation == -1

Surface.ROTATION_0: orientation >= 315 || orientation < 45

Surface.ROTATION_90: orientation >= 225 && orientation < 315

Surface.ROTATION_180: orientation >= 135 && orientation < 225

Surface.ROTATION_270: orientation >= 45 && orientation < 135

Once the target rotation is obtained, use it with Preview.setTargetRotation(int) to update the rotation. Example:


 Preview preview = new Preview.Builder().setTargetRotation(targetRotation).build();
 ViewPort viewPort = previewView.getViewPort(targetRotation);
 UseCaseGroup useCaseGroup =
     new UseCaseGroup.Builder().setViewPort(viewPort).addUseCase(preview).build();
 cameraProvider.bindToLifecycle(this, cameraSelector, useCaseGroup);
 

Note that for non-display rotation to work, the mode must be set to PreviewView.ImplementationMode.COMPATIBLE.

Parameters
targetRotation int: A rotation value, expressed as one of Surface.ROTATION_0, Surface.ROTATION_90, Surface.ROTATION_180, or Surface.ROTATION_270.

Returns
ViewPort

onTouchEvent

public boolean onTouchEvent (MotionEvent event)

Parameters
event MotionEvent

Returns
boolean

setImplementationMode

public void setImplementationMode (PreviewView.ImplementationMode implementationMode)

Sets the PreviewView.ImplementationMode for the PreviewView.

PreviewView displays the preview with either a SurfaceView or a TextureView depending on the mode. If not set, the default value is PreviewView.ImplementationMode.PERFORMANCE.

Parameters
implementationMode PreviewView.ImplementationMode

setScaleType

public void setScaleType (PreviewView.ScaleType scaleType)

Applies a PreviewView.ScaleType to the preview.

Note that the PreviewView.ScaleType.FILL_CENTER is applied to the preview by default.

Parameters
scaleType PreviewView.ScaleType: A PreviewView.ScaleType to apply to the preview.

Protected methods

onAttachedToWindow

protected void onAttachedToWindow ()

onDetachedFromWindow

protected void onDetachedFromWindow ()