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What are Branches?

Drawees are made up of different image “branches”, one or more of which may be actually displayed at a time.

This page outlines the different branches that can be displayed in a Drawee, and how they are set.

Except for the actual image, all of them can be set by an XML attribute. The value in XML must be either an Android drawable or color resource.

They can also be set by a method in the GenericDraweeHierarchyBuilder class, if setting programmatically. In code, the value can either be from resources or be a custom subclass of Drawable.

Some of the items can even be changed on the fly after the hierarchy has been built. These have a method in the GenericDraweeHierarchy class.

Several of the drawables can be scaled.

Actual

The actual image is the target; everything else is either an alternative or a decoration. This is specified using a URI, which can point to an image over the Internet, a local file, a resource, or a content provider.

This is a property of the controller, not the hierarchy. It therefore is not set by any of the methods used by the other Drawee branches.

Instead, use the setImageURI method or set a controller programmatically.

In addition to the scale type, the hierarchy exposes other methods only for the actual image. These are:

  • the focus point (used for the focusCrop scale type only)
  • a color filter

Default scale type: centerCrop

Placeholder

The placeholder is shown in the Drawee when it first appears on screen. After you have called setController or setImageURI to load an image, the placeholder continues to be shown until the image has loaded.

In the case of a progressive JPEG, the placeholder only stays until your image has reached the quality threshold, whether the default, or one set by your app.

XML attribute: placeholderImage Hierarchy builder method: setPlaceholderImage Hierarchy mutation method: setPlaceholderImage Default value: None Default scale type: centerInside

Failure

The failure image appears if there is an error loading your image. The most common cause of this is an invalid URI, or lack of connection to the network.

XML attribute: failureImage Hierarchy builder method: setFailureImage Hierarchy mutation method: setFailureImage Default value: None Default scale type: centerInside

Retry

The retry image appears instead of the failure image if you have set your controller to enable the tap-to-retry feature.

You must build your own Controller to do this. Then add the following line

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.setTapToRetryEnabled(true)

The image pipeline will then attempt to retry an image if the user taps on it. Up to four attempts are allowed before the failure image is shown instead.

XML attribute: retryImage Hierarchy builder method: setRetryImage Hierarchy mutation method: setRetryImage Default value: None Default scale type: centerInside

Progress Bar

If specified, the progress bar image is shown as an overlay over the Drawee until the final image is set.

For more details, see the progress bar page.

XML attribute: progressBarImage Hierarchy builder method: setProgressBarImage Hierarchy mutation method: setProgressBarImage Default value: None Default scale type: centerInside

Backgrounds

Background drawables are drawn first, “under” the rest of the hierarchy.

Only one can be specified in XML, but in code more than one can be set. In that case, the first one in the list is drawn first, at the bottom.

Background images don’t support scale-types and are scaled to the Drawee size.

XML attribute: backgroundImage Hierarchy builder method: setBackground, setBackgrounds Default value: None Default scale type: N/A

Overlays

Overlay drawables are drawn last, “over” the rest of the hierarchy.

Only one can be specified in XML, but in code more than one can be set. In that case, the first one in the list is drawn first, at the bottom.

Overlay images don’t support scale-types and are scaled to the Drawee size.

XML attribute: overlayImage Hierarchy builder method: setOverlay, setOverlays Default value: None Default scale type: N/A

Pressed State Overlay

The pressed state overlay is a special overlay shown only when the user presses the screen area of the Drawee. For example, if the Drawee is showing a button, this overlay could have the button change color when pressed.

The pressed state overlay doesn’t support scale-types.

XML attribute: pressedStateOverlayImage Hierarchy builder method: setPressedStateOverlay Default value: None Default scale type: N/A