我如何可以扩展使用共享单元转换textviews？ [英] How can I scale textviews using shared element transitions?

问题描述

我能够得到TextViews完美两项活动之间使用 ActivityOptions.makeSceneTransitionAnimation 过渡。不过，我想使文本向上扩展，因为它的转换。我可以看到材料设计实例在接触扩大文本阿方索Engelking卡过渡。

I am able to get TextViews to transition perfectly between two activities using ActivityOptions.makeSceneTransitionAnimation. However I want to make the text scale up as it transitions. I can see the material design example scaling up the text "Alphonso Engelking" in the contact card transition.

我试过设置目的地TextView的规模属性和使用changeTransform共享元素的过渡，但它不能扩展和文本最终被截断，因为它的转换。

I've tried setting the scale attributes on the destination TextView and using the changeTransform shared element transitions, but it doesn't scale and the text ends up being truncated as it transitions.

我如何可以扩展使用共享单元转换TextViews？

How can I scale TextViews using shared element transition?

推荐答案

您可以创建动画一个的TextView 的文字大小的自定义转换如下：

You can create a custom transition that animates a TextView's text size as follows:

public class TextSizeTransition extends Transition {
    private static final String PROPNAME_TEXT_SIZE = "alexjlockwood:transition:textsize";
    private static final String[] TRANSITION_PROPERTIES = { PROPNAME_TEXT_SIZE };

    private static final Property<TextView, Float> TEXT_SIZE_PROPERTY =
            new Property<TextView, Float>(Float.class, "textSize") {
                @Override
                public Float get(TextView textView) {
                    return textView.getTextSize();
                }

                @Override
                public void set(TextView textView, Float textSizePixels) {
                    textView.setTextSize(TypedValue.COMPLEX_UNIT_PX, textSizePixels);
                }
            };

    public TextSizeTransition() {
    }

    public TextSizeTransition(Context context, AttributeSet attrs) {
        super(context, attrs);
    }

    @Override
    public String[] getTransitionProperties() {
        return TRANSITION_PROPERTIES;
    }

    @Override
    public void captureStartValues(TransitionValues transitionValues) {
        captureValues(transitionValues);
    }

    @Override
    public void captureEndValues(TransitionValues transitionValues) {
        captureValues(transitionValues);
    }

    private void captureValues(TransitionValues transitionValues) {
        if (transitionValues.view instanceof TextView) {
            TextView textView = (TextView) transitionValues.view;
            transitionValues.values.put(PROPNAME_TEXT_SIZE, textView.getTextSize());
        }
    }

    @Override
    public Animator createAnimator(ViewGroup sceneRoot, TransitionValues startValues, 
                                   TransitionValues endValues) {
        if (startValues == null || endValues == null) {
            return null;
        }

        Float startSize = (Float) startValues.values.get(PROPNAME_TEXT_SIZE);
        Float endSize = (Float) endValues.values.get(PROPNAME_TEXT_SIZE);
        if (startSize == null || endSize == null || 
            startSize.floatValue() == endSize.floatValue()) {
            return null;
        }

        TextView view = (TextView) endValues.view;
        view.setTextSize(TypedValue.COMPLEX_UNIT_PX, startSize);
        return ObjectAnimator.ofFloat(view, TEXT_SIZE_PROPERTY, startSize, endSize);
    }
}

由于改变了的TextView 的文本尺寸将导致其布局界限，以动画的过程中改变，让过渡到正常工作将需要一些更多的努力不是简单地抛出一个 ChangeBounds 过渡到同一个 TransitionSet 。什么，你需要做的是手动测量/布局视图在其结束状态的 SharedElementCallback 。

Since changing the TextView's text size will cause its layout bounds to change during the course of the animation, getting the transition to work properly will take a little more effort than simply throwing a ChangeBounds transition into the same TransitionSet. What you will need to do instead is manually measure/layout the view in its end state in a SharedElementCallback.

我已经发布实例项目 GitHub上 这说明了这个概念（请注意，该项目定义了两个摇篮产品的口味......人使用活动转变，另一个使用片段转换）。

I've published an example project on GitHub that illustrates the concept (note that the project defines two Gradle product flavors... one uses Activity Transitions and the other uses Fragment Transitions).

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