ArcShape 的 Android 自定义动画

问题描述

首先让我解释一下我的目标.我正在尝试制作一个 Animation 来改变 ArcShape 的属性.ArcShape 的 构造函数采用两个字段:startAngle 和 sweepAngle.我想为 sweepAngle 设置动画，使其在屏幕上显示为一个不断缩小的圆圈.

First let me explain my goal. I am trying to make an Animation that changes the properties of an ArcShape. An ArcShape's constructor takes two fields: startAngle and sweepAngle. I want to animate the sweepAngle so that it appears on screen as a continuously shrinking circle.

你可以想象吃豆人来描绘这个动画.想象他的嘴是闭着的.这个动画类似于他越来越多地张开上颚，直到没有吃豆人.

You can picture this animation by imagining PacMan. Imagine his mouth is closed. This animation would be akin to him opening his upper jaw more and more until there was no more PacMan.

现在...我在实现这个时遇到了一些问题.首先，一旦创建了 ArcShape，就没有内置的方法可以改变它的 sweepAngle.这让我想到了我的第一个问题:有没有办法覆盖 ArcShape 并实现一些 setSweepAngle 方法?或者我是否必须为我希望显示的每个 sweepAngle 创建一个 new ArcShape?

Now... I have a couple of issues with implementing this. First, once an ArcShape is created, there are no built in methods of changing it's sweepAngle. This brings me to my first question: Is there any way to override ArcShape and implement some setSweepAngle method? Or will I have to create a new ArcShape for each sweepAngle I wish to display?

现在进入第二个问题...假设我找到了第一个问题的解决方案，我该如何创建这个Animation?这是我现在拥有的要点:

Now on to the second issue... Assuming I found a solution to the first issue, how could I create this Animation? This is the gist of what I have now:

public class OpenPacman extends Animation {
  public OpenPacman(float startAngle, float sweepAngle) {
    mStartAngle = startAngle;
    mSweepAngle = sweepAngle;
  }

  @Override
  protected void applyTransformation(float interpolatedTime, Transformation t) {
    /* This represents the current sweepAngle */
    float currAngle = mStartAngle + ((mSweepAngle - mStartAngle) * interpolatedTime);

    //Now I need to update the ArcShape's sweepAngle to currAngle. But HOW?
  }
}

推荐答案

我找到了解决方案.我有一个扩展 View 的类我们称之为 Pacman 我在这个 Pacman 类中嵌套了我的自定义 Animation.这允许我访问 Pacman 类的 成员变量.

I have found a solution. I have a class that extends View We'll call this Pacman I nested my custom Animation within this Pacman class. This allowed me to access the member variables of the Pacman class.

public class Pacman extends View {
  float mSweepAngle;
  ...
  //include constructors
  //override onMeasure
  ...

  /* Here we override onDraw */
  @Override
  protected void onDraw(final Canvas canvas) {
    Paint p = new Paint(Paint.ANTI_ALIAS_FLAG);
    RectF oval = new RectF(canvas.getClipBounds());
    canvas.drawArc(oval, 0, mCurrAngle, true, p);
  }

  /* Here we define our nested custom animation */
  public class OpenPacman extends Animation {
    float mStartAngle;
    float mSweepAngle;

    public OpenPacman (int startAngle, int sweepAngle, long duration) {
      mStartAngle = startAngle;
      mSweepAngle = sweepAngle;
      setDuration(duration);
      setInterpolator(new LinearInterpolator());
    }

    @Override
    protected void applyTransformation(float interpolatedTime, Transformation t) {
      float currAngle = mStartAngle + ((mSweepAngle - mStartAngle) * interpolatedTime);
      Pacman.this.mCurrAngle = -currAngle; //negative for counterclockwise animation.
    }
  }
}

现在，当自定义动画更新容器类 mCurrAngle 时，会自动调用 onDraw，从而绘制适当的 ArcShape.

Now when the custom animation updates the container classes mCurrAngle, onDraw is automatically called, which draws the appropriate ArcShape.

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