Android中的动画详解系列【3】——自定义动画研究

在上一篇中我们使用到了位移动画TranslateAnimation,下面我们先来看看TranslateAnimation是如何实现Animation中的抽象方法的：

/*
 * Copyright (C) 2006 The Android Open Source Project
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package android.view.animation;

import android.content.Context;
import android.content.res.TypedArray;
import android.util.AttributeSet;

/**
 * An animation that controls the position of an object. See the
 * {@link android.view.animation full package} description for details and
 * sample code.
 *
 */
public class TranslateAnimation extends Animation {
    private int mFromXType = ABSOLUTE;
    private int mToXType = ABSOLUTE;

    private int mFromYType = ABSOLUTE;
    private int mToYType = ABSOLUTE;

    private float mFromXValue = 0.0f;
    private float mToXValue = 0.0f;

    private float mFromYValue = 0.0f;
    private float mToYValue = 0.0f;

    private float mFromXDelta;
    private float mToXDelta;
    private float mFromYDelta;
    private float mToYDelta;

    /**
     * Constructor used when a TranslateAnimation is loaded from a resource.
     *
     * @param context Application context to use
     * @param attrs Attribute set from which to read values
     */
    public TranslateAnimation(Context context, AttributeSet attrs) {
        super(context, attrs);

        TypedArray a = context.obtainStyledAttributes(attrs,
                com.android.internal.R.styleable.TranslateAnimation);

        Description d = Description.parseValue(a.peekValue(
            com.android.internal.R.styleable.TranslateAnimation_fromXDelta));
        mFromXType = d.type;
        mFromXValue = d.value;

        d = Description.parseValue(a.peekValue(
                com.android.internal.R.styleable.TranslateAnimation_toXDelta));
        mToXType = d.type;
        mToXValue = d.value;

        d = Description.parseValue(a.peekValue(
            com.android.internal.R.styleable.TranslateAnimation_fromYDelta));
        mFromYType = d.type;
        mFromYValue = d.value;

        d = Description.parseValue(a.peekValue(
            com.android.internal.R.styleable.TranslateAnimation_toYDelta));
        mToYType = d.type;
        mToYValue = d.value;

        a.recycle();
    }

    /**
     * Constructor to use when building a TranslateAnimation from code
     *
     * @param fromXDelta Change in X coordinate to apply at the start of the
     *        animation
     * @param toXDelta Change in X coordinate to apply at the end of the
     *        animation
     * @param fromYDelta Change in Y coordinate to apply at the start of the
     *        animation
     * @param toYDelta Change in Y coordinate to apply at the end of the
     *        animation
     */
    public TranslateAnimation(float fromXDelta, float toXDelta, float fromYDelta, float toYDelta) {
        mFromXValue = fromXDelta;
        mToXValue = toXDelta;
        mFromYValue = fromYDelta;
        mToYValue = toYDelta;

        mFromXType = ABSOLUTE;
        mToXType = ABSOLUTE;
        mFromYType = ABSOLUTE;
        mToYType = ABSOLUTE;
    }

    /**
     * Constructor to use when building a TranslateAnimation from code
     *
     * @param fromXType Specifies how fromXValue should be interpreted. One of
     *        Animation.ABSOLUTE, Animation.RELATIVE_TO_SELF, or
     *        Animation.RELATIVE_TO_PARENT.
     * @param fromXValue Change in X coordinate to apply at the start of the
     *        animation. This value can either be an absolute number if fromXType
     *        is ABSOLUTE, or a percentage (where 1.0 is 100%) otherwise.
     * @param toXType Specifies how toXValue should be interpreted. One of
     *        Animation.ABSOLUTE, Animation.RELATIVE_TO_SELF, or
     *        Animation.RELATIVE_TO_PARENT.
     * @param toXValue Change in X coordinate to apply at the end of the
     *        animation. This value can either be an absolute number if toXType
     *        is ABSOLUTE, or a percentage (where 1.0 is 100%) otherwise.
     * @param fromYType Specifies how fromYValue should be interpreted. One of
     *        Animation.ABSOLUTE, Animation.RELATIVE_TO_SELF, or
     *        Animation.RELATIVE_TO_PARENT.
     * @param fromYValue Change in Y coordinate to apply at the start of the
     *        animation. This value can either be an absolute number if fromYType
     *        is ABSOLUTE, or a percentage (where 1.0 is 100%) otherwise.
     * @param toYType Specifies how toYValue should be interpreted. One of
     *        Animation.ABSOLUTE, Animation.RELATIVE_TO_SELF, or
     *        Animation.RELATIVE_TO_PARENT.
     * @param toYValue Change in Y coordinate to apply at the end of the
     *        animation. This value can either be an absolute number if toYType
     *        is ABSOLUTE, or a percentage (where 1.0 is 100%) otherwise.
     */
    public TranslateAnimation(int fromXType, float fromXValue, int toXType, float toXValue,
            int fromYType, float fromYValue, int toYType, float toYValue) {

        mFromXValue = fromXValue;
        mToXValue = toXValue;
        mFromYValue = fromYValue;
        mToYValue = toYValue;

        mFromXType = fromXType;
        mToXType = toXType;
        mFromYType = fromYType;
        mToYType = toYType;
    }

    @Override
    protected void applyTransformation(float interpolatedTime, Transformation t) {
        float dx = mFromXDelta;
        float dy = mFromYDelta;
        if (mFromXDelta != mToXDelta) {
            dx = mFromXDelta + ((mToXDelta - mFromXDelta) * interpolatedTime);
        }
        if (mFromYDelta != mToYDelta) {
            dy = mFromYDelta + ((mToYDelta - mFromYDelta) * interpolatedTime);
        }
        t.getMatrix().setTranslate(dx, dy);
    }

    @Override
    public void initialize(int width, int height, int parentWidth, int parentHeight) {
        super.initialize(width, height, parentWidth, parentHeight);
        mFromXDelta = resolveSize(mFromXType, mFromXValue, width, parentWidth);
        mToXDelta = resolveSize(mToXType, mToXValue, width, parentWidth);
        mFromYDelta = resolveSize(mFromYType, mFromYValue, height, parentHeight);
        mToYDelta = resolveSize(mToYType, mToYValue, height, parentHeight);
    }

可以看到实际上重写了两个方法：initialize和applyTransformation

    /**
     * Initialize this animation with the dimensions of the object being
     * animated as well as the objects parents. (This is to support animation
     * sizes being specifed relative to these dimensions.)
     *
     * <p>Objects that interpret Animations should call this method when
     * the sizes of the object being animated and its parent are known, and
     * before calling {@link #getTransformation}.
     *
     *
     * @param width Width of the object being animated
     * @param height Height of the object being animated
     * @param parentWidth Width of the animated object's parent
     * @param parentHeight Height of the animated object's parent
     */
    public void initialize(int width, int height, int parentWidth, int parentHeight) {
        reset();
        mInitialized = true;
    }

    /**
     * Helper for getTransformation. Subclasses should implement this to apply
     * their transforms given an interpolation value.  Implementations of this
     * method should always replace the specified Transformation or document
     * they are doing otherwise.
     *
     * @param interpolatedTime The value of the normalized time (0.0 to 1.0)
     *        after it has been run through the interpolation function.
     * @param t The Transofrmation object to fill in with the current
     *        transforms.
     */
    protected void applyTransformation(float interpolatedTime, Transformation t) {
    }

从initialize方法的注释上看，这个方法的主要作用是：初始化对象的尺寸以及父容器尺寸（为了确定和父容器的相对位置）。

从applyTransformation方法的注释上看，这个方法应该被实现，这个方法给出了一个interpolation值，并帮助获得Transformation对象，应该自己设置transformation对象来实现自己的动画效果。

好吧，基于以上研究，我们试着来重写一个Animation

package com.example.testanimation;

import android.graphics.Camera;
import android.graphics.Matrix;
import android.view.animation.Animation;
import android.view.animation.LinearInterpolator;
import android.view.animation.Transformation;

/**
 * 自定义动画
 * @author 阳光小强
 *
 */
public class MyAnimation extends Animation{

	private float centerX;
	private float centerY;
	private int duration;
	private Camera camera = new Camera();
	public MyAnimation(float x, float y, int duration){
		this.centerX = x;
		this.centerY = y;
		this.duration = duration;
	}

	@Override
	public void initialize(int width, int height, int parentWidth,
			int parentHeight) {
		super.initialize(width, height, parentWidth, parentHeight);

		setDuration(duration);

		setFillAfter(true);

		setInterpolator(new LinearInterpolator());
	}

	@Override
	protected void applyTransformation(float interpolatedTime, Transformation t) {
		camera.save();
		camera.translate(100f - 100f * interpolatedTime, 150f * interpolatedTime -150, 80f - 80f * interpolatedTime);
		camera.rotateY(360 * interpolatedTime);
		camera.rotateX(360 * interpolatedTime);
		Matrix matrix = t.getMatrix();
		camera.getMatrix(matrix);
		matrix.preTranslate(-centerX,  -centerY);
		matrix.postTranslate(centerX, centerY);
		camera.restore();
	}
}

代码解释：

1、setDuration(duration):设置动画时间

2、setFillAfter(true):设置动画结束后保持，如果设为false则动画结束后回到原来状态。

3、setInterpolator(new LinearInterpolator()):Interpolater实际上是控制补间动画的插入帧的频率的，所以就会有加速、减速、匀速动画。

4、Camera:一个空间变换工具，类似于Matrix，提供了各种变换方法，如上面的translate和rotateY等。

5、Matrix:一个三维的矩阵变换函数。

6、camera.getMatrix(matrix):计算当前的矩阵变换，并将其复制到矩阵matrix中。

7、matrix.preTranslate :执行矩阵指定的转换。

8、matrix.postTranslate:执行矩阵指定的转换（后面两个方法怎么转换，有什么区别，这就是数学知识了，一两句也说不清）。