Android动画分析之3D翻转效果

Android中的翻转动画效果的实现，首先看一下运行效果如上图所示.

Android中并没有提供直接做3D翻转的动画，所以关于3D翻转的动画效果需要我们自己实现，那么我们首先来分析一下Animation 和 Transformation。

Animation动画的主要接口，其中主要定义了动画的一些属性比如开始时间，持续时间，是否重复播放等等。而Transformation中则包含一个矩阵和alpha值，矩阵是用来做平移，旋转和缩放动画的，而alpha值是用来做alpha动画的，要实现3D旋转动画我们需要继承自Animation类来实现，我们需要重载getTransformation和applyTransformation，在getTransformation中Animation会根据动画的属性来产生一系列的差值点，然后将这些差值点传给applyTransformation，这个函数将根据这些点来生成不同的Transformation。下面是具体实现：

package com.example.textviewtest;

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

public class Rotate3dAnimation extends Animation {
	// 开始角度
	private final float mFromDegrees;
	// 结束角度
	private final float mToDegrees;
	// 中心点
	private final float mCenterX;
	private final float mCenterY;
	private final float mDepthZ;
	// 是否需要扭曲
	private final boolean mReverse;
	// 摄像头
	private Camera mCamera;

	public Rotate3dAnimation(float fromDegrees, float toDegrees, float centerX,
			float centerY, float depthZ, boolean reverse) {
		mFromDegrees = fromDegrees;
		mToDegrees = toDegrees;
		mCenterX = centerX;
		mCenterY = centerY;
		mDepthZ = depthZ;
		mReverse = reverse;
	}

	@Override
	public void initialize(int width, int height, int parentWidth,
			int parentHeight) {
		super.initialize(width, height, parentWidth, parentHeight);
		mCamera = new Camera();
	}

	// 生成Transformation
	@Override
	protected void applyTransformation(float interpolatedTime, Transformation t) {
		final float fromDegrees = mFromDegrees;
		// 生成中间角度
		float degrees = fromDegrees
				+ ((mToDegrees - fromDegrees) * interpolatedTime);

		final float centerX = mCenterX;
		final float centerY = mCenterY;
		final Camera camera = mCamera;

		final Matrix matrix = t.getMatrix();

		camera.save();
		if (mReverse) {
			camera.translate(0.0f, 0.0f, mDepthZ * interpolatedTime);
		} else {
			camera.translate(0.0f, 0.0f, mDepthZ * (1.0f - interpolatedTime));
		}
		camera.rotateY(degrees);
		// 取得变换后的矩阵
		camera.getMatrix(matrix);
		camera.restore();

		matrix.preTranslate(-centerX, -centerY);
		matrix.postTranslate(centerX, centerY);
	}
}

其中包括了旋转的开始和结束角度，中心点、是否扭曲、和一个Camera，这里我们主要分析applyTransformation函数，其中第一个参数就是通过getTransformation函数传递的差指点，然后我们根据这个差值通过线性差值算法计算出一个中间角度degrees，Camera类是用来实现绕Y轴旋转后透视投影的，因此我们首先通过t.getMatrix()取得当前的矩阵，然后通过camera.translate来对矩阵进行平移变换操作，camera.rotateY进行旋转。这样我们就可以很轻松的实现3D旋转效果了。

下面是布局文件main.xml:

MainActivity的代码如下：

package com.example.textviewtest;

import android.app.Activity;
import android.os.Bundle;
import android.view.Menu;
import android.view.View;
import android.view.animation.AccelerateInterpolator;
import android.view.animation.Animation;
import android.view.animation.DecelerateInterpolator;
import android.widget.Button;
import android.widget.TextView;

public class MainActivity extends Activity {
	private TextView tv;
	private Button btn;
	private int count = 1;

	@Override
	protected void onCreate(Bundle savedInstanceState) {
		super.onCreate(savedInstanceState);
		setContentView(R.layout.activity_main);
		tv = (TextView) findViewById(R.id.tv);
		tv.setText(String.valueOf(count));
		btn = (Button) findViewById(R.id.next_btn);
		applyRotation(0, 90);

		btn.setOnClickListener(new View.OnClickListener() {

			@Override
			public void onClick(View v) {
				applyRotation(0, 90);
			}
		});

	}

	private void applyRotation(float start, float end) {
		// 计算中心点
		final float centerX = tv.getWidth() / 2.0f;
		final float centerY = tv.getHeight() / 2.0f;

		final Rotate3dAnimation rotation = new Rotate3dAnimation(start, end,
				centerX, centerY, 310.0f, true);
		rotation.setDuration(500);
		rotation.setFillAfter(true);
		rotation.setInterpolator(new AccelerateInterpolator());
		// 设置监听
		rotation.setAnimationListener(new DisplayNextView());

		tv.startAnimation(rotation);
	}

	private final class DisplayNextView implements Animation.AnimationListener {

		public void onAnimationStart(Animation animation) {
		}

		// 动画结束
		public void onAnimationEnd(Animation animation) {
			tv.post(new SwapViews());
		}

		public void onAnimationRepeat(Animation animation) {
		}
	}

	private final class SwapViews implements Runnable {

		public void run() {
			final float centerX = tv.getWidth() / 2.0f;
			final float centerY = tv.getHeight() / 2.0f;
			Rotate3dAnimation rotation = null;

			tv.requestFocus();

			rotation = new Rotate3dAnimation(90, 0, centerX, centerY, 310.0f,
					false);
			rotation.setDuration(500);
			rotation.setFillAfter(true);
			rotation.setInterpolator(new DecelerateInterpolator());
			// 开始动画
			tv.startAnimation(rotation);
			tv.setText(String.valueOf(count++));
		}
	}

	@Override
	public boolean onCreateOptionsMenu(Menu menu) {
		getMenuInflater().inflate(R.menu.activity_main, menu);
		return true;
	}

}

看懂了吗？呵呵。