Android 超好用的 ValueAnimator Tween類別

大家好，我是奶綠茶
在開發 Android, 經常會需要做一些動畫
在新版的 SDK 裡有個 ValueAnimator 可以使用
法簡單好學, 寫起來跟 Flash 的 TweenMax 差不多, 這就是我們要的
可惜官方說需要 SDK 11 以上的機子才能跑
經過測試也還真的需要 11 以上, (11 是代號 HoneyComb)
後來想到 Android 是 OpenSource, 就把他的類別拿來改一下, 這樣就可以在 2.2 的舊機子上使用

轉載請註明出處

bounceAnim = ValueAnimator.ofFloat( 起始值, 目標值);
bounceAnim.setDuration( 1500 ); // 時間
bounceAnim.addUpdateListener 偵聽更新事件。

看吧，簡單好學, 不過這樣的方法依然無法使用 ObjectAnimator 這個類別, 反正 ValueAnimator 就己經夠用了 以下程式碼是改至官方提供的 API, 我把他改成 2.2 也可以跑的範例

package milkmidi.demo;

import java.util.ArrayList;

import milkmidi.android.animation.ValueAnimator;
import android.app.Activity;
import android.content.Context;
import android.graphics.Canvas;
import android.graphics.Paint;
import android.graphics.RadialGradient;
import android.graphics.Shader;
import android.graphics.drawable.ShapeDrawable;
import android.graphics.drawable.shapes.OvalShape;
import android.os.Bundle;
import android.view.View;
import android.view.animation.AccelerateInterpolator;
import android.widget.Button;
import android.widget.LinearLayout;

public class Ch6_05_sdk15ExampleActivity extends Activity {
 @Override
 public void onCreate( Bundle savedInstanceState ) {
  super.onCreate( savedInstanceState );
  setContentView( R.layout.animation_reversing );
  LinearLayout container = (LinearLayout) findViewById( R.id.container );
  final MyAnimationView animView = new MyAnimationView( this );
  container.addView( animView );

  Button starter = (Button) findViewById( R.id.startButton );
  starter.setOnClickListener( new View.OnClickListener() {
   public void onClick( View v ) {
    animView.startAnimation();
   }
  } );

  Button reverser = (Button) findViewById( R.id.reverseButton );
  reverser.setOnClickListener( new View.OnClickListener() {
   public void onClick( View v ) {
    animView.reverseAnimation();
   }
  } );

 }

 public class MyAnimationView extends View  {

  public final ArrayList balls  = new ArrayList();
  ValueAnimator      bounceAnim = null;
  ShapeHolder       ball  = null;

  public MyAnimationView( Context context ) {
   super( context );
   ball = createBall( 25, 25 );
  }

  private void createAnimation() {
   if ( bounceAnim == null ) {  
    // 這個不能使用
    //bounceAnim = ObjectAnimator.ofFloat(ball, "y", ball.getY(), getHeight() - 50f);
    bounceAnim = ValueAnimator.ofFloat( ball.getY(), getHeight() - 50f );
    bounceAnim.setDuration( 1500 );   
    bounceAnim.addUpdateListener(new ValueAnimator.AnimatorUpdateListener() {
           public void onAnimationUpdate(ValueAnimator animation) {
            //float valueY = (Float)animation.getAnimatedValue("y");            
            float value = (Float) animation.getAnimatedValue();
            ball.setY( value );
            invalidate();
           }
       });
    bounceAnim.setInterpolator( new AccelerateInterpolator( 2f ) );
   }
  }

  public void startAnimation() {
   createAnimation();
   bounceAnim.start();
  }

  public void reverseAnimation() {
   createAnimation();
   bounceAnim.reverse();
  }

  public void seek( long seekTime ) {
   createAnimation();
   bounceAnim.setCurrentPlayTime( seekTime );
  }

  private ShapeHolder createBall( float x, float y ) {
   OvalShape circle = new OvalShape();
   circle.resize( 50f, 50f );
   ShapeDrawable drawable = new ShapeDrawable( circle );
   ShapeHolder shapeHolder = new ShapeHolder( drawable );
   shapeHolder.setX( x - 25f );
   shapeHolder.setY( y - 25f );
   int red = (int) (Math.random() * 255);
   int green = (int) (Math.random() * 255);
   int blue = (int) (Math.random() * 255);
   int color = 0xff000000 | red << 16 | green << 8 | blue;
   Paint paint = drawable.getPaint(); // new
            // Paint(Paint.ANTI_ALIAS_FLAG);
   int darkColor = 0xff000000 | red / 4 << 16 | green / 4 << 8 | blue
     / 4;
   RadialGradient gradient = new RadialGradient( 37.5f, 12.5f, 50f,
     color, darkColor, Shader.TileMode.CLAMP );
   paint.setShader( gradient );
   shapeHolder.setPaint( paint );
   return shapeHolder;
  }

  @Override
  protected void onDraw( Canvas canvas ) {
   canvas.save();
   canvas.translate( ball.getX(), ball.getY() );
   ball.getShape().draw( canvas );
   canvas.restore();
  }


 }
}

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