android實現上下滾動的TextView

一 說明
    這裡重要應用類 AutoTextView，這是一個自定義的類，繼承至TextSwitcher，下面臨 AutoTextView類做簡要說明：

    1. 該類應用的重點，在於設置兩個動畫， setInAnimation(...)  和 setOutAnimation(...)，分離是文字進入的動畫和文字退出的動畫；

    2. 類中定義了一個外部類-Rotate3dAnimation，重要靠該類實現文字進出動畫，該外部類繼承至Animation。說來偶合，這個恰好是在apiDemo中看到了，自定義Animation我還是第一次應用，動畫邏輯均在void applyTransformation(float interpolatedTime, Transformation t)中實現，代碼相當鋒利，我在原來的基礎上，更改了一下，實現了上述的效果，

二 代碼部分：
1.AutoTextView.java
復制代碼 代碼如下:
package com.example.animtextview;

import android.content.Context;
import android.content.res.TypedArray;
import android.graphics.Camera;
import android.graphics.Matrix;
import android.util.AttributeSet;
import android.view.Gravity;
import android.view.View;
import android.view.animation.AccelerateInterpolator;
import android.view.animation.Animation;
import android.view.animation.Transformation;
import android.widget.TextSwitcher;
import android.widget.TextView;
import android.widget.ViewSwitcher;

public class AutoTextView extends TextSwitcher implements
  ViewSwitcher.ViewFactory {

 private float mHeight;
 private Context mContext;
 //mInUp,mOutUp分離構成向下翻頁的進出動畫
 private Rotate3dAnimation mInUp;
 private Rotate3dAnimation mOutUp;

 //mInDown,mOutDown分離構成向下翻頁的進出動畫
 private Rotate3dAnimation mInDown;
 private Rotate3dAnimation mOutDown;

 public AutoTextView(Context context) {
  this(context, null);
  // TODO Auto-generated constructor stub
 }

 public AutoTextView(Context context, AttributeSet attrs) {
  super(context, attrs);
  // TODO Auto-generated constructor stub
  TypedArray a = context.obtainStyledAttributes(attrs, R.styleable.auto3d);
  mHeight = a.getDimension(R.styleable.auto3d_textSize, 36);
  a.recycle();
  mContext = context;
  init();
 }

 private void init() {
  // TODO Auto-generated method stub
  setFactory(this);
  mInUp = createAnim(-90, 0 , true, true);
  mOutUp = createAnim(0, 90, false, true);
  mInDown = createAnim(90, 0 , true , false);
  mOutDown = createAnim(0, -90, false, false);
  //TextSwitcher重要用於文件切換，比如 從文字A 切換到 文字 B，
  //setInAnimation()後，A將執行inAnimation，
  //setOutAnimation()後，B將執行OutAnimation
        setInAnimation(mInUp);
        setOutAnimation(mOutUp);
 }

 private Rotate3dAnimation createAnim(float start, float end, boolean turnIn, boolean turnUp){
        final Rotate3dAnimation rotation = new Rotate3dAnimation(start, end, turnIn, turnUp);
        rotation.setDuration(800);
        rotation.setFillAfter(false);
        rotation.setInterpolator(new AccelerateInterpolator());
        return rotation;
 }

 //這裡返回的TextView，就是我們看到的View
 @Override
 public View makeView() {
  // TODO Auto-generated method stub
  TextView t = new TextView(mContext);
  t.setGravity(Gravity.CENTER);
  t.setTextSize(mHeight);
  t.setMaxLines(2);
  return t;
 }
 //定義動作，向下滾動翻頁
 public void previous(){
  if(getInAnimation() != mInDown){
   setInAnimation(mInDown);
  }
  if(getOutAnimation() != mOutDown){
   setOutAnimation(mOutDown);
  }
 }
 //定義動作，向上滾動翻頁
 public void next(){
  if(getInAnimation() != mInUp){
   setInAnimation(mInUp);
  }
  if(getOutAnimation() != mOutUp){
   setOutAnimation(mOutUp);
  }
 }

  class Rotate3dAnimation extends Animation {
      private final float mFromDegrees;
      private final float mToDegrees;
      private float mCenterX;
      private float mCenterY;
      private final boolean mTurnIn;
      private final boolean mTurnUp;
      private Camera mCamera;

      public Rotate3dAnimation(float fromDegrees, float toDegrees, boolean turnIn, boolean turnUp) {
          mFromDegrees = fromDegrees;
          mToDegrees = toDegrees;
          mTurnIn = turnIn;
          mTurnUp = turnUp;
      }

      @Override
      public void initialize(int width, int height, int parentWidth, int parentHeight) {
          super.initialize(width, height, parentWidth, parentHeight);
          mCamera = new Camera();
          mCenterY = getHeight() / 2;
          mCenterX = getWidth() / 2;
      }

      @Override
      protected void applyTransformation(float interpolatedTime, Transformation t) {
          final float fromDegrees = mFromDegrees;
          float degrees = fromDegrees + ((mToDegrees - fromDegrees) * interpolatedTime);

          final float centerX = mCenterX ;
          final float centerY = mCenterY ;
          final Camera camera = mCamera;
          final int derection = mTurnUp ? 1: -1;

          final Matrix matrix = t.getMatrix();

          camera.save();
          if (mTurnIn) {
              camera.translate(0.0f, derection *mCenterY * (interpolatedTime - 1.0f), 0.0f);
          } else {
              camera.translate(0.0f, derection *mCenterY * (interpolatedTime), 0.0f);
          }
          camera.rotateX(degrees);
          camera.getMatrix(matrix);
          camera.restore();

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

2. MainActivity.java
復制代碼 代碼如下:
package com.example.animtextview;

import android.os.Bundle;
import android.app.Activity;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;

public class MainActivity extends Activity implements OnClickListener {

 private Button mBtnNext;
 private Button mBtnPrev;
 private AutoTextView mTextView02;
 private static int sCount = 10;
 @Override
 protected void onCreate(Bundle savedInstanceState) {
  super.onCreate(savedInstanceState);
  setContentView(R.layout.activity_main);
  init();
 }
 private void init() {
  // TODO Auto-generated method stub
  mBtnNext = (Button) findViewById(R.id.next);
  mBtnPrev = (Button) findViewById(R.id.prev);
  mTextView02 = (AutoTextView) findViewById(R.id.switcher02);
  mTextView02.setText("Hello world!");
  mBtnPrev.setOnClickListener(this);
  mBtnNext.setOnClickListener(this);
 }

 @Override
 public void onClick(View arg0) {
  // TODO Auto-generated method stub
  switch (arg0.getId()) {
  case R.id.next:
   mTextView02.next();
   sCount++;
   break;
  case R.id.prev:
   mTextView02.previous();
   sCount--;
   break;
  }
  mTextView02.setText(sCount%2==0 ?
    sCount+"AAFirstAA" :
    sCount+"BBBBBBB");
  System.out.println("getH: ["+mTextView02.getHeight()+"]");

 }
}

3. activity_main.xml
復制代碼 代碼如下:
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:auto3d="http://schemas.android.com/apk/res/com.example.animtextview"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical" >

    <RelativeLayout
        android:layout_width="match_parent"
        android:layout_height="wrap_content" >

        <Button
            android:id="@+id/next"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_alignParentLeft="true"
            android:layout_alignParentTop="true"
            android:text="@string/next" />

        <Button
            android:id="@+id/prev"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_alignParentRight="true"
            android:layout_alignParentTop="true"
            android:text="@string/prev" />
    </RelativeLayout>

    <com.example.animtextview.AutoTextView
        android:id="@+id/switcher02"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:background="@android:color/holo_green_dark"
        auto3d:textSize="30sp" />

</LinearLayout>

    代碼中沒寫太多注釋，不過結構還算清晰，應該不難看懂！

三 小結
    我認為該控件實現的難點在於 動畫文件的編寫，即Rotate3dAnimation中applyTransformation(...)方法的實現，通過控制camara在Y方向上挪動和在X方向上的旋轉，從而造成上下翻滾的視覺感，然後將該值轉換到matrix上，從而改變了參數（..，Transformation t）.有興致的朋友可以直接改寫該方法，便可失掉不同動畫效果的TextSwitcher.