android实现上下滚动的TextView

一 说明
    这里重要应用类 autotextview，这是一个自定义的类，继承至textswitcher，下面临 autotextview类做简要说明：

    1. 该类应用的重点，在于设置两个动画， setinanimation(...)  和 setoutanimation(...)，分离是文字进入的动画和文字退出的动画；

    2. 类中定义了一个外部类-rotate3danimation，重要靠该类实现文字进出动画，该外部类继承至animation。说来偶合，这个恰好是在apidemo中看到了，自定义animation我还是第一次应用，动画逻辑均在void applytransformation(float interpolatedtime, transformation t)中实现，代码相当锋利，我在原来的基础上，更改了一下，实现了上述的效果，

二 代码部分：
1.autotextview.java

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分离构成向下翻页的进出动画
 private rotate3danimation minup;
 private rotate3danimation moutup;

 //mindown,moutdown分离构成向下翻页的进出动画
 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重要用于文件切换，比如 从文字a 切换到 文字 b，
  //setinanimation()后，a将执行inanimation，
  //setoutanimation()后，b将执行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;
 }

 //这里返回的textview，就是我们看到的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;
 }
 //定义动作，向下滚动翻页
 public void previous(){
  if(getinanimation() != mindown){
   setinanimation(mindown);
  }
  if(getoutanimation() != moutdown){
   setoutanimation(moutdown);
  }
 }
 //定义动作，向上滚动翻页
 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

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

<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>

    代码中没写太多注释，不过结构还算清晰，应该不难看懂！

三 小结
    我认为该控件实现的难点在于 动画文件的编写，即rotate3danimation中applytransformation(...)方法的实现，通过控制camara在y方向上挪动和在x方向上的旋转，从而造成上下翻滚的视觉感，然后将该值转换到matrix上，从而改变了参数（..，transformation t）.有兴致的朋友可以直接改写该方法，便可失掉不同动画效果的textswitcher.