实现仿知乎的开场动画，图片zoomin的效果，实现原理，没加动效

package com.carbs.testandroidimage;

import android.app.Activity;
import android.graphics.Bitmap;
import android.graphics.Canvas;
import android.graphics.Matrix;
import android.graphics.PixelFormat;
import android.graphics.drawable.Drawable;
import android.os.Bundle;
import android.util.Log;
import android.view.View;
import android.widget.Button;
import android.widget.ImageView;

public class MainActivity extends Activity implements View.OnClickListener {

     private ImageView iv;
     private Button bt1_refine;
     private Button bt2_zoomin;
     
     private int iv_height = 0;
     private int iv_width = 0;
     private int dr_height = 0;
     private int dr_width = 0;

     @Override
     protected void onCreate(Bundle savedInstanceState) {
           super.onCreate(savedInstanceState);
          setContentView(R.layout. activity_main);

           iv = (ImageView) this.findViewById(R.id.iv);
           bt1_refine = (Button) this.findViewById(R.id.bt1);
           bt2_zoomin = (Button) this.findViewById(R.id.bt2);

           bt1_refine.setOnClickListener(this);
           bt2_zoomin.setOnClickListener(this);
          
           iv.post( new Runnable() {
              
               @Override
               public void run() {
               //获取imageview的宽和高、获取drawable的宽和高
                   Drawable d = iv.getDrawable();
                    //drawable的宽高，存储到全局变量中
                    dr_width = d.getIntrinsicWidth();
                    dr_height = d.getIntrinsicHeight();
                   //imageview的宽高，存储到全局变量中
                    iv_height = iv .getMeasuredHeight();
                    iv_width = iv.getMeasuredWidth();
                   Log. d("a", "onClick() --> dr_width is " + dr_width + " | dr_height is " + dr_height + " | iv_height is " + iv_height + " | iv_width is " + iv_width);
              }
          });
     }
     
     @Override
     public void onClick(View v) {
          
           switch (v.getId()) {
          
           case R.id.bt1 :
              
               if((iv_height * dr_width > dr_height * iv_width)){
                    //如果iv更细高，也就是我们需要调整其中图片的高度，使其高度和imageview的高度一致，这样算出scale后，使drawable的宽高同时放大scale倍。由于matrix模式下，调整scale后imageview显示图片依然是从左上角开始显示的，因此需要调整imageview的左右平移，使显示的drawable正好位于正中间。另一种情况（如果iv更宽扁）同理
                   //计算出高度需要放大多少倍
                    float scale1 = ((float)iv_height )/((float)dr_height);
                   //计算出左右平移多少
                    float offset1 = (dr_width *scale1 - (float)iv_width )/2;
                   Log. d("1223", "offset1 is " + offset1);
               
                   Matrix matrix1 = new Matrix();
                   matrix1.postScale(scale1, scale1);
                   matrix1.postTranslate(-offset1, 0);
                    iv.setImageMatrix(matrix1);
                             
              } else{
                    //如果iv更宽扁，同理
                    float scale2 = ((float)iv_width )/((float)dr_width);
                   
                    float offset2 = (dr_height *scale2 - (float)iv_height )/2;
                   Log. d("1223", "offset2 is " + offset2);
                    //产生新的大小但Bitmap对象  
                   Matrix matrix2 = new Matrix();  
                   matrix2.postScale(scale2, scale2);
                   matrix2.postTranslate(0, -offset2);
                    iv.setImageMatrix(matrix2);
              }
              
               break;
              
           case R.id.bt2 :
             
              Matrix ma = iv.getImageMatrix();

               float[] dValues = new float[9];
              
              ma.getValues(dValues);
              
              dValues[0] = dValues[0] + 0.1f;
              dValues[4] = dValues[4] + 0.1f;
              
               float offsetheight = (dr_height *dValues[0] - (float)iv_height )/2;
              dValues[5] = - offsetheight;
               float offsetwidth = (dr_width *dValues[0] - (float)iv_width )/2;
              dValues[2] = - offsetwidth;
              
              Matrix m = new Matrix();
              m.setValues(dValues);
              
               iv.setImageMatrix(m);
               break;
          }
     }
     
     public String printMyMatrix(Matrix m){
          String s = "";
           float[] valueFloat = new float[9];
          m.getValues(valueFloat);
          
           for(int i = 0; i < 9; i++){
              s = s + " [ " + valueFloat[i] + " ] " ;
          }
          
           return s;
     }
     
}