应该是这样的吧？

if(mImageView.getX()>iv_null_imageView.getX()){
   //往左移动
   translateAnimation = new TranslateAnimation(0.1f, -mImageView.getWidth(), 0.1f,0.1f );
   Toast.makeText(this,"往左移动",Toast.LENGTH_LONG).show();
}else  if (mImageView.getX()<iv_null_imageView.getX()){
   //往右移动
   translateAnimation = new TranslateAnimation(0.1f,  mImageView.getWidth(), 0.1f, 0.1f);
}else if (mImageView.getY()>iv_null_imageView.getY()){
   //往上移动
   translateAnimation = new TranslateAnimation(0.1f,0.1f, 0.1f,  -mImageView.getHeight());
}else if (mImageView.getY()<iv_null_imageView.getY()){
   //往下移动
   translateAnimation = new TranslateAnimation(0.1f,0.1f, 0.1f,  mImageView.getHeight());
}