gallery 从最左边开始显示并且默认选中第一个

import android.content.Context;
import android.graphics.Camera;
import android.graphics.Matrix;
import android.util.AttributeSet;
import android.view.MotionEvent;
import android.view.View;
import android.view.animation.Transformation;
import android.widget.Gallery;

public class MyGallery extends Gallery {
private Camera mCamera;
private int mWidth;
private int mPaddingLeft;
private boolean flag;
private static int firstChildWidth;
private static int firstChildPaddingLeft;

/*
* 构造方法
*/
public MyGallery(Context context) {
super(context);
mCamera = new Camera();
this.setStaticTransformationsEnabled(true);
}

/*
* 构造方法
*/
public MyGallery(Context context, AttributeSet attrs) {
super(context, attrs);
mCamera = new Camera();
this.setStaticTransformationsEnabled(true);
}

/*
* 构造方法
*/
public MyGallery(Context context, AttributeSet attrs, int defStyle) {
super(context, attrs, defStyle);
mCamera = new Camera();
this.setStaticTransformationsEnabled(true);
}

protected boolean getChildStaticTransformation(View child, Transformation t) {
t.clear();
t.setTransformationType(Transformation.TYPE_MATRIX);
mCamera.save();
final Matrix imageMatrix = t.getMatrix();
if (flag) {
firstChildWidth = getChildAt(0).getWidth();
firstChildPaddingLeft = getChildAt(0).getPaddingLeft();
flag = false;
}
mCamera.translate(firstChildWidth / 2 + firstChildPaddingLeft + mPaddingLeft - mWidth / 2, 0f, 0f);
mCamera.getMatrix(imageMatrix);
mCamera.restore();
return true;
}

protected void onSizeChanged(int w, int h, int oldw, int oldh) {
if (!flag) {
mWidth = w ;
getLayoutParams().width = mWidth;
flag = true;
}
super.onSizeChanged(w, h, oldw, oldh);
}

@Override
public boolean onFling(MotionEvent e1, MotionEvent e2, float velocityX, float velocityY) {
return super.onFling(e1, e2, 0, velocityY);//方法一：只去除翻页惯性
}

@Override
public boolean onScroll(MotionEvent e1, MotionEvent e2, float distanceX, float distanceY) {
// TODO Auto-generated method stub
return super.onScroll(e1, e2, distanceX, distanceY);
// TODO Auto-generated method stub
}

}
在程序中调用MyGallery就可以实现，调用方面跟Gallery一样