Gallery下面的小圆点实现

一日项目要实现这个功能，我也不知道如何实现，从网上搜了一大堆，好像没有现成的demo，后来无意间从eoe论坛上看到一个帖子，贴出了解决方案和思路，

我也顺利实现了该功能。

解决思路是这样的：重写在Gallery下面View（xml布局在Gallery下），画出和相片数量相当的圆点，当前选中的是那个相片，就在对应position的位置将那个圆点绘制成两点。

绘制圆点主要就是重写onDraw函数。

代码：

xml：

    android:gravity="center_vertical"
    android:layout_width="fill_parent" android:layout_height="fill_parent">

                  android:layout_width="fill_parent"
               android:layout_height="wrap_content"
   />
          android:id="@+id/pageView"
       android:layout_width="fill_parent"
       android:layout_height="wrap_content"
   />

重写的View代码：

package com.example.android.apis.view;

import com.example.android.apis.R;

import android.content.Context;
import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.Paint;
import android.graphics.Rect;
import android.util.AttributeSet;
import android.util.Log;
import android.view.View;

public class PageIndicatorView extends View {
    private String TAG = "PageIndicatorView";
    private int mCurrentPage = -1;
    private int mTotalPage = 0;

    public PageIndicatorView(Context context) {
        super(context);
    }

    public PageIndicatorView(Context context, AttributeSet attrs) {
        super(context, attrs);
    }

    public void setTotalPage(int nPageNum) {
        mTotalPage = nPageNum;
        if (mCurrentPage >= mTotalPage)
            mCurrentPage = mTotalPage - 1;
    }

    public int getCurrentPage() {
        return mCurrentPage;
    }

    public void setCurrentPage(int nPageIndex) {
        if (nPageIndex < 0 || nPageIndex >= mTotalPage)
            return;

        if (mCurrentPage != nPageIndex) {
            mCurrentPage = nPageIndex;
            this.invalidate();
        }
    }

    @Override
    protected void onDraw(Canvas canvas) {
        super.onDraw(canvas);
        Log.d(TAG, "on draw...");
        Paint paint = new Paint(Paint.ANTI_ALIAS_FLAG | Paint.FILTER_BITMAP_FLAG);
        paint.setStyle(Paint.Style.FILL);
        paint.setColor(Color.BLACK);

        Rect r = new Rect();
        this.getDrawingRect(r);

        int iconWidth = 9;
        int iconHeight = 9;
        int space = 12;

        int x = (r.width() - (iconWidth * mTotalPage + space * (mTotalPage - 1))) / 2;
        int y = (r.height() - iconHeight) / 2;

        for (int i = 0; i < mTotalPage; i++) {

            int resid = R.drawable.dot_selected;

            if (i == mCurrentPage) {
                resid = R.drawable.dot_unselected;
            }

            Rect r1 = new Rect();
            r1.left = x;
            r1.top = y;
            r1.right = x + iconWidth;
            r1.bottom = y + iconHeight;

            Bitmap bmp = BitmapFactory.decodeResource(getResources(), resid);
            canvas.drawBitmap(bmp, null, r1, paint);

            x += iconWidth + space;

        }

    }

}

界面代码：

/*
 * Copyright (C) 2007 The Android Open Source Project
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package com.example.android.apis.view;

import com.example.android.apis.R;
import android.app.Activity;
import android.content.Context;
import android.content.res.TypedArray;
import android.os.Bundle;
import android.view.ContextMenu;
import android.view.MenuItem;
import android.view.View;
import android.view.ViewGroup;
import android.view.ContextMenu.ContextMenuInfo;
import android.widget.AdapterView;
import android.widget.BaseAdapter;
import android.widget.ImageView;
import android.widget.Toast;
import android.widget.AdapterView.AdapterContextMenuInfo;
import android.widget.AdapterView.OnItemClickListener;
import android.widget.AdapterView.OnItemSelectedListener;

public class Gallery1 extends Activity {

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.gallery_1);

        // Reference the Gallery view
        Gallery g = (Gallery) findViewById(R.id.gallery);
        final PageIndicatorView mPageView = (PageIndicatorView)findViewById(R.id.pageView);
        mPageView.setTotalPage(8);
        // Set the adapter to our custom adapter (below)
        g.setAdapter(new ImageAdapter(this));
        g.setOnItemSelectedListener(new OnItemSelectedListener() {
              @Override
              public void onItemSelected(AdapterView arg0, View arg1, int arg2,
                long arg3) {
               mPageView.setCurrentPage(arg2);
               Toast.makeText(Gallery1.this, "select" + arg2, Toast.LENGTH_SHORT).show();
              }
              @Override
              public void onNothingSelected(AdapterView arg0) {
               // TODO Auto-generated method stub
                  
              }
            });
        // Set a item click listener, and just Toast the clicked position
        g.setOnItemClickListener(new OnItemClickListener() {
            public void onItemClick(AdapterView parent, View v, int position, long id) {
//                Toast.makeText(Gallery1.this, "" + position, Toast.LENGTH_SHORT).show();
                mPageView.setCurrentPage(position);
            }
        });
        
        // We also want to show context menu for longpressed items in the gallery
        registerForContextMenu(g);
    }

    @Override
    public void onCreateContextMenu(ContextMenu menu, View v, ContextMenuInfo menuInfo) {
        menu.add(R.string.gallery_2_text);
    }
    
    @Override
    public boolean onContextItemSelected(MenuItem item) {
        AdapterContextMenuInfo info = (AdapterContextMenuInfo) item.getMenuInfo();
        Toast.makeText(this, "Longpress: " + info.position, Toast.LENGTH_SHORT).show();
        return true;
    }

    public class ImageAdapter extends BaseAdapter {
        int mGalleryItemBackground;
        
        public ImageAdapter(Context c) {
            mContext = c;
            // See res/values/attrs.xml for the that defines
            // Gallery1.
            TypedArray a = obtainStyledAttributes(R.styleable.Gallery1);
            mGalleryItemBackground = a.getResourceId(
                    R.styleable.Gallery1_android_galleryItemBackground, 0);
            a.recycle();
        }

        public int getCount() {
            return mImageIds.length;
        }

        public Object getItem(int position) {
            return position;
        }

        public long getItemId(int position) {
            return position;
        }

        public View getView(int position, View convertView, ViewGroup parent) {
            ImageView i = new ImageView(mContext);

            i.setImageResource(mImageIds[position]);
            i.setScaleType(ImageView.ScaleType.FIT_XY);
            i.setLayoutParams(new Gallery.LayoutParams(160, 120));
            
            // The preferred Gallery item background
            i.setBackgroundResource(mGalleryItemBackground);
            
            return i;
        }

        private Context mContext;

        private Integer[] mImageIds = {
                R.drawable.gallery_photo_1,
                R.drawable.gallery_photo_2,
                R.drawable.gallery_photo_3,
                R.drawable.gallery_photo_4,
                R.drawable.gallery_photo_5,
                R.drawable.gallery_photo_6,
                R.drawable.gallery_photo_7,
                R.drawable.gallery_photo_8
        };
    }

}