android之路Gallery 画廊

Gallery是一个内部元素能够水平滚动，而且能够把当前选择的子元素定位在它中心的布局组件。

我们还是直接看看样例的执行效果。

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1.新疆项目HelloGallery

2.把须要展示的图片放入res/drawable文件夹。woman01.jpg。woman02.jpg，woman03.jpg

3.res/layout/activity_main.xml文件的内容例如以下：

<FrameLayout  xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:id="@+id/FrameLayout01"
   >
	<ImageView android:layout_width="match_parent"
	    android:layout_height="match_parent"
	    android:id="@+id/ImageView01"
	    android:src="@drawable/woman01"/>

	<Gallery android:layout_width="match_parent"
	    android:layout_height="wrap_content"
	    android:id="@+id/gallery01"
	    android:spacing="5dp"/>

</FrameLayout >

我们使用FrameLayout来实现叠加效果，使用ImageView来显示大图。Gallery来展示画廊，android:spacing="5dp" 属性则是用来设置元素之间的间隔。

4.在res/values/文件夹中新建一个attrs.xml内容例如以下：

<?xml version="1.0" encoding="utf-8"?>
<resources>
   <declare-styleable name="HelloGallery">
         <attr name="android:galleryItemBackground">
        </attr>
   </declare-styleable>
</resources>

5.主activity,MainActivity的代码例如以下：

<pre name="code" class="java">package com.howlaa.hellogallery;

import android.os.Bundle;
import android.app.Activity;
import android.view.Menu;
import android.view.View;
import android.view.ViewGroup;
import android.widget.AdapterView;
import android.widget.AdapterView.OnItemClickListener;
import android.widget.BaseAdapter;
import android.widget.Gallery;
import android.widget.ImageView;
import android.widget.Toast;

public class MainActivity extends Activity {

	@Override
	protected void onCreate(Bundle savedInstanceState) {
		super.onCreate(savedInstanceState);
		setContentView(R.layout.activity_main);
		final ImageView iv = (ImageView)findViewById(R.id.ImageView01);
		Gallery g = (Gallery) findViewById(R.id.gallery01);
		//设置图片匹配器
        g.setAdapter(new ImageAdapter(this));
        //设置AdapterView点击监听器，Gallery是AdapterView的子类
        g.setOnItemClickListener(new OnItemClickListener() {

            @Override
            public void onItemClick(AdapterView<?> parent, View view,
                            int position, long id) {
                    //显示点击的是第几张图片
                    Toast.makeText(MainActivity.this, "" + position,
                                    Toast.LENGTH_LONG).show();
                    //设置背景部分的ImageView显示当前Item的图片
                    iv.setImageResource(((ImageView)view).getId());
	            }
	    });
	}

}

6.ImageAdapter的代码例如以下：

package com.howlaa.hellogallery;

import android.content.Context;
import android.content.res.TypedArray;
import android.view.View;
import android.view.ViewGroup;
import android.widget.BaseAdapter;
import android.widget.Gallery;
import android.widget.ImageView;
import android.widget.SpinnerAdapter;

public class ImageAdapter extends BaseAdapter {

	//Item的修饰背景
    int mGalleryItemBackground;

    //上下文对象
    private Context mContext;

    //图片数组
    private Integer[] mImageIds ={R.drawable.woman01,R.drawable.woman02,R.drawable.woman03};
	  //构造方法
    public ImageAdapter(Context c){
            mContext = c;
	    //读取styleable资源
	    TypedArray a = mContext.obtainStyledAttributes(R.styleable.HelloGallery);
	    mGalleryItemBackground = a.getResourceId(
	            R.styleable.HelloGallery_android_galleryItemBackground, 0);
	    a.recycle();
    }

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

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

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

	@Override
	public View getView(int position, View convertView, ViewGroup parent) {
		ImageView iv = new ImageView(mContext);
		iv.setImageResource(mImageIds[position]);
		  //给生成的ImageView设置Id，不设置的话Id都是-1
        iv.setId(mImageIds[position]);
        iv.setLayoutParams(new Gallery.LayoutParams(120, 160));
        iv.setScaleType(ImageView.ScaleType.FIT_XY);
        iv.setBackgroundResource(mGalleryItemBackground);
		return iv;
	}

}