GridView实践

     Grid为网格视图，例如实现类似九宫格的效果，可以首选GridView,该组件中的每一个条目通过ListAdapter和该组件进行关联。

GridViewExample.java代码如下：

package com.example.lenovo.a1106;
import android.app.Activity;
import android.content.Intent;
import android.content.pm.ResolveInfo;
import android.os.Bundle;
import android.view.View;
import android.view.ViewGroup;
import android.widget.BaseAdapter;
import android.widget.GridView;
import android.widget.ImageView;



import java.util.List;


public class GridViewExample extends Activity {
    private GridView myGridView;
    private List<ResolveInfo> myAppIcon;     //声明变量，存放桌面应用程序图标

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.gridview);
        myGridView = (GridView) findViewById(R.id.myGrid);
        loadAppIcon(); //加载桌面图片
        BaseAdapter adapter = new BaseAdapter() {
            @Override
            public int getCount() {    //项目个数
                return myAppIcon.size();
            }

            @Override
            public Object getItem(int position) {  //获取指定位置的项目
                return myAppIcon.get(position);
            }

            @Override
            public long getItemId(int position) {   //获取指定位置项目id
                return position;
            }

            //定义每一项显示的内容
            @Override
            public View getView(int position, View convertView, ViewGroup parent) {
                ImageView imageView;
                if (convertView == null) {
                    imageView = new ImageView(GridViewExample.this);
                    //创建Image对象

                    imageView.setScaleType(ImageView.ScaleType.FIT_CENTER);
                    //设置图片的填充方式，这里按比例拉伸图片
                    imageView.setLayoutParams(new GridView.LayoutParams(50, 50));
                    //设置ImageView的大小为50*50
                } else {

                    imageView = (ImageView) convertView;
                }
                ResolveInfo info = myAppIcon.get(position);
                //获取myAppIcon中下标为position的ResolveInfo
                imageView.setImageDrawable(info.activityInfo.loadIcon(getPackageManager()));
                return imageView;

            }
        };
       myGridView.setAdapter(adapter);

      //  myListView.setAdapter(adapter);
    }

    private void loadAppIcon() {

        Intent mainIntent = new Intent(Intent.ACTION_MAIN, null);
        //创建Intent
        mainIntent.addCategory(Intent.CATEGORY_LAUNCHER);
        //添加桌面应用程序列表到Intent
        myAppIcon = getPackageManager().queryIntentActivities(mainIntent, 0);
    }
}

gridview.xml代码如下：

<?xml version="1.0" encoding="utf-8"?>

<GridView
    xmlns:android="http://schemas.android.com/apk/res/android"
    android:id="@+id/myGrid"
    android:orientation="vertical"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:padding="10dp"
    android:numColumns="auto_fit"
    android:horizontalSpacing="10dp"
    android:verticalSpacing="10dp"
    android:stretchMode="columnWidth"
    android:gravity="center" />

当时遇到了个错误

说是空对象，然而没有想到是没有加载布局文件！！！得长记性！！！