Android 淺談MatrixCursor

如果想得到一個Cursor, 而此時又沒有數據庫返回一個Cursor，此時可以通過MatrixCursor來返回一個Cursor

具體使用方法，請見下文：
假如有一個如下的數據庫表結構 _id name price R.drawable.ic_launcher zhangsan 39 R.drawable.ic_launcher lisi 40 R.drawable.ic_launcher wangwu 41 R.drawable.ic_launcher zhaoliu 42
現在咱們就通過MatrixCursor這個東西，來虛構出一張上面那樣的表結構，下面通過一個例子，就可以完全理解MatrixCursor這個東西啦！！ (原文鏈接：http://blog.csdn.net/yelangjueqi/article/details/21232659 歡迎轉載，尊重他人勞動成果，轉載時請注明出處！！) 通過一個例子來分析一下：

package com.test.matrixcursor;

import android.app.ListActivity;
import android.database.MatrixCursor;
import android.os.Bundle;
import android.support.v4.widget.SimpleCursorAdapter;
import android.view.View;
import android.widget.ListView;
import android.widget.Toast;

public class MainActivity extends ListActivity {
     private static final String[] COLUMN_NAME = { "_id", "name", "price" };
     private MatrixCursor matrixCursor;

     @Override
     protected void onCreate(Bundle savedInstanceState) {
          super.onCreate(savedInstanceState);
           createList();
           //createList2();
     }

     private void createList() {
          matrixCursor = new MatrixCursor(COLUMN_NAME, 1);
          startManagingCursor(matrixCursor);

          matrixCursor.addRow(new Object[] { R.drawable.ic_launcher, "zhangsan",
                    39 });
          matrixCursor
                    .addRow(new Object[] { R.drawable.ic_launcher, "lisi", 40 });
          matrixCursor
                    .addRow(new Object[] { R.drawable.ic_launcher, "wangwu", 41 });

          matrixCursor.addRow(new Object[] { R.drawable.ic_launcher, "zhaoliu",
                    42 });
          matrixCursor
                    .addRow(new Object[] { R.drawable.ic_launcher, "sunqi", 43 });

          setListAdapter(new SimpleCursorAdapter(this, R.layout.activity_main,
                    matrixCursor, COLUMN_NAME, new int[] { R.id.icon, R.id.name,
                              R.id.price }));
     }

     private void createList2() {
          matrixCursor = new MatrixCursor(COLUMN_NAME, 1);
          startManagingCursor(matrixCursor);

          MatrixCursor.RowBuilder builder1 = matrixCursor.newRow();
          builder1.add(R.drawable.ic_launcher);
          builder1.add("zhangsan");
          builder1.add(39);

          MatrixCursor.RowBuilder builder2 = matrixCursor.newRow();
          builder2.add(R.drawable.ic_launcher);
          builder2.add("lisi");
          builder2.add(40);

          MatrixCursor.RowBuilder builder3 = matrixCursor.newRow();
          builder3.add(R.drawable.ic_launcher);
          builder3.add("wangwu");
          builder3.add(41);

          setListAdapter(new SimpleCursorAdapter(this, R.layout.activity_main,
                    matrixCursor, COLUMN_NAME, new int[] { R.id.icon, R.id.name,
                              R.id.price }));
     }

     @Override
     protected void onListItemClick(ListView l, View v, int position, long id) {
          super.onListItemClick(l, v, position, id);
          matrixCursor.moveToPosition(position);
          StringBuilder builder = new StringBuilder();
          builder.append("Name:")
                    .append(matrixCursor.getString(matrixCursor
                              .getColumnIndex("name"))).append("\n");

          builder.append("Price:")
                    .append(matrixCursor.getString(matrixCursor
                              .getColumnIndex("price"))).append("\n");

          Toast.makeText(getApplicationContext(), builder.toString(), 1000)
                    .show();
     }
}

實現步驟僅需3步，下面通過字符數組來說明： 步驟1.首先創建一個字符數組，且字符數組的值對應著表的字段，如下： String[] COLUMN_NAME = { "_id", "name", "price" }; 步驟2.利用MatrixCursor的構造方法，構造一個MatrixCursor，傳入的參數即是步驟1中創建的字段數組，如下： MatrixCursormatrixCursor=newMatrixCursor(COLUMN_NAME); 也可以指定初始大小，如： matrixCursor=newMatrixCursor( COLUMN_NAME, 10);
步驟3. 通過matrixCursor 的addRow方法添加一行值，相當於向數據庫中插入一條記錄，如下： matrixCursor.addRow(new Object[] { R.drawable.ic_launcher, "zhangsan",39 });
注：步驟3也可以通過構造一個MatrixCursor.RowBuilder來實現，也是相當於向數據庫中插入一條記錄，如下： MatrixCursor.RowBuilder builder1 = matrixCursor.newRow();
builder1.add(R.drawable.ic_launcher);
builder1.add("zhangsan");
builder1.add(39);
//builder1.add(399999); 通過上面三步即可完成MatrixCursor 的構造。從MatrixCursor 中取出數據的過程與Cursor相同，不再贅述！

注釋：如果builder1對象add的數量大於字段的個數，即打開builder1.add(399999);注釋，那麼將會報以下錯誤：
02-27 19:00:44.882: W/dalvikvm(29036): threadid=1: thread exiting with uncaught exception (group=0x41e689a8)
02-27 19:00:44.882: W/dalvikvm(29036): threadid=1: uncaught exception occurred
02-27 19:00:44.883: W/System.err(29036): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.test.matrixcursor/com.test.matrixcursor.MainActivity}:android.database.CursorIndexOutOfBoundsException: No more columns left.
02-27 19:00:44.883: W/System.err(29036): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2356)
02-27 19:00:44.883: W/System.err(29036): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2408)
02-27 19:00:44.883: W/System.err(29036): at android.app.ActivityThread.access$600(ActivityThread.java:167)
02-27 19:00:44.883: W/System.err(29036): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1378)
02-27 19:00:44.883: W/System.err(29036): at android.os.Handler.dispatchMessage(Handler.java:107)
02-27 19:00:44.883: W/System.err(29036): at android.os.Looper.loop(Looper.java:194)
02-27 19:00:44.884: W/System.err(29036): at android.app.ActivityThread.main(ActivityThread.java:5405)
02-27 19:00:44.884: W/System.err(29036): at java.lang.reflect.Method.invokeNative(Native Method)
02-27 19:00:44.884: W/System.err(29036): at java.lang.reflect.Method.invoke(Method.java:525)
02-27 19:00:44.884: W/System.err(29036): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:838)
02-27 19:00:44.884: W/System.err(29036): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:605)
02-27 19:00:44.884: W/System.err(29036): at dalvik.system.NativeStart.main(Native Method)
02-27 19:00:44.886: W/System.err(29036): Caused by: android.database.CursorIndexOutOfBoundsException: No more columns left.
02-27 19:00:44.887: W/System.err(29036): at android.database.MatrixCursor$RowBuilder.add(MatrixCursor.java:206)
02-27 19:00:44.887: W/System.err(29036): at com.test.matrixcursor.MainActivity.createList(MainActivity.java:46)
02-27 19:00:44.888: W/System.err(29036): at com.test.matrixcursor.MainActivity.onCreate(MainActivity.java:20)
02-27 19:00:44.889: W/System.err(29036): at android.app.Activity.performCreate(Activity.java:5127)
02-27 19:00:44.889: W/System.err(29036): at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1151)
02-27 19:00:44.890: W/System.err(29036): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2320) 程序運行結果：