关于android的坑

坑1：

使用SQLiteOpenHelper的时候如果建立的表中存在不为空的字段，但是用ContentValues()的方式来插入数据的话恰好没有往这个字段里插入数据，那么执行后市没法往数据库里插入数据的。单是写在这里可能觉得这个问题很平常，下面以代码的形式展示出来。

MySqliteDatabase.java

 1 package com.jikexueyuan.hellonotes;
 2
 3 import android.content.Context;
 4 import android.database.sqlite.SQLiteDatabase;
 5 import android.database.sqlite.SQLiteDatabase.CursorFactory;
 6 import android.database.sqlite.SQLiteOpenHelper;
 7
 8 public class MySqliteDatabase extends SQLiteOpenHelper {
 9     public static final String _ID = "_id";
10     public static final String CONTENT = "content";
11     public static final String TIME = "time";
12     public static final String TABLE = "mydiary";
13     public static final String TABLE_DRAFT = "draft";
14     public static final String DATABASENAME = "wyldb.db";
15
16     public MySqliteDatabase(Context context, String name,
17             CursorFactory factory, int version) {
18         super(context, name, factory, version);
19         // TODO Auto-generated constructor stub
20
21     }
22
23     /**
24      * 三个参数的构造器
25      *
26      * @param context
27      * @param name
28      * @param factory
29      */
30     public MySqliteDatabase(Context context) {
31         this(context, DATABASENAME, null, 1);
32         System.out.println("MySqliteDatabase.MySqliteDatabase()构造器，新建表："
33                 + DATABASENAME + "...");
34     }
35
36     @Override
37     public void onCreate(SQLiteDatabase db) {
38         // TODO Auto-generated method stub
39         System.out.println("MySqliteDatabase.onCreate(),创建表...");
40         db.execSQL("create table mydiary(_id integer primary key autoincrement,content text not null,time text not null)");
41         db.execSQL("create table draft(_id integer primary key autoincrement,content text not null,time text not null)");
42     }
43
44     @Override
45     public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
46         // TODO Auto-generated method stub
47
48     }
49
50 }

DetailActivity.java

 1 package com.jikexueyuan.hellonotes;
 2
 3 import java.text.SimpleDateFormat;
 4 import java.util.Date;
 5
 6 import android.app.Activity;
 7 import android.content.ContentValues;
 8 import android.content.Intent;
 9 import android.database.sqlite.SQLiteDatabase;
10 import android.os.Bundle;
11 import android.view.View;
12 import android.view.View.OnClickListener;
13 import android.widget.Button;
14 import android.widget.EditText;
15 import android.widget.Toast;
16
17 public class DetailActivity extends Activity implements OnClickListener {
18     EditText et_detail;
19     Button btn_edit, btn_delete, btn_detail_save;
20     String val;
21
22     @Override
23     protected void onCreate(Bundle savedInstanceState) {
24         // TODO Auto-generated method stub
25         super.onCreate(savedInstanceState);
26         setContentView(R.layout.detail);
27         et_detail = (EditText) findViewById(R.id.et_detail);
28         btn_edit = (Button) findViewById(R.id.btn_edit);
29         btn_delete = (Button) findViewById(R.id.btn_delete);
30         btn_detail_save = (Button) findViewById(R.id.btn_detail_save);
31         btn_edit.setOnClickListener(this);
32         btn_delete.setOnClickListener(this);
33         btn_detail_save.setOnClickListener(this);
34         Intent intent = getIntent();
35         val = intent.getExtras().getString(FirstActivity.KEY_CONTENT);
36         if (!val.equals("") || val == null) {
37             // Toast.makeText(this, "获取的值不为空，已经设置，，", 0).show();
38             et_detail.setText(val);
39             et_detail.setSelection(val.length());// 设置光标到最后
40         }
41
42     }
43
44     @Override
45     public void onClick(View v) {
46         // TODO Auto-generated method stub
47         MySqliteDatabase db = new MySqliteDatabase(DetailActivity.this);
48         SQLiteDatabase sdb = db.getWritableDatabase();
49         switch (v.getId()) {
50         case R.id.btn_edit:
51             et_detail.setEnabled(true);// 设置文本克可编辑
52             // 可编辑的时候删除按钮隐藏，保存按钮可见
53             btn_delete.setVisibility(View.GONE);
54             btn_detail_save.setVisibility(View.VISIBLE);
55             System.out.println("===val:" + val + ",====");
56             // 同时还要删除
57             sdb.delete(MySqliteDatabase.TABLE, MySqliteDatabase.CONTENT + "=?",
58                     new String[] { val });// 有报错，暂时不处理
59             break;
60         case R.id.btn_detail_save:
61             String content = et_detail.getText().toString();
62             ContentValues cv = new ContentValues();
63
64             SimpleDateFormat format = new SimpleDateFormat();
65             Date date = new Date();
66             String time = format.format(date);
67             cv.put(MySqliteDatabase.CONTENT, content);
68             /*
69              * 之前没有插入time这个值，但是因为这个表里的time字段不能够为空，导致下main的代码都
70              * 没正确执行，即不能够按照预期把文本内容插入到数据库。
71              */
72             cv.put(MySqliteDatabase.TIME, time);
73             System.out.println("-----btn_detail_save：content=  ----");
74             sdb.insert(MySqliteDatabase.TABLE, null, cv);
75             Intent intent = new Intent(DetailActivity.this, FirstActivity.class);
76             startActivity(intent);
77             finish();
78             break;
79
80         default:
81             break;
82         }
83     }
84 }

具体代码：http://pan.baidu.com/s/1sjIJRit