安卓绿豆通讯录移动开发weixin42623237的博客-

activity_main.xml

<?xml version="1.0" encoding="utf-8"?> <RelativeLayout xmlns:android="https://schemas.android.com/apk/res/android"     xmlns:tools="https://schemas.android.com/tools"     android:layout_width="match_parent"     android:layout_height="match_parent"     android:background="@drawable/bg"     android:paddingBottom="16dp"     android:paddingLeft="16dp"     android:paddingRight="16dp"     android:paddingTop="16dp"     tools:context=".MainActivity"> <LinearLayout         android:id="@+id/ll_name"         android:layout_width="match_parent"         android:layout_height="wrap_content"         android:layout_above="@+id/ll_phone"         android:layout_alignLeft="@+id/ll_btn"         android:layout_alignStart="@+id/ll_btn"> <TextView             android:layout_width="wrap_content"             android:layout_height="wrap_content"             android:textSize="18sp"             android:text="姓  名 ：" /> <EditText             android:id="@+id/et_name"             android:layout_width="match_parent"             android:layout_height="wrap_content"             android:textSize="16sp"             android:hint="请输入姓名" /> </LinearLayout> <LinearLayout         android:layout_width="match_parent"         android:layout_height="wrap_content"         android:id="@+id/ll_phone"         android:layout_marginBottom="10dp"         android:layout_above="@+id/ll_btn"         android:layout_alignLeft="@+id/ll_name"         android:layout_alignStart="@+id/ll_name"> <TextView             android:layout_width="wrap_content"             android:layout_height="wrap_content"             android:textSize="18sp"             android:text="电  话 ：" /> <EditText             android:id="@+id/et_phone"             android:layout_width="match_parent"             android:layout_height="wrap_content"             android:textSize="16sp"             android:hint="请输入手机号码" /> </LinearLayout> <LinearLayout         android:layout_width="match_parent"         android:layout_height="wrap_content"         android:id="@+id/ll_btn"         android:layout_centerVertical="true" > <Button             android:id="@+id/btn_add"             android:layout_width="0dp"             android:layout_height="wrap_content"             android:layout_weight="1"             android:textSize="18sp"             android:background="#B9B9FF"             android:layout_marginRight="2dp"             android:text="添加" /> <Button             android:id="@+id/btn_query"             android:layout_width="0dp"             android:layout_height="wrap_content"             android:layout_weight="1"             android:textSize="18sp"             android:background="#DCB5FF"             android:layout_marginRight="2dp"             android:text="查询" /> <Button             android:id="@+id/btn_update"             android:layout_width="0dp"             android:layout_height="wrap_content"             android:layout_weight="1"             android:textSize="18sp"             android:background="#E6CAFF"             android:layout_marginRight="2dp"             android:text="修改" /> <Button             android:id="@+id/btn_delete"             android:layout_width="0dp"             android:layout_height="wrap_content"             android:layout_weight="1"             android:textSize="18sp"             android:background="#ACD6FF"             android:text="删除" /> </LinearLayout> <TextView         android:id="@+id/tv_show"         android:layout_width="match_parent"         android:layout_height="wrap_content"         android:layout_marginTop="25dp"         android:layout_below="@+id/ll_btn"         android:textSize="20sp" /> </RelativeLayout> 

MyHelper.java

package cn.itcast.directory; import android.content.Context; import android.database.sqlite.SQLiteDatabase; import android.database.sqlite.SQLiteOpenHelper; import androidx.annotation.NonNull; import androidx.annotation.Nullable; public class MyHelper extends SQLiteOpenHelper { public MyHelper(Context context) { super(context, "itcast.db", null, 1); } //当数据库第一次创建的时候执行 @Override public void onCreate(SQLiteDatabase db) {         db.execSQL("CREATE TABLE information(_id INTEGER PRIMARY KEY AUTOINCREMENT, name VARCHAR(20),  phone VARCHAR(20))"); } @Override public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) { } } 

MainActivity.java

package cn.itcast.directory; import androidx.appcompat.app.AppCompatActivity; import android.content.ContentValues; import android.database.Cursor; import android.database.sqlite.SQLiteDatabase; import android.os.Bundle; import android.view.View; import android.widget.Button; import android.widget.EditText; import android.widget.TextView; import android.widget.Toast; import static cn.itcast.directory.R.*; public class MainActivity extends AppCompatActivity implements View.OnClickListener { private  MyHelper myHelper; private EditText mEtName; private EditText mEtPhone; private TextView mTvShow; private Button mBtnAdd; private Button mBtnQuery; private Button mBtnUpdate; private Button mBtnDelete; @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(layout.activity_main);         myHelper = new MyHelper(this); init(); //初始化控件 } private void init() {         mEtName = (EditText) findViewById(id.et_name);         mEtPhone = (EditText) findViewById(id.et_phone);         mTvShow = (TextView) findViewById(id.tv_show);         mBtnAdd = (Button) findViewById(id.btn_add);         mBtnQuery = (Button) findViewById(id.btn_query);         mBtnUpdate = (Button) findViewById(id.btn_update);         mBtnDelete = (Button) findViewById(id.btn_delete);         mBtnAdd.setOnClickListener(this);         mBtnQuery.setOnClickListener(this);         mBtnUpdate.setOnClickListener(this);         mBtnDelete.setOnClickListener(this); } @Override public void onClick(View v) {         String name;         String phone;         SQLiteDatabase db;         ContentValues values; switch (v.getId()) { case R.id.btn_add: //添加数据                 name = mEtName.getText().toString();                 phone = mEtPhone.getText().toString();                 db = myHelper.getWritableDatabase();//获取可读写SQLiteDatabse对象                 values = new ContentValues(); // 创建ContentValues对象                 values.put("name", name); // 将数据添加到ContentValues对象                 values.put("phone", phone);                 db.insert("information", null, values);                 Toast.makeText(this, "信息已添加", Toast.LENGTH_SHORT).show();                 db.close(); break; case id.btn_query: //查询数据                 db = myHelper.getReadableDatabase();                 Cursor cursor = db.query("information", null, null, null, null,                         null, null); if (cursor.getCount() == 0) {                     mTvShow.setText("");                     Toast.makeText(this, "没有数据", Toast.LENGTH_SHORT).show(); } else {                     cursor.moveToFirst();                     mTvShow.setText("Name :  " + cursor.getString(1) + "  ；Tel :  " + cursor.getString(2)); } while (cursor.moveToNext()) {                     mTvShow.append("n" + "Name :  " + cursor.getString(1) + "  ；Tel :  " + cursor.getString(2)); }                 cursor.close();                 db.close(); break; case id.btn_update: //更新数据                 db = myHelper.getWritableDatabase();                 values = new ContentValues(); // 要修改的数据                 values.put("phone", phone = mEtPhone.getText().toString());                 db.update("information", values, "name=?", new String[]{mEtName.getText().toString()}); // 更新并得到行数                 Toast.makeText(this, "信息已修改", Toast.LENGTH_SHORT).show();                 db.close(); break; case id.btn_delete: //删除数据                 db = myHelper.getWritableDatabase();                 db.delete("information", null, null);                 Toast.makeText(this, "信息已删除", Toast.LENGTH_SHORT).show();                 mTvShow.setText("");                 db.close(); break; } } }