Android之自定义ContentProvider的实现（Very Very 用心）

Android之自定义ContentProvider的实现（Very Very 用心）

刚开始学习ContentProvider时是学的系统的ContentProvider，没碰到什么问题，但是在学习自定义ContentProvider的实现时，唉，碰到好几个问题，花了我好多时间。

 

我碰到的问题：

1.  java.lang.IllegalArgumentException: column '_id' does not exist

解决方法：创建数据表时插入一个名为_id的列，类型为自增量，因为在使用Cursor相关的Adapter时需要用到这个列

2.Failed to find provider for user 0 ; expected to find a valid ContentProvider for

解决方法：在第一个应用的AndroidManifest.xml中添加如下代码

但是当我使用API 30时却还是会报错，报空指针异常，到现在还没解决，真的菜啊，所以为了让程序运行起来，我就选择API 29 ，就能正常运行了

3.注意：在数据库类里写sql语句时，最容易出错，比如少了空格拼接起来就是错误的sql语句，英文逗号写成中文逗号，进行增删改查时表名，列名要写正确

4.Uri里的authorities也非常容易搞错，搞错了就会报 uri 找不到异常

5.还有很多小问题就不一一描述了，细心认真点，相信你们自己能解决

为了让你们（新手,包括我自己）能正确的运行起我的程序来，我把所有类，布局文件和配置信息都贴出来。如果你去看别人写的自定义ContentProvider的实现，你会发现有这几个问题，不敢说全部，大多数是这样，自定义ContentProvider的实现本来就是面向新手的，所以把信息都写全来才好去学习和模仿加创新。

1.缺少布局文件，对于我这种小白来说真的就离谱，id都不知道哪个是哪个

2.缺少一些类，不如数据库类。

3.只贴出一些重要代码片段来，对于小白来说，的确不好搞

4.缺少配置信息，这只能看看，要想模仿就难了，一大堆BUG等着你

5.完整的源码要VIP或者收费

项目里的代码详解我就不说了，大多数都有解释，实在不懂的，可以自行百度，肯定比我在这说的清楚详细易懂，我这篇给文章主要还是让各位实现自定义ContentProvider，能跑起来

先来看看我效果

20211021

注意：视频中的删除我是按序号删除的，比如表中有一条记录：

序号：1  姓名：小明  工作：Android Development

然后我在输入框中输入，只要序号是1，不管姓名和工作输的是什么，都会将

序号：1  姓名：小明  工作：Android Development 这条记录删除。

（感兴趣的可以自己去改改）

首先看一下我的项目结构，你就知道要写哪些类和布局文件了

 

模块gamedemo是第一个应用

MainActivity代码如下

import android.app.Activity;
import android.content.ContentResolver;
import android.content.ContentValues;
import android.database.Cursor;
import android.database.sqlite.SQLiteDatabase;
import android.net.Uri;
import android.os.Bundle;
import android.text.TextUtils;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import android.widget.TextView;
import android.widget.Toast;

public class MainActivity extends Activity implements View.onClickListener {

    private static final String TAG = "lzs";
    private DbHelp dbHelp;
    private SQLiteDatabase db;
    private TextView userTv;
    private Button btn_query;
    private Button btn_insert;
    private Button btn_delete;
    private Button btn_update;
    private int m=2;
    private int n=3;
    private EditText xuhao;
    private EditText xingming;
    private EditText zhiye;
    private int id;
    private String name;
    private String job;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        this.dbHelp = new DbHelp(this); //创建数据库
        this.db = this.dbHelp.getWritableDatabase();
        init(); //初始化控件
    }

    private void init() {
        btn_query = findViewById(R.id.btn_query);
        btn_insert = findViewById(R.id.btn_insert);
        btn_delete = findViewById(R.id.btn_delete);
        btn_update = findViewById(R.id.btn_update);
        xuhao = findViewById(R.id.xuhao);
        xingming = findViewById(R.id.xingming);
        zhiye = findViewById(R.id.zhiye);

        btn_query.setonClickListener(this);
        btn_insert.setonClickListener(this);
        btn_delete.setonClickListener(this);
        btn_update.setonClickListener(this);
    }

    @Override
    protected void onStart() {
        super.onStart();
    }

    @Override
    protected void onDestroy() {
        super.onDestroy();
        db.close();
        dbHelp.close();
    }

    @Override
    public void onClick(View view) {
        switch (view.getId()){
            case R.id.btn_query:
                btn_query();
                break;
            case R.id.btn_insert:
                btn_insert();
                break;
            case R.id.btn_delete:
                btn_delete();
                break;
            case R.id.btn_update:
                btn_update();
                break;
        }
    }


    //查询函数
    private void btn_query(){

        Cursor user = this.db.query("user", null, null, null, null, null, null);
        this.userTv = findViewById(R.id.id_user_db);

        //清空文本，防止重复查询而多次显示
        if(!TextUtils.isEmpty(this.userTv.getText()))
        {
            this.userTv.setText("");
        }

        while (user.moveTonext()){
            String id = user.getString(0);
            String name = user.getString(1);
            String jobs = user.getString(2);
            this.userTv.append("序号:"+id+"  姓名:"+name+"  工作:"+jobs+"n");
        }
    }
    //插入函数(没有用SQL语句，用的是Android的方式)
    private void btn_insert(){
        if(!TextUtils.isEmpty(xuhao.getText())&&!TextUtils.isEmpty(xingming.getText())&&!TextUtils.isEmpty(zhiye.getText())){
            id = Integer.parseInt(xuhao.getText().toString());
            name = xingming.getText().toString();
            job = zhiye.getText().toString();
            Cursor result=db.rawQuery("select * from user where _id = "+id,null);
            if(!result.isAfterLast()){
                Toast.makeText(MainActivity.this,"插入失败，改记录已存在或序号重复！",Toast.LENGTH_SHORT).show();
            }else {
                Uri uri_user = Uri.parse("content://cn.sch.myprovider/user");
                // 向user表插入数据
                ContentValues values3 = new ContentValues();
                values3.put("_id", id);
                values3.put("name", name);
                values3.put("jobs", job);
                // 获取ContentResolver
                ContentResolver resolver3 = getContentResolver();
                // 通过ContentResolver 根据URI 向ContentProvider中插入数据
                resolver3.insert(uri_user, values3);
                Toast.makeText(MainActivity.this,"插入成功",Toast.LENGTH_SHORT).show();
            }

        }else {
            Toast.makeText(MainActivity.this,"请填写完整，不能为空！",Toast.LENGTH_SHORT).show();
        }
    }
    //删除函数(利用SQL语句删除，你也可以用Android的方式删除)，因为序号是唯一的，所以直接根据提供的序号删除就可以了
    private void btn_delete(){
        if(!TextUtils.isEmpty(xuhao.getText())){
            id = Integer.parseInt(xuhao.getText().toString());
            Cursor result=db.rawQuery("select _id from user where _id="+id,null);
            if(!result.isAfterLast()){
                db.execSQL("delete from user where _id="+id);
                Toast.makeText(MainActivity.this,"删除成功",Toast.LENGTH_SHORT).show();
            }else {
                Toast.makeText(MainActivity.this,"删除失败，没有该条记录！",Toast.LENGTH_SHORT).show();
            }

        }else {
            Toast.makeText(MainActivity.this,"请填写完整，不能为空！",Toast.LENGTH_SHORT).show();
        }

    }
    //更新函数(利用SQL语句更新，你也可以用Android的方式更新)，因为序号唯一，所以直接根据输入的序号更改就可以了
    private void btn_update(){
        if(!TextUtils.isEmpty(xuhao.getText())&&!TextUtils.isEmpty(xingming.getText())&&!TextUtils.isEmpty(zhiye.getText())){
            id = Integer.parseInt(xuhao.getText().toString());
            name = xingming.getText().toString();
            job = zhiye.getText().toString();
            Cursor result=db.rawQuery("select * from user where _id="+id,null);
            if(!result.isAfterLast()){
                db.execSQL("update user set _id="+id +" where _id="+id);
                db.execSQL("update user set name='"+name +"' where _id="+id);//注意是 set='name'  如果不清楚可以再去看看数据库的知识
                db.execSQL("update user set jobs='"+job +"' where _id="+id);
                Toast.makeText(MainActivity.this,"更新成功",Toast.LENGTH_SHORT).show();
            }else {

                Toast.makeText(MainActivity.this,"更新失败，改记录不存在！",Toast.LENGTH_SHORT).show();
            }

        }else {
            Toast.makeText(MainActivity.this,"请填写完整，不能为空！",Toast.LENGTH_SHORT).show();
        }

    }

}

MainActivity的布局文件activity_main.xml 代码如下

MyProvide代码如下

import android.content.ContentProvider;
import android.content.ContentValues;
import android.content.Context;
import android.content.UriMatcher;
import android.database.Cursor;
import android.database.sqlite.SQLiteDatabase;
import android.net.Uri;


public class MyProvide extends ContentProvider {

    private Context mContext;
    private DbHelp dbHelp = null;
    private SQLiteDatabase db = null;

    public static final String AUTHORITY = "cn.sch.myprovider";

    public static final int User_Code = 1;

    private UriMatcher mMatcher;

    @Override
    public boolean onCreate() {
        mContext = getContext();
        mMatcher = new UriMatcher(UriMatcher.NO_MATCH);
        //初始化
        // 若URI资源路径 = content://cn.sch.myprovider/user ，则返回注册码User_Code
        mMatcher.addURI(AUTHORITY, "user", User_Code);

        dbHelp = new DbHelp(mContext);
        this.db = dbHelp.getWritableDatabase();
        // 初始化表的数据
        db.execSQL("delete from user");
        db.execSQL("insert into user values(1,'xiaoming','Android Development')");
        db.execSQL("insert into user values(2,'xiaohua','Java Development')");
        return true;
    }

    @Override
    public Cursor query( Uri uri,  String[] projection, String selection,  String[] selectionArgs, String sortOrder) {
        String tableName = getTableName(uri);
        return db.query(tableName,projection,selection,selectionArgs,null,null,sortOrder,null);
    }

    @Override
    public String getType( Uri uri) {
        return null;
    }

    @Override
    public Uri insert( Uri uri,  ContentValues values) {
        String tableName = getTableName(uri);
        //向表中插入数据
        db.insert(tableName,null,values);
        mContext.getContentResolver().notifyChange(uri,null);
        return uri;
    }

    @Override
    public int delete( Uri uri,  String selection,  String[] selectionArgs) {
        String tableName = getTableName(uri);
        int count=db.delete(tableName, null, null);
        if(count>0){
            getContext().getContentResolver().notifyChange(uri, null);
            return count;
        }
        return 0;
    }

    @Override
    public int update( Uri uri,  ContentValues values,  String selection,  String[] selectionArgs) {
        String tableName = getTableName(uri);
        int count = db.update(tableName, values, selection,selectionArgs);
        if(count>0){
            getContext().getContentResolver().notifyChange(uri, null);
            return count;
        }
        return 0;
    }


    private String getTableName(Uri uri) {
        String tableName = null;
        switch (mMatcher.match(uri)){
            case User_Code:
                tableName = DbHelp.USER_TABLE_NAME;
                break;
        }
        return tableName;
    }

}

DbHelp代码如下

import android.content.Context;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteOpenHelper;

public class DbHelp extends SQLiteOpenHelper {
    // 数据库名
    private static final String DATAbase_NAME = "finch.db";
    // 表名
    public static final String USER_TABLE_NAME = "user";
    //数据库版本号
    private static final int DATAbase_VERSION = 1;

    public DbHelp(Context context) {
        super(context, DATAbase_NAME, null, DATAbase_VERSION);
    }

    @Override
    public void onCreate(SQLiteDatabase db) {
        //创建数据库表
        //注意;如果你第一次运行后第二次又改动创建数据语句时，并且只改动了属性，没有该表名，那么当你再次运行App时会发现会报错，新改动的属性不存在
        //解决方法：手动将已建好的那个表删除，或者删除App重新安装，这样你改动的属性才能生效
        db.execSQL("CREATE TABLE IF NOT EXISTS "+USER_TABLE_NAME+"(_id INTEGER PRIMARY KEY AUTOINCREMENT,"+" name TEXT,"+"jobs TEXT)");
    }

    @Override
    public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {

    }
}

第一个应用的AndroidManifest.xml

第一个应用的build.gradle

plugins {
    id 'com.android.application'
}

android {
    compileSdk 29

    defaultConfig {
        applicationId "com.example.gamedemo"
        minSdk 21
        targetSdk 29
        versionCode 1
        versionName "1.0"

        testInstrumentationRunner "androidx.test.runner.AndroidJUnitRunner"
    }

    buildTypes {
        release {
            minifyEnabled false
            proguardFiles getDefaultProguardFile('proguard-android-optimize.txt'), 'proguard-rules.pro'
        }
    }
    compileOptions {
        sourceCompatibility JavaVersion.VERSION_1_8
        targetCompatibility JavaVersion.VERSION_1_8
    }
}

dependencies {

    implementation 'androidx.appcompat:appcompat:1.2.0'
    implementation 'com.google.android.material:material:1.3.0'
    implementation 'androidx.constraintlayout:constraintlayout:2.0.4'
    testImplementation 'junit:junit:4.+'
    androidTestImplementation 'androidx.test.ext:junit:1.1.2'
    androidTestImplementation 'androidx.test.espresso:espresso-core:3.3.0'
}

模块contentprovidertest是第二个应用

MainActivity代码如下

package com.example.contentprovidertest;

import android.Manifest;
import android.content.ContentResolver;
import android.content.ContentValues;
import android.content.pm.PackageManager;
import android.database.Cursor;
import android.net.Uri;
import android.os.Bundle;
import android.text.TextUtils;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import android.widget.TextView;
import android.widget.Toast;

import androidx.appcompat.app.AppCompatActivity;
import androidx.core.app.ActivityCompat;

public class MainActivity extends AppCompatActivity implements View.onClickListener {

    private static final String TAG = "lzs";
    private TextView userTv;
    private Button btn_query2;
    private Button btn_insert2;
    private Button btn_delete2;
    private Button btn_update2;
    private EditText xuhao2;
    private EditText xingming2;
    private EditText zhiye2;
    private int id;
    private String name;
    private String job;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        this.userTv = findViewById(R.id.id_tv);

        //动态获取权限
        if(ActivityCompat.checkSelfPermission(this, Manifest.permission.READ_EXTERNAL_STORAGE)==PackageManager.PERMISSION_GRANTED
                ||ActivityCompat.checkSelfPermission
                (this, Manifest.permission.WRITE_EXTERNAL_STORAGE)==PackageManager.PERMISSION_GRANTED) {
            init(); //初始化控件
        }else {
            ActivityCompat.requestPermissions(this,new String[]{Manifest.permission.READ_EXTERNAL_STORAGE,Manifest.permission.WRITE_EXTERNAL_STORAGE},0x10);
        }
    }

    private void init() {

        xuhao2 = findViewById(R.id.xuhao2);
        xingming2 = findViewById(R.id.xingming2);
        zhiye2 = findViewById(R.id.zhiye2);

        btn_query2 = findViewById(R.id.btn_query2);
        btn_insert2 = findViewById(R.id.btn_insert2);
        btn_delete2 = findViewById(R.id.btn_delete2);
        btn_update2 = findViewById(R.id.btn_update2);

        btn_query2.setonClickListener(this);
        btn_insert2.setonClickListener(this);
        btn_delete2.setonClickListener(this);
        btn_update2.setonClickListener(this);
    }

    @Override
    public void onClick(View view) {
        switch (view.getId()){
            case R.id.btn_query2:
                btn_query2();
                break;
            case R.id.btn_insert2:
                btn_insert2();
                break;
            case R.id.btn_delete2:
                btn_delete2();
                break;
            case R.id.btn_update2:
                btn_update2();
                break;
        }
    }

    private void btn_update2() {
        id = Integer.parseInt(xuhao2.getText().toString());
        name = xingming2.getText().toString();
        job = zhiye2.getText().toString();
        if(!TextUtils.isEmpty(xuhao2.getText())&&!TextUtils.isEmpty(xingming2.getText())&&!TextUtils.isEmpty(zhiye2.getText())){
            Uri uri = Uri.parse("content://cn.sch.myprovider/user");
            ContentResolver resolver2 = getContentResolver();
            ContentValues values2 = new ContentValues();
            values2.put("_id", id);
            values2.put("name", name);
            values2.put("jobs", job);
            resolver2.update(uri,values2,"_id="+id,null);
            Toast.makeText(MainActivity.this, "更新成功", Toast.LENGTH_SHORT).show();
        }else {
            Toast.makeText(MainActivity.this,"请填写完整，不能为空！",Toast.LENGTH_SHORT).show();
        }

    }

    private void btn_delete2() {
        id = Integer.parseInt(xuhao2.getText().toString());
        if(!TextUtils.isEmpty(xuhao2.getText())){
            Uri uri = Uri.parse("content://cn.sch.myprovider/user");
            ContentResolver resolver2 = getContentResolver();
            resolver2.delete(uri,"_id ="+id,null);
            Toast.makeText(MainActivity.this, "删除成功", Toast.LENGTH_SHORT).show();
        }else {
            Toast.makeText(MainActivity.this,"请填写完整，不能为空！",Toast.LENGTH_SHORT).show();
        }

    }

    private void btn_insert2() {

        this.userTv.setText("");
        id = Integer.parseInt(xuhao2.getText().toString());
        name = xingming2.getText().toString();
        job = zhiye2.getText().toString();
        if(!TextUtils.isEmpty(xuhao2.getText())&&!TextUtils.isEmpty(xingming2.getText())&&!TextUtils.isEmpty(zhiye2.getText())){
            Uri uri = Uri.parse("content://cn.sch.myprovider/user");
            // 插入表中数据
            ContentValues values2 = new ContentValues();
            values2.put("_id", id);
            values2.put("name", name);
            values2.put("jobs", job);
            // 获取ContentResolver
            ContentResolver resolver2 = getContentResolver();
            // 通过ContentResolver 根据URI 向ContentProvider中插入数据
            resolver2.insert(uri, values2);
            // 通过ContentResolver 向ContentProvider中查询数据
            Cursor cursor2 = resolver2.query(uri, new String[]{"_id", "name","jobs"}, null, null, null);
            while (cursor2.moveTonext()) {
                // 将表中数据全部输出
                this.userTv.append("    序号:" + cursor2.getInt(0) + "    姓名:" + cursor2.getString(1) +"    工作:"+cursor2.getString(2)+ "n");
            }
            Toast.makeText(MainActivity.this,"插入成功",Toast.LENGTH_SHORT).show();
            // 关闭游标
            cursor2.close();

        }else {
            Toast.makeText(MainActivity.this,"请填写完整，不能为空！",Toast.LENGTH_SHORT).show();
        }
    }

    private void btn_query2() {
        Uri uri  = Uri.parse("content://cn.sch.myprovider/user");

        Cursor query = getContentResolver().query(uri, null, null, null, null);
        //清空文本，防止重复查询而多次显示
        if(!TextUtils.isEmpty(this.userTv.getText()))
        {
            this.userTv.setText("");
        }
        while (query.moveTonext()) {
            int id = query.getInt(0);
            String name = query.getString(1);
            String job = query.getString(2);

            this.userTv.append("    序号:" + id + "    姓名:" + name +"    工作:"+job+ "n");
        }
        query.close();
    }
}

MainActivity的activity_main.xml代码如下

第二个应用的AndroidManifest.xml

第二个应用的build.gradle

plugins {
    id 'com.android.application'
}

android {
    compileSdk 29

    defaultConfig {
        applicationId "com.example.contentprovidertest"
        minSdk 21
        targetSdk 29
        versionCode 1
        versionName "1.0"

        testInstrumentationRunner "androidx.test.runner.AndroidJUnitRunner"
    }

    buildTypes {
        release {
            minifyEnabled false
            proguardFiles getDefaultProguardFile('proguard-android-optimize.txt'), 'proguard-rules.pro'
        }
    }
    compileOptions {
        sourceCompatibility JavaVersion.VERSION_1_8
        targetCompatibility JavaVersion.VERSION_1_8
    }
}

dependencies {

    implementation 'androidx.appcompat:appcompat:1.2.0'
    implementation 'com.google.android.material:material:1.3.0'
    implementation 'androidx.constraintlayout:constraintlayout:2.0.4'
    testImplementation 'junit:junit:4.+'
    androidTestImplementation 'androidx.test.ext:junit:1.1.2'
    androidTestImplementation 'androidx.test.espresso:espresso-core:3.3.0'
}

如果又遇到啥问题，可以留言，一起来解决。

到此所有代码展示完毕，希望你们喜欢，觉得不错的可以给我个赞哈，嘿嘿。