Android：week 11总结 内容提供者、数据库

目录

Monday

1.内容提供者

 

Tuesday

1.数据库

 

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Monday

1.内容提供者

创建方式： (URL Authorities和文件夹路径名保持一致)

自动生成

 

Tuesday

1.数据库

1.新建SQL的java代码

DBaseHelper：

package com.example.myapplication;

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

public class DBaseHelper extends SQLiteOpenHelper {
    public DBaseHelper(Context context){
        super(context, "provider.db", null, 1);
    }
    @Override
    public void onCreate(SQLiteDatabase db){
        //整数、主键、自动增加、类型
        db.execSQL("create table info(_id integer primary key autoincrement, name varchar(20))");
    }
    public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion){}
}

2.创建ContentProvider

MyContentProvider：

package com.example.myapplication;

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

public class MyContentProvider extends ContentProvider {
    private static UriMatcher uriMatcher = new UriMatcher(-1);//匹配失败的返回值-1
    private DBaseHelper helper;
    static {
        uriMatcher.addURI("com.example.mycontentprovider", "info", 1);
    }
    public MyContentProvider() {
    }

    @Override
    public int delete(Uri uri, String selection, String[] selectionArgs) {
        // Implement this to handle requests to delete one or more rows.
        if(uriMatcher.match(uri) == 1){
            SQLiteDatabase database = helper.getWritableDatabase();//打开数据库
            int cont = database.delete("info", selection, selectionArgs);//删除的数量
            database.close();
            return cont;
        }
        else
            throw new IllegalArgumentException("Uri is error.");
    }

    @Override
    public String getType(Uri uri) {
        // TODO: Implement this to handle requests for the MIME type of the data
        // at the given URI.
        return null;
    }

    @Override
    public Uri insert(Uri uri, ContentValues values) {
        // TODO: Implement this to handle requests to insert a new row.
        if(uriMatcher.match(uri) == 1){
            SQLiteDatabase database = helper.getWritableDatabase();
            //空为null 否则values
            database.insert("info", null, values);
            database.close();
            return uri;
        }
        else
            throw new IllegalArgumentException("Uri is error.");
    }

    @Override
    public boolean onCreate() {
        // TODO: Implement this to initialize your content provider on startup.
        helper = new  DBaseHelper(getContext());//实例化
        return false;
    }

    @Override
    public Cursor query(Uri uri, String[] projection, String selection,
                        String[] selectionArgs, String sortOrder) {
        // TODO: Implement this to handle query requests from clients.
        if(uriMatcher.match(uri) == 1){ //匹配
            SQLiteDatabase database = helper.getReadableDatabase();
            //执行对数据库的查询
            Cursor cursor = database.query("info", projection, selection, selectionArgs, null, null, sortOrder);
            database.close();
            return cursor;
        }
        else
            throw new UnsupportedOperationException("Uri is error.");
    }

    @Override
    public int update(Uri uri, ContentValues values, String selection,
                      String[] selectionArgs) {
        // TODO: Implement this to handle requests to update one or more rows.
        if(uriMatcher.match(uri) == 1){
            SQLiteDatabase database = helper.getWritableDatabase();
            int cont = database.update("info", values, selection, selectionArgs);
            database.close();
            return cont;
        }
        else
            throw new IllegalArgumentException("Uri is error.");
    }
}

activity_main:

MainActivity：

package com.example.myapplication;

import androidx.appcompat.app.AppCompatActivity;

import android.content.ContentResolver;
import android.content.ContentValues;
import android.net.Uri;
import android.os.Bundle;
import android.util.Log;
import android.view.View;

public class MainActivity extends AppCompatActivity {
    private ContentResolver resolver;
    private Uri uri;
    private int count = 0;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        DBaseHelper helper = new DBaseHelper(this);
    }
    public void click(View view){
        uri = Uri.parse("content://com.example.myapplication/info");
        resolver = getContentResolver();

        switch (view.getId()){
            case R.id.add:
                ContentValues values = new ContentValues();
                values.put("name", "software"+count ++);
                resolver.insert(uri, values);
                Log.d("***", "insert");
                break;
            case R.id.delete:
                resolver.delete(uri,"name=?", new String[]{"software0"});
                Log.d("***", "delete");
                break;
            case R.id.query:
                break;
            case R.id.update:
                break;
        }
    }
}