Android ContentProvider学习

Android ContentProvider学习
一、 ContentProvider介绍
ContentProvider提供了对接数据库的接口，需要我们通过SQLiteOpenHelper来实现数据库本身的增删改查。ContentProvider不能简单理解数据库接口，因为当我们在其他app里面调用getContentResolver并进行增删改查的时候，能调到自定义ContentProvider的接口里面，这有点像进程间通信，实际上也的确是，底层利用Binder机制实现了跨进程调用ContentProvider。当然如果我们不在Manifest里面的Provider标签添加android:exported=“true”，那么其他app也无法使用这个contentProvider,当然这个时候也不需要利用ContentProvider了，可以使用更轻量级的SharedPreference来存储。

通过ContentResolver来查找ContentProvider是通过URI来查找的，一般URI的格式为schema+authority+path+id,如下图

我们知道URL是URI的一种，所以可以使用一般的http url来理解，比如我CSDN的首页https://blog.csdn.net/xiaoshixiu, schema为http://,authoriity为blog.csdn.net，path为xiaoshixiu，id为空。

二、 Demo
首先是ContentProvider端，自定义ContentProvider后，需要在Manifest里添加，当然Android Studio会自动添加。

注意两个属性
android:authorities="MyContentProviderAuthority"，一般Authority可以写成包名，比如com.mypackage.myapp
android:exported="true"，表示其他app可以通过ContentResolver搜到本Provider提供的数据。

然后是自定义Provider

package com.example.providertest;

import android.content.ContentProvider;
import android.content.ContentUris;
import android.content.ContentValues;
import android.content.Context;
import android.content.UriMatcher;
import android.database.Cursor;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteOpenHelper;
import android.net.Uri;
import android.util.Log;

import androidx.annotation.Nullable;

public class MyContentProvider extends ContentProvider {

    
    private UriMatcher uriMatcher=new UriMatcher(UriMatcher.NO_MATCH);
    private SQLiteDatabase db;
    private static String TABLE_NAME="MyTable";

    public MyContentProvider() {
        //Authority在Manifest里面就定义了，实际上对比uri时，到ContentProvider里已经对比了Authority
        uriMatcher.addURI("MyContentProviderAuthority","MY",0);
    }

    //目前仅实现了onCreate，insert，query
    @Override
    public int delete(Uri uri, String selection, String[] selectionArgs) {
        // Implement this to handle requests to delete one or more rows.
        Log.d("MyContentProvider","delete");
        throw new UnsupportedOperationException("Not yet implemented");
    }

    @Override
    public String getType(Uri uri) {
        // TODO: Implement this to handle requests for the MIME type of the data
        // at the given URI.
        Log.d("MyContentProvider","getType");
        throw new UnsupportedOperationException("Not yet implemented");
    }

//注意现在不能插入两条相同数据，会崩溃
    @Override
    public Uri insert(Uri uri, ContentValues values) {
        // TODO: Implement this to handle requests to insert a new row.
        Log.d("MyContentProvider","insert");
        long row;
        if(uriMatcher.match(uri)==0){
            row =db.insert(TABLE_NAME,null,values);
            if(row>=0){
                getContext().getContentResolver().notifyChange(uri,null);
                return ContentUris.withAppendedId(uri,row);
            }
        }
        throw new UnsupportedOperationException("Not yet implemented");
    }

    @Override
    public boolean onCreate() {
        // TODO: Implement this to initialize your content provider on startup.
        Log.d("MyContentProvider","onCreate");
        db=new MyDBHelper(getContext(),"MyDB",null,1).getWritableDatabase();
        return true;
    }

    @Override
    public Cursor query(Uri uri, String[] projection, String selection,
                        String[] selectionArgs, String sortOrder) {
        // TODO: Implement this to handle query requests from clients.
        Log.d("MyContentProvider","query");
        if(uriMatcher.match(uri)==0){
            return db.query(TABLE_NAME,projection,selection,selectionArgs,null,null,sortOrder,null);
        }
        throw new UnsupportedOperationException("Not yet implemented");
    }

    @Override
    public int update(Uri uri, ContentValues values, String selection,
                      String[] selectionArgs) {
        // TODO: Implement this to handle requests to update one or more rows.
        Log.d("MyContentProvider","update");
        throw new UnsupportedOperationException("Not yet implemented");
    }

    //自定义SQLiteOpenHelper，实现sql相关操作
    public class MyDBHelper extends SQLiteOpenHelper{


        public MyDBHelper(@Nullable Context context, @Nullable String name, @Nullable SQLiteDatabase.CursorFactory factory, int version) {
            super(context, name, factory, version);
        }

        @Override
        public void onCreate(SQLiteDatabase db) {
            Log.d("MyDBHelper","onCreate");
            db.execSQL("CREATE TABLE IF NOT EXISTS "+TABLE_NAME+" (id INTEGER PRIMARY KEY,name VARCHAR(20))");
        }

        @Override
        public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
            Log.d("MyDBHelper","onUpgrade");
        }


    }
}

然后是Activity和Layout

package com.example.providertest;

import androidx.appcompat.app.AppCompatActivity;

import android.content.ContentValues;
import android.net.Uri;
import android.os.Bundle;
import android.view.View;
import android.widget.EditText;

public class MainActivity extends AppCompatActivity {

    private EditText editText_id;
    private EditText editText_name;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        editText_id=(EditText)findViewById(R.id.et_input_id);
        editText_name=(EditText)findViewById(R.id.et_input_name);
    }

    //点击按钮则从EditText中获取数据，向ContentProvider里面插入数据
    public void onClickInput(View view){
        String id=editText_id.getText().toString();
        String name=editText_name.getText().toString();
        ContentValues contentValues=new ContentValues();
        contentValues.put("id",id);
        contentValues.put("name",name);
        getContentResolver().insert(Uri.parse("content://"+"MyContentProviderAuthority"+"/MY"),contentValues);
    }
}

Layout文件

接下来运行app

点击按钮后打印如下log:

05-03 15:16:13.129 29876-29876/com.example.providertest D/MyContentProvider: insert

接下来我们另外起一个进程，用来跨进程查找数据

package com.example.querycontent;

import androidx.appcompat.app.AppCompatActivity;

import android.content.ContentValues;
import android.database.Cursor;
import android.net.Uri;
import android.os.Bundle;
import android.view.View;
import android.widget.EditText;
import android.widget.TextView;

public class MainActivity extends AppCompatActivity {

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

    //可以跨进程查找ContentProvider数据
    public void onclickquery(View view){
        TextView textView=(TextView)findViewById(R.id.tv_query);
        Cursor cursor=getContentResolver().query(Uri.parse("content://"+"MyContentProviderAuthority"+"/MY"),new String[]{"id","name"},
                null,null,null);
        StringBuffer stringBuffer=new StringBuffer();
        while (cursor.moveToNext()){
            stringBuffer.append("id:"+cursor.getInt(cursor.getColumnIndex("id"))+"\n");
            stringBuffer.append("name:"+cursor.getString(cursor.getColumnIndex("name"))+"\n");
        }
        textView.setText(stringBuffer.toString());
    }

    //也可以跨进程插入数据
    public void onClickInput(View view){
        EditText editText_id;
        EditText editText_name;
        editText_id=(EditText)findViewById(R.id.et_input_id);
        editText_name=(EditText)findViewById(R.id.et_input_name);
        String id=editText_id.getText().toString();
        String name=editText_name.getText().toString();
        ContentValues contentValues=new ContentValues();
        contentValues.put("id",id);
        contentValues.put("name",name);
        getContentResolver().insert(Uri.parse("content://"+"MyContentProviderAuthority"+"/MY"),contentValues);
    }
}

Layout文件：

运行app

点击query:

最后是资源链接：
https://download.csdn.net/download/xiaoshixiu/12385628