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[文章] 内容提供者-什么是内容提供者？

内容提供者内容提供者，作为android的四大组件之一，说明他的重要性。但是我还是一再强调，它在实际开发中，使用得比较比较少的。什么是内容提供者？

2019-10-30 23:39 · 内容提供者 / provider / android / 数据共享 / 安卓开发

[问答] Android11以上使用ContentResolver报错

这是内容提供者应用主要的代码

2024-03-31 14:03 · Android / 内容提供者 / ContentResolver

[问答] 安卓跨程序无法获取内容提供者

1.在写TestProvider时报了个Failed to find provider info for com.example.contentprvider3的异常

Logcat报错部分

2021-11-29 07:31:15.268 5562-5562/com.example.testprovider D/MainActivity: onClick

2021-11-29 07:31:15.271 5562-5562/com.example.testprovider D/MainActivity: cursor------null

2021-11-29 07:31:15.271 5562-5562/com.example.testprovider W/System.err: java.lang.NullPointerException: Attempt to invoke interface method 'java.lang.String[] android.database.Cursor.getColumnNames()' on a null object reference

2021-11-29 07:31:15.271 5562-5562/com.example.testprovider W/System.err: at com.example.testprovider.MainActivity.RemoteUser(MainActivity.java:34)

2021-11-29 07:31:15.271 5562-5562/com.example.testprovider W/System.err: at java.lang.reflect.Method.invoke(Native Method)

2021-11-29 07:31:15.271 5562-5562/com.example.testprovider W/System.err: at java.lang.reflect.Method.invoke(Method.java:372)

2021-11-29 07:31:15.271 5562-5562/com.example.testprovider W/System.err: at androidx.appcompat.app.AppCompatViewInflater$DeclaredOnClickListener.onClick(AppCompatViewInflater.java:409)

2021-11-29 07:31:15.271 5562-5562/com.example.testprovider W/System.err: at android.view.View.performClick(View.java:4780)

2021-11-29 07:31:15.271 5562-5562/com.example.testprovider W/System.err: at com.google.android.material.button.MaterialButton.performClick(MaterialButton.java:1119)

2021-11-29 07:31:15.271 5562-5562/com.example.testprovider W/System.err: at android.view.View$PerformClick.run(View.java:19866)

2021-11-29 07:31:15.271 5562-5562/com.example.testprovider W/System.err: at android.os.Handler.handleCallback(Handler.java:739)

2021-11-29 07:31:15.271 5562-5562/com.example.testprovider W/System.err: at android.os.Handler.dispatchMessage(Handler.java:95)

2021-11-29 07:31:15.271 5562-5562/com.example.testprovider W/System.err: at android.os.Looper.loop(Looper.java:135)

2021-11-29 07:31:15.271 5562-5562/com.example.testprovider W/System.err: at android.app.ActivityThread.main(ActivityThread.java:5254)

2021-11-29 07:31:15.271 5562-5562/com.example.testprovider W/System.err: at java.lang.reflect.Method.invoke(Native Method)

2021-11-29 07:31:15.271 5562-5562/com.example.testprovider W/System.err: at java.lang.reflect.Method.invoke(Method.java:372)

2021-11-29 07:31:15.271 5562-5562/com.example.testprovider W/System.err: at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:903)

2021-11-29 07:31:15.271 5562-5562/com.example.testprovider W/System.err: at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:698)

2.项目ContentProvider部分代码

package com.example.contentprvider3.Provider;

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;

import androidx.annotation.NonNull;
import androidx.annotation.Nullable;

import com.example.contentprvider3.utils.Constants;
import com.example.contentprvider3.Databasehelper.UserDatabasehelper;


public class UserProvider extends ContentProvider {
    private static final  String SCHEMA="content://";
    private static  final  String AUTHORITY="com.example.contentprvider3.Provider.UserProvider";
    private static  Uri uri_provider =Uri.parse(SCHEMA+AUTHORITY);

    private UserDatabasehelper muserDatabaseHelper = null;
    private static final  int User_Match_Code = 1;
    private static UriMatcher suriMatcher = new UriMatcher(UriMatcher.NO_MATCH);
    static {
        suriMatcher.addURI(AUTHORITY,null,User_Match_Code);
    }

    @Override
    public boolean onCreate() {
        muserDatabaseHelper = new UserDatabasehelper(getContext());
        return false;
    }

    @Nullable
    @Override
    public Cursor query(@NonNull Uri uri, @Nullable String[] projection, @Nullable String selection, @Nullable String[] selectionArgs, @Nullable String sortOrder) {
      //分配规则
        int result = suriMatcher.match(uri);
        if (result==User_Match_Code){
            SQLiteDatabase db = muserDatabaseHelper.getReadableDatabase();
            Cursor cursor = db.query(Constants.TABLE_NAME, projection, selection, selectionArgs, null, null, sortOrder);

        }else{
            //不匹配规则
            throw new IllegalArgumentException("参数错误");
        }

        return null;
    }

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

    @Nullable
    @Override
    public Uri insert(@NonNull Uri uri, @Nullable ContentValues values) {
        return null;
    }

    @Override
    public int delete(@NonNull Uri uri, @Nullable String selection, @Nullable String[] selectionArgs) {
        return 0;
    }

    @Override
    public int update(@NonNull Uri uri, @Nullable ContentValues values, @Nullable String selection, @Nullable String[] selectionArgs) {
        return 0;
    }
}

3.ContentProvider的Manifest文件

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="com.example.contentprvider3">
<permission android:name="contentprvider3._READ_PERMISSION"
    android:protectionLevel="normal"/>
    <permission android:name="contentprvider3._WRITE_PERMISSION"
        android:protectionLevel="normal"/>
    <application
        android:allowBackup="true"
        android:icon="@mipmap/ic_launcher"
        android:label="@string/app_name"
        android:roundIcon="@mipmap/ic_launcher_round"
        android:supportsRtl="true"
        android:theme="@style/Theme.ContentPrvider3">
        <activity
            android:name=".MainActivity"
            android:exported="true">
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />
                <action android:name="android.intent.action.VIEW"/>
                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
        </activity>
        <provider
            android:exported="true"
            android:authorities="com.example.contentprvider3.Provider.UserProvider"
            android:grantUriPermissions="true"
            android:name=".Provider.UserProvider"/>

    </application>

</manifest>

4.TestProvider部分代码

package com.example.testprovider;

import androidx.appcompat.app.AppCompatActivity;

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

public class MainActivity extends AppCompatActivity {
 private static final  String SCHEMA="content://";
 private static  final  String AUTHORITY="com.example.contentprvider3.Provider.UserProvider";
 private static  Uri uri_provider =Uri.parse(SCHEMA+AUTHORITY);
    private static final String TAG = "MainActivity";

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

    }

    public void RemoteUser(View view) {
        Log.d(TAG, "onClick");
        ContentResolver contentResolver = getContentResolver();

        Cursor cursor = contentResolver.query(uri_provider, null, null, null, null);

        try {

            Log.d(TAG, "cursor------"+cursor);
            String[] columnNames2 = cursor.getColumnNames();
            for (String columnName : columnNames2) {
                Log.d(TAG, "columnName---" + columnName);
            }

            while (cursor.moveToNext()) {
                Log.d(TAG, "------------");
                for (String columnName : columnNames2) {
                    int columnname = cursor.getColumnIndex(columnName);
                    String value = cursor.getString(columnname);
                    Log.d(TAG, columnName + "------" + value);
                    Log.d(TAG, "----------------");
                }

            }
            cursor.close();
        }catch (Exception e){e.printStackTrace();

        }


        }


         }

5.TestProvider的Manifest文件

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="com.example.testprovider">
    
    <uses-permission android:name="ContentPrivider3._READ_PERMISSION"/>
    <uses-permission android:name="ContentPrivider3._WRITE_PERMISSION"/>
    
<queries>
    <package android:name="com.example.contentprvider3"/>
    <provider android:authorities="com.example.contentprvider3.Provider.UserProvider"/>

</queries>

    <application
        android:allowBackup="true"
        android:icon="@mipmap/ic_launcher"
        android:label="@string/app_name"
        android:roundIcon="@mipmap/ic_launcher_round"
        android:supportsRtl="true"
        android:theme="@style/Theme.TestProvider">
        <activity
            android:name=".MainActivity"
            android:exported="true">
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />
                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
        </activity>
    </application>

</manifest>

2021-11-29 15:38 · AndroidProvider

[问答] 内容提供者P17(图片媒体库),获取表结构报错

在打印输出图片媒体库表结构过程中,打印部分属性后报错Unable to convert BLOB to string

完整的报错信息如下:

该部分的代码为:

package com.example.imagepicker;

import android.annotation.SuppressLint;
import android.content.ContentResolver;
import android.database.Cursor;
import android.net.Uri;
import android.os.Bundle;
import android.provider.MediaStore;
import android.util.Log;

import androidx.annotation.NonNull;
import androidx.annotation.Nullable;
import androidx.appcompat.app.AppCompatActivity;
import androidx.loader.app.LoaderManager;
import androidx.loader.content.CursorLoader;
import androidx.loader.content.Loader;

import java.io.InputStream;
import java.io.OutputStream;
import java.sql.Blob;
import java.sql.SQLException;

public class PickerActivity extends AppCompatActivity {

    private static final String TAG = "PickerActivity";
    private static final int LOADER_ID = 1;

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

        ContentResolver contentResolver = getContentResolver();
//        Uri imageUri = MediaStore.Images.Media.EXTERNAL_CONTENT_URI;
//        Log.d(TAG, "imageUri ------> " + imageUri);
        Uri imageUri = MediaStore.Files.getContentUri("external");
        Cursor cursor = contentResolver.query(imageUri, null, null, null, null);
        String[] columnNames = cursor.getColumnNames();
        while (cursor.moveToNext()) {
            Log.d(TAG, "==============");
            for (String columnName : columnNames) {
                @SuppressLint("Range") String value = cursor.getString(cursor.getColumnIndex(columnName));
                Log.d(TAG, columnName + "------> " + value);
            }
            Log.d(TAG, "==============");
        }
        cursor.close();
//        initLoadManger();
    }

    private void initLoadManger() {
        LoaderManager loaderManager = LoaderManager.getInstance(this);
        loaderManager.initLoader(LOADER_ID, null, new LoaderManager.LoaderCallbacks<Cursor>() {
            @NonNull
            @Override
            public Loader<Cursor> onCreateLoader(int id, @Nullable Bundle args) {
                if (id == LOADER_ID) {
                    return new CursorLoader(PickerActivity.this,
                            MediaStore.Images.Media.EXTERNAL_CONTENT_URI,
                            new String[]{"_data", "_display_name", "date_modified"},
                            null, null, "data_added DESC");
                }
                return null;
            }

            @SuppressLint("Range")
            @Override
            public void onLoadFinished(@NonNull Loader<Cursor> loader, Cursor data) {
                if (data != null) {
                    String[] columnNames = data.getColumnNames();
                    while(data.moveToNext()) {
                        Log.d(TAG, "==============");
                        for (String columnName : columnNames) {
//                            @SuppressLint("Range") String value = data.getString(data.getColumnIndex(columnName));
                            Log.d(TAG, columnName + "------> " + data.getString(data.getColumnIndex(columnName)));
                        }
                        Log.d(TAG, "==============");
                    }
                    data.close();
                }
            }

            @Override
            public void onLoaderReset(@NonNull Loader<Cursor> loader) {

            }
        });
    }
}

尝试过网上的一些解决方案,但都没能成功解决这个问题,希望各位大佬指点一二,不甚感激

2022-10-08 10:35 · 求助 / 内容提供者