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>
