java - 由于 mContext 对象，Android 中的编译错误

Question

我在我的 Linux 机器 Ubuntu 15.04 上运行 Android Studio。我在编译过程中遇到了这个问题。错误是由于在使用此指针时使用了 mContext 对象。gradle 编译消息是:

Information:Gradle tasks [:app:assembleDebug,:app:assembleDebugAndroidTest]
:app:preBuild UP-TO-DATE
:app:preDebugBuild UP-TO-DATE
:app:checkDebugManifest
:app:preReleaseBuild UP-TO-DATE
:app:prepareComAndroidSupportAppcompatV72300Library UP-TO-DATE
:app:prepareComAndroidSupportSupportV42300Library UP-TO-DATE
:app:prepareDebugDependencies
:app:compileDebugAidl UP-TO-DATE
:app:compileDebugRenderscript UP-TO-DATE
:app:generateDebugBuildConfig UP-TO-DATE
:app:generateDebugAssets UP-TO-DATE
:app:mergeDebugAssets UP-TO-DATE
:app:generateDebugResValues UP-TO-DATE
:app:generateDebugResources UP-TO-DATE
:app:mergeDebugResources UP-TO-DATE
:app:processDebugManifest UP-TO-DATE
:app:processDebugResources UP-TO-DATE
:app:generateDebugSources UP-TO-DATE
:app:processDebugJavaRes UP-TO-DATE
:app:compileDebugJavaWithJavac
Note: Some input files use or override a deprecated API.
Note: Recompile with -Xlint:deprecation for details.
:app:compileDebugNdk UP-TO-DATE
:app:compileDebugSources
:app:preDexDebug UP-TO-DATE
:app:dexDebug
Picked up JAVA_TOOL_OPTIONS: -javaagent:/usr/share/java/jayatanaag.jar 
:app:validateDebugSigning
:app:packageDebug
:app:zipalignDebug
:app:assembleDebug
:app:preDebugAndroidTestBuild UP-TO-DATE
:app:prepareDebugAndroidTestDependencies
:app:compileDebugAndroidTestAidl UP-TO-DATE
:app:processDebugAndroidTestManifest UP-TO-DATE
:app:compileDebugAndroidTestRenderscript UP-TO-DATE
:app:generateDebugAndroidTestBuildConfig UP-TO-DATE
:app:generateDebugAndroidTestAssets UP-TO-DATE
:app:mergeDebugAndroidTestAssets UP-TO-DATE
:app:generateDebugAndroidTestResValues UP-TO-DATE
:app:generateDebugAndroidTestResources UP-TO-DATE
:app:mergeDebugAndroidTestResources UP-TO-DATE
:app:processDebugAndroidTestResources UP-TO-DATE
:app:generateDebugAndroidTestSources UP-TO-DATE
:app:processDebugAndroidTestJavaRes UP-TO-DATE
:app:compileDebugAndroidTestJavaWithJavac
/home/devkrishna/AndroidStudioProjects/Sunshine/app/src/androidTest/java/com/example/android/sunshine/app/test/TestDb.java
Error:(19, 29) error: constructor WeatherDbHelper in class WeatherDbHelper cannot be applied to given types;
required: Context,String,CursorFactory,int
found: Context
reason: actual and formal argument lists differ in length
Error:(35, 36) error: constructor WeatherDbHelper in class WeatherDbHelper cannot be applied to given types;
required: Context,String,CursorFactory,int
found: Context
reason: actual and formal argument lists differ in length
Error:Execution failed for task  ':app:compileDebugAndroidTestJavaWithJavac'.
> Compilation failed; see the compiler error output for details.
Information:BUILD FAILED
Information:Total time: 33.089 secs
Information:3 errors
Information:0 warnings
Information:See complete output in console

这是文件 TestDb.java 的代码。它在内部产生错误在行中扩展 androidTestCase 的 TestCreateDb() 方法:

SQLiteDatabase db = new WeatherDbHelper(this.mContext).getWritableDatabase();

所以，请看完这句话。

package com.example.android.sunshine.app.test;

import android.content.ContentValues;
import android.database.Cursor;
import android.database.sqlite.SQLiteDatabase;
import android.test.AndroidTestCase;
import android.util.Log;

import com.example.android.sunshine.app.data.WeatherContract.LocationEntry;
import com.example.android.sunshine.app.data.WeatherContract.WeatherEntry;
import com.example.android.sunshine.app.data.WeatherDbHelper;

public class TestDb extends AndroidTestCase {

public static final String LOG_TAG = TestDb.class.getSimpleName();

public void testCreateDb() throws Throwable {
    mContext.deleteDatabase(WeatherDbHelper.DATABASE_NAME);
    SQLiteDatabase db = new WeatherDbHelper(
            this.mContext).getWritableDatabase();
    assertEquals(true, db.isOpen());
    db.close();
}

public void testInsertReadDb() {

    // Test data we're going to insert into the DB to see if it works.
    String testLocationSetting = "99705";
    String testCityName = "North Pole";
    double testLatitude = 64.7488;
    double testLongitude = -147.353;

    // If there's an error in those massive SQL table creation Strings,
    // errors will be thrown here when you try to get a writable database.
    WeatherDbHelper dbHelper = new WeatherDbHelper(mContext);
    SQLiteDatabase db = dbHelper.getWritableDatabase();

    // Create a new map of values, where column names are the keys
    ContentValues values = new ContentValues();
    values.put(LocationEntry.COLUMN_LOCATION_SETTING, testLocationSetting);
    values.put(LocationEntry.COLUMN_CITY_NAME, testCityName);
    values.put(LocationEntry.COLUMN_COORD_LAT, testLatitude);
    values.put(LocationEntry.COLUMN_COORD_LONG, testLongitude);

    long locationRowId;
    locationRowId = db.insert(LocationEntry.TABLE_NAME, null, values);

    // Verify we got a row back.
    assertTrue(locationRowId != -1);
    Log.d(LOG_TAG, "New row id: " + locationRowId);

    // Data's inserted.  IN THEORY.  Now pull some out to stare at it and verify it made
    // the round trip.

    // Specify which columns you want.
    String[] columns = {
            LocationEntry._ID,
            LocationEntry.COLUMN_LOCATION_SETTING,
            LocationEntry.COLUMN_CITY_NAME,
            LocationEntry.COLUMN_COORD_LAT,
            LocationEntry.COLUMN_COORD_LONG
    };

    // A cursor is your primary interface to the query results.
    Cursor cursor = db.query(
            LocationEntry.TABLE_NAME,  // Table to Query
            columns,
            null, // Columns for the "where" clause
            null, // Values for the "where" clause
            null, // columns to group by
            null, // columns to filter by row groups
            null // sort order
    );

    // If possible, move to the first row of the query results.
    if (cursor.moveToFirst()) {
        // Get the value in each column by finding the appropriate column index.
        int locationIndex = cursor.getColumnIndex(LocationEntry.COLUMN_LOCATION_SETTING);
        String location = cursor.getString(locationIndex);

        int nameIndex = cursor.getColumnIndex((LocationEntry.COLUMN_CITY_NAME));
        String name = cursor.getString(nameIndex);

        int latIndex = cursor.getColumnIndex((LocationEntry.COLUMN_COORD_LAT));
        double latitude = cursor.getDouble(latIndex);

        int longIndex = cursor.getColumnIndex((LocationEntry.COLUMN_COORD_LONG));
        double longitude = cursor.getDouble(longIndex);

        // Hooray, data was returned!  Assert that it's the right data, and that the database
        // creation code is working as intended.
        // Then take a break.  We both know that wasn't easy.
        assertEquals(testCityName, name);
        assertEquals(testLocationSetting, location);
        assertEquals(testLatitude, latitude);
        assertEquals(testLongitude, longitude);

        // Fantastic.  Now that we have a location, add some weather!
    } else {
        // That's weird, it works on MY machine...
        fail("No values returned :(");
    }

    // Fantastic.  Now that we have a location, add some weather!
    ContentValues weatherValues = new ContentValues();
    weatherValues.put(WeatherEntry.COLUMN_LOC_KEY, locationRowId);
    weatherValues.put(WeatherEntry.COLUMN_DATETEXT, "20141205");
    weatherValues.put(WeatherEntry.COLUMN_DEGREES, 1.1);
    weatherValues.put(WeatherEntry.COLUMN_HUMIDITY, 1.2);
    weatherValues.put(WeatherEntry.COLUMN_PRESSURE, 1.3);
    weatherValues.put(WeatherEntry.COLUMN_MAX_TEMP, 75);
    weatherValues.put(WeatherEntry.COLUMN_MIN_TEMP, 65);
    weatherValues.put(WeatherEntry.COLUMN_SHORT_DESC, "Asteroids");
    weatherValues.put(WeatherEntry.COLUMN_WIND_SPEED, 5.5);
    weatherValues.put(WeatherEntry.COLUMN_WEATHER_ID, 321);

    dbHelper.close();
}

weatherDbhelper.java 的源代码是:

package com.example.android.sunshine.app.data;

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

import com.example.android.sunshine.app.data.WeatherContract.LocationEntry;
import com.example.android.sunshine.app.data.WeatherContract.WeatherEntry;

/**
* Created by devkrishna on 9/3/15.
*/
public class WeatherDbHelper extends SQLiteOpenHelper {
    private static final int DATABASE_VERSION=1;
public static final String DATABASE_NAME="weather.db";

public WeatherDbHelper(Context context, String name, SQLiteDatabase.CursorFactory factory, int version) {
    super(context, DATABASE_NAME, null, DATABASE_VERSION);
}

@Override
public void onCreate(SQLiteDatabase sqLiteDatabase) {

    final String SQL_CREATE_WEATHER_TABLE=
            "CREATE TABLE" + WeatherEntry.TABLE_NAME + " (" +
                    WeatherEntry._ID + " INTEGER PRIMARY KEY AUTOINCREMENT," +
                    WeatherEntry.COLUMN_LOC_KEY + " INTEGER NOT NULL, " +
                    WeatherEntry.COLUMN_DATETEXT + " TEXT NOT NULL, " +
                    WeatherEntry.COLUMN_SHORT_DESC + " TEXT NOT NULL, " +
                    WeatherEntry.COLUMN_WEATHER_ID + "INTEGER NOT NULL, " +
                    WeatherEntry.COLUMN_MIN_TEMP + " REAL NOT NULL, " +
                    WeatherEntry.COLUMN_MAX_TEMP + " REAL NOT NULL, " +
                    WeatherEntry.COLUMN_HUMIDITY + " REAL NOT NULL, " +
                    WeatherEntry.COLUMN_PRESSURE + " REAL NOT NULL, " +
                    WeatherEntry.COLUMN_WIND_SPEED + " REAL NOT NULL, " +
                    WeatherEntry.COLUMN_DEGREES + " REAL NOT NULL, " +

                    "FOREIGN KEY (" +WeatherEntry.COLUMN_LOC_KEY + ") REFERENCES " +
                    LocationEntry.TABLE_NAME + " (" + LocationEntry._ID + "), " +

                    "UNIQUE (" + WeatherEntry.COLUMN_DATETEXT + ", " +
                    WeatherEntry.COLUMN_LOC_KEY + ") ON CONFLICT REPLACE);";

    final String SQL_CREATE_LOCATION_TABLE=
            "CREATE TABLE" + LocationEntry.TABLE_NAME + " (" +
                    LocationEntry._ID + " INTEGER PRIMARY KEY," +
                    LocationEntry.COLUMN_LOCATION_SETTING + "TEXT UNIQUE NOT NULL, " +
                    LocationEntry.COLUMN_CITY_NAME + "TEXT NOT NULL, " +
                    LocationEntry.COLUMN_COORD_LAT + "REAL NOT NULL, " +
                    LocationEntry.COLUMN_COORD_LONG + "REAL NOT NULL, " +
                    "UNIQUE (" +LocationEntry.COLUMN_LOCATION_SETTING + ") ON CONFLICT IGNORE"+
                    " );";
    sqLiteDatabase.execSQL(SQL_CREATE_LOCATION_TABLE);
    sqLiteDatabase.execSQL(SQL_CREATE_WEATHER_TABLE);

}

@Override
public void onUpgrade(SQLiteDatabase sqLiteDatabase, int i, int i1) {
    sqLiteDatabase.execSQL("DROP TABLE IF EXIXTS " + LocationEntry.TABLE_NAME);
    sqLiteDatabase.execSQL("DROP TABLE IF EXISTS " + WeatherEntry.TABLE_NAME);
    onCreate(sqLiteDatabase);

}

Answer 1

试试这个

 public class TestDb extends AndroidTestCase {

Context mContext;
public void TestDb (Context mContext){
 this.mContext = mContext;
} 
public static final String LOG_TAG = TestDb.class.getSimpleName();

public void testCreateDb() throws Throwable {
    mContext.deleteDatabase(WeatherDbHelper.DATABASE_NAME);
    SQLiteDatabase db = new WeatherDbHelper(
            this.mContext).getWritableDatabase();
    assertEquals(true, db.isOpen());
    db.close();
}