实现OpenStreetMap时出错

我正在尝试在android studio中实现OpenStreetMap。我成功地添加了如下所示的库。

这是我的主要活动:

package com.example.re.osm;

import org.osmdroid.views.MapController;
import org.osmdroid.views.MapView;

import android.app.Activity;
import android.os.Bundle;
import android.support.v7.app.AppCompatActivity;

import com.example.harjotkaur.osm.R;

    public class MainActivity extends Activity {

        private MapView myOpenMapView;
        private MapController myMapController;

        /** Called when the activity is first created. */
        @Override
        public void onCreate(Bundle savedInstanceState) {
            super.onCreate(savedInstanceState);
            setContentView(R.layout.activity_main);

            myOpenMapView = (MapView)findViewById(R.id.openmapview);
            myOpenMapView.seharjotkaurtBuiltInZoomControls(true);
            myMapController = myOpenMapView.getController();
            myMapController.setZoom(4);
        }

    }

这是我的身材。gradle文件:

apply plugin: 'com.android.application'

android {
    compileSdkVersion 26
    buildToolsVersion "26.0.0"
    defaultConfig {
        applicationId "com.example.re.osm"
        minSdkVersion 15
        targetSdkVersion 26
        versionCode 1
        versionName "1.0"
        testInstrumentationRunner "android.support.test.runner.AndroidJUnitRunner"
    }
    buildTypes {
        release {
            minifyEnabled false
            proguardFiles getDefaultProguardFile('proguard-android.txt'), 'proguard-rules.pro'
        }
    }
}

dependencies {
    compile fileTree(include: ['*.jar'], dir: 'libs')
    androidTestCompile('com.android.support.test.espresso:espresso-core:2.2.2', {
        exclude group: 'com.android.support', module: 'support-annotations'
    })
    compile 'com.android.support:appcompat-v7:26.+'
    compile 'com.android.support.constraint:constraint-layout:1.0.2'
    testCompile 'junit:junit:4.12'
    compile files('libs/slf4j-android-1.5.8.jar')
compile files('libs/osmdroid-android-3.0.8.jar')

}

这是我的清单文件:

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="com.example.re.osm"
    android:versionCode="1"
    android:versionName="1.0" >

    <uses-sdk android:minSdkVersion="10" />
    <uses-permission android:name="android.permission.ACCESS_NETWORK_STATE"/>
    <uses-permission android:name="android.permission.INTERNET"/>
    <uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE" />

    <application
        android:icon="@drawable/ic_launcher"
        android:label="OSM" >
        <activity
            android:name=".MainActivity"
            android:label="OSM" >
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />

                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
        </activity>
    </application>

</manifest>

但是当我运行应用程序时,我只能看到小矩形,而看不到地图。

有什么好主意吗?

谢谢