java - 无法让 Android Tutorial 工作，初级程序员

Question

我是 Android 编程的新手，总的来说我缺乏编程技能。我一直在关注 Head Start 教程，尽管我知道它在技术上已被删除以进行更新或其他内容。不管怎样，我到了他们只是希望您复制并粘贴代码以使 NASA RSS 提要和 Android 应用程序相互通信的部分，但由于某些或其他原因没有任何显示。我只是得到一个白屏，并且 logcat 错误似乎对我所看到的其他应用程序没有太大影响。我使用的测试数据有效，所以我认为 xml 很好，所以也许是我的 Java。我似乎找不到任何东西。任何人都可以看到我做错了什么。整个周末都在努力。这可能是复制粘贴的代码，但我不明白。

    package love.android.nasadailyimage;

import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.support.v7.app.ActionBarActivity;
import android.os.Bundle;
import android.view.Menu;
import android.view.MenuItem;
import android.widget.ImageView;
import android.widget.TextView;

import org.xml.sax.InputSource;
import org.xml.sax.SAXException;
import org.xml.sax.XMLReader;
import org.xml.sax.helpers.DefaultHandler;

import java.io.IOException;
import java.io.InputStream;
import java.net.HttpURLConnection;
import java.net.URL;
import java.util.jar.Attributes;

import javax.xml.parsers.SAXParser;
import javax.xml.parsers.SAXParserFactory;


public class NasaDailyImage extends ActionBarActivity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_nasa_daily_image);
        IotdHandler handler = new IotdHandler();
        handler.processFeed();
        resetDisplay(handler.getTitle(), handler.getDate(), handler.getImage(), handler.getDescription());
    }


    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        // Inflate the menu; this adds items to the action bar if it is present.
        getMenuInflater().inflate(R.menu.menu_nasa_daily_image, menu);
        return true;
    }

    @Override
    public boolean onOptionsItemSelected(MenuItem item) {
        // Handle action bar item clicks here. The action bar will
        // automatically handle clicks on the Home/Up button, so long
        // as you specify a parent activity in AndroidManifest.xml.
        int id = item.getItemId();

        //noinspection SimplifiableIfStatement
        if (id == R.id.action_settings) {
            return true;
        }

        return super.onOptionsItemSelected(item);
    }

    public class IotdHandler extends DefaultHandler {
        private String url = "http://www.nasa.gov/rss/dyn/image_of_the_day.rss";
        private boolean inUrl = false;
        private boolean inTitle = false;
        private boolean inDescription = false;
        private boolean inItem = false;
        private boolean inDate = false;
        private Bitmap image = null;
        private String title = null;
        private StringBuffer description = null;
        private String date = null;


        public void processFeed() {
            try {
                SAXParserFactory factory =
                        SAXParserFactory.newInstance();
                SAXParser parser = factory.newSAXParser();
                XMLReader reader = parser.getXMLReader();
                reader.setContentHandler(this);
                InputStream inputStream = new URL(url).openStream();
                reader.parse(new InputSource(inputStream));
            } catch (Exception e) {
            }
        }

        private Bitmap getBitmap(String url) {
            try {
                HttpURLConnection connection = (HttpURLConnection) new URL(url).openConnection();
                connection.setDoInput(true);
                connection.connect();
                InputStream input = connection.getInputStream();
                Bitmap bitmap = BitmapFactory.decodeStream(input);
                input.close();
                return bitmap;
            } catch (IOException ioe) {
                return null;
            }
        }

        public void startElement(String uri, String localName, String qName,
                                 Attributes attributes) throws SAXException {
            if (localName.equals("url")) {
                inUrl = true;
            } else {
                inUrl = false;
            }
            if (localName.startsWith("item")) {
                inItem = true;
            } else if (inItem) {
                if (localName.equals("title")) {
                    inTitle = true;
                } else {
                    inTitle = false;
                }
                if (localName.equals("description")) {
                    inDescription = true;
                } else {
                    inDescription = false;
                }
                if (localName.equals("pubDate")) {
                    inDate = true;
                } else {
                    inDate = false;
                }
            }
        }


        public void characters(char ch[], int start, int length) {
            String chars = new String(ch).substring(start, start + length);
            if (inUrl && url == null) {
                image = getBitmap(chars);
            }
            if (inTitle && title == null) {
                title = chars;
            }
            if (inDescription) {
                description.append(chars);
            }
            if (inDate && date == null) {
                date = chars;
            }
        }

        public Bitmap getImage() {
            return image;
        }


        public String getTitle() {
            return title;
        }

        public StringBuffer getDescription() {
            return description;
        }

        public String getDate() {
            return date;
        }
    }


    private void resetDisplay(String title, String date, Bitmap image, StringBuffer description){
        TextView titleView = (TextView) findViewById(R.id.imageTitle);
        titleView.setText(title);

        TextView dateView = (TextView) findViewById(R.id.imageDate);
        dateView.setText(date);

        ImageView imageView = (ImageView) findViewById(R.id.imageDisplay);
        imageView.setImageBitmap(image);/////////////////////////////////////////

        TextView descriptionView = (TextView) findViewById(R.id.imageDescription);
        descriptionView.setText(description);
    }

}

XML 以防有帮助

    <ScrollView xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent">

    <LinearLayout xmlns:tools="http://schemas.android.com/tools"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:orientation="vertical"

        tools:context=".NasaDailyImage">

        <TextView
            android:id="@+id/imageTitle"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="@string/image_title" />

        <TextView
            android:id="@+id/imageDate"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="@string/image_date" />

        <ImageView
            android:id="@+id/imageDisplay"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:src="@mipmap/galaxy"
            android:scaleType="fitXY"
            android:adjustViewBounds="true"/>


        <TextView
            android:id="@+id/imageDescription"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:text="@string/image_description" />


    </LinearLayout>
</ScrollView>

任何帮助将不胜感激。我会问这里的人，但在我的国家“纳米比亚”，很少有人能接触到我能接触到的 android 编程。

我的 S4 设备上的 LogCat

    04-20 11:07:17.204  25660-25660/love.android.nasadailyimage W/IInputConnectionWrapper﹕ getExtractedText on inactive InputConnection
04-20 11:07:17.204  25660-25660/love.android.nasadailyimage W/IInputConnectionWrapper﹕ getTextBeforeCursor on inactive InputConnection
04-20 11:07:17.209  25660-25660/love.android.nasadailyimage W/IInputConnectionWrapper﹕ getSelectedText on inactive InputConnection
04-20 11:07:17.209  25660-25660/love.android.nasadailyimage W/IInputConnectionWrapper﹕ getTextAfterCursor on inactive InputConnection
04-20 11:12:38.244  25660-25660/love.android.nasadailyimage W/IInputConnectionWrapper﹕ getExtractedText on inactive InputConnection
04-20 11:12:38.244  25660-25660/love.android.nasadailyimage W/IInputConnectionWrapper﹕ getTextBeforeCursor on inactive InputConnection
04-20 11:12:38.244  25660-25660/love.android.nasadailyimage W/IInputConnectionWrapper﹕ getSelectedText on inactive InputConnection
04-20 11:12:38.249  25660-25660/love.android.nasadailyimage W/IInputConnectionWrapper﹕ getTextAfterCursor on inactive InputConnection
04-20 11:16:06.154  30742-30742/love.android.nasadailyimage W/ApplicationPackageManager﹕ getCSCPackageItemText()
04-20 11:16:06.154  30742-30742/love.android.nasadailyimage I/PersonaManager﹕ getPersonaService() name persona_policy
04-20 11:16:06.229  30742-30742/love.android.nasadailyimage I/dalvikvm﹕ Could not find method android.view.ViewGroup.onNestedScrollAccepted, referenced from method android.support.v7.internal.widget.ActionBarOverlayLayout.onNestedScrollAccepted
04-20 11:16:06.229  30742-30742/love.android.nasadailyimage W/dalvikvm﹕ VFY: unable to resolve virtual method 12208: Landroid/view/ViewGroup;.onNestedScrollAccepted (Landroid/view/View;Landroid/view/View;I)V
04-20 11:16:06.229  30742-30742/love.android.nasadailyimage D/dalvikvm﹕ VFY: replacing opcode 0x6f at 0x0000
04-20 11:16:06.229  30742-30742/love.android.nasadailyimage I/dalvikvm﹕ Could not find method android.view.ViewGroup.onStopNestedScroll, referenced from method android.support.v7.internal.widget.ActionBarOverlayLayout.onStopNestedScroll
04-20 11:16:06.229  30742-30742/love.android.nasadailyimage W/dalvikvm﹕ VFY: unable to resolve virtual method 12214: Landroid/view/ViewGroup;.onStopNestedScroll (Landroid/view/View;)V
04-20 11:16:06.229  30742-30742/love.android.nasadailyimage D/dalvikvm﹕ VFY: replacing opcode 0x6f at 0x0000
04-20 11:16:06.234  30742-30742/love.android.nasadailyimage I/dalvikvm﹕ Could not find method android.support.v7.internal.widget.ActionBarOverlayLayout.stopNestedScroll, referenced from method android.support.v7.internal.widget.ActionBarOverlayLayout.setHideOnContentScrollEnabled
04-20 11:16:06.234  30742-30742/love.android.nasadailyimage W/dalvikvm﹕ VFY: unable to resolve virtual method 9779: Landroid/support/v7/internal/widget/ActionBarOverlayLayout;.stopNestedScroll ()V
04-20 11:16:06.234  30742-30742/love.android.nasadailyimage D/dalvikvm﹕ VFY: replacing opcode 0x6e at 0x000e
04-20 11:16:06.244  30742-30742/love.android.nasadailyimage I/dalvikvm﹕ Could not find method android.content.res.TypedArray.getChangingConfigurations, referenced from method android.support.v7.internal.widget.TintTypedArray.getChangingConfigurations
04-20 11:16:06.244  30742-30742/love.android.nasadailyimage W/dalvikvm﹕ VFY: unable to resolve virtual method 392: Landroid/content/res/TypedArray;.getChangingConfigurations ()I
04-20 11:16:06.244  30742-30742/love.android.nasadailyimage D/dalvikvm﹕ VFY: replacing opcode 0x6e at 0x0002
04-20 11:16:06.244  30742-30742/love.android.nasadailyimage I/dalvikvm﹕ Could not find method android.content.res.TypedArray.getType, referenced from method android.support.v7.internal.widget.TintTypedArray.getType
04-20 11:16:06.244  30742-30742/love.android.nasadailyimage W/dalvikvm﹕ VFY: unable to resolve virtual method 414: Landroid/content/res/TypedArray;.getType (I)I
04-20 11:16:06.244  30742-30742/love.android.nasadailyimage D/dalvikvm﹕ VFY: replacing opcode 0x6e at 0x0002
04-20 11:16:06.244  30742-30742/love.android.nasadailyimage I/dalvikvm﹕ Could not find method android.content.res.Resources.getDrawable, referenced from method android.support.v7.internal.widget.ResourcesWrapper.getDrawable
04-20 11:16:06.249  30742-30742/love.android.nasadailyimage W/dalvikvm﹕ VFY: unable to resolve virtual method 355: Landroid/content/res/Resources;.getDrawable (ILandroid/content/res/Resources$Theme;)Landroid/graphics/drawable/Drawable;
04-20 11:16:06.249  30742-30742/love.android.nasadailyimage D/dalvikvm﹕ VFY: replacing opcode 0x6e at 0x0002
04-20 11:16:06.249  30742-30742/love.android.nasadailyimage I/dalvikvm﹕ Could not find method android.content.res.Resources.getDrawableForDensity, referenced from method android.support.v7.internal.widget.ResourcesWrapper.getDrawableForDensity
04-20 11:16:06.249  30742-30742/love.android.nasadailyimage W/dalvikvm﹕ VFY: unable to resolve virtual method 357: Landroid/content/res/Resources;.getDrawableForDensity (IILandroid/content/res/Resources$Theme;)Landroid/graphics/drawable/Drawable;
04-20 11:16:06.249  30742-30742/love.android.nasadailyimage D/dalvikvm﹕ VFY: replacing opcode 0x6e at 0x0002
04-20 11:16:06.369  30742-30742/love.android.nasadailyimage D/dalvikvm﹕ GC_FOR_ALLOC freed 130K, 6% free 16994K/18052K, paused 15ms, total 15ms
04-20 11:16:06.389  30742-30742/love.android.nasadailyimage I/dalvikvm-heap﹕ Grow heap (frag case) to 28.887MB for 11943952-byte allocation
04-20 11:16:06.404  30742-30751/love.android.nasadailyimage D/dalvikvm﹕ GC_FOR_ALLOC freed 4K, 4% free 28654K/29720K, paused 12ms, total 12ms
04-20 11:16:06.479  30742-30742/love.android.nasadailyimage I/System.out﹕ main(HTTPLog):SmartBonding Enabling is false, log to file is false, DBG is false
04-20 11:16:06.594  30742-30742/love.android.nasadailyimage D/OpenGLRenderer﹕ Enabling debug mode 0

AndroidManifest 请求

    <?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="love.android.nasadailyimage" >

    <application
        android:allowBackup="true"
        android:icon="@mipmap/ic_launcher"
        android:label="@string/app_name"
        android:theme="@style/AppTheme" >
        <activity
            android:name=".NasaDailyImage"
            android:label="@string/app_name" >
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />

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

</manifest>

构建.gradle

    apply plugin: 'com.android.application'

android {
    compileSdkVersion 21
    buildToolsVersion "21.1.2"

    defaultConfig {
        applicationId "love.android.nasadailyimage"
        minSdkVersion 11
        targetSdkVersion 21
        versionCode 1
        versionName "1.0"
    }
    buildTypes {
        release {
            minifyEnabled false
            proguardFiles getDefaultProguardFile('proguard-android.txt'), 'proguard-rules.pro'
        }
    }
}

dependencies {
    compile fileTree(dir: 'libs', include: ['*.jar'])
    compile 'com.android.support:appcompat-v7:22.0.0'
}

编辑:添加了我的 LogCat 和我的 AndroidManifest

Answer 1

在 StackOverflow 上发现了一个问题，该问题遵循与您相同的教程。也许这对你有帮助

Android Head First "NASA daily image App"

如前所述，您应该使用 AsyncTask，并在请求返回时处理请求 (onPostExecute)。您的代码的问题是，您发送了一个请求，并且在您调用 resetDisplay 之后，响应还没有返回...这就是您看到空白屏幕的原因。