Question

我对这个应用程序有问题应该是简单的修复，但我无法弄清楚我到底做错了什么...所有的应用程序都是下载图像在一个线程中，并将图像设置在另一个线程中。我改变了ReadFile类，将一个Drawable对象返回到变量finalImage，然后我有onPostExecute将该图像设置为ImageView但是......它唯一显示的是Android图标。任何建议，将不胜感激。我猜测它与我从ReadFile类返回Drawable的方式有关，但我无法弄清楚到底是什么。

package com.example.imageviewer;

import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.net.URL;

import android.os.AsyncTask;
import android.os.Bundle;
import android.app.Activity;
import android.content.Context;
import android.graphics.drawable.Drawable;
import android.util.Log;
import android.widget.ImageView;

public class MainActivity extends Activity {

    private final String URL_STRING = "http://cdn.theatlantic.com/static/infocus/putin091311/s_p15_0RTXUL0R.jpg";
    private final String FILENAME = "s_p15_0RTXUL0R.jpg";
    private ImageView fileImageView; 
    public Drawable finalImage;

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

        fileImageView = (ImageView) findViewById(R.id.fileImageView);

        new DownloadFile().execute();
        new ReadFile().execute();

    }

    class DownloadFile extends AsyncTask<Void, Void, String> {
        @Override
        protected String doInBackground(Void... params) {
            // download and write the file
            try{
                // get the URL object
                URL url = new URL(URL_STRING);

                // get the input stream
                InputStream in = url.openStream();

                // get the output stream
                FileOutputStream out = 
                        openFileOutput(FILENAME, Context.MODE_PRIVATE);

                // read input and write output
                byte[] buffer = new byte[1024];
                int bytesRead = in.read(buffer);
                while (bytesRead != -1)
                {
                    out.write(buffer, 0, bytesRead);
                    bytesRead = in.read(buffer);
                }
                out.close();
                in.close();

                // return a message
                return "File downloaded";
            }
            catch (IOException e) {
                return "Error: " + e.toString();
            }
        }

        @Override
        protected void onPostExecute(String message) {
            Log.d("Test", message);

            fileImageView.setImageDrawable(finalImage);

        }                
    }

        public class ReadFile extends AsyncTask <Void, Void, Drawable>{

            @Override
            protected Drawable doInBackground(Void...params){
                try {
                    FileInputStream in = openFileInput(FILENAME);
                    Drawable image = Drawable.createFromStream(in, FILENAME);
                    fileImageView.setImageDrawable(image);
                    Log.d("Test", "File read");            
                } 
                catch (Exception e) {
                    Log.e("Test", "Error: " + e.toString());
                }
                return finalImage;
            }

        }

}

Answer 1

你应该返回＆＃34;图像＆＃34;而不是＆＃34; finalImage＆＃34;来自ReadFile任务。

此外，您可以尝试使用此代替onPostExecute：

public class MainActivity extends Activity implements AsyncResponse {
    ...

    void processFinish(Drawable output) {
        fileImageView.setImageDrawable(finalImage);
    }
}

AsyncResponse.java：

public interface AsyncResponse {
    void processFinish(Drawable output);
}

ReadFile.java：

        public class ReadFile extends AsyncTask <Void, Void, Drawable>{

            @Override
            protected Drawable doInBackground(Void...params){
                Drawable image;
                try {
                    FileInputStream in = openFileInput(FILENAME);
                    image = Drawable.createFromStream(in, FILENAME);
                    Log.d("Test", "File read");            
                } 
                catch (Exception e) {
                    Log.e("Test", "Error: " + e.toString());
                }
                return image;
            }



    @Override
    protected void onPostExecute(Drawable result) {
        delegate.processFinish(result);
    } 
}

Answer 2

你的问题在这里：

new DownloadFile().execute();
new ReadFile().execute();

由于这些是异步任务，它们会同时运行，而ReadFile正在尝试在DownloadFile完成之前打开您的图像文件。

您只需将new ReadFile().execute();移至onPostExecute()的{{1}}方法。

然后还将以下内容添加到DownloadFile，以使ImageView刷新：

ReadFile

我进行了测试以确保所需要的一切，并得到普京与狗的照片。

有Drawable对象的问题

2 个答案: