Question

我创建了一个应用程序，通过单击列表项，在点击按钮时从Internet下载图像（同时它将url放在EditText上用户查看url是什么。

最初我在隐藏模式下设置ProgressBar和TextView（表示Loading....）。但是当下载开始时，我想将TextView和ProgressBar同时打开到UI上，一旦下载完成，就想让它们都不可见。

要发布的LogCat上没有错误消息。我相信我错过了一些棘手的东西:)。如果需要任何其他信息，请与我们联系。提前谢谢。

以下XML：LinearLayout应为ON/OFF

<LinearLayout
        android:id="@+id/loadingSection"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_below="@+id/downloadImage"
        android:visibility="gone"
        android:orientation="vertical" >

        <TextView
            android:id="@+id/loadingMessage"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:text="Loading....."
            android:gravity="center"
            android:textAppearance="?android:attr/textAppearanceSmall" />

        <ProgressBar
            android:id="@+id/progressBar"
            style="?android:attr/progressBarStyleSmall"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:indeterminate="true" />

    </LinearLayout>

以下是Java文件：

public class DownloadImages_HandlerMainActivity extends Activity implements OnItemClickListener {
private EditText editText;
private ListView listView;
private TextView textView;
private String[] listOfImages;
private Button downloadImage;
private ProgressBar progressBar;
private LinearLayout loadingSection = null;
private Handler handler;

@Override
protected void onCreate(Bundle savedInstanceState) {
    // TODO Auto-generated method stub
    super.onCreate(savedInstanceState);
    setContentView(R.layout.downloadimages_main);
    editText = (EditText) findViewById(R.id.downloadURL);
    textView = (TextView) findViewById(R.id.loadingMessage);
    listView = (ListView) findViewById(R.id.urlList);
    downloadImage = (Button) findViewById(R.id.downloadImage);
    progressBar = (ProgressBar) findViewById(R.id.progressBar);
    listOfImages = getResources().getStringArray(R.array.imageURLs);

    listView.setOnItemClickListener(this);
    handler = new Handler();
}

@Override
public void onItemClick(AdapterView<?> arg0, View view, int position,
        long id) {
    editText.setText(listOfImages[position]);
}

public void downloadImage(View view) {
    String url = editText.getText().toString();
    Thread myThread = new Thread(new DownloadImagesThread(url));
    myThread.start();
}

public boolean downloadImageUsingThreads(String url) {

    boolean successful = false;
    URL downloadURL = null;
    HttpURLConnection connection = null;
    InputStream inputStream = null;
    File file = null;
    FileOutputStream fileOutputStream = null;

    try {
        downloadURL = new URL(url);
        connection = (HttpURLConnection) downloadURL.openConnection();
        inputStream = connection.getInputStream();

        file = new File(Environment.getExternalStoragePublicDirectory(
                Environment.DIRECTORY_PICTURES).getAbsolutePath()
                + "/" + Uri.parse(url).getLastPathSegment());
        fileOutputStream = new FileOutputStream(file);
        int read = -1;
        byte[] buffer = new byte[1024];
        while ((read = inputStream.read(buffer)) != -1) {
            fileOutputStream.write(buffer, 0, read);
            //Log.d("BRK0018", " " + read);
            successful = true;
        }

    } catch (MalformedURLException e) {
        e.printStackTrace();
        Log.d("BRK0018", " " + e);
    } catch (IOException e) {
        e.printStackTrace();
        Log.d("BRK0018", " " + e);
    } finally {
        // This is the HANDLER INSTANCE in place of thread
        handler.post(new Runnable() {

            @Override
            public void run() {
                try {
                    loadingSection.setVisibility(View.GONE); // Making the ProgressBar INVISIBLE

                } catch (Exception e) {
                    Log.d("BRK0018", " " + e);                  
                }
            }
        });
        if (connection != null) {
            connection.disconnect();
        }
        if (inputStream != null) {
            try {
                inputStream.close();
            } catch (IOException e) {
                e.printStackTrace();
                Log.d("BRK0018", " " + e);
            }
        }
    }
    return successful;
}

@Override
public boolean onCreateOptionsMenu(Menu menu) {
    getMenuInflater().inflate(R.menu.main, menu);
    return true;
}

private class DownloadImagesThread implements Runnable {
    private String url;
    public DownloadImagesThread(String url) {
        this.url = url;
    }

    // This is the HANDLER INSTANCE in place of thread
    @Override
    public void run() {
        handler.post(new Runnable() {

            @Override
            public void run() {
                try {
                    // TODO Auto-generated method stub
                    loadingSection.setVisibility(View.VISIBLE); // Making the ProgressBar VISIBLE

                } catch (Exception e) {
                    Log.d("BRK0018", " " + e);
                }
            }
        });
        downloadImageUsingThreads(url);
    }
}
}

Answer 1

此处的问题是loadingSection null 。由于您在try/catch块中更改了其可见性，因此该应用不会崩溃。在onCreate()：

中初始化布局

loadingSection = (LinearLayout) findViewById(R.id.loadingSection);

Answer 2

首先，当你打电话

  handler.post(new Runnable() {

                @Override
                public void run() {
                    try {
                        // TODO Auto-generated method stub
                        loadingSection.setVisibility(View.VISIBLE); 
                        Thread.sleep(1000);
                    } catch (Exception e) {
                        Log.d("BRK0018", " " + e);
                    }
                }
            });

Handler.class运行在UI线程中的代码之上。您不能在UI线程中调用Thread.sleep(1000)。（但无论如何要记住必须在UI线程中调用loadingSection.setVisibility(View.VISIBLE);）

修复它。是否有帮助写信给我。

在下载过程中无法显示和隐藏ProgressBar

2 个答案: