Question

我看到了大部分相关问题，但我找不到任何解决问题的方法。

这是我的代码，我不知道我做错了什么。

static class NamedFile {
    public File f;

    public String name;
    public String ext;
    public String path;
    public BitmapDrawable icon;

    public NamedFile (File file) {
        f = file;
        name = f.getName();
        if (f.isFile()) {
            if (name.indexOf('.') != -1) {
                ext = name.substring(name.lastIndexOf('.') + 1).trim().toLowerCase();
            } else {
                ext = "unknown";
            }
        }
        path = f.getAbsolutePath();

        if (ext == null) {
            icon = mFolderIcon;
        } else {
            BitmapDrawable i = icons.get(ext);
            if (i == null) {
                    try {
                        int rid = R.drawable.class.getField(ext).getInt(R.drawable.class);
                        icons.put(ext, new BitmapDrawable(Bitmap.createScaledBitmap(BitmapFactory.decodeResource(res, rid, mOpts), iconSize, iconSize, false)));
                        icon = icons.get(ext);
                    } catch (Exception e1) {}
            } else {
                icon = i;
            }
        }/* else if (ext.equals("jpeg") || ext.equals("jpg") || ext.equals("bmp") || ext.equals("gif") || ext.equals("png")) {
            Bitmap b = BitmapFactory.decodeFile(path, mOpts);
            if (b != null) {
                icon = new BitmapDrawable(Bitmap.createScaledBitmap(b, iconSize, iconSize, false));
            }
        }*/

        if (ext != null && (ext.equals("jpeg") || ext.equals("jpg") || ext.equals("bmp") || ext.equals("gif") || ext.equals("png"))) {
            /*
            Bitmap b = BitmapFactory.decodeFile(path, mOpts);
            if (b != null) {
                icon = new BitmapDrawable(Bitmap.createScaledBitmap(b, iconSize, iconSize, false));
            }
            */

            final Handler handler = new Handler() {
                @Override
                public void handleMessage(Message message) {
                    HashMap<String, Object> m = ((HashMap<String, Object>)message.obj);
                    sendThumbnail ((String)m.get("path"), (byte[])m.get("data"));
                }
            };


            Thread thread = new Thread() {
                public void writeInt (byte[] buff, int pos, int value) {
                    buff[pos] = (byte)(value >>> 24);
                    buff[pos + 1] = (byte)(value >>> 16);
                    buff[pos + 2] = (byte)(value >>> 8);
                    buff[pos + 3] = (byte)value;
                }

                @Override
                public void run() {
                    try {
                        Bitmap b = BitmapFactory.decodeFile(path, mOpts);
                        if (b.getHeight() > 256 || b.getWidth() > 256) {
                            float r;
                            if (b.getHeight() > b.getWidth()) {
                                r = 128f / b.getHeight();
                            } else {
                                r = 128f / b.getWidth();
                            }

                            b = Bitmap.createScaledBitmap(b, (int)(r * b.getWidth()), (int)(r * b.getHeight()), false);

                            byte[] buffer = new byte[b.getWidth() * b.getHeight() * 4 + 8];

                            writeInt (buffer, 0, b.getWidth());
                            writeInt (buffer, 4, b.getHeight());

                            int i = 8;
                            for (int y = 0; y < b.getHeight(); y ++) {
                                for (int x = 0; x < b.getWidth(); x ++) {
                                    writeInt (buffer, i, b.getPixel(x, y));

                                    i += 4;
                                }
                            }

                            HashMap<String, Object> msg = new HashMap<String, Object>();

                            msg.put("path", path);
                            msg.put("data", buffer);

                            Message message = handler.obtainMessage(1, msg);
                            handler.sendMessage(message);
                        }
                    } catch (Exception e) {
                        sendLog (e.toString());
                    }
                }
            };
            thread.start();


        }

        if (icon == null) {
            icon = mFileIcon;
        }
    }
    public NamedFile () {
    }

    public NamedFile simpleClone () {
        final NamedFile nf = new NamedFile();

        nf.name = name;
        nf.ext = ext;
        nf.path = path;

        return nf;
    }
}

这嵌套在静态类'构造函数中的if语句中，静态类位于扩展ListActivity的公共类中。我是Java的新手。

错误：

05-01 20:21:58.810: E/AndroidRuntime(584): Uncaught handler: thread AsyncTask #1 exiting due to uncaught exception
05-01 20:21:58.830: E/AndroidRuntime(584): java.lang.RuntimeException: An error occured while executing doInBackground()
05-01 20:21:58.830: E/AndroidRuntime(584):  at android.os.AsyncTask$3.done(AsyncTask.java:200)
05-01 20:21:58.830: E/AndroidRuntime(584):  at java.util.concurrent.FutureTask$Sync.innerSetException(FutureTask.java:273)
05-01 20:21:58.830: E/AndroidRuntime(584):  at java.util.concurrent.FutureTask.setException(FutureTask.java:124)
05-01 20:21:58.830: E/AndroidRuntime(584):  at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:307)
05-01 20:21:58.830: E/AndroidRuntime(584):  at java.util.concurrent.FutureTask.run(FutureTask.java:137)
05-01 20:21:58.830: E/AndroidRuntime(584):  at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1068)
05-01 20:21:58.830: E/AndroidRuntime(584):  at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:561)
05-01 20:21:58.830: E/AndroidRuntime(584):  at java.lang.Thread.run(Thread.java:1096)
05-01 20:21:58.830: E/AndroidRuntime(584): Caused by: java.lang.RuntimeException: Can't create handler inside thread that has not called Looper.prepare()
05-01 20:21:58.830: E/AndroidRuntime(584):  at android.os.Handler.<init>(Handler.java:121)
05-01 20:21:58.830: E/AndroidRuntime(584):  at greg.projects.FileTransfer.FileTransferActivity$NamedFile$1.<init>(FileTransferActivity.java:588)
05-01 20:21:58.830: E/AndroidRuntime(584):  at greg.projects.FileTransfer.FileTransferActivity$NamedFile.<init>(FileTransferActivity.java:588)
05-01 20:21:58.830: E/AndroidRuntime(584):  at greg.projects.FileTransfer.FileTransferActivity$GesturesLoadTask.doInBackground(FileTransferActivity.java:489)
05-01 20:21:58.830: E/AndroidRuntime(584):  at greg.projects.FileTransfer.FileTransferActivity$GesturesLoadTask.doInBackground(FileTransferActivity.java:1)
05-01 20:21:58.830: E/AndroidRuntime(584):  at android.os.AsyncTask$2.call(AsyncTask.java:185)
05-01 20:21:58.830: E/AndroidRuntime(584):  at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:305)
05-01 20:21:58.830: E/AndroidRuntime(584):  ... 4 more

（FileTransferActivity.java:588是final Handler handler = new Handler() {）

Answer 1

Handler基本上是一个回调类，当你发送某种形式的消息时，Android会用它来异步运行代码。为了使Handler在UI线程的单独线程中接收和处理消息，它必须保持线程打开。这就是Looper类的用武之地。就像在页面示例中一样，在Looper.prepare()方法的顶部调用run()，然后在底部调用Looper.loop()。线程将保持打开状态，直到您明确销毁它。为了销毁Looper主题，您必须在Thread类中使用调用Looper.getMyLooper().quit()的方法。

示例线程类将是这样的：

class LooperThread extends Thread {
  public Handler mHandler;
  private volatile Looper mMyLooper;

  public void run() {
    Looper.prepare();

    mHandler = new Handler() {
       public void handleMessage(Message msg) {
          // process incoming messages here
       }
    };

    mMyLooper = Looper.getMyLooper();

    Looper.loop();
  }

  public void killMe(){
     mMyLooper.quit();
  }
}

通过创建一个新对象来正常运行线程。

LooperThread myLooperThread = new LooperThread();

保留对它的引用。然后致电：

myLooperThread.killMe();

每当你想要线程死亡时。这通常位于活动的onPause()，onStop()或onDestroy()方法中。

请注意，当活动关闭时，此类的主题将保持打开状态，因此您必须在用户退出之前将其终止。

Answer 2

在UI线程上运行指定的操作

 ActivityName.runOnUiThread(new Runnable() {
 public void run()
    {
     //put your logic here
    }
 });

Answer 3

我建议使用HandlerThread，因为它为你准备了looper。

http://developer.android.com/reference/android/os/HandlerThread.html

Java无法在未调用Looper.prepare（）的线程内创建处理程序

3 个答案: