Android高效AsyncTask

Question

我有一个 EditText，用户可以在其中输入公司名称。我在此 EditText 下方还有一个 ListView，它建议用户了解已添加到数据库中的内容...

<EditText android:id="@+id/txtBusinessName" android:hint="Name of Business" />
<ListView android:id="@+id/suggestionList" 
   android:layout_width="fill_parent" android:layout_height="wrap_content">
</ListView>

现在，当用户输入时，我会检查他们在数据库中输入的关键字，并检索必须在数据库中向用户显示的内容。列表视图。目前，在触发的每个按键事件中，我都以这种方式调用一个新的 AsyncTask...

        EditText txtBusinessName = (EditText) findViewById(R.id.txtBusinessName);
                txtBusinessName.setOnKeyListener(new View.OnKeyListener() {
                    @Override
                    public boolean onKey(View v, int keyCode, KeyEvent event) {
                        if (event.getAction() == KeyEvent.ACTION_UP) {
                            if (v instanceof EditText) {
                                EditText txtBusinessName = ((EditText) v);

                                if (txtBusinessName.length() > 0) {
                                   if (suggestionTask != null) {
                                    suggestionTask.cancel(true);
                                    suggestionTask = null;
                                   }
                                   suggestionTask = new GetCompaniesByKeywordAsyncTask(
                                        AddBusinessActivity.this, s);
                                   suggestionTask.execute(txtBusinessName.getText()
                                        .toString());
                                }
                            }
                        }
                        return false;
                    }
                });

有没有办法我只有一个 AsyncTask 实例，并要求它在用户在 EditText 中键入时检索名称？因为创建太多AsyncTask效率不高，最终会出现异常。我将在收到名称后填充 ListView，我可以要求 ListView 根据其中的内容重新调整自身大小吗？

Answer 1

为了制作单个AsyncTask，您需要重构AsyncTask以基于请求队列来运行。队列包含您要处理的所有关键字。然后，您可以在侦听器外部运行此 AsyncTask 一次，并添加 OnKeylistener 中的关键字。

为了更新ListView，我们将利用onProgressUpdate，它将根据doInBackground的结果更新ListView。

修改AsyncTask的骨架代码

    @Override
    protected Integer doInBackground(Void... params) {
        int errorCode = 0;

        try {
            // while running in the context of your activity
            // you should set this boolean to false once you have leave the activity
            while(!isRunning){
                // blocking call to get the next keyword that is added to the queue
                String responseData = getNextKeyword();

                // once you get the next keyword, you publish the progress
                // this would be executed in the UI Thread and basically would update the ListView
                publishProgress(responseData);
            }
        } catch(Exception e) {
            // error handling code that assigns appropriate error code
        }

        return errorCode;

    }

    @Override
    protected void onPostExecute(Integer errorCode) {
        // handle error on UI Thread based on errorCode
    }

    @Override
    protected void onProgressUpdate(String... values) {
        String searchKeyword = values[0];

        // handle the searchKeyword here by updating the listView
    }

    /***
     * Stub code for illustration only
     * Get the next keyword from the queue
     * @return The next keyword in the BlockingQueue
     */
    private String getNextKeyword() {
        return null;
    }

    /***
     * Stub code for illustration only
     * Add new keyword to the queue, this is called from the onKey method
     * @param keyword
     */
    public void addKeyword(String keyword) {
        // add the keyword to the queue
    }

然后你的代码被粗略地修改为：

// instantiate AsyncTask once
suggestionTask = new GetCompaniesByKeywordAsyncTask(
        AddBusinessActivity.this, s);

// run only one AsyncTask that is waiting for any keyword in the queue
suggestionTask.execute();

EditText txtBusinessName = (EditText) findViewById(R.id.txtBusinessName);
txtBusinessName.setOnKeyListener(new View.OnKeyListener() {
    @Override
    public boolean onKey(View v, int keyCode, KeyEvent event) {
        if (event.getAction() == KeyEvent.ACTION_UP) {
            if (v instanceof EditText) {
                EditText txtBusinessName = ((EditText) v);

                if (txtBusinessName.length() > 0) {
                   // add new keyword to the queue for processing
                   suggestionTask.addKeyword(txtBusinessName.getText()
                        .toString());
                }
            }
        }
        return false;
    }
});