Question

我正在实现AsyncTask的示例，并从此处的示例AsyncTask Android example开始。

但是，我要进行更改。在我的GUI中，我想放置一个文本框，用户可以在其中键入内容，并且每隔10秒，该名称就会出现在标签上。

这样，如果用户输入了新值，它将显示在标签上，而不是现在显示的静态文本“ Executed”。

我的代码在下面。

XML

    <?xml version="1.0" encoding="utf-8"?>
    <LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
        android:layout_width="fill_parent"
        android:layout_height="fill_parent"
        android:orientation="vertical" >
        <ProgressBar
            android:id="@+id/progressBar"
            style="?android:attr/progressBarStyleHorizontal"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:indeterminate="false"
            android:max="10"
            android:padding="10dip">
        </ProgressBar>
        <Button
            android:id="@+id/button1"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="Start Progress" >
        </Button>
        <TextView android:id="@+id/output"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:text="Replace"/>

        <EditText
            android:id="@+id/textInput"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:ems="10"
            android:inputType="textPersonName"
            android:text="Name" />
    </LinearLayout>

MainActivity.java

import android.app.Activity;
import android.os.AsyncTask;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import android.widget.TextView;

public class MainActivity extends Activity implements View.OnClickListener {

    Button btn;
    EditText textInput;

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        btn = (Button) findViewById(R.id.button1);
        textInput = findViewById(R.id.textInput);
        // because we implement OnClickListener we only have to pass "this"
        // (much easier)
        btn.setOnClickListener(this);
    }

    public void onClick(View view) {
        // detect the view that was "clicked"
        switch (view.getId()) {
            case R.id.button1:
                new LongOperation().execute("");
                break;
        }
    }

    private class LongOperation extends AsyncTask<String, Void, String> {

        String input;

        @Override
        protected String doInBackground(String... params) {
            for (int i = 0; i < 5; i++) {
                try {
                    Thread.sleep(1000);
                    input = textInput.getText().toString();
                } catch (InterruptedException e) {
                    Thread.interrupted();
                }
            }
            return "Executed";
        }

        @Override
        protected void onPostExecute(String result) {
            TextView txt = (TextView) findViewById(R.id.output);
            txt.setText(input); // txt.setText(result);
            // might want to change "executed" for the returned string passed
            // into onPostExecute() but that is upto you
        }

        @Override
        protected void onPreExecute() {}

        @Override
        protected void onProgressUpdate(Void... values) {}
    }
}

我将把代码放在哪里听？我希望更改标签，例如每10秒检查一次文本框中是否有更改...

编辑

基于答案，我可以这样离开无限循环吗？如果需要，如何停止此AsyncTask？

private class LongOperation extends AsyncTask<String, String, String> {

    String input;

    @Override
    protected String doInBackground(String... params) {
        while (true)
            try {
                Thread.sleep(1000);
                input = textInput.getText().toString();
                publishProgress(input);

            } catch (InterruptedException e) {
                Thread.interrupted();
                return "Executed";
            }
    }

    @Override
    protected void onPostExecute(String result) {

    }

    @Override
    protected void onPreExecute() {}

    @Override
    protected void onProgressUpdate(String... values) {
        TextView txt = (TextView) findViewById(R.id.output);
        txt.setText(values[0]);
        // update the UI with Data received from publishprogress
    }
}

Answer 1

您可以使用publishprogess从后台线程更新UI。

将Void更改为String以传递字符串类型并更新progressUpdate中的UI

private class LongOperation extends AsyncTask<String, String, String> {
//                                                    ^^^^^^
        String input;

        @Override
        protected String doInBackground(String... params) {
            for (int i = 0; i < 5; i++) {
                try {
                    Thread.sleep(1000);
                    input = textInput.getText().toString();
                    publishProgress(input);
                   //^^^^^^^^^ pass the data to update UI
                } catch (InterruptedException e) {
                    Thread.interrupted();
                }
            }
            return "Executed";
        }

        @Override
        protected void onPostExecute(String result) {
            TextView txt = (TextView) findViewById(R.id.output);
            txt.setText(input); // txt.setText(result);
            // might want to change "executed" for the returned string passed
            // into onPostExecute() but that is upto you
        }

        @Override
        protected void onPreExecute() {}

        @Override
        protected void onProgressUpdate(String... values) {
            TextView txt = (TextView) findViewById(R.id.output);
            txt.setText(values[0]);
            // update the UI with Data received from publishprogress
        }
    }

请注意：您可以将textView的初始化oncreate移到oncreate之外的地方进行声明，以避免一次又一次地初始化，这是一个昂贵的过程

编辑：要停止循环，您可以使用

while(!isCancelled()){ // run as long as task is not cancelled

}

要取消任务，请先存储参考

AsynchTask task = new LongOperation().execute("");
task.cancel(true);

使用循环的AsyncTask示例

1 个答案: