AsyncTask 不通用？

发布于 2024-09-10 13:15:01 字数 1716 浏览 1 评论 0原文

当我尝试编译以下代码时，出现两个错误：

描述资源路径位置类型标记“void”上的语法错误，无效表达式 AsyncTask.java /AsyncTask Project/src/org/me/asynctask 第 19 行 Java 问题

描述资源路径位置类型 AsyncTask 类型不是通用的；它不能使用参数 进行参数化； AsyncTask.java /AsyncTask Project/src/org/me/asynctask 第 25 行 Java 问题

package org.me.asynctask;

import android.app.Activity;
import android.content.Context;
import android.os.Bundle;
import android.widget.TextView;
import android.widget.Toast;
import android.os.*;
public class AsyncTask extends Activity {
    /** Called when the activity is first created. */
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);

        TextView mytextview = new TextView(this);
        TextView secondtextview = new TextView(this);

        new MyAsyncClass().execute(mytextview, void, secondtextview);
    }

    private class MyAsyncClass extends AsyncTask<TextView, Void, Void> {
    protected TextView doInBackground(TextView tv)
    {
        tv.setText("Your AsyncTask was successful!");
        return tv;
    }

    protected void onPostExecute(TextView Result)
    {
        Context context = context.getApplicationContext();
        Toast mytoast = Toast.makeText(context, "AsyncTask processing complete", Toast.LENGTH_LONG);
        mytoast.show();
    }
}

显然 AsyncTask 是一个泛型（http://developer.android.com/reference/android/os/AsyncTask.html#execute(Params.. .) 那么为什么我会收到这些错误呢？

原文

When I try to compile to following code, I get two errors:

Description Resource Path Location Type
Syntax error on token "void", invalid Expression AsyncTask.java /AsyncTask Project/src/org/me/asynctask line 19 Java Problem

Description Resource Path Location Type
The type AsyncTask is not generic; it cannot be parameterized with arguments <TextView, Void, Void> AsyncTask.java /AsyncTask Project/src/org/me/asynctask line 25 Java Problem

package org.me.asynctask;

import android.app.Activity;
import android.content.Context;
import android.os.Bundle;
import android.widget.TextView;
import android.widget.Toast;
import android.os.*;
public class AsyncTask extends Activity {
    /** Called when the activity is first created. */
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);

        TextView mytextview = new TextView(this);
        TextView secondtextview = new TextView(this);

        new MyAsyncClass().execute(mytextview, void, secondtextview);
    }

    private class MyAsyncClass extends AsyncTask<TextView, Void, Void> {
    protected TextView doInBackground(TextView tv)
    {
        tv.setText("Your AsyncTask was successful!");
        return tv;
    }

    protected void onPostExecute(TextView Result)
    {
        Context context = context.getApplicationContext();
        Toast mytoast = Toast.makeText(context, "AsyncTask processing complete", Toast.LENGTH_LONG);
        mytoast.show();
    }
}

Obviously AsyncTask IS a generic (http://developer.android.com/reference/android/os/AsyncTask.html#execute(Params...) so why do I get those errors?

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泪是无色的血 2024-09-17 13:15:01

您正在使用错误的类型重写 AsyncTask 方法。它定义为：

AsyncTask<Params, Progress, Result>

doInBackground 方法定义为
protected abstract Result doInBackground (Params... params)

所以根据你的定义，你应该有
protected Void doInBackround(TextView... params);

onPostExecute 的定义也不正确。

You are overriding the AsyncTask methods with the wrong types. It is defined as:

AsyncTask<Params, Progress, Result>

and the doInBackground method is defined as
protected abstract Result doInBackground (Params... params)

so according to your definition, you should have
protected Void doInBackround(TextView... params);

onPostExecute is also incorrectly defined.

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奢欲 2024-09-17 13:15:01

有几个问题，其中两个是：

您定义了一个类 AsyncTask，它与 android.os.AsyncTask 隐藏/冲突。也许您打算将其称为 AsyncTaskDemo.java 或 AsyncTaskActivity.java 或其他名称。
您正在尝试通过调用 doInBackground 内部的 tv.setText 从后台线程更改 UI。这违背了 AsyncTask 的目的。 doInBackground 中的代码不应触及主（或“UI”）线程。对于 doInBackground 内的中期任务更新，请使用 AsyncTask.publishProgress。