Question

我在Android应用的第一个活动之前引入了启动画面。此启动屏幕使用AsyncTask在第一个活动开始之前下载一些信息。由于这可能需要5秒钟，因此我有一个进度条来向用户显示进度。 AsyncTask按预期启动，但我可以通过创建一个单独的Thread来获得启动闪屏的唯一方法。如果我不使用单独的线程，则不会显示闪屏。该应用程序只显示一个空白屏幕，AsyncTask在后台运行，然后应用程序转换为主要活动。

所以它在功能上有效，但是我想启动AsyncTask而不会产生一个单独的Thread。我有什么选择？

我要删除的代码部分如下。

new Thread(){
            public void run()
            {
                startDownloadTask(); //kicks off the AsyncTask.
            };          
        }.start();

这是我的代码。

AppManifest.xml

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="com.drillexams.android"
    android:versionCode="1"
    android:versionName="1.0" >

    <uses-permission android:name="android.permission.INTERNET" />
    <uses-permission android:name="android.permission.MANAGE_ACCOUNTS" />
    <uses-permission android:name="android.permission.GET_ACCOUNTS" />
    <uses-permission android:name="android.permission.USE_CREDENTIALS" />
    <uses-permission android:name="android.permission.ACCESS_NETWORK_STATE" />

    <uses-sdk
        android:minSdkVersion="8"
        android:targetSdkVersion="19" />

    <application
        android:allowBackup="true"
        android:icon="@drawable/ic_app_icon"
        android:label="@string/app_name"
        android:theme="@style/AppTheme" >
        <uses-library android:name="android.test.runner" />

        <activity
            android:name="com.drillexams.android.WorkInProgressActivity">
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />
                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
        </activity>
        <activity
            android:name="com.drillexams.android.ExamListActivity">
            <intent-filter>
                <action android:name="android.intent.action.EXAMSLIST" />
                <category android:name="android.intent.category.DEFAULT" />
            </intent-filter>
        </activity>
        <activity
            android:name="com.drillexams.android.SettingsActivity"
            android:parentActivityName="com.drillexams.android.ExamListActivity">
            <!-- Parent activity meta-data to support API level 7+ -->
            <meta-data
                android:name="android.support.PARENT_ACTIVITY"
                android:value="com.drillexams.android.ExamListActivity" />
        </activity>
        <activity
            android:name="com.drillexams.android.DrillQuestionActivity"
            android:parentActivityName="com.drillexams.android.ExamListActivity">
            <!-- Parent activity meta-data to support API level 7+ -->
            <meta-data
                android:name="android.support.PARENT_ACTIVITY"
                android:value="com.drillexams.android.ExamListActivity" />
        </activity>
    </application>

    <instrumentation
        android:name="android.test.InstrumentationTestRunner"
        android:label="Android tests"
        android:targetPackage="com.drillexams.android" />

</manifest>

activity_work_in_progress.xml

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:paddingBottom="@dimen/activity_vertical_margin"
    android:paddingLeft="@dimen/activity_horizontal_margin"
    android:paddingRight="@dimen/activity_horizontal_margin"
    android:paddingTop="@dimen/activity_vertical_margin"
    tools:context=".WorkInProgressActivity" >

    <ImageView
        android:id="@+id/drillExamsLogoImageView"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_centerInParent="true"
        android:contentDescription="@string/drill_exams_logo_content_description"
        android:src="@drawable/ic_drill_exams_logo" />

    <ProgressBar
        android:id="@+id/progressBar"
        style="?android:attr/progressBarStyleHorizontal"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_below="@+id/drillExamsLogoImageView"
        android:layout_centerHorizontal="true"
        android:layout_marginTop="20dp" />

</RelativeLayout>

WorkInProgressActivity.java

package com.drillexams.android;

import java.net.MalformedURLException;
import java.net.URL;
import java.util.List;
import java.util.concurrent.ExecutionException;

import android.content.Intent;
import android.os.AsyncTask;
import android.os.Bundle;
import android.os.SystemClock;
import android.widget.ProgressBar;

import com.actionbarsherlock.app.SherlockActivity;
import com.drillexams.android.service.DrillExamsService;
import com.drillexams.android.sync.util.DownloadExamListHelper;
import com.drillexams.android.util.DrillExamsLogger;
import com.drillexams.model.Exam;

public class WorkInProgressActivity extends SherlockActivity {

    ProgressTask task = new ProgressTask();



    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        DrillExamsLogger.start("WorkInProgressActivity.onCreate");
        setContentView(R.layout.activity_work_in_progress);

        new Thread(){
            public void run()
            {
                startDownloadTask();
            };          
        }.start();

        DrillExamsLogger.end("WorkInProgressActivity.onCreate");
    }


    public void startDownloadTask() {  
        DrillExamsLogger.start("WorkInProgressActivity.startDownloadTask");
        try {
            task.execute(new URL(DrillExamsService.EXAM_URL));  
            task.get();
        } catch (MalformedURLException e) {
            DrillExamsLogger.e(e);
        } catch (ExecutionException e) {
            DrillExamsLogger.e(e);
        } catch (InterruptedException e) {
            DrillExamsLogger.e(e);
        }
        DrillExamsLogger.end("WorkInProgressActivity.startDownloadTask");          
    }  

    public void stopProgress() {  
        task.cancel(true);    
    }  

    private class ProgressTask extends AsyncTask<URL, Integer, List<Exam>> {     
        private ProgressBar progressBar;
        private String token;

        @Override
        protected void onPreExecute() {
            super.onPreExecute();

            progressBar = (ProgressBar)findViewById(R.id.progressBar);
            progressBar.bringToFront();         

        }

        protected List<Exam> doInBackground(URL... urls) {
            List<Exam> examsList = null;
            DrillExamsLogger.start("DownloadExamList.doInBackground");
            int start=0;  
            for(int i=start;i<=100;i+=5){  
                try {  
                    if(!isCancelled()){  
                        publishProgress(i);
                        progressBar.setProgress(i);
                        DrillExamsLogger.v("increment " + i);  
                        SystemClock.sleep(300);  
                    }  
                } catch (Exception e) {  
                    DrillExamsLogger.e(e);  
                }     
            }  
        return null;  
        }  


        protected void onPostExecute(List<Exam> params) {
            super.onPostExecute(params);
            DrillExamsLogger.start("WorkInProgressActivity.onPostExecute");
            Intent intent = new Intent(WorkInProgressActivity.this, ExamListActivity.class);
            startActivity(intent);
            finish();
            DrillExamsLogger.end("WorkInProgressActivity.onPostExecute");
        }
    }   
}

Answer 1

这不是代理模式的典型应用吗？您的代理正在显示启动屏幕并更新进度条，直到所有内容都已加载！

Answer 2

您正在AsyncTask背景方法中调用progressBar.setProgress(i); - 不允许从与其创建线程不同的线程更新UI元素，并且可能会抛出异常。

此外，您正在调用publishProgress(i)，但您还没有覆盖onProgressUpdate（）方法，因此它不会产生任何影响。

尝试重写onProgressUpdate（）方法并从那里更新progressBar：

@Override
protected void onProgressUpdate(Integer... progress) {
    progressBar.setProgress(progress[0]);
}

Answer 3

您必须创建线程的原因是您调用

task.get();

这使得AsyncTask在UI线程上运行，阻塞直到它完成。

因此，只需删除task.get（）：

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    DrillExamsLogger.start("WorkInProgressActivity.onCreate");
    setContentView(R.layout.activity_work_in_progress);

    startDownloadTask();

    DrillExamsLogger.end("WorkInProgressActivity.onCreate");
}


public void startDownloadTask() {  
    DrillExamsLogger.start("WorkInProgressActivity.startDownloadTask");
    try {
        task.execute(new URL(DrillExamsService.EXAM_URL));  
    } catch (MalformedURLException e) {
        DrillExamsLogger.e(e);
    } catch (ExecutionException e) {
        DrillExamsLogger.e(e);
    } catch (InterruptedException e) {
        DrillExamsLogger.e(e);
    }
    DrillExamsLogger.end("WorkInProgressActivity.startDownloadTask");          
}

带有AsyncTask的Android Splash屏幕

3 个答案: