java - 尝试在服务中处理不同的场景

Question

我有一个问题，我想不出如何解决它。

目标是，当用户点击按钮时，根据在设置中选择的内容加载 URL。

问题是，我无法以正确的方式进行设置。

逻辑上(对我而言)，我尝试在服务中设置它。单击按钮 > 服务启动 > URL 从“IF ELSE”加载。问题是，我在“IF ELSE”中收到错误 - “必须从 UI 线程调用方法长度，当前推断的线程是工作线程。

public static class Service extends IntentService {
    public Service() {
        super("wallpaperchanger-download");
    }

    @Override
    protected void onHandleIntent(Intent intent) {
        MainActivity mainActivity;
        mainActivity = new MainActivity();

        if (mainActivity.mEditTextHashtag.length() > 2) {

            WallpaperManager wm = WallpaperManager.getInstance(this);
            int height = wm.getDesiredMinimumHeight();
            int width = wm.getDesiredMinimumWidth();

            String url = "https://source.unsplash.com/all/?" + mainActivity.mEditTextHashtag.getText() + "/" + width + "x" + height + "/";
            try {
                InputStream input = new URL(url).openStream();
                Log.v(TAG, url);
                wm.setStream(input);
                input.close();
            } catch (Exception e) {
                e.printStackTrace();
            }
            loading = false;
        }

    }
}

好的，很公平。我创建了新方法 getPhoto();在 UI Thread 中并将代码放在那里。然后，我调用了 mainActivity.getPhoto();在服务中。问题是，我收到一个错误 - “尝试在空对象引用上调用虚拟方法‘int android.widget.EditText.length()’”

关于我应该做什么的任何想法？

所有荣耀的完整代码:

package com.edip.splashwallpaper;

import android.app.AlarmManager;
import android.app.IntentService;
import android.app.PendingIntent;
import android.app.WallpaperManager;
import android.content.BroadcastReceiver;
import android.content.Context;
import android.content.Intent;
import android.os.Bundle;
import android.util.Log;
import android.view.View;
import android.widget.ArrayAdapter;
import android.widget.Button;
import android.widget.EditText;
import android.widget.Spinner;
import android.widget.Switch;
import android.widget.Toast;

import java.io.InputStream;
import java.net.URL;

public class MainActivity extends android.app.Activity {

    final static String TAG = "AllInOne";
    final static int CHANGE_INTERVAL = 30 * 1000; //30 sec for testing
    static boolean loading = false;
    WallpaperManager wm;

    //Layout Views
    Switch mSwitchFixedPhoto, mSwitchControls, mSwitchSave, mSwitchPause;
    Spinner mSpinnerCategories, mSpinnerInterval;
    EditText mEditTextHashtag;
    Button mWallpaperButton;


    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        //Layout Views Initialized
        mSwitchFixedPhoto = (Switch) findViewById(R.id.sw_fixedphoto);
        mSwitchControls = (Switch) findViewById(R.id.switch_controls);
        mSwitchSave = (Switch) findViewById(R.id.switch_save);
        mSwitchPause = (Switch) findViewById(R.id.switch_pause);
        mSpinnerCategories = (Spinner) findViewById(R.id.spinner_categories);
        mSpinnerInterval = (Spinner) findViewById(R.id.spinner_interval);
        mEditTextHashtag = (EditText) findViewById(R.id.et_hashtag);
        mWallpaperButton = (Button) findViewById(R.id.btn_set_wallpaper);


        // Create an ArrayAdapter using the string array and a default spinner layout
        ArrayAdapter<CharSequence> adapterCategory = ArrayAdapter.createFromResource(this,
                R.array.categories_array, R.layout.dialog_spinner_layout);
        // Specify the layout to use when the list of choices appears
        adapterCategory.setDropDownViewResource(R.layout.dialog_spinner_layout);
        // Apply the adapter to the spinner
        mSpinnerCategories.setAdapter(adapterCategory);

        ArrayAdapter<CharSequence> adapterInterval = ArrayAdapter.createFromResource(this,
                R.array.interval_array, R.layout.dialog_spinner_layout);
        adapterInterval.setDropDownViewResource(R.layout.dialog_spinner_layout);
        mSpinnerInterval.setAdapter(adapterInterval);

        mWallpaperButton.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {

                PendingIntent pending = PendingIntent.getBroadcast(MainActivity.this,
                        666, new Intent("com.edip.splashwallpaper.CHANGE_WALLPAPTER_TIMER"),
                        PendingIntent.FLAG_CANCEL_CURRENT);

                ((AlarmManager) getSystemService(Context.ALARM_SERVICE))
                        .setRepeating(AlarmManager.RTC, System.currentTimeMillis(),
                                CHANGE_INTERVAL, pending);

            }
        });

    }

    public void getPhoto() {

        if (mEditTextHashtag.length() > 2) {

            wm = WallpaperManager.getInstance(this);
            int height = wm.getDesiredMinimumHeight();
            int width = wm.getDesiredMinimumWidth();

            String url = "https://source.unsplash.com/all/?" + mEditTextHashtag.getText() + "/" + width + "x" + height + "/";
            try {
                InputStream input = new URL(url).openStream();
                Log.v(TAG, url);
                wm.setStream(input);
                input.close();
            } catch (Exception e) {
                e.printStackTrace();
            }
            loading = false;

        } else {

            Toast.makeText(this, "Something else", Toast.LENGTH_SHORT).show();

        }

    }

    public static class Service extends IntentService {
        public Service() {
            super("wallpaperchanger-download");
        }

        @Override
        protected void onHandleIntent(Intent intent) {
            MainActivity mainActivity;
            mainActivity = new MainActivity();

            mainActivity.getPhoto();
        }
    }

    public static class AlarmReceiver extends BroadcastReceiver {
        @Override
        public void onReceive(final Context context, Intent intent) {
            if (!loading) {
                loading = true;
                context.startService(new Intent(context, Service.class));
            }
        }
    }
}

谢谢:)

Answer 1

首先，您应该永远不要自己实例化一个 Activity 。

其次，作为最佳实践，您的服务不应该知道您的 Activity ，或者它有编辑文本。相反，当创建 PendingIntent 时，您应该发送 URL 以加载到您的 Intent 中，如下所示:

Intent intent  = new Intent("com.edip.splashwallpaper.CHANGE_WALLPAPTER_TIMER");
intent.putExtra("USER_URL", "https://source.unsplash.com/all/?" + mEditTextHashtag.getText() + "/" + width + "x" + height + "/");
PendingIntent pending = PendingIntent.getBroadcast(MainActivity.this,
                    666, intent, PendingIntent.FLAG_CANCEL_CURRENT);

然后在您的服务中，像这样读取 url:

@Override 
protected void onHandleIntent(Intent intent) {
    String url = intent.getStringExtra("USER_URL");
    // ... 
}