Question

在我的应用程序中，我注意到这三件事：

- 从一个活动转到另一个活动时启用后退按钮，使用户能够单击回原始活动。问题是我不希望用户在我的应用程序中的某个点上单击“返回”。我不想在我的应用程序中完全禁用后退按钮，只有在调用一个intent时。我怎么能这样做？

- 我注意到一些奇怪的事情...当我的应用程序中弹出一个Toast通知时，一切都很好，直到我退出我的应用程序。当我退出我的应用程序时，一些Toast通知是残留的并且正在我的应用程序之外弹出。这有什么理由吗？我是否错过了活动生命周期中的某些内容来处理特定点的吐司取消？

最后，这个很难解决。如何锁定我的屏幕，以便当用户旋转设备时，活动不会再次被调用，并且asynctask仍然可以恢复而不重新开始？

非常感谢你的时间。只是好奇为什么会发生这些事情以及我应该注意什么？

这是我的代码：

//Main Activity.java

package com.example.Patient_Device;

import android.app.Activity;
import android.app.ProgressDialog;
import android.content.Context;
import android.content.Intent;
import android.database.sqlite.SQLiteDatabase;
import android.os.AsyncTask;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;

import java.io.*;


public class MainActivity extends Activity {

    //fields
    private ProgressDialog progressBar;
    private Context context;


    /**
     * Called when the activity is first created.
     */
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.start_setup);
        //Set the context
        context = this;

        //Initialize the start setup button and add an onClick event listener to the button
        final Button start_setup_button = (Button) findViewById(R.id.start_setup_button);
        start_setup_button.setOnClickListener(new View.OnClickListener() {
            public void onClick(View view) {

                //Executes the AsyncTask
                new RetrieveInfoTask().execute();

                //Instantiates the intent to launch a new activity
                Intent myIntent = new Intent(MainActivity.this, RetrieveInfoActivity.class);
                MainActivity.this.startActivity(myIntent);

            }
        });
    }

    public class RetrieveInfoTask extends AsyncTask<Void, Void, Void> {

        //Called on the UI thread to execute progress bar
        @Override
        protected void onPreExecute() {
            super.onPreExecute();

            progressBar = new ProgressDialog(context);
            progressBar.setIndeterminate(true);
            progressBar.setCancelable(false);
            progressBar.setMessage(MainActivity.this.getString(R.string.retrieve_info));
            progressBar.show();
        }

        //Methods that retrieves information from the user device. This is performed in the Background thread
        private void retrieveInfo() {

            try {

                //Reading the drawable resource line by line
                String str="";
                StringBuffer buf = new StringBuffer();
                InputStream is = MainActivity.this.getResources().openRawResource(R.drawable.user_info);
                BufferedReader reader = new BufferedReader(new InputStreamReader(is));
                if (is!=null) {
                    while ((str = reader.readLine()) != null) {
                        buf.append(str + "\n" );
                    }
                }
                is.close();

            } catch (Exception e) {
                e.printStackTrace();
            }
        }


        //doInBackground calls retrieveInfo() to perform action in Background
        @Override
        protected Void doInBackground(Void... params) {

            retrieveInfo();
            return null;
        }

        //When the background task is done, dismiss the progress bar
        @Override
        protected void onPostExecute(Void result) {
            if (progressBar!=null) {
                progressBar.dismiss();
            }
        }


    }
}

//RetrieveInfoActivity.java

package com.example.Patient_Device;

import android.app.Activity;
import android.content.BroadcastReceiver;
import android.content.Context;
import android.content.Intent;
import android.content.IntentFilter;
import android.content.res.Resources;
import android.os.BatteryManager;
import android.os.Bundle;
import android.util.Log;
import android.widget.TextView;
import android.widget.Toast;

public class RetrieveInfoActivity extends Activity {

    private static String TAG = "RetrieveInfoActivity";
    private Context context;
    String fileLastSync = "09-18-2014 03:47 PM";

   @Override
   public void onCreate(Bundle savedInstanceState) {

            context = this;

            super.onCreate(savedInstanceState);
            setContentView(R.layout.retrieve_info);

            //Once the new activity is launched, the setup is complete
            Toast.makeText(getApplicationContext(), "Setup Complete!",
                    Toast.LENGTH_LONG).show();

            //Gets the 'last synced' string and sets to datetime of the last sync
            Resources resources = context.getResources();
            String syncString = String.format(resources.getString(R.string.last_sync), fileLastSync);

            //Dynamically sets the datetime of the last sync string
            TextView lastSyncTextView = ((TextView) findViewById(R.id.last_sync) );
            lastSyncTextView.setText(syncString);

            //calls registerReceiver to receive the broadcast for the state of battery
            this.registerReceiver(this.mBatInfoReceiver,new
                    IntentFilter(Intent.ACTION_BATTERY_CHANGED));


   }

    private BroadcastReceiver mBatInfoReceiver = new BroadcastReceiver()  {

        @Override
        public void onReceive(Context arg0, Intent intent) {

            //Battery level
            int level = intent.getIntExtra("level", 0);

            //Dynamically sets the value of the battery level
            TextView batteryTextView = ((TextView) findViewById(R.id.battery) );
            batteryTextView.setText("Battery Level: " + String.valueOf(level)+ "%");

            //If the battery level drops below 25%, then announce the battery is low
            //TODO: Add 25 to constants file.
            if(level < 25) {

                Toast.makeText(getApplicationContext(), "Low Battery!",
                        Toast.LENGTH_LONG).show();


            }
            //Plugged in Status
            int plugged = intent.getIntExtra(BatteryManager.EXTRA_PLUGGED, -1);

            //Battery Status
            int status = intent.getIntExtra(BatteryManager.EXTRA_STATUS, -1);

            //If the device is charging or contains a full status, it's charging
            boolean isCharging = status == BatteryManager.BATTERY_STATUS_CHARGING ||
                    status == BatteryManager.BATTERY_STATUS_FULL;

            //If the device isCharging and plugged in, then show that the battery is charging
            if(isCharging && plugged == BatteryManager.BATTERY_PLUGGED_AC || plugged == BatteryManager.BATTERY_PLUGGED_USB) {

                Toast.makeText(getApplicationContext(), "Charging.." + String.valueOf(level)+ "%",
                        Toast.LENGTH_LONG).show();

            }else{
                Toast.makeText(getApplicationContext(), "Unplugged!",
                        Toast.LENGTH_LONG).show();
            }


        }

    };

    @Override
    public void onDestroy() {

        try {
            super.onDestroy();
            unregisterReceiver(this.mBatInfoReceiver);
        }
        catch (Exception e) {
            Log.e(RetrieveInfoctivity.TAG, getClass() + " Releasing receivers-" + e.getMessage());
        }

    }

}

//StartSetupActivity.java


import android.app.Activity;
import android.content.Intent;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;

public class StartSetupActivity extends Activity {

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);


    }
}

//FragmentsActivity.java


import android.app.Fragment;
import android.os.Bundle;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;

public class FragmentsActivity extends Fragment{
    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {

        return inflater.inflate(R.layout.main, container, false);
    }
}

Answer 1

首先，每当你想禁用后退时，只需覆盖onBackPressed（）方法并删除super。像这样：

@Override
public void onBackPressed() {
    //super.onBackPressed();
}

其次，您使用应用程序上下文来显示吐司。使用活动背景。

Toast.makeText(this or YourActivity.this, "Setup Complete!", Toast.LENGTH_LONG).show();

第三，只需将此属性添加到清单类中即可。这将避免在方向更改时重新调整您的活动

android:configChanges="orientation"

Answer 2

我会按顺序回答这些问题：

后退按钮

您可以在Activity中覆盖onBackPressed并确定是要使用它还是让Android处理它。

@Override
public void onBackPressed()
{
    // Set this how you want based on your app logic
    boolean disallowBackPressed = false; 

    if (!disallowBackPressed)
    {
        super.onBackPressed();
    }
}

<强>干杯

Toasts与通知管理器一起排队。如果您连续显示多个Toasts，它们会排队并一次显示一个，直到队列为空。

锁定活动方向

在清单中的活动元素上使用android：screenOrientation =“landscape”或android：screenOrientation =“portrait”来锁定方向。

Answer 3

我认为应该单独询问这些问题，因为问题的每个项目的详细答案都太长了，但我希望这会有所帮助：

- 从一个活动转到另一个活动时启用后退按钮，使用户能够单击回原始活动。该问题是我不希望用户在某一点点击Back 在我的申请中。我不想完全禁用后退按钮在我的应用程序中，只有在调用一个intent时。我怎么能这样做？

您可以覆盖不希望用户返回的活动的onBackPressed。

@Override
public void onBackPressed() {
        //Leave it blank so it doesn't do anything
}

- 我注意到一些奇怪的事情...当我的应用程序中弹出一个Toast通知时，一切都很好，直到我退出我的应用程序。当我退出我的应用程序，一些Toast通知是残留的弹出我的应用程序。这有什么理由吗？我有没有？错过活动生命周期中的某些东西来处理取消在某一点敬酒？

我认为其背后的原因是即使应用程序不再可见，烤面包也会进入，并按顺序显示。

最后，这个很难解决。如何锁定我的屏幕当用户旋转设备时，活动不会再次调用，asynctask仍然可以在不启动的情况下恢复又一次？

为此，您可以在清单中使用以下代码

android:configChanges="orientation|screenSize"/>

但是谷歌不建议这样做，我建议您阅读以下链接以获取有关如何处理方向更改的更多信息： http://developer.android.com/guide/topics/resources/runtime-changes.html

Android设备上的错误。我该怎么做才能修复它们？

3 个答案: