在Android中按下后退按钮销毁数据

Question

I have few activity files that contains almost same code as shown below. Well i have not included onDestroy and finish() method in all of my activity files, before moving forward i want to be sure of the code posted below.

public class Three extends AppCompatActivity {
    Button forwardB,backwardB,homeB;
    TextView textView2,textView4,textView5;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.one);
        //Place advertisement here
        AdView adView = (AdView) findViewById(R.id.adView);
        AdRequest adRequest = new AdRequest.Builder()
            .build();
        adView.loadAd(adRequest);
        //
        //find widget by Id
        forwardB = (Button) findViewById(R.id.forwardB);
        backwardB = (Button) findViewById(R.id.backwardB);
        homeB = (Button) findViewById(R.id.homeB);
        textView2= (TextView) findViewById(R.id.textView2);
        textView4 = (TextView) findViewById(R.id.textView4);
        textView5 = (TextView) findViewById(R.id.textView5);
        textView5.setText("3/50");
        //set text inside textView3 and textView4
        textView2.setText("Apfel");textView4.setText("apple");
        //set on click listener for forward,backward and home button
        forwardB.setOnClickListener(new View.OnClickListener() {
            public void onClick(View v) {
                Intent i = new Intent(getApplicationContext(), Two.class);
                i.setFlags(Intent.FLAG_ACTIVITY_NEW_TASK | Intent.FLAG_ACTIVITY_CLEAR_TASK);
                startActivity(i);
                finish();
            }
        });
        homeB.setOnClickListener(new View.OnClickListener() {
            public void onClick(View v) {
                Intent i = new Intent(getApplicationContext(), MainActivity.class);
                i.setFlags(Intent.FLAG_ACTIVITY_NEW_TASK | Intent.FLAG_ACTIVITY_CLEAR_TASK);
                startActivity(i);
                finish();
            }
        });
        backwardB.setOnClickListener(new View.OnClickListener() {
            public void onClick(View v) {
                Intent i = new Intent(getApplicationContext(), Four.class);
                i.setFlags(Intent.FLAG_ACTIVITY_NEW_TASK | Intent.FLAG_ACTIVITY_CLEAR_TASK);
                startActivity(i);
                finish();
            }
        });
    }
    @Override
    protected void onDestroy() {
        super.onDestroy();
    }
}

After running the application i found a serious issue with data,it looks like android keeps data in background. How can i avoid this?

Everytime i run app and check the data it seems to be increasing.

Well this is my MainActivity.java:

public class MainActivity extends Activity {
    Button btnflashcards;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setRequestedOrientation(ActivityInfo.SCREEN_ORIENTATION_PORTRAIT);
        requestWindowFeature(Window.FEATURE_NO_TITLE);
        setContentView(R.layout.activity_main);

        //create widget ids that are usable forw rest of the code
        btnflashcards = (Button) findViewById(R.id.btnflashcards);
    }
    //on flash card button click
    public void findFlashCards(View v){
        Intent i = new Intent(this, FlashCardSelection.class);
        startActivity(i);
    }
    @Override
    public void onBackPressed() {
        Intent intent = new Intent(Intent.ACTION_MAIN);
        intent.addCategory(Intent.CATEGORY_HOME);
        intent.setFlags(Intent.FLAG_ACTIVITY_NEW_TASK);
        startActivity(intent);
    }

    @Override
    protected void onDestroy() {
        super.onDestroy();
    }
}

Answer 1

You will need to explicitly clear the application's user data every time you exit the aplication or at any point of time you want to during the use of your app.

Use this: ActivityManager's clearApplicationUserData() method

As per documentation this will:

Permits an application to erase its own data from disk. This is equivalent to the user choosing to clear the app's data from within the device settings UI. It erases all dynamic data associated with the app -- its private data and data in its private area on external storage -- but does not remove the installed application itself, nor any OBB files.

Answer 2

Give something like this a shot

import java.io.File;

import android.app.Activity;
import android.content.Context;
import android.os.Bundle;

public class HelloWorld extends Activity {

   /** Called when the activity is first created. */
   @Override
   public void onCreate(Bundle *) {
      super.onCreate(*);
      setContentView(R.layout.main);
   }

   @Override
   protected void onStop(){
      super.onStop();
   }

   //Fires after the OnStop() state
   @Override
   protected void onDestroy() {
      super.onDestroy();
      try {
         trimCache(this);
      } catch (Exception e) {
         // TODO Auto-generated catch block
         e.printStackTrace();
      }
   }

   public static void trimCache(Context context) {
      try {
         File dir = context.getCacheDir();
         if (dir != null && dir.isDirectory()) {
            deleteDir(dir);
         }
      } catch (Exception e) {
         // TODO: handle exception
      }
   }

   public static boolean deleteDir(File dir) {
      if (dir != null && dir.isDirectory()) {
         String[] children = dir.list();
         for (int i = 0; i < children.length; i++) {
            boolean success = deleteDir(new File(dir, children[i]));
            if (!success) {
               return false;
            }
         }
      }

      // The directory is now empty so delete it
      return dir.delete();
   }

}