如何在Android中的Activity之间传递数据

Question

How do I pass data between Activities in Android?

Example: I made a group CardView is in the second activitys, and I collected this card (It shows the user how much card there is in this activity)

I would like to pass the card number to the first activity

Second activity

public class Skin extends AppCompatActivity   {
    private Toolbar toolbar;
    public TextView tx;
    private  static  int mysize;
    public List<SettersAndGetters> lstPress;



    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_mainm);
        TextView tt = (TextView) findViewById(R.id.titel_card);
        Button add = (Button) findViewById(R.id.add);

        toolbar = (Toolbar) findViewById(R.id.toolbar20);
        setSupportActionBar(toolbar);
        getSupportActionBar().setDisplayShowTitleEnabled(false);
        toolbar.setNavigationOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v)
            {
                v.setFocusableInTouchMode(true);
                v.requestFocus();
                onBackPressed();
            }
        });


        add.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                Intent intent = new Intent(Skin.this, ADD.class);
                startActivity(intent);
            }
        });

//The contents of the card that you collected
        tt.setText(R.string.cn1);

        lstPress = new ArrayList<>();
        lstPress.add(new SettersAndGetters(R.string.cr5, R.string.c2, R.string.com1, R.string.des5, R.drawable.p5, 120, 55, 10000005));
        lstPress.add(new SettersAndGetters(R.string.cr1, R.string.c2, R.string.com1, R.string.des1, R.drawable.p2, 12, 12, 1800000));
        lstPress.add(new SettersAndGetters(R.string.cr1, R.string.c2, R.string.com1, R.string.des1, R.drawable.p2, 12, 12, 1800000));
        lstPress.add(new SettersAndGetters(R.string.cr1, R.string.c2, R.string.com1, R.string.des1, R.drawable.p2, 12, 12, 1800000));
        lstPress.add(new SettersAndGetters(R.string.cr1, R.string.c2, R.string.com1, R.string.des1, R.drawable.p2, 12, 12, 1800000));
        lstPress.add(new SettersAndGetters(R.string.cr1, R.string.c2, R.string.com1, R.string.des1, R.drawable.p2, 12, 12, 1800000));

        tx = (TextView) findViewById(R.id.c);
        int size = lstPress.size();     //here This line works great for me, but I want it in the first class (pass it to a class before it)
        tx.setText("" + size);
        mysize=size;



        Toast.makeText(getApplicationContext(),"Size="+size,Toast.LENGTH_LONG).show();




        RecyclerView myr = (RecyclerView) findViewById(R.id.recycler_view);
        RecyclerViewAdapter myAdapter = new RecyclerViewAdapter(this, lstPress);
        myr.setLayoutManager(new GridLayoutManager(this, 2));
        myr.setAdapter(myAdapter);



    }

    @Override
    public boolean onPrepareOptionsMenu(Menu menu) {

        return true;

    }


    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        // Inflate the menu; this adds items to the action bar if it is present.
        getMenuInflater().inflate(R.menu.menu_add, menu);
        // Inflate switch
        ImageButton re = (ImageButton) menu.findItem(R.id.item_switch2)
                .getActionView().findViewById(R.id.back2);






        re.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                onBackPressed();
                Toast.makeText(Skin.this, "hhi", Toast.LENGTH_SHORT).show();
            }
        });



        ImageButton btnubload = (ImageButton) menu.findItem(R.id.item_switch2)
                .getActionView().findViewById(R.id.btnaddUPLOAD);






        btnubload.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                Intent intent = new Intent(Skin.this, ADD.class);
                startActivity(intent);



            }
        });





        return true;




    }

    @Override
    protected void attachBaseContext(Context newBase) {
        super.attachBaseContext(ViewPumpContextWrapper.wrap(newBase));
    }

    @Override
    public boolean onSupportNavigateUp() {
        onBackPressed();
        return true;
    }




public static int getMysize(){


        return mysize;

}


}

MainActivity is first activity

    public class MainActivity extends AppCompatActivity implements BootShett.BottomSheetListener {


protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_mainm);
        TextView tt = (TextView) findViewById(R.id.Number_of_badges)


 int c=Skin.getMysize();
        tt.setText(""+c);


}

Answer 1

To pass data between activities use Intents .

For example set some data before opening the an Activity:

Intent intent = new Intent(Skin.this, ADD.class);
intent.putExtra("key_a", "hello world");
intent.putExtra("key_b", 123);
intent.putExtra("key_c", true);
startActivity(intent);

And to retrieve it in the other activity:

protected void onCreate(Bundle savedInstanceState) {
    ....
    final String valueA = this.getIntent().getStringExtra("key_a");
    final int valueB = this.getIntent().getIntExtra("key_b", 0);
    final boolean valueC = this.getIntent().getBooleanExtra("key_c", false);
    ....
}

If instead , you need to return a value from the second activity, so in reverse mode, then start the second activity with startActivityForResult (and not startActivity), and then override in the first activity the onActivityResult method to handle the result. See this link for more documentation about returning values from activities.

Example:

1. In the first activity you must start the second activity with startActivityForResult :

    Intent intent = new Intent(this, SecondActivity.class); this.startActivityForResult(intent, YUR_REQUEST_CODE);

2. In the second activity before closing it by calling finish , set the return value using setResult :

    public void onClick(View view) { final Intent intent = new Intent(); intent.putExtra("key_a", 1234567890); setResult(YUR_REQUEST_CODE, intent); finish(); }

3. When back into the first activity you will automatically get the result in the method onActivityResult

   @Override protected void onActivityResult(int requestCode, int resultCode, Intent data) { super.onActivityResult(requestCode, resultCode, data); if (requestCode == YOUR_REQUEST_CODE) { final int value = data.getIntExtra("key_a", 0); .... }

   }

Answer 2

You can also use Shared Preferences:

Add this code in first activity

SharedPreferences sp;
sp = getSharedPreferences("card",MODE_PRIVATE);
int cardNumber = Skin.getMysize();
sp.edit().putInt("card_number", cardNumber).apply();

Add this code in second activity

SharedPreferences sp;
sp = getSharedPreferences("card",MODE_PRIVATE);
int cardNumber = sp.getInt("card_number", "");

Answer 3

In that case just do this in the second activity just put:

Intent intent = new Intent();
intent.putExtra(key, value);
setResult(result key, intent); 
finish();

And in your 1st activity get the result through onActivityResult