What is Intent from onActivityResult Parameters

问题:

Here is my first activity code from where I call the second Activity:

@Override
public boolean onKeyDown(int keyCode, KeyEvent event) {
  if (keyCode == KeyEvent.KEYCODE_DPAD_LEFT){       
    startActivityForResult(new Intent("chap.two.Chapter2Activity2"),request_Code);          
  }    
  return false;
}

@Override
public void onActivityResult(int requestCode, int resultCode, Intent data) {
  if (requestCode == request_Code) {
    if (resultCode == RESULT_OK) 
      Toast.makeText(this,data.getData().toString(),Toast.LENGTH_SHORT).show();             
  }
}

And here is a code of chap.two.Chapter2Activity2:

Button n = (Button) findViewById(R.id.btn_OK);
n.setOnClickListener(new View.OnClickListener() {               
   @Override
   public void onClick(View v) {
     // TODO Auto-generated method stub

     Intent data = new Intent();
     //---get the EditText view---
     EditText txt_username =(EditText) findViewById(R.id.txt_username);
     //---set the data to pass back---
     data.setData(Uri.parse(txt_username.getText().toString()));
     setResult(RESULT_OK, data);
     //---closes the activity---
     finish();

   }
});

here I see that setResult(RESULT_OK, data) has two arguments but
onActivityResult(int requestCode, int resultCode, Intent data) has three and I want know how onActivityResult gets value for third parameter? How it works can anyone tell me? Why isn't this error ?

回答1:

When you call Activity.startActivityForResult(), you set the requestCode. Later, this request code is needed by onActivityResult() in order to determine what Activity is sending data to it. We don't need to supply requestCode again on setResult() because the requestCode is carried along.

The data is intent data returned from launched intent. We usually use this data when we set extras on the called intent.

Consider this example:

CALL SECOND ACTIVITY

Intent i = new Intent(MainActivity.this, CheckActivity.class);
startActivityForResult(i, REQUEST_CODE_CHECK);

ON SECOND ACTIVITY, SET INTENT RESULT

getIntent().putExtra("TADA", "bla bla bla");
setResult(RESULT_OK, getIntent());
finish();

BACK TO FIRST ACTIVITY, ONACTIVITYRESULT()

if(requestCode == REQUEST_CODE_CHECK && resultCode == RESULT_OK){
    text1.setText(data.getExtras().getString("TADA") );
}

There you go. You should now understand what is Intent data and how to set and fetch the value.

回答2:

Third parameter is Intent, which you sent from the sub-Activity(Second Activity, which is going to finish).

If you want to perform some calculations or fetch some username/password in sub-activity and you want to send the result to the main activity, then you place the data in the intent and will return to the Main activity before finish().

After that you will check in onActivityResult(int, int, Intent) in main activity for the result with Intent parameter.

Example:: MainActivity:

public void onClick(View view) {
  Intent i = new Intent(this, subActivity.class);
  startActivityForResult(i, REQUEST_CODE);
} 

@Override
protected void onActivityResult(int requestCode, int resultCode, Intent data) {
  if (resultCode == RESULT_OK && requestCode == REQUEST_CODE) {
    if (data.hasExtra("username") && data.hasExtra("password")) {
      String username =  data.getExtras().getString("username");
      String password =  data.getExtras().getString("password");

    }
  }

subActivity::

@Override
public void finish() {
  // Create one data intent 
  Intent data = new Intent();
  data.putExtra("username", "Bla bla bla..");
  data.putExtra("password", "*****");
  setResult(RESULT_OK, data);
  super.finish();
}