使用Intent传值及回传值

        findViewById(R.id.button).setOnClickListener(new View.OnClickListener(){
            @Override
            public void onClick(View v) {
                Intent intent = new Intent(FirstActivity.this, SecondActivity.class);
                intent.putExtra("extra_data","data"); // 传字符串, 更多传值方法
                startActivity(intent);
            }
        });

  @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_second);
        // 获取Intent对象
        Intent intent = getIntent();
        // 根据key获取value
        String extra_data = intent.getStringExtra("extra_data");
        // 获取一个没有的可以 结果 null
        String extra_data2 = intent.getStringExtra("extra_data2");
        Log.i(TAG, "onCreate: " + extra_data + extra_data2);
   }

/**
 * 监听获取activity返回的数据
 * @param requestCode 传入的请求码
 * @param resultCode 处理结果码
 * @param data intent数据
 */
@Override
protected void onActivityResult(int requestCode, int resultCode, Intent data) {
    switch (requestCode) {
        case 1:
            if (resultCode == RESULT_OK) {
                String resultData = data.getStringExtra("data_return");
                Log.i(TAG, "onActivityResult: " + resultData);
            }
            break;
        default:
    }
}

        button = (Button) findViewById(R.id.button2);
        button.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                Intent intent = new Intent();
                intent.putExtra("data_return", "hello FirstActivity");
                // 给上一个活动返回数据
                setResult(RESULT_OK, intent);// 回调(FirstActivity.java中)onActivityResult方法
                finish();
            }
        });