FLAG_ACTIVITY_FORWARD_RESULT的使用

这是个很基础的知识点，然而，最近又被坑了一次。于是写个demo 巩固一下。

需求很简单，就是 从 Activity A跳到B，再从B跳到C，并且希望 A中可以直接拿到C返回的结果，而B只是起到一个过渡的作用。

Activity A-B-C的demo代码如下：

//Activity A
//A  startActivityForResult 想要从B 拿到结果
public class AAActivity extends AppCompatActivity {

    private Button mButton;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        mButton = (Button) findViewById(R.id.btn);
        mButton.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                Intent intent = new Intent(AAActivity.this, BBActivity.class);
                startActivityForResult(intent, 100);
            }
        });
    }

    @Override
    protected void onActivityResult(int requestCode, int resultCode, Intent data) {
        super.onActivityResult(requestCode, resultCode, data);
        Log.e("forwardresult","AAActivity requestCode:" + requestCode + ", resultCode:" + resultCode);
    }
}

//Activity B
//B 作为过渡页在跳转C时 添加了FLAG_ACTIVITY_FORWARD_RESULT flag 将会使 C返回的结果不经过B 而直接到A 
public class BBActivity extends Activity{

    private Button mButton;

    @Override
    protected void onCreate(@Nullable Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_bb);

        mButton = (Button) findViewById(R.id.btn);
        mButton.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                Intent intent = new Intent(BBActivity.this, CCActivity.class);
                intent.addFlags(Intent.FLAG_ACTIVITY_FORWARD_RESULT);
                startActivity(intent);
            }
        });
    }
}

//Activity C
//C setResult给调用者
public class CCActivity extends Activity {

    private Button mButton;

    @Override
    protected void onCreate(@Nullable Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_cc);

        mButton = findViewById(R.id.btn);
        mButton.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                setResult(RESULT_OK);
                finish();
            }
        });
    }
}

Intent.FLAG_ACTIVITY_FORWARD_RESULT 这个flag 不能和startActivityForResult 一起使用，否则会报android.util.AndroidRuntimeException: FORWARD_RESULT_FLAG used while also requesting a result, 也很好理解，FORWARD_RESULT_FLAG 就是希望 不接受返回结果，而startActivityForResult 是希望获取结果，相互矛盾。下面这样写法会crash

        mButton.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                Intent intent = new Intent(BBActivity.this, CCActivity.class);
                intent.addFlags(Intent.FLAG_ACTIVITY_FORWARD_RESULT);
                startActivityForResult(intent, 1000);
            }
        });