android setResult()返回码为0

setResult()->finish()

setResult()必须保证在finish()之前执行，否则返回码设置失效，为默认值0。

要搞懂原因，必须先回到源码中：

// protected by synchronized (this)
int mResultCode = RESULT_CANCELED;
Intent mResultData = null;
/*省略部分代码*/
public final void setResult(int resultCode) {
    synchronized (this) {
        mResultCode = resultCode;
        mResultData = null;
    }
}
public final void setResult(int resultCode, Intent data) {
    synchronized (this) {
        mResultCode = resultCode;
        mResultData = data;
    }
}
/*省略部分代码*/
public void finish() {
    finish(DONT_FINISH_TASK_WITH_ACTIVITY);
}
/*省略部分代码*/
private void finish(int finishTask) {
    if (mParent == null) {
        int resultCode;
        Intent resultData;
        synchronized (this) {
            resultCode = mResultCode;
            resultData = mResultData;
        }
        if (false) Log.v(TAG, "Finishing self: token=" + mToken);
        try {
            if (resultData != null) {
                resultData.prepareToLeaveProcess(this);
            }
            if (ActivityManagerNative.getDefault()
                    .finishActivity(mToken, resultCode, resultData, finishTask)) {
                mFinished = true;
            }
        } catch (RemoteException e) {
            // Empty
        }
    } else {
        mParent.finishFromChild(this);
    }
}

可以发现setResult()只是给 mResultCode 和 mResultData 赋值，finish()将mResultCode 和 mResultData传给了native层。所以setResult()必须保证在finish()之前执行，否则返回码设置失效，为默认值0。