Activity之间返回结果

一 、实现：

1、在MainActivity中：

1)onCreate()中：

Intent intent = new Intent(MainActivity.this,OtherActivity.class);
startActivityForResult(intent,0); //startActivityForResult(Intent intent,int requestcode)

2)重写onActivityResult():

@override
protected void onActivityResult(int requestCode, int resultCode, Intent data) {
        super.onActivityResult(requestCode, resultCode, data);

        //处理返回的数据
        String name = data.getBundleExtra("data").getString("name");
        message.setText(name);

    }

2、在OtherActivity中：

1)onCreate()中：

Intent intent = this.getIntent();
Bundle bundle = new Bundle();
bundle.put("name","Jack");
intent.putExtra("BundleKey",bundle);
setResult(0,intent); //setResult(int resultCode, Intent intent);

二 、过程：

1)首先，来看startActivityForResult(intent,0);

进入FragmentActivity.java:

/**
     * Modifies the standard behavior to allow results to be delivered to fragments.
     * This imposes a restriction that requestCode be <= 0xffff.
     */
    @Override
    public void startActivityForResult(Intent intent, int requestCode) {
        if (requestCode != -1 && (requestCode&0xffff0000) != 0) {
            throw new IllegalArgumentException("Can only use lower 16 bits for requestCode");
        }
        super.startActivityForResult(intent, requestCode);
    }

判断requestCode是否小于16 bits，

如果requestCode <= 16bits,再进入Activity.java:

/**
     * Same as calling {@link #startActivityForResult(Intent, int, Bundle)}
     * with no options.
     *
     * @param intent The intent to start.
     * @param requestCode If >= 0, this code will be returned in
     *                    onActivityResult() when the activity exits.
     *
     * @throws android.content.ActivityNotFoundException
     *
     * @see #startActivity
     */
    public void startActivityForResult(Intent intent, int requestCode) {
        startActivityForResult(intent, requestCode, null);
    }

    /**
     * @param intent The intent to start.
     * @param requestCode If >= 0, this code will be returned in
     *                    onActivityResult() when the activity exits.
     * @param options Additional options for how the Activity should be started.
     * See {@link android.content.Context#startActivity(Intent, Bundle)
     * Context.startActivity(Intent, Bundle)} for more details.
     *
     * @throws android.content.ActivityNotFoundException
     *
     * @see #startActivity
     */
    public void startActivityForResult(Intent intent, int requestCode, @Nullable Bundle options) {
        if (mParent == null) {
            Instrumentation.ActivityResult ar =
                mInstrumentation.execStartActivity(
                    this, mMainThread.getApplicationThread(), mToken, this,
                    intent, requestCode, options);
            if (ar != null) {
                mMainThread.sendActivityResult(
                    mToken, mEmbeddedID, requestCode, ar.getResultCode(),
                    ar.getResultData());
            }
            if (requestCode >= 0) {              
                mStartedActivity = true;
            }

            cancelInputsAndStartExitTransition(options);
            // TODO Consider clearing/flushing other event sources and events for child windows.
        } else {
            if (options != null) {
                mParent.startActivityFromChild(this, intent, requestCode, options);
            } else {
                // Note we want to go through this method for compatibility with
                // existing applications that may have overridden it.
                mParent.startActivityFromChild(this, intent, requestCode);
            }
        }
    }

判断requestCode是否大于0，
If requestCode >= 0, this code will be returned in onActivityResult() when the activity exits.

2)然后，来看setResult(0,intent);

进入Activity.java:

/**
     * Call this to set the result that your activity will return to its
     * caller.
     *
     * <p>As of {@link android.os.Build.VERSION_CODES#GINGERBREAD}, the Intent
     * you supply here can have {@link Intent#FLAG_GRANT_READ_URI_PERMISSION
     * Intent.FLAG_GRANT_READ_URI_PERMISSION} and/or {@link Intent#FLAG_GRANT_WRITE_URI_PERMISSION
     * Intent.FLAG_GRANT_WRITE_URI_PERMISSION} set.  This will grant the
     * Activity receiving the result access to the specific URIs in the Intent.
     * Access will remain until the Activity has finished (it will remain across the hosting
     * process being killed and other temporary destruction) and will be added
     * to any existing set of URI permissions it already holds.
     *
     * @param resultCode The result code to propagate back to the originating
     *                   activity, often RESULT_CANCELED or RESULT_OK
     * @param data The data to propagate back to the originating activity.
     *
     * @see #RESULT_CANCELED
     * @see #RESULT_OK
     * @see #RESULT_FIRST_USER
     * @see #setResult(int)
     */
    public final void setResult(int resultCode, Intent data) {
        synchronized (this) {
            mResultCode = resultCode;
            mResultData = data;
        }
    }

把resultCode,data返回给MainActivity的onActivityResult(int requestCode, int resultCode, Intent data)

3)@override

protected void onActivityResult(int requestCode, int resultCode, Intent data) {
        super.onActivityResult(requestCode, resultCode, data);

        //处理返回的数据
    }

明白其中的原理，学起来会很快，加油！