registerForActivityResult()方法的简单理解和使用-Toy模板网

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最近学到了registerForActivityResult,简单理解一下：
1、使用registerForActivityResult为获取到的结果注册结果回调，但其本身不会启动intent跳转
2、registerForActivityResult最后会返回一个ActivityResultLauncher对象用于启动intent跳转
3、registerForActivityResult第一个参数是ActivityResultContracts，除了通用的StartActivityForResult，还有TakePicture（拍照）、RequestPermission（请求单个权限）、PickContact（从通讯录获取联系人）等预定义好的contract
4、第二个参数中的onActivityResult() 方法用于处理获取到的数据结果

深入理解参考以下两篇文章：
https://www.cnblogs.com/–here–gold–you–want/p/14841024.html
http://www.icodebang.com/article/264591

SecondActivity的数据返回给FirstActivity，代码如下：文章来源地址https://www.toymoban.com/news/detail-418854.html

一、FirstActivity.java

public class FirstActivity extends AppCompatActivity {

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

        //该方法要放在onCreate里面，不能放在监听器里
        ActivityResultLauncher launcher = registerForActivityResult(new ActivityResultContracts.StartActivityForResult(), new ActivityResultCallback<ActivityResult>() {
            @Override
            public void onActivityResult(ActivityResult result) {
                if(result.getResultCode() == Activity.RESULT_OK){
                    Log.d("data_return", result.getData().getStringExtra("data_return"));
                }
            }
        });

        Button button1 = (Button) findViewById(R.id.button_1);
        button1.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                Intent intent = new Intent(FirstActivity.this,SecondActivity.class);
                launcher.launch(intent);//启动intent跳转
            }
        });
    }
}

二、SecondActivity.java

public class SecondActivity extends AppCompatActivity {

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

        Button button2 = (Button) findViewById(R.id.button_2);
        button2.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                Intent intent = new Intent();
                intent.putExtra("data_return","the data of returning to FirstActivity");
                setResult(RESULT_OK,intent);
                finish();
            }
        });
    }
}