1. Add controls to the layout of FirstActivity:
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical"
tools:context="com.example.firstactivitya.FirstActivity">
<Button
android:id="@+id/goto_second_btn"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:text="to SecondActivity"/>
</LinearLayout>2. Modify the code in FirstActivity:
public class FirstActivity extends AppCompatActivity {
private Button gotoSecondBtn;
private static final String TAG = "FirstActivity";
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_first);
gotoSecondBtn = findViewById(R.id.goto_second_btn);
//对按钮进行监听
gotoSecondBtn.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
//使用intent进行跳转
Intent intent = new Intent(FirstActivity.this, SecondActivity.class);
//启动跳转，这里使用startActivityForResult（）方法，这个方法会在跳转到的活动页面销毁时，返回一个数据给上一个活动
/**
* param1:intent
* param2：请求码，用于回调时判断数据的来源
*/
startActivityForResult(intent, 1);
}
});
}
}3. Send a message in SecondActivity:
public class SecondActivity extends AppCompatActivity {
private Button secondBtn;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_second);
secondBtn = findViewById(R.id.second_btn);
secondBtn.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
//创建Intent对象
Intent intent = new Intent();
//通过put（）以键值对的方式赋值
intent.putExtra("hi", "hi FirstActivity");
//通过setResult（）方法向上一个活动返回结果 param1：处理结果代号
setResult(1, intent);
finish();
}
});
}
}4. Finally, overwrite onActivityResult() in FirstActivity to receive the message:
@Override
protected void onActivityResult(int requestCode, int resultCode, Intent data) {
super.onActivityResult(requestCode, resultCode, data);
Log.e(TAG, "onActivityResult1: "+data );
switch (resultCode) {
//下面的1为startActivityForResult(intent, 1);中的1
case 1:
//这里的1为setResult(1, intent);中的1
if (resultCode==1){
String str = data.getStringExtra("hello");
Log.e(TAG, "onActivityResult2: "+str );
String str2 = data.getStringExtra("hi");
Log.e(TAG, "onActivityResult3: "+str2 );
}
break;
default:
break;
}
}
}OK, so you can pass the value, but you may have to ask again, where does String str = data.getStringExtra("hello"); come from, this is the code I will write below, and add it in SecondActivity:
@Override
public void onBackPressed() {
// super.onBackPressed();
Intent intent = new Intent();
intent.putExtra("hello","Hello FirstActivity");
setResult(1,intent);
finish();
}It is possible to return the data without clicking the button but clicking the return key. If you look at my code carefully, you can see that I have commented out // super.onBackPressed(); because if it is not commented, it will call The default processing method of onBackPressed() cannot implement returning data to the previous activity. This is a mistake I made. Of course, the previous method can be used to monitor the back button:
@Override
public boolean onKeyDown(int keyCode, KeyEvent event) {
if (keyCode == KeyEvent.KEYCODE_BACK) {
Intent intent = new Intent();
intent.putExtra("hello", "Hello FirstActivity");
setResult(1, intent);
finish();
}
return super.onKeyDown(keyCode, event);
}Finally, you can look at the operation effect:
