Android Development Study Notes (1) Click the corresponding button

Because a small project requires the development of Android APP, I am here to learn Android. At the same time, I have not touched JAVA, so I don't have a deep understanding of various grammars for the time being. Only a record of how to use it is convenient for copying and pasting.

Reference learning video: 30 hours of Android Android development to get Baidu map from scratch (2020 Android development full set of tutorials)

The event of the corresponding button:

public void sendMessage(View view){
        EditText msg = findViewById(R.id.message);
        String s = msg.getText().toString();
        //页面切换
写法一：class跳转
         Intent intent = new Intent(this,secondActivity.class);
		 this.startActivity(intent);
写法二：包名.类名
//        Intent intent = new Intent();
//        intent.setClassName(this,"cn.edu.cdut.mainactivity.secondActivity");
//        startActivity(intent);
//这个写法不知道为什么点击之后软件会崩溃，暂不作细究
写法三：ComponentName
//        Intent intent = new Intent();
//        ComponentName cname= new ComponentName(this,secondActivity.class);
//        intent.setComponent(cname);
//        startActivity(intent);
隐式启动：写法一
//        Intent intent = new Intent();
//        intent.setAction("action.nextActivity");
//        startActivity(intent);
写法二：
        Intent intent = new Intent("action.nextActivity");
        startActivity(intent);
    }
注：action.nextActivity为 xml文件中自定义的action名字

The part of AndroidManifest.xml file is:

   	   <activity android:name=".secondActivity">
            <intent-filter>
                <action android:name="action.nextActivity" />
                <category android:name="android.intent.category.DEFAULT" />
            </intent-filter>
        </activity>

The category defaults to LAUNCHER, which will generate a new APP icon