1, Create and load layouts

app/src/main/res/new/directory, create a directory named layout, and right-click / layout resource file/

Add button code

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:orientation="vertical"
    android:layout_width="match_parent"
    android:layout_height="match_parent">
    <Button
        android:id="@+id/button_1"//Define an id in xml with +. No need for reference+
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:text="Button_1"
        />
</LinearLayout>

Add in onCreate() in firstactivity

public class firstactivity extends AppCompatActivity {
    @Overrideprotected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.first_layout);
}
}

Two

Register in the Android manifest file

Please refer to the first line of code for details of main activities to be configured, and add the label of < intent Filter > in < activity >

Source code after modification

<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="activitytest.example.com.activitytest">

    <application
        android:allowBackup="true"
        android:icon="@mipmap/ic_launcher"
        android:label="@string/app_name"
        android:supportsRtl="true"
        android:theme="@style/AppTheme">
        <activity
            android:name=".firstactivity"
            android:label="This is firstactivity">
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />
                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
        </activity>
    </application>
</manifest>

Three

Using toast in an activity

To define a starting point, use the previous button to add code to the onCreate () method

protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.first_layout);
    Button button1 = (Button) findViewById(R.id.button_1);//Get the elements defined in the layout file and convert them to a BUtton object
    button1.setOnClickListener(new View.OnClickListener(){//Register a listener
        @Override
        public void onClick(View v){
            Toast.makeText(firstactivity.this,"You clicked Button 1",
       
                    Toast.LENGTH_SHORT).show();//The first parameter is the context required by Toast. The second parameter is the real content. The third parameter is the display time
        }


    });
}

Using menu

<menu xmlns:android="http://schemas.android.com/apk/res/android" >
    <item
        android:id="@+id/add_item"
        android:title="ADD"/>
    <item
        android:id="@+id/remove_item"//Specific labels
        android:title="REMOVE"/>
</menu>

IV. destruction activities

5. Use explicit and implicit intent

Fireactivity code (three, four, five)

package activitytest.example.com.activitytest;

import android.content.Intent;
import android.net.Uri;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.widget.Button;
import android.widget.Toast;

public class firstactivity extends AppCompatActivity {

    @Override



    public boolean onCreateOptionsMenu(Menu menu) {

        // TODO Auto-generated method stub

        getMenuInflater().inflate(R.menu.main, menu);

        return true;

    }

    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.first_layout);
        Button button1 = (Button) findViewById(R.id.button_1);//Get the elements defined in the layout file and convert them to a BUtton object
        button1.setOnClickListener(new View.OnClickListener(){//Register a listener
            @Override
            public void onClick(View v){
                Toast.makeText(firstactivity.this,"You clicked Button 1",
              //  finish(); / / destroy the activity
                        Toast.LENGTH_SHORT).show();//The first parameter is the context required by Toast. The second parameter is the real content. The third parameter is the display time
                //Intent intent = new Intent(firstactivity.this,SecondActivity.class); / / first we build an intent, the first as the context, and the second as the target activity (explicit intent)
               // Intent intent= new Intent(Intent.ACTION_VIEW);
                //intent.addCategory("activitytest.example.com.activitytest.MY_CATEGORY");
                //intent.setData(Uri.parse("http://www.baidu.com"));
                //startActivity(intent); / / open the second one based on the first one and execute the intent
            }


        });
    }


    @Override

    public boolean onOptionsItemSelected(MenuItem item) {


        switch (item.getItemId()){

            case R.id.add_item:

                Toast.makeText(this, "you clicked ADD", Toast.LENGTH_SHORT).show();

                break;

            case R.id.remove_item:

                Toast.makeText(this, "you clicked REMOVE", Toast.LENGTH_SHORT).show();

                break;

            default:

        }

        return true;
    }}