1.新建类继承Activity或其子类，现在一般继承AppCompatActivity

public class TestActivity extends AppCompatActivity {
    @Override
    protected void onCreate(@Nullable Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_test);
    }
}

2.在AndroidManifest文件中声明这个activity

<activity android:name=".TestActivity">
</activity>

3.创建layout布局文件并在activity中的onCreate中设置

public class TestActivity extends AppCompatActivity {
    @Override
    protected void onCreate(@Nullable Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
 setContentView(R.layout.activity_test);
    }
}

在AndroidManifest中设置启动activity

<activity android:name=".HelloWorldActivity"
    android:label="lidahua"
    >
<intent-filter>
        <action android:name="android.intent.action.MAIN" />
        <category android:name="android.intent.category.LAUNCHER" />
    </intent-filter>
</activity>


不适用系统自带的titlebar

    <application
        android:allowBackup="true"
        android:icon="@mipmap/ic_launcher"
        android:label="@string/app_name"
        android:supportsRtl="true"
android:theme="@style/Theme.AppCompat.Light.NoActionBar">
        <activity android:name=".HelloWorldActivity"
            android:label="lidahua"  --给titlebar重新设置标题
            >
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />
                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
        </activity>
        <activity android:name=".TestActivity">
        </activity>
    </application>

</manifest>

Android activity创建三部曲