[Android]笔记1-HelloWorld

一、使用XML布局文件控制UI界面
XML

    <TextView
        android:id="@+id/show"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_alignParentTop="true"
        android:layout_centerInParent="true"
        android:text="Hello World!" />

    <Button
        android:text="单击我"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_below="@id/show"
        android:layout_alignParentLeft="true"
        android:layout_alignParentStart="true"
        android:layout_marginTop="23dp"
        android:onClick="clickHandler"
        android:id="@+id/button" />

MainActivity .java

public class MainActivity extends AppCompatActivity {

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

    public  void clickHandler(android.view.View source)
    {
        TextView tv=(TextView) findViewById(R.id.show);
        tv.setText("Hello Android-"+new java.util.Date());
    }
}

二、在代码中控制UI界面

public class MainActivity extends AppCompatActivity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        //创建一个线性布局管理器
        LinearLayout layout =new LinearLayout(this);
        //设置该Activity 显示layout
        super.setContentView(layout);
        layout.setOrientation(LinearLayout.VERTICAL);
        // 创建一个TextView
        final TextView show =new TextView(this);
        //创建一个按钮
        Button bn=new Button(this);
        bn.setText(R.string.app_name);
        bn.setLayoutParams(new ViewGroup.LayoutParams(
                ViewGroup.LayoutParams.WRAP_CONTENT,ViewGroup.LayoutParams.WRAP_CONTENT
        ));
        //向layout容器中添加textview
        layout.addView(show);
        //向layout容器中添加按钮
        layout.addView(bn);
        bn.setOnClickListener(new View.OnClickListener(){
                @Override
                public void onClick(View v)
                {
                    show.setText("Hello,Android,"+new java.util.Date());
                }
        });



    }
}