Android编程基础

public class MainActivity extends AppCompatActivity {
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        //退出
        Button btn1 = (Button) findViewById(R.id.btn_exit);
        btn1.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                finish();
            }
        });
        //测试
        Button btn2 = (Button) findViewById(R.id.btn_test);
        btn2.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                TextView tv = (TextView) findViewById(R.id.msg);
                tv.setText("Hello");
            }
        });
    }
}

public class MainActivity extends AppCompatActivity {
    class BtnClickListener implements View.OnClickListener{

        @Override
        public void onClick(View v) {
            switch (v.getId()){
                case R.id.btn_test:
                    TextView tv = (TextView) findViewById(R.id.msg);
                    tv.setText("Hello");
                    break;
                case R.id.btn_exit:
                    finish();
                    break;
            }
        }
    }
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        Button btn1 = (Button) findViewById(R.id.btn_test);
        Button btn2 = (Button) findViewById(R.id.btn_exit);
        BtnClickListener listener = new BtnClickListener();
        btn1.setOnClickListener(listener);
        btn2.setOnClickListener(listener);
    }
}