Android 开发Missing contentDescription attribute on image in XML

public class Main extends Activity {
 
    Button page;
 
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);
 
        page = (Button) findViewById(R.id.open);
 
        page.setOnClickListener(new OnClickListener(){
            @Override
            public void onClick(View source) {
                Intent intent = new Intent(Main.this, NewPage.class);
 
                // 启动 intent 对应的 Activity ，并且等待其返回结果，其中 0 是标识码
                startActivityForResult(intent, 0);
            }
        });
     
    @Override
    public void onActivityResult(int requestCode, int resultCode, Intent intent){
         
        if( requestCode == 0 && resultCode == 0 ){ // 确认请求标识码和反馈结果标识码同为 0
            // 改变本页面或其他操作
        }
    }
 
}

public class NewPage extends Activity {
 
    Button cancel;
 
    Intent intent;
 
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.newpage);
         
        // 获取到上一个页面传过来的 Intent
        intent = this.getIntent();
 
        cancel = (Button) findViewById(R.id.confirm);
        cancel.setOnClickListener(new OnClickListener() {
            @Override
            public void onClick(View source) {
                // 反馈结果，将 intent 传回上一个 Activity ，这时在上一页触发 onActivityResult 方法，重写该方法可以对原页面作出调整
                NewPage.this.setResult(0, intent);
                NewPage.this.finish();
            }
        });
 
    }
 
}