Question

我想在数据库连接失败时更改布局。

我在考虑执行setContentView(R.layout.no_connection); 每当从doInBackground();方法抛出异常，但它无法正常工作时，我的应用程序崩溃了。

class Connect extends AsyncTask <String, Void, String> {

        private Exception exception;

        TextView tv = (TextView) findViewById(R.id.textView);
        String result = "";

        public Connect(TextView tv) {
            this.tv = tv;
        }

        protected String doInBackground(String... urls) {

            try {

               // StrictMode.ThreadPolicy policy = new StrictMode.ThreadPolicy.Builder().permitAll().build();
               // StrictMode.setThreadPolicy(policy);
                final String url = "jdbc:mysql://192.168.1.4:3308/demo"; //192.168.43.137:3308
                final String user = "Vishal"; //testUser
                String pass = "password"; //test

                Class.forName("com.mysql.jdbc.Driver");
                Connection conn = DriverManager.getConnection(url, user, pass); //(urls[0], urls[1], urls[2])

                Statement st = conn.createStatement();
                ResultSet rs = st.executeQuery("SELECT * from user_info");
                ResultSetMetaData rand = rs.getMetaData();

                while(rs.next()){
                    result  += rs.getInt(1)+"  " + rs.getString(2)+"  "  + rs.getString(3)+"\n " ;
                }
                //Toast.makeText(MainActivity.this, "Connection Successful", Toast.LENGTH_LONG).show();

                //result = "Database Connection Success\n";
                //Toast.makeText(MainActivity.this, "Success", Toast.LENGTH_SHORT).show();
                return result;

            } catch (Exception e) {
                this.exception = e;


                //Toast.makeText(MainActivity.this, "Failure", Toast.LENGTH_SHORT).show();

                return e.toString();
            }
        }

        protected void onPostExecute(String feed) {
            // TODO: check this.exception
            // TODO: do something with the feed
            if(result == null){
                Toast.makeText(MainActivity.this, "Result null", Toast.LENGTH_SHORT).show();

            }
            if(feed == null){
                Toast.makeText(MainActivity.this, "feed null", Toast.LENGTH_SHORT).show();


            }
            tv.setText(feed);

            Toast.makeText(MainActivity.this, "Connection Successful", Toast.LENGTH_LONG).show();
        }


    }

    ;

我使用abc = new Connect(tv).execute(url).toString();在主UI线程中调用它有没有更好的方法呢？请建议，我是一个noobie。

Answer 1

您应该以这种方式更新您的用户界面：

Runnable r = new Runnable() {
    public void run() {
        // here update UI methods
    }
};
runOnUiThread(r);

Answer 2

如果要使用AsynkTask更新视图，则应该在方法onPostExecute（）中进行，因为方法doInBackGround performed in other thread

如何使用AsyncTask更改相同活动的布局？

2 个答案: