Question

我是Android编程的新手。

我已经为自己构建了一些代码，我想要做的是：

加载MainActivity时，请勿显示按钮。
当JSON成功加载时，显示toggleButton
根据JSON数据，toggleButton加载为ON或OFF

我不知道怎么做，所以我采用了以下策略。在MainActivity.onCreate中，我声明了toggleButton toggleSugar 。

下载JSON时，我将 toggleSugar 更新为VISIBLE或INVISIBLE。

但是 toggleSugar 在方法onCreate中，而JSON活动在方法doInBackground中的子类中GetButtonState扩展ASyncClass（）

因此，当我尝试从JSON成功代码块更新 toggleSugar 时，它无法访问 toggleSugar 对象。

第二个策略是在onCreate之前在MainActivity root下声明 toggleSugar 。这会让应用程序崩溃。

我的代码如下：

package com.cyberialearning.aswitch;

import android.app.AlertDialog;
import android.content.DialogInterface;
import android.os.AsyncTask;
import android.os.Bundle;
import android.support.v7.app.AppCompatActivity;
import android.util.Log;
import android.view.KeyEvent;
import android.view.View;
import android.widget.CompoundButton;
import android.widget.ProgressBar;
import android.widget.TextView;
import android.widget.Toast;
import android.widget.ToggleButton;

import org.json.JSONException;
import org.json.JSONObject;

public class MainActivity extends AppCompatActivity {

    private String TAG=MainActivity.class.getSimpleName();

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

       ToggleButton toggleSugar = (ToggleButton) findViewById(R.id.toggleButton);
        toggleSugar.setVisibility(View.INVISIBLE);
        new GetButtonState().execute();

        final TextView statusmsg = (TextView) findViewById(R.id.textView);
        boolean dataReceived=true;

        if (dataReceived==false) {
            toggleSugar.setVisibility(View.INVISIBLE);
        }

        toggleSugar.setOnCheckedChangeListener(new CompoundButton.OnCheckedChangeListener() {
            public void onCheckedChanged(CompoundButton buttonView, boolean isChecked) {
                if (isChecked) {
                    statusmsg.setText("ButtonisOn");
                } else {
                    statusmsg.setText("ButtonisOff");
                    ;
                }
            }
        });

    }

    void testfunction() {
        Log.e(TAG, "testfunction");
        toggleSugar.setVisibility(View.VISIBLE);

    }

    private class GetButtonState extends AsyncTask<Void, Void, Void> {

        final TextView statusmsg = (TextView) findViewById(R.id.textView);
        boolean dataReceived=true;          
        ProgressBar bar = (ProgressBar) findViewById(R.id.progressBar2);   
        @Override
        protected void onPreExecute() {
            super.onPreExecute();
            statusmsg.setText("Please wait. Connecting ...");
            Toast.makeText(MainActivity.this,"Trying to get JSON data",Toast.LENGTH_LONG).show();

        }
        @Override
        protected Void doInBackground(Void... arg0) {
            HttpHandler sh = new HttpHandler();

            String url = "http://www.nusantara.com.my/testjson.html";
            String jsonStr=null;
            try {
                jsonStr = sh.makeServiceCall(url);
                jsonStr = jsonStr.replace("callBackFunction(", "");
            } catch (Exception e) {

                System.out.println("Cannot Communicate With "+url);
                runOnUiThread(new Runnable() { @Override public void run() {
                    AlertDialog aDialog = new AlertDialog.Builder(MainActivity.this).setMessage("It is possible that the server is down temporarily.\n\nDoes this device have internet access?").setTitle("Cannot communicate with server.")
                            .setNeutralButton("Shutdown App", new AlertDialog.OnClickListener() { public void onClick(final DialogInterface dialog, final int which) { finish(); } }).create();
                    //disable the back button
                    aDialog.setOnKeyListener(new DialogInterface.OnKeyListener() { @Override public boolean onKey(DialogInterface dialog, int keyCode, KeyEvent event) { return true; } });                        
                    dataReceived=false;    

                } });
                return null;
            }
            jsonStr = jsonStr.replace (");","");
            Log.e(TAG, "Response from url: " + jsonStr);

            if (jsonStr != null) {
                try {
                    JSONObject jsonObj = new JSONObject(jsonStr);
                    String currentStatus = jsonObj.getString("status");
                    Log.e(TAG, "received JSON status: " + currentStatus);                                            
                    testfunction();
                } catch (final JSONException e) {

                    Log.e(TAG, "Invalid JSON format (test with curiousconcepts) : " + e.getMessage()); runOnUiThread(new Runnable() { @Override public void run() { Toast.makeText(getApplicationContext(), "Json parsing error: " + e.getMessage(), Toast.LENGTH_LONG).show(); }});
                    }
            } else {
             MESSAGE IS NULL : POSSIBLE SERVER PROBLEM - hosting
                Log.e(TAG, "JSON is null.");
                runOnUiThread(new Runnable() {
                    @Override
                    public void run() {
                        Toast.makeText(getApplicationContext(),
                                "Couldn't get json from server. Check LogCat for possible errors!",
                                Toast.LENGTH_LONG).show();
                        dataReceived=false;
                        statusmsg.setText("Please wait. Connecting ...");


                    }
                });
            }
            return null;
        }
        protected void onPostExecute(Void result) {
            super.onPostExecute(result);
            Log.e(TAG,"in onPostExecute function.");

        }

    }
}

我也尝试过：

toggleSugar.setVisibility(View.VISIBLE);

当JSON成功下载时，但它不起作用。

我还尝试调用子类 testFunction（）之外的函数来引用子类之外的 toggleSugar ，但这也没有工作

请帮忙。

Answer 1

首先，您需要从onCreate方法移动ToggleButton的声明，并在类的开头声明它，如下所示：

public class MainActivity extends AppCompatActivity {

ToggleButton  toggleSugar ;

//......

}

然后获取onCreate方法内的切换按钮的参考：

toggleSugar = (ToggleButton) findViewById(R.id.toggleButton);

之后，您可以通过onPostExcute方法访问它，如下所示：

protected void onPostExecute(Void result) {

            super.onPostExecute(result);

            toggleSugar.setVisibility(View.VISIBLE);
        }

如何创建仅在下载数据后出现的togglebutton？

1 个答案: