Question

我目前正在android studio中开发一个应用程序。我的应用程序的目标是让一个页面（MainActivity.java和amp; activityMain.xml）显示一个微调器。此微调器中的项是来自远程数据库的项。当用户选择此微调器中的项目时，我希望所选项目显示在单独的页面中（Map.java map.xml）。我在MainActivity中使用了一个putExtra方法将所选项存储到字符串变量中：

@Override
public void onItemSelected(AdapterView<?> parent, View view, int position,
                           long id) {
    Toast.makeText(
            getApplicationContext(),
            parent.getItemAtPosition(position).toString() + " Selected" ,
            Toast.LENGTH_LONG).show();

    Intent intent = new Intent(MainActivity.this, Map.class);
    String text = spinnerFood.getSelectedItem().toString();
    intent.putExtra("SPINNER_KEY", text);
    startActivity(intent);

}

然后在我的Map类中，我使用getExtras调用该字符串：

String spinnerString;
    if (savedInstanceState == null) {
        Bundle extras = getIntent().getExtras();
        if(extras == null) {
            spinnerString= null;
        } else {
            spinnerString= extras.getString("STRING_I_NEED");
        }
    } else {
        spinnerString= (String) savedInstanceState.getSerializable("STRING_I_NEED");
    }

我可以将此字符串从MainActivity成功传递给Map。我的问题是当我尝试显示此字符串时，我运行应用程序时不会出现在XML页面或手机上。我使用以下代码尝试显示字符串：

TextView e = (TextView)findViewById(R.id.textView);
        e.setText(spinnerString);

有人可以告诉我哪里出错了吗？

这是我的MainActivity类：

package com.example.cillin.infoandroidhivespinnermysql;

import java.util.ArrayList;
...

public class MainActivity extends Activity implements OnItemSelectedListener {

    private Button btnAddNewCategory;
    private TextView txtCategory;
    public Spinner spinnerFood;
    //public String spinnerValue;

    // array list for spinner adapter
    private ArrayList<Category> categoriesList;
    ProgressDialog pDialog;

    // API urls
    // Url to create new category
    private String URL_NEW_CATEGORY = "http://food_api/new_category.php";
    // Url to get all categories
    private String URL_CATEGORIES = "http://food_api/get_categories.php";

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

        btnAddNewCategory = (Button) findViewById(R.id.btnAddNewCategory);
        spinnerFood = (Spinner) findViewById(R.id.spinFood);
        txtCategory = (TextView) findViewById(R.id.txtCategory);

        categoriesList = new ArrayList<Category>();

        // spinner item select listener
        spinnerFood.setOnItemSelectedListener(this);

        // Add new category click event
        btnAddNewCategory.setOnClickListener(new View.OnClickListener() {

            @Override
            public void onClick(View v) {
                if (txtCategory.getText().toString().trim().length() > 0) {

                    // new category name
                    String newCategory = txtCategory.getText().toString();

                    // Call Async task to create new category
                    new AddNewCategory().execute(newCategory);
                } else {
                    Toast.makeText(getApplicationContext(),
                            "Please enter category name", Toast.LENGTH_SHORT)
                            .show();
                }
            }
        });

        new GetCategories().execute();

    }

    /**
     * Adding spinner data
     * */
    public void populateSpinner() {
        List<String> lables = new ArrayList<String>();

        txtCategory.setText("");

        for (int i = 0; i < categoriesList.size(); i++) {
            lables.add(categoriesList.get(i).getName());
        }


        // Creating adapter for spinner
        ArrayAdapter<String> spinnerAdapter = new ArrayAdapter<String>(this,
                android.R.layout.simple_spinner_item, lables);

        // Drop down layout style - list view with radio button
        spinnerAdapter
                .setDropDownViewResource(android.R.layout.simple_spinner_dropdown_item);

        // attaching data adapter to spinner
        spinnerFood.setAdapter(spinnerAdapter);

        //String text = spinnerFood.getSelectedItem().toString();

    }


    /**
     * Async task to get all food categories
     * */
    private class GetCategories extends AsyncTask<Void, Void, Void> {

        @Override
        protected void onPreExecute() {
            super.onPreExecute();
            pDialog = new ProgressDialog(MainActivity.this);
            pDialog.setMessage("Fetching food categories..");
            pDialog.setCancelable(false);
            pDialog.show();

        }

        @Override
        protected Void doInBackground(Void... arg0) {
            ServiceHandler jsonParser = new ServiceHandler();
            String json = jsonParser.makeServiceCall(URL_CATEGORIES, ServiceHandler.GET);

            Log.e("Response: ", "> " + json);

            if (json != null) {
                try {
                    JSONObject jsonObj = new JSONObject(json);
                    if (jsonObj != null) {
                        JSONArray categories = jsonObj
                                .getJSONArray("categories");

                        for (int i = 0; i < categories.length(); i++) {
                            JSONObject catObj = (JSONObject) categories.get(i);
                            Category cat = new Category(catObj.getInt("id"),
                                    catObj.getString("name"));
                            categoriesList.add(cat);
                        }
                    }

                } catch (JSONException e) {
                    e.printStackTrace();
                }

            } else {
                Log.e("JSON Data", "Didn't receive any data from server!");
            }

            return null;
        }

        @Override
        protected void onPostExecute(Void result) {
            super.onPostExecute(result);
            if (pDialog.isShowing())
                pDialog.dismiss();
            populateSpinner();
        }
    }

    /**
     * Async task to create a new food category
     * */
    private class AddNewCategory extends AsyncTask<String, Void, Void> {

        boolean isNewCategoryCreated = false;

        @Override
        protected void onPreExecute() {
            super.onPreExecute();
            pDialog = new ProgressDialog(MainActivity.this);
            pDialog.setMessage("Creating new category..");
            pDialog.setCancelable(false);
            pDialog.show();

        }

        @Override
        protected Void doInBackground(String... arg) {

            String newCategory = arg[0];

            // Preparing post params
            List<NameValuePair> params = new ArrayList<NameValuePair>();
            params.add(new BasicNameValuePair("name", newCategory));

            ServiceHandler serviceClient = new ServiceHandler();

            String json = serviceClient.makeServiceCall(URL_NEW_CATEGORY,
                    ServiceHandler.POST, params);

            Log.d("Create Response: ", "> " + json);

            if (json != null) {
                try {
                    JSONObject jsonObj = new JSONObject(json);
                    boolean error = jsonObj.getBoolean("error");
                    // checking for error node in json
                    if (!error) {
                        // new category created successfully
                        isNewCategoryCreated = true;
                    } else {
                        Log.e("Create Category Error: ", "> " + jsonObj.getString("message"));
                    }

                } catch (JSONException e) {
                    e.printStackTrace();
                }

            } else {
                Log.e("JSON Data", "Didn't receive any data from server!");
            }

            return null;
        }

        @Override
        protected void onPostExecute(Void result) {
            super.onPostExecute(result);
            if (pDialog.isShowing())
                pDialog.dismiss();
            if (isNewCategoryCreated) {
                runOnUiThread(new Runnable() {
                    @Override
                    public void run() {
                        // fetching all categories
                        new GetCategories().execute();
                    }
                });
            }
        }

    }

    @Override
    public void onItemSelected(AdapterView<?> parent, View view, int position,
                               long id) {
        Toast.makeText(
                getApplicationContext(),
                parent.getItemAtPosition(position).toString() + " Selected" ,
                Toast.LENGTH_LONG).show();

        Intent intent = new Intent(MainActivity.this, Map.class);
        String text = spinnerFood.getSelectedItem().toString();
        intent.putExtra("SPINNER_KEY", text);
        startActivity(intent);

    }

    @Override
    public void onNothingSelected(AdapterView<?> arg0) {
    }
}

这是Map.java：

package com.example.cillin.infoandroidhivespinnermysql;

import android.app.Activity;
import android.content.Intent;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import android.widget.ImageView;
import android.widget.Spinner;
import android.widget.TextView;

/**
 * Created by cillin on 06/07/2015.
 */
public class Map extends Activity
{

    public void onCreate(Bundle savedInstanceState)
    {
        super.onCreate(savedInstanceState);


        //This page layout is located in the menu XML file
        //SetContentView links a Java file, to its XML file for the layout
        setContentView(R.layout.map);

        /*Spinner mySpinner = (Spinner)findViewById(R.id.spinFood);
        String text = mySpinner.getSelectedItem().toString();
        EditText e = (EditText) findViewById (R.id.editText1);
        e.setText(text);*/

        String spinnerString;
        if (savedInstanceState == null) {
            Bundle extras = getIntent().getExtras();
            if(extras == null) {
                spinnerString= null;
            } else {
                spinnerString= extras.getString("STRING_I_NEED");
            }
        } else {
            spinnerString= (String) savedInstanceState.getSerializable("STRING_I_NEED");
        }
        /*if (getIntent() != null && getIntent().getExtras() != null) {
            Bundle bundle = getIntent().getExtras();
            if (bundle.getString("SPINNER_KEY") != null) {
                spinnerString = bundle.getString("SPINNER_KEY");
            }
        }*/

        //String a = "ddd";

        TextView e = (TextView)findViewById(R.id.textView);
        e.setText(spinnerString);

        Button mainm = (Button)findViewById(R.id.mainmenu);
        mainm.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                //This button is linked to the map page
                Intent i = new Intent(Map.this, MainMenu.class);

                //Activating the intent
                startActivity(i);
            }
        });
    }

}

这是我的map.xml文件：

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:orientation="vertical" android:layout_width="match_parent"
    android:layout_height="match_parent">

    <ImageView
        android:layout_width="300dp"
        android:layout_height="300dp"
        android:id="@+id/imageView"
        android:adjustViewBounds="true"
        android:scaleType="fitCenter"
        android:src="@drawable/map_image"
        android:contentDescription="@string/map"
        android:layout_alignParentTop="true"
        android:layout_centerHorizontal="true"
        android:layout_marginTop="46dp" />

    <Button
        android:id="@+id/mainmenu"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginLeft="140dp"
        android:layout_marginTop = "450dp"
        android:text="Main Menu" />

    <TextView
        android:layout_width="200dp"
        android:layout_height="20dp"
        android:id="@+id/textView"
        android:layout_below="@+id/imageView"
        android:layout_alignRight="@+id/imageView"
        android:layout_alignEnd="@+id/imageView" />

</RelativeLayout>

Answer 1

你必须使用getIntent().getStringExtra("STRING_I_NEED");

只有在调用活动

中传递getIntent.getExtras()时，

Bundle才有效

Answer 2

我修好了它：

String spinnerString;
    if (savedInstanceState == null) {
        Bundle extras = getIntent().getExtras();
        if(extras == null) {
            spinnerString= null;
        } else {
            spinnerString= extras.getString("STRING_I_NEED");
        }
    } else {
        spinnerString= (String) savedInstanceState.getSerializable("STRING_I_NEED");
    }

我改变了＃34; STRING_I_NEED＆＃34;到＆＃34; SPINNER_KEY＆＃34;

空文本视图

2 个答案: