在不使用 Web 服务的情况下使用 json 文件填充微调器

Question

我是安卓开发的新手。我在android studio 工作。我有一些json 文件放在我的assets 文件夹中。现在我想将 json 文件中的数据填充到微调器中。我确实知道如何使用微调器并使用web service 填充数据，但我不知道如何使用json 文件。此外，我找不到任何教程，但我确实找到了how to read data from json file，但我想在微调器中填充它。以下是我的json 文件数据之一。

ref.json

{"reference":
    [
     {"ref_no":"11111111111111","Name":"Faisal"},

     {"ref_no":"22222222222222","Name":"Salman"},

     {"ref_no":"33333333333333","Name":"Asim"},

     {"ref_no":"44444444444444","Name":"Asad"},

     {"ref_no":"55555555555555","Name":"Mateen"},

     {"ref_no":"66666666666666","Name":"Omar"},

     {"ref_no":"77777777777777","Name":"Usama"}

     ]}

下面是spinner的布局

<Spinner
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:id="@+id/dd_ref"
    android:layout_alignParentTop="true"
    android:layout_alignParentLeft="true"
    android:layout_alignParentStart="true" />

我想从 JSON 文件中获取 ref_no 并将它们显示到微调器中。

更新 1

阅读答案和建议后，我做了以下

ArrayList<String> refList;

public static final String LOG_TAG = MainActivity.class.getSimpleName();
@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);

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

public void loadData() throws JSONException {
    JSONArray jsonArray;
    JSONObject jobj;


   try
   {
       jobj = new JSONObject(loadJSONFromAssest());
       jsonArray = jobj.getJSONArray("reference");

       for(int i = 0; i<jsonArray.length();i++)
       {
           jobj = jsonArray.getJSONObject(i);
           Log.d("Details-->", jobj.getString("ref_no"));
           String ref = jobj.getString("ref_no");

           refList.add(ref);
       }


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

    dd_ref.setAdapter(new ArrayAdapter<String>(MainActivity.this, android.R.layout.simple_spinner_dropdown_item, refList));


    dd_ref.setOnItemSelectedListener(new AdapterView.OnItemSelectedListener() {
        @Override
        public void onItemSelected(AdapterView<?> parent, View view, int position, long id) {

            refr_no = String.valueOf(refList.get(position));

            Log.i(LOG_TAG,refr_no);

        }

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

        }
    });

}

public String loadJSONFromAssest() {

    String json = " ";

    try{
        InputStream is = getAssets().open("ref.json");

        int size = is.available();

        byte[] buffer = new byte[size];

        is.read(buffer);
        is.close();

        json = new String(buffer, "UTF-8");
    } catch (IOException e) {
        e.printStackTrace();
        return null;
    }

    return json;


}

当我运行应用程序时，我收到以下错误

 FATAL EXCEPTION: main
                                                                           Process: com.example.accurat.application, PID: 7336
                                                                           java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.accurat.application/com.example.accurat.application.MainActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'boolean java.util.ArrayList.add(java.lang.Object)' on a null object reference
                                                                               at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2442)
                                                                               at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2506)
                                                                               at android.app.ActivityThread.-wrap11(ActivityThread.java)
                                                                               at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1363)
                                                                               at android.os.Handler.dispatchMessage(Handler.java:102)
                                                                               at android.os.Looper.loop(Looper.java:148)
                                                                               at android.app.ActivityThread.main(ActivityThread.java:5491)
                                                                               at java.lang.reflect.Method.invoke(Native Method)
                                                                               at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:728)
                                                                               at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:618)
                                                                            Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'boolean java.util.ArrayList.add(java.lang.Object)' on a null object reference
                                                                               at com.example.accurat.application.MainActivity.loadData(MainActivity.java:59)
                                                                               at com.example.accurat.application.MainActivity.onCreate(MainActivity.java:37)
                                                                               at android.app.Activity.performCreate(Activity.java:6270)
                                                                               at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1130)
                                                                               at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2395)
                                                                               at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2506) 
                                                                               at android.app.ActivityThread.-wrap11(ActivityThread.java) 
                                                                               at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1363) 
                                                                               at android.os.Handler.dispatchMessage(Handler.java:102) 
                                                                               at android.os.Looper.loop(Looper.java:148) 
                                                                               at android.app.ActivityThread.main(ActivityThread.java:5491) 
                                                                               at java.lang.reflect.Method.invoke(Native Method) 
                                                                               at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:728) 
                                                                               at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:618) 

下面是我调试的图像

错误位于refList.add(ref);，因为它告诉refList 为空。

我坚持下去，不知道该怎么做。

任何帮助将不胜感激。

Answer 1

要从assets 文件夹中加载 json 文件，您可以使用以下方法：

public static JSONObject loadJsonObjectFromAsset(String assetName) {
    try {
        String json = loadStringFromAsset(assetName);
        if (json != null)
            return new JSONObject(json);
    } catch (Exception e) {
        Log.e("JsonUtils", e.toString());
    }

    return null;
}

private static String loadStringFromAsset(String assetName) throws Exception {
    InputStream is = CraveApplication.getContext().getAssets().open(assetName);
    int size = is.available();
    byte[] buffer = new byte[size];
    is.read(buffer);
    is.close();
    return new String(buffer, "UTF-8");
}

然后调用：

JSONObject json = loadJsonObjectFromAsset("ref.json");

第二步将解析这个json对象并创建一个列表：

JSONObject json = loadJsonObjectFromAsset("ref.json");
List<String> refList = new ArrayList<>();
try {
    JSONArray refArray = json.getJSONArray("reference");
    for(int i = 0; i< refArray.length(); i++){
        String ref = refArray.getJSONObject(i).getString("ref_no");
        refList.add(ref);
    }

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

最后一步是用我们创建的新列表填充微调器：

Spinner spinner = (Spinner) findViewById(R.id.spinner);
ArrayAdapter<String> arrayAdapter = new ArrayAdapter<>(
        this, 
        android.R.layout.simple_spinner_dropdown_item, 
        refList);
spinner.setAdapter(arrayAdapter);

Answer 2

试试这个

public void methodName() throws JSONException {

    ArrayList<String> spinnerArray  =new ArrayList<String>();

    final JSONArray ja = new JSONObject(loadJSONFromAsset()).getJSONArray("reference");

    for (int q = 0; q < ja.getJSONArray(0).length(); q++) {
        //String name = ja.getJSONArray(0).getJSONObject(q).getString("Name");
        String refNo = ja.getJSONArray(0).getJSONObject(q).getString("ref_no");
        spinnerArray.add(refNo);
    }

    //set spinnerArray in spinner adapter 

}


public String loadJSONFromAsset() {
    String json = null;
    try {

        InputStream is = context_.getAssets().open("file_name.json");

        int size = is.available();

        byte[] buffer = new byte[size];

        is.read(buffer);

        is.close();

        json = new String(buffer, "UTF-8");


    } catch (IOException ex) {
        ex.printStackTrace();
        return null;
    }
    return json;

}

Answer 3

您可以通过将 Gson 库添加到您的 build.gradle 来做到这一点

compile 'com.google.code.gson:gson:2.8.0'


//Create a model class     
public class Reference
{
   @SerializedName ("ref_no")
   public String ref_no;

   @SerializedName ("ref_no")
   public String ref_no;
}

public void getListFromJsonFile()
{
   Gson gson = new Gson();
   JsonReader reader = new JsonReader(new FileReader("file_name.json"));
   List<Reference> data = gson.fromJson(reader, new TypeToken<List<Review>>() {}.getType());
}