Question

我有一个json文件，我想在点击btn时保存，然后另一个btn将在textview中显示已解码的json文件

    public class MainActivity extends Activity {
/** Called when the activity is first created. */

String result = "";
InputStream is = null;
TextView one = (TextView) findViewById(R.id.showView);
HttpEntity entity = null;

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


    //pulls a file from my server then saves it
    Button btn1 = (Button) findViewById(R.id.downloadBtn);
    btn1.setOnClickListener(new View.OnClickListener() {

        @Override
        public void onClick(View v) {


            saveJson();

        //end of onClick    
        }
    //end of onClickListener
    });

    //should show the saved file
    Button btn2 = (Button) findViewById(R.id.showBtn);
    btn2.setOnClickListener(new View.OnClickListener() {

        @Override
        public void onClick(View v) {

            showJson();

        //end of onClick    
        }
    //end of onClickListener
    });

//end of oncreate()    
}

public void saveJson(){

    TextView one = (TextView) findViewById(R.id.showView);

    try{
            HttpClient httpClient = new DefaultHttpClient();
            HttpPost httpPost = new HttpPost("http://10.0.2.2/textures_story_list.php");

            HttpResponse response = httpClient.execute(httpPost);
            entity = response.getEntity();
//from here what do i need to add to save the file as .json
    }catch(Exception e) {
        one.setText("error3");
    }


//end of returnJson()   
}

public void showJson(){

    //from here what should i have to show the file story_list.json

try{



        is = entity.getContent();
        BufferedReader reader = new BufferedReader(new InputStreamReader(is,"iso-8859-1"), 8);                      
        StringBuilder sb = new StringBuilder();
            String line = null;
            while ((line = reader.readLine()) != null) {
                sb.append(line + "\n");
            }
            is.close();
            result = sb.toString();

    }catch(Exception e) {
        }

    try{
        JSONArray jArray = new JSONArray(result);
        String storyNames = "";
        for(int i = 0;i<jArray.length();i++){
                storyNames += jArray.getJSONObject(i).getString("story_name") + "\n"; 
        }
        one.setText(storyNames);
    }
    catch(JSONException e) {
    }
        return;


//end of returnJson()   
}



//end of class body    
}

它在启动时崩溃_

runtimeExecption unable to instatiate activity ComponentInfo nullpointer

oK这里修复的问题是我添加保存然后显示文件的代码

    public class MainActivity extends Activity {
/** Called when the activity is first created. */

String result = "";
InputStream is = null;
HttpEntity entity = null;
HttpEntity readString = null;
@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.main);


    //pulls a file from my server then saves it
    Button btn1 = (Button) findViewById(R.id.downloadBtn);
    btn1.setOnClickListener(new View.OnClickListener() {

        @Override
        public void onClick(View v) {


            saveJson();

        //end of onClick    
        }
    //end of onClickListener
    });

    //should show the saved file
    Button btn2 = (Button) findViewById(R.id.showBtn);
    btn2.setOnClickListener(new View.OnClickListener() {

        @Override
        public void onClick(View v) {

            showJson();

        //end of onClick    
        }
    //end of onClickListener
    });

//end of oncreate()    
}

public void saveJson(){

    TextView one = (TextView) findViewById(R.id.showView);

    try{
            HttpClient httpClient = new DefaultHttpClient();
            HttpPost httpPost = new HttpPost("http://10.0.2.2/textures_story_list.php");

            HttpResponse response = httpClient.execute(httpPost);
            entity = response.getEntity();
//from here what do i need to add to save the file as .json
    }catch(Exception e) {
        one.setText("error3");
    }
    try{

        HttpEntity text = entity;
        FileOutputStream fOut = openFileOutput("story.json",MODE_WORLD_READABLE);
        OutputStreamWriter osw = new OutputStreamWriter(fOut);
        osw.write(text);
        osw.flush();
        osw.close();
        }catch(IOException ioe){
        }   

//end of returnJson()   
}

public void showJson(){

    //from here what should i have to show the file story_list.json

    try{
        FileInputStream fIn = openFileInput("story.json");
        InputStreamReader isr = new InputStreamReader(fIn);
        char[] inputBuffer = new char[11];
        //len is the length of that saved string in the file

        isr.read(inputBuffer);

       // String readString = new String(inputBuffer);





        isr = readString.getContent();
        BufferedReader reader = new BufferedReader(new InputStreamReader(is,"iso-8859-1"), 8);                      
        StringBuilder sb = new StringBuilder();
            String line = null;
            while ((line = reader.readLine()) != null) {
                sb.append(line + "\n");
            }
            is.close();
            result = sb.toString();

    }catch(Exception e) {
        }

    try{
        JSONArray jArray = new JSONArray(result);
        String storyNames = "";
        for(int i = 0;i<jArray.length();i++){
                storyNames += jArray.getJSONObject(i).getString("story_name") + "\n"; 
        }
        TextView one = (TextView) findViewById(R.id.showView);

        one.setText(storyNames);
    }
    catch(JSONException e) {
    }
        return;


//end of returnJson()   
}



//end of class body    
}

有人可以帮我修复错误或告诉我我做错了吗？

Answer 1

两个建议：

1）将此分配移动到onCreate（）方法中：

one = (TextView) findViewById(R.id.showView);

2）如果您仍然遇到问题，请单步执行代码以确定您尝试取消引用空指针的确切位置。我猜它可能是你的“findViewById（）”调用之一。

将json文件保存到内部存储器，然后再调用该文件

1 个答案: