android - android中 Activity 的导航

Question

你好，我正在尝试学习android中的屏幕导航

• 虽然没有语法错误，但我收到了这个错误
• 我已经在下面贴出了相关类的代码

---

CopperChimneyPhotos.java

public class CopperChimneyPhotos extends Activity{

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        // TODO Auto-generated method stub
        super.onCreate(savedInstanceState);
        setContentView(R.layout.copper_chimney_photos);

        Button btn=(Button) findViewById(R.id.PhotoButton);

        btn.setOnClickListener(new OnClickListener() {

            @Override
            public void onClick(View v) {
                // TODO Auto-generated method stub
                Intent pt=new Intent(CopperChimneyPhotos.this,CopperChimneyDesc.class);
                startActivity(pt);
            }

        });
    }
}

CopperChimneyDesc.java

public class CopperChimneyDesc extends Activity{

    private static String url = "http://url:7002/xxxx/";
    private static String url1 = "http://url:7002/xxxx/";



    @Override
    protected void onCreate(Bundle savedInstanceState) {
        // TODO Auto-generated method stub
        super.onCreate(savedInstanceState);
        setContentView(R.layout.copperchimney_desc_screen);

        //getting info from listview to display the name in TopNavigationBarCopperChimneyDescActivityName
        TextView topdisp=(TextView) findViewById(R.id.TopNavigationBarCopperChimneyDescActivityName);
        topdisp.setText(getIntent().getExtras().getString("CC_RES"));


        // Creating JSON Parser instance
        JSONObjParser jParser = new JSONObjParser();

        // getting JSON string from URL
        JSONArray json = jParser.getJSONFromUrl(url);

        // getting JSON string from URL
        JSONArray json1 = jParser.getJSONFromUrl(url1);


        try {
            for (int i = 0; i < json1.length(); i++) {
                JSONObject c = json1.getJSONObject(i);


                // Storing each json item in variable
                int id = c.getInt("_id");
                String TIME = c.getString("RestaurantTime");

                TimeMap.put(id, TIME);

            }
        } catch (JSONException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }


        try {
            for (int i = 0; i < json.length(); i++) {
                JSONObject c = json.getJSONObject(i);

                           // remaining code


            }
        } catch (JSONException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }

        Button BACKBUTTON=(Button) findViewById(R.id.TopNavigationBarCopperChimneyDescActivityBackButton);
        BACKBUTTON.setOnClickListener(new OnClickListener() {

            @Override
            public void onClick(View v) {
                // TODO Auto-generated method stub
                Intent emp1=new Intent(CopperChimneyDesc.this,MainActivity.class);
                startActivity(emp1);
            }
        });


        Button PHOTOBUTTON=(Button) findViewById(R.id.CopperChimneyPhotosButton);

Answer 1

你还没有在这里添加任何额外内容

 @Override
        public void onClick(View v) {
            // TODO Auto-generated method stub
            Intent pt=new Intent(CopperChimneyPhotos.this,CopperChimneyDesc.class);
            startActivity(pt);

在 CopperChimneyPhotos 中，所以 getIntent().getExtras().getString("CC_RES")); 将返回 null。

我不确定您希望该值从何而来，但需要将其添加到启动此 Activity 的 Intent 中，例如

 @Override
        public void onClick(View v) {
            // TODO Auto-generated method stub
            Intent pt=new Intent(CopperChimneyPhotos.this,CopperChimneyDesc.class);
            pt.putExtra("CC_RES", stringToAdd);
            startActivity(pt);

在分配对某事的值(value)。当您从 MainActivity 转到 Desc 时，您有 extras 但当您从 Photos 转到 Desc 时，您没有。