java - 嗨，我想弄清楚如何将字符串从一个类传递到另一个类

Question

对所有代码感到抱歉。我试图传递的字符串是内容。如果您需要更多信息，请告诉我

我是java新手，所以我可能会犯一些愚蠢的错误。我尝试过使用不同的方法来传递字符串，但没有成功。如果我能够让字符串出现在编辑文本框中，那就太好了。

我是这个网站的新手；抱歉，如果我犯了菜鸟错误。

主类:

package com.app.david.booktracker; 


public class MainActivity extends AppCompatActivity {

    static final String ACTION_SCAN = "com.google.zxing.client.android.SCAN";


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

    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        // Inflate the menu; this adds items to the action bar if it is present.
        getMenuInflater().inflate(R.menu.menu_main, menu);
        return true;
    }

    public void initToolBar() {

        Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
        toolbar.setTitle("Book Tracker");
        setSupportActionBar(toolbar);


    }

    public void newBook(View view) {
        Intent intent = new Intent(this, NewBook.class);
        startActivity(intent);
    }

    public void showListBook(View view) {
        Intent intent = new Intent(this, ShowAllBooks.class);
        startActivity(intent);
    }


    public void scanBar(View v) {
        try {
            Intent intent = new Intent(ACTION_SCAN);
            intent.putExtra("SCAN_MODE", "PRODUCT_MODE");
            startActivityForResult(intent, 0);
        } catch (ActivityNotFoundException e) {
            showDialog(MainActivity.this, "No Scanner Found",
                    "Download a scanner code activity?", "Yes", "No").show();
        }
    }


    private static AlertDialog showDialog(final AppCompatActivity act,
                                          CharSequence title, CharSequence message, CharSequence buttonYes,
                                          CharSequence buttonNo) {

        AlertDialog.Builder dowloadDialog = new AlertDialog.Builder(act);
        dowloadDialog
                .setTitle(title)
                .setMessage(message)
                .setPositiveButton(buttonYes,
                        new DialogInterface.OnClickListener() {

                            @Override
                            public void onClick(DialogInterface dialog,
                                                int which) {
                                Uri uri = Uri.parse("market://search?q=pname:"
                                        + "com.google.zxing.client.android");

                                Intent intent = new Intent(Intent.ACTION_VIEW,
                                        uri);
                                try {
                                    act.startActivity(intent);
                                } catch (ActivityNotFoundException e) {
                                }

                            }
                        })
                .setNegativeButton(buttonNo,
                        new DialogInterface.OnClickListener() {

                            @Override
                            public void onClick(DialogInterface dialog,
                                                int which) {
                            }
                        });

        return dowloadDialog.show();
    }

    @Override
    protected void onActivityResult(int requestCode, int resultCode, Intent intent) {
        if(requestCode == 0) {
            if(resultCode == RESULT_OK) {
                String contents = intent.getStringExtra("SCAN_RESULT");
                String format = intent.getStringExtra("SCAN_RESULT_FORMAT");
                Toast.makeText(this,
                        "Content:" + contents + " Format:" + format,
                        Toast.LENGTH_LONG).show();
            }
        }
    }





    @Override
    public boolean onOptionsItemSelected(MenuItem item) {
        // Handle action bar item clicks here. The action bar will
        // automatically handle clicks on the Home/Up button, so long
        // as you specify a parent activity in AndroidManifest.xml.
        int id = item.getItemId();

        //noinspection SimplifiableIfStatement
        if (id == R.id.action_settings) {
            return true;
        }

目标类别:

package com.app.david.booktracker;

public class NewBook extends AppCompatActivity {

    private final static String TAG= "group4.NewBook";

    private EditText ean;

    @Override

    protected  void onCreate(Bundle savedInstanceState){
        super.onCreate(savedInstanceState);
        setContentView(R.layout.new_book);
        //initToolBar();
    }

    @Override
    public boolean onCreateOptionsMenu(Menu menu)
    {
        // Inflate the menu; this adds items to the action bar if it is present.
        getMenuInflater().inflate(R.menu.menu_main, menu);
        return true;
    }


    public void initToolBar(){
        Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
        toolbar.setTitle("Book Tracker");

        setSupportActionBar(toolbar);

        toolbar.setNavigationIcon(R.drawable.ic_toolbar_arrow);
        toolbar.setNavigationOnClickListener(
                new View.OnClickListener() {
                    @Override
                    public void onClick(View v) {
                        Intent intent = new Intent(v.getContext(), MainActivity.class);
                        startActivity(intent);
                    }
                }
        );
    }



    public void newBook(View view)
    {
        //Get the
        Intent intent=new Intent(this, MainActivity.class);
        EditText editTextBTitle=(EditText) findViewById(R.id.editTextFirstName);
        EditText editTextBAuthor=(EditText) findViewById(R.id.editTextSurname);

        String booktitle=editTextBTitle.getText().toString();
        String bookauthor=editTextBAuthor.getText().toString();

        String contents = intent.getStringExtra("SCAN_RESULT");
        DataHolder.bookadded(booktitle, bookauthor, contents);
        Log.d(TAG, " Added: " + booktitle + "  " + bookauthor + " " + contents);

        Toast.makeText(this, "Book Added! ", Toast.LENGTH_LONG).show();
        startActivity(intent);
    }

}

Answer 1

如果希望能够访问类外部的属性，首选方法是将它们初始化为私有(private)属性并具有“getter”方法。像这样的简单方法:

public static String getContents () {
    return contents;
}

会起作用的。但是，您必须将变量初始化为类的属性，如下所示:

private static String contents;

它必须在类中的任何函数之外声明(即在public static class MainActivityextents AppCombatActivity {之后)。不要忘记将最初初始化它的行从 Stringcontents 更改为 contents。

不过，我不禁注意到，您正在 NewBook 类中初始化一个同名的字符串。这是您尝试插入原始内容的地方吗？如果是这样，只要您已完成上述所有操作，您所需要做的就是调用 MainActivity.getContents()，它应该返回您正在查找的字符串。