java - 从另一个 Activity 获取字符串值后，我的 TextView 中不断出现空值

Question

我使用以下方法将字符串解析为其他 Activity :

 Intent i=new Intent(this,Solve.class);

            String thepoint = mshow2.getText().toString();
            i.putExtra("thepoint", gpapointstring);

         startActivity(i);

我使用以下方式收到它:

 Bundle gpadata =getIntent().getExtras();
           String fgpapoint=gpadata.getString("thepoint");
           TextView mgpaView =(TextView) findViewById(R.id.gpa_point);
           mgpaView.setText(""+ fgpapoint);

Mainactivity.java:

public class MainActivity extends Activity {


private Spinner mcourse9gr, mcourse9un, mcourse8gr, mcourse8un, mcourse7gr, mcourse7un, mcourse6gr, mcourse6un, mcourse5gr, mcourse5un, mcourse4gr, mcourse4un, mcourse3gr, mcourse3un, mcourse2gr, mcourse2un, mcourse1gr, mcourse1un;


public TextView mshow;    public TextView mshow1;    public TextView mshow2;

public double unit1;    public double coursegrade1;    public double grade1;    public double unit2;    public double coursegrade2;    public double grade3;    public double grade2;    public double unit3;    public double coursegrade3;    public double unit4;    public double grade4;    public double coursegrade4;    public double unit5;    public double grade5;    public double unit6;    public double coursegrade5;    public double grade6;    public double coursegrade6;    public double unit7;    public double grade7;    public double coursegrade7;    public double unit8;    public double unit9;    public double grade8; public double grade9;
public double coursegrade8;    public double coursegrade9;    public double totalunit;    public double gpapoint;    public double totalcoursegrade;    public String gpapointstring;



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


    mshow = (TextView) findViewById(R.id.show);
    mshow1 = (TextView) findViewById(R.id.show1);
    mshow2 = (TextView) findViewById(R.id.show2);

}

public void addItemsOnSpinner() {
    mcourse1gr = (Spinner) findViewById(R.id.course1gr);
    mcourse2gr = (Spinner) findViewById(R.id.course2gr);
    mcourse3gr = (Spinner) findViewById(R.id.course3gr);
    mcourse4gr = (Spinner) findViewById(R.id.course4gr);
    mcourse5gr = (Spinner) findViewById(R.id.course5gr);
    mcourse6gr = (Spinner) findViewById(R.id.course6gr);
    mcourse7gr = (Spinner) findViewById(R.id.course7gr);
    mcourse8gr = (Spinner) findViewById(R.id.course8gr);
    mcourse9gr = (Spinner) findViewById(R.id.course9gr);
    mcourse1un = (Spinner) findViewById(R.id.course1un);
    mcourse2un = (Spinner) findViewById(R.id.course2un);
    mcourse3un = (Spinner) findViewById(R.id.course3un);
    mcourse4un = (Spinner) findViewById(R.id.course4un);
    mcourse5un = (Spinner) findViewById(R.id.course5un);
    mcourse6un = (Spinner) findViewById(R.id.course6un);
    mcourse7un = (Spinner) findViewById(R.id.course7un);
    mcourse8un = (Spinner) findViewById(R.id.course8un);
    mcourse9un = (Spinner) findViewById(R.id.course9un);


    Integer[] items = new Integer[]{0, 1, 2, 3, 4, 5};
    ArrayAdapter<Integer> adapter = new ArrayAdapter<>(this, android.R.layout.simple_spinner_item, items);

    mcourse1un.setAdapter(adapter);
    mcourse2un.setAdapter(adapter);
    mcourse3un.setAdapter(adapter);
    mcourse4un.setAdapter(adapter);
    mcourse5un.setAdapter(adapter);
    mcourse6un.setAdapter(adapter);
    mcourse7un.setAdapter(adapter);
    mcourse8un.setAdapter(adapter);
    mcourse9un.setAdapter(adapter);

    String[] itemsgr = new String[]{"F", "E", "D", "C", "B", "A"};
    ArrayAdapter<String> adaptergr = new ArrayAdapter<>(this, android.R.layout.simple_spinner_item, itemsgr);
    mcourse1gr.setAdapter(adaptergr);
    mcourse2gr.setAdapter(adaptergr);
    mcourse3gr.setAdapter(adaptergr);
    mcourse4gr.setAdapter(adaptergr);
    mcourse5gr.setAdapter(adaptergr);
    mcourse6gr.setAdapter(adaptergr);
    mcourse7gr.setAdapter(adaptergr);
    mcourse8gr.setAdapter(adaptergr);
    mcourse9gr.setAdapter(adaptergr);
}

public void OnItemSelectedListener() {

    mcourse1un.setOnItemSelectedListener(new AdapterView.OnItemSelectedListener()
    {
        @Override
        public void onItemSelected(AdapterView<?> parent, View view, int position, long id) {
            unit1 = mcourse1un.getSelectedItemPosition();
            updateunit();
        }
        @Override
        public void onNothingSelected(AdapterView<?> parent) {

        }
    });
    mcourse1gr.setOnItemSelectedListener(new AdapterView.OnItemSelectedListener()
    {
        @Override
        public void onItemSelected(AdapterView<?> parent, View view, int position, long id) {
            grade1 = mcourse1gr.getSelectedItemPosition();
            coursegrade1 = grade1 * unit1;
        }
        @Override
        public void onNothingSelected(AdapterView<?> parent) {
        }
    });

    mcourse2un.setOnItemSelectedListener(new AdapterView.OnItemSelectedListener()
    {
        @Override
        public void onItemSelected(AdapterView<?> parent, View view, int position, long id) {
            unit2 = mcourse2un.getSelectedItemPosition();
            updateunit();
        }
        @Override
        public void onNothingSelected(AdapterView<?> parent) {
        }
    });
    mcourse2gr.setOnItemSelectedListener(new AdapterView.OnItemSelectedListener()
    {
        @Override
        public void onItemSelected(AdapterView<?> parent, View view, int position, long id) {
            grade2 = mcourse2gr.getSelectedItemPosition();
            coursegrade2 = grade2 * unit2;
        }
        @Override
        public void onNothingSelected(AdapterView<?> parent) {
        }
    });

    mcourse3un.setOnItemSelectedListener(new AdapterView.OnItemSelectedListener()
    {
        @Override
        public void onItemSelected(AdapterView<?> parent, View view, int position, long id) {
            unit3 = mcourse3un.getSelectedItemPosition();
            updateunit();
        }
        @Override
        public void onNothingSelected(AdapterView<?> parent) {
        }
    });
    mcourse3gr.setOnItemSelectedListener(new AdapterView.OnItemSelectedListener()
    {
        @Override
        public void onItemSelected(AdapterView<?> parent, View view, int position, long id) {
            grade3 = mcourse3gr.getSelectedItemPosition();
            coursegrade3 = grade3 * unit3;
        }
        @Override
        public void onNothingSelected(AdapterView<?> parent) {
        }
    });
    mcourse4un.setOnItemSelectedListener(new AdapterView.OnItemSelectedListener()
    {
        @Override
        public void onItemSelected(AdapterView<?> parent, View view, int position, long id) {
            unit4 = mcourse4un.getSelectedItemPosition();
            updateunit();
        }
        @Override
        public void onNothingSelected(AdapterView<?> parent) {
        }
    });
    mcourse4gr.setOnItemSelectedListener(new AdapterView.OnItemSelectedListener()
    {
        @Override
        public void onItemSelected(AdapterView<?> parent, View view, int position, long id) {
            grade4 = mcourse4gr.getSelectedItemPosition();
            coursegrade4 = grade4 * unit4;
        }
        @Override
        public void onNothingSelected(AdapterView<?> parent) {
        }
    });
    mcourse5un.setOnItemSelectedListener(new AdapterView.OnItemSelectedListener()
    {
        @Override
        public void onItemSelected(AdapterView<?> parent, View view, int position, long id) {
            unit5 = mcourse5un.getSelectedItemPosition();
            updateunit();
        }
        @Override
        public void onNothingSelected(AdapterView<?> parent) {
        }
    });
    mcourse5gr.setOnItemSelectedListener(new AdapterView.OnItemSelectedListener()
    {
        @Override
        public void onItemSelected(AdapterView<?> parent, View view, int position, long id) {
            grade5 = mcourse5gr.getSelectedItemPosition();
            coursegrade5 = grade5 * unit5;
        }
        @Override
        public void onNothingSelected(AdapterView<?> parent) {
        }
    });
    mcourse6un.setOnItemSelectedListener(new AdapterView.OnItemSelectedListener()
    {
        @Override
        public void onItemSelected(AdapterView<?> parent, View view, int position, long id) {
            unit6 = mcourse6un.getSelectedItemPosition();
            updateunit();
        }
        @Override
        public void onNothingSelected(AdapterView<?> parent) {
        }
    });
    mcourse6gr.setOnItemSelectedListener(new AdapterView.OnItemSelectedListener()
    {
        @Override
        public void onItemSelected(AdapterView<?> parent, View view, int position, long id) {
            grade6 = mcourse6gr.getSelectedItemPosition();
            coursegrade6 = grade6 * unit6;
        }
        @Override
        public void onNothingSelected(AdapterView<?> parent) {
        }
    });
    mcourse7un.setOnItemSelectedListener(new AdapterView.OnItemSelectedListener()
    {
        @Override
        public void onItemSelected(AdapterView<?> parent, View view, int position, long id) {
            unit7 = mcourse7un.getSelectedItemPosition();
            updateunit();
        }
        @Override
        public void onNothingSelected(AdapterView<?> parent) {
        }
    });
    mcourse7gr.setOnItemSelectedListener(new AdapterView.OnItemSelectedListener()
    {
        @Override
        public void onItemSelected(AdapterView<?> parent, View view, int position, long id) {
            grade7 = mcourse7gr.getSelectedItemPosition();
            coursegrade7 = grade7 * unit7;
        }
        @Override
        public void onNothingSelected(AdapterView<?> parent) {
        }
    });
    mcourse8un.setOnItemSelectedListener(new AdapterView.OnItemSelectedListener()
    {
        @Override
        public void onItemSelected(AdapterView<?> parent, View view, int position, long id) {
            unit8 = mcourse8un.getSelectedItemPosition();
            updateunit();
        }
        @Override
        public void onNothingSelected(AdapterView<?> parent) {
        }
    });
    mcourse8gr.setOnItemSelectedListener(new AdapterView.OnItemSelectedListener()
    {
        @Override
        public void onItemSelected(AdapterView<?> parent, View view, int position, long id) {
            grade8 = mcourse8gr.getSelectedItemPosition();
            coursegrade8 = grade8 * unit8;
        }
        @Override
        public void onNothingSelected(AdapterView<?> parent) {
        }
    });
    mcourse9un.setOnItemSelectedListener(new AdapterView.OnItemSelectedListener()
    {
        @Override
        public void onItemSelected(AdapterView<?> parent, View view, int position, long id) {
            unit9 = mcourse9un.getSelectedItemPosition();
            updateunit();
        }
        @Override
        public void onNothingSelected(AdapterView<?> parent) {
        }
    });
    mcourse9gr.setOnItemSelectedListener(new AdapterView.OnItemSelectedListener()
    {
        @Override
        public void onItemSelected(AdapterView<?> parent, View view, int position, long id) {
            grade9 = mcourse9gr.getSelectedItemPosition();
            coursegrade9 = grade9 * unit9;
        }
        @Override
        public void onNothingSelected(AdapterView<?> parent) {
        }
    });

}
    public void onClick(View view) {
        updategrade1();
        updategrade2();
        updategrade3();
        updategrade4();
        updategrade5();
        updategrade6();
        updategrade7();
        updategrade8();
        updategrade9();
        updatetotalgrade();
        setGpapoint();
        Intent i=new Intent(this,Solve.class);

            String thepoint = mshow2.getText().toString();
            i.putExtra("thepoint", gpapointstring);

         startActivity(i);
         }

    public  void updategrade1(){
        coursegrade1 = grade1 * unit1;
    }
    public  void updategrade2() {
        coursegrade2 = grade2 * unit2;
    }
    public  void updategrade3() {
        coursegrade3 = grade3 * unit3;
     }
    public  void updategrade4() {
     coursegrade4 = grade4 * unit4;
    }
    public  void updategrade5() {
        coursegrade5 = grade5 * unit5;
     }
    public  void updategrade6() {
        coursegrade6 = grade6 * unit6;
    }
    public  void updategrade7() {
        coursegrade7 = grade7 * unit7;
    }
    public  void updategrade8() {
        coursegrade8 = grade8 * unit8;
    }
    public  void updategrade9() {
        coursegrade9 = grade9 * unit9;
    }

    public double updatetotalgrade(){
        double totalcoursegrade = coursegrade1 + coursegrade2 + coursegrade3 + coursegrade4 + coursegrade5 + coursegrade6 + coursegrade7 + coursegrade8 + coursegrade9;
        mshow.setText(""+ totalcoursegrade);
        return totalcoursegrade;
    }

    public double updateunit(){
        double totalunit = unit1 + unit2 + unit3 + unit4 + unit5 + unit6 + unit7 + unit8 + unit9;
        // i uesd this to make sure i am getting a value an not null
        mshow1.setText("" + totalunit);
        return totalunit;
    }

public double setGpapoint() {
    double totalunit = unit1 + unit2 + unit3 + unit4 + unit5 + unit6 + unit7 + unit8 + unit9;
    double totalcoursegrade = coursegrade1 + coursegrade2 + coursegrade3 + coursegrade4 + coursegrade5 + coursegrade6 + coursegrade7 + coursegrade8 + coursegrade9;
        double gpapoint = (totalcoursegrade/totalunit);
    String gpapointstring =String.format("your GPA: %.2f",gpapoint);
    // i uesd this to make sure i am getting a value an not null
    mshow2.setText(String.format("your GPA: %.2f",gpapoint));
    return gpapoint;
}
}

解决.java:

public class Solve  extends Activity {
    Button button;

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


        Bundle gpadata = getIntent().getExtras();
        String fgpapoint = gpadata.getString("thepoint");
        TextView mgpaView = (TextView) findViewById(R.id.gpa_point);
        mgpaView.setText("" + fgpapoint);
    }

    public void addListenerOnButton() {
        final Context context =
                this;
        button = (Button) findViewById(R.id.home);
        button.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View arg0) {
                Intent intent =
                        new
                                Intent(context, MainActivity.class);
                startActivity(intent);
            }
        });
    }
}

Answer 1

您需要使用实际具有值的字符串引用

String thepoint = mshow2.getText().toString();
i.putExtra("thepoint", thepoint);

或

gpapointstring= mshow2.getText().toString();
i.putExtra("thepoint", gpapointstring);

第二:如果某个值已经是字符串，则不需要 ""+ 连接(额外的开销)，所以只需这样做

mgpaView.setText(fgpapoint); 

第三:不需要额外的支架

final Context context = this;

只需使用

Intent intent = new Intent(Solve.this, MainActivity.class);