Question

在我的代码中，我使用简单的editText和textView，使用editText获取值，并在main.java中进行计算。并在textview上写下结果。

但问题是在app中运行，有

引起：java.lang.NullPointerException

...

...

com.example.jk.kktae0034_sec.MainActivity。   （MainActivity.java:52）

第52行是

TextView recText = (TextView) findViewById (R.id.rec_WH); //here is first error

...

EditText editFck = (EditText) findViewById (R.id.fck); //if first error is // than here is occur error

public class MainActivity extends AppCompatActivity {

    Button btnCal;

    TextView recText = (TextView)findViewById(R.id.rec_WH);
    TextView wheelStr = (TextView)findViewById(R.id.wheelStr);
    TextView ironStr = (TextView)findViewById(R.id.ironStr);

    EditText editFck = (EditText)findViewById(R.id.fck);
    EditText editFy = (EditText)findViewById(R.id.fy);
    EditText edit_life_load = (EditText)findViewById(R.id.life_load);
    EditText edit_dead_load = (EditText)findViewById(R.id.dead_load);
    EditText editL = (EditText)findViewById(R.id.l);
    EditText editRatio = (EditText)findViewById(R.id.ratio);

    double b, d, roh, Mn, Mu, pi=0.85, w, L, fy, fck, roh_max, roh_min, h, a, c, beta1, strain_t, As;
    double life_load, dead_load, ratio;

    double AA[][] = {
        {9.53,71.3,142.6,213.9,285.2,356.5,427.8,499.1,570.4,641.7,713},
        {12.7,126.7,253.4,380,1,506.8,633.5,760.2,886.9,1014,1140},
        {15.9,198.6,397.2,595.8,794.4,993.0,1191,1390,1589,1787,1986},
        {19.1,286.5,573.0,859.5,1146,1433,1719,2006,2292,2579,2865},
        {22.2,387.1,774.2,1161,1548,1935,2322,2710,3097,3484,3871},
        {25.4,506.7,1013.4,1520,2027,2534,3040,3547,4054,4560,5067},
        {28.6,642.4,1285,1927,2570,3212,3854,4497,5139,5782,6424},
        {31.8,794.2,1588,2383,3177,3971,4765,5559,6354,7148,7942},
        {34.9,956.6,1913,2870,3826,4783,5740,6696,7653,8609,9566},
        {38.1,1140,2280,3420,4560,5700,6840,7980,9120,10260,11400}
    };

    int num[] = {10,13,16,19,22,25,29,32,35,38 };

    public void settingHeight(int i){
        int j, cnt=0;
        h = d + 0.5 * AA[i][0] + 12.7 + 40;
        for(j = 0; j < 10000; j++){
            if(j*10 > h){
                h = j*10;
                cnt++;
                break;
            }
            if(cnt > 0)
                break;
        }
        d = h - (0.5 * AA[i][0] + 12.7 + 40);
    }

    void reSetting(){
        a = As * fy / (0.85 * fck * b);
        c = a / beta1;
        strain_t = (d - c) / c * 0.003;
        if (strain_t > 0.005)
            pi = 0.85;
        else if (strain_t > 0.002)
            pi = 0.65 + (0.0043 - 0.002) * 200 / 3;
        else
            pi = 0.65;
        Mn = As * fy * (d - a / 2);
        Mu = pi * Mn;

        recText.setText("B = "+String.format("%.2f", b)+"mm, D = "+String.format("%.2f", d)+"mm");
        wheelStr.setText("Mu = "+String.format("%.2f", Mu/1000000)+"KN*m");
    }

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

        fck = Double.parseDouble(editFck.getText().toString());
        fy = Double.parseDouble(editFy.getText().toString());
        life_load = Double.parseDouble(edit_life_load.getText().toString());
        dead_load = Double.parseDouble(edit_dead_load.getText().toString());
        L = Double.parseDouble(editL.getText().toString());
        ratio = Double.parseDouble(editRatio.getText().toString());

        btnCal = (Button)findViewById(R.id.btnCal);

        btnCal.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                //steel ratio
                roh = 0.85 * 0.85 * fck / fy * 0.003 / (0.003 + 0.005);

                //main
                w = 1.2 * dead_load + 1.6 * life_load;
                Mu = w * L*L / 8;

                //setting side
                int i, cnt = 0;
                double bdd;
                bdd = Mu*1000000 / (pi*roh*fy*(1 - 0.59*roh*fy / fck));
                bdd = bdd / (ratio*ratio);
                b = Math.pow(bdd,0.33333333);

                for (i = 1;i<=10000;i++) {
                    if (i * 10 > b)  {
                        b = i * 10;
                        cnt++;
                        break;
                    } if (cnt > 0)
                        break;
                }
                d = b * ratio;

                //setting steel
                int x, y, cnt_1, cnt_2;
                double Ass;
                Ass = roh * b * d;
                for (x = 0; x < 10; x++) {
                    for (y = 0; y < 10; y++) {
                        if (AA[x][y] >= Ass) {
                            roh_max = 0.85 * 0.85 * fck / fy * 0.003 / 0.007;
                            if (0.25 * Math.sqrt(fck) / fy > 1.4 / fy)
                                roh_min = 1.4 / fy;
                            else
                                roh_min = 0.25 * Math.sqrt(fck) / fy;
                            roh = AA[x][y] / b / d;
                            if (roh > roh_min && roh < roh_max) {
                                cnt_2 = y;
                                cnt_1 = x;
                                As = AA[x][y];

                                ironStr.setText("철근"+cnt_2+" -D "+num[cnt_1]);
                                settingHeight(cnt);
                                reSetting();
                            }
                        }
                    }
                }
            }
        });
    }
}

布局

<RelativeLayout
    android:id="@+id/mainRelayout">

    <RelativeLayout
        android:orientation="vertical"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:id="@+id/input_text_Layout">

        <TextView
            android:id="@+id/life_load_text"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="Life_Load"
            android:textSize="15pt"/>

        <TextView
            android:id="@+id/dead_load_text"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="Dead_Load"
            android:textSize="15pt"
            android:layout_below="@+id/life_load_text"/>

        <TextView
            android:id="@+id/l_text"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="L"
            android:textSize="15pt"
            android:layout_below="@+id/dead_load_text"/>

        <TextView
            android:id="@+id/fck_text"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="Fck"
            android:textSize="15pt"
            android:layout_below="@+id/l_text"/>

        <TextView
            android:id="@+id/fy_text"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="Fy"
            android:textSize="15pt"
            android:layout_below="@+id/fck_text"/>

        <TextView
            android:id="@+id/ratio_text"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="ratio"
            android:textSize="15pt"
            android:layout_below="@+id/fy_text"/>

    </RelativeLayout>

    <RelativeLayout
        android:id="@+id/input_Layout"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_gravity="center_horizontal"
        android:layout_toRightOf="@+id/input_text_Layout">

        <EditText
            android:id="@+id/life_load"
            android:labelFor="@+id/life_load"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:inputType="number"
            android:ems="10" />

        <EditText
            android:id="@+id/dead_load"
            android:labelFor="@+id/dead_load"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:inputType="number"
            android:ems="10"
            android:layout_below="@+id/life_load"/>

        <EditText
            android:id="@+id/l"
            android:labelFor="@+id/l"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:inputType="number"
            android:ems="10"
            android:layout_below="@+id/dead_load"/>

        <EditText
            android:id="@+id/fck"
            android:labelFor="@+id/fck"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:inputType="number"
            android:ems="10"
            android:layout_below="@+id/l"/>

        <EditText
            android:id="@+id/fy"
            android:labelFor="@+id/fy"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:inputType="number"
            android:ems="10"
            android:layout_below="@+id/fck"/>

        <EditText
            android:id="@+id/ratio"
            android:labelFor="@+id/ratio"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:inputType="number"
            android:ems="10"
            android:layout_below="@+id/fy"/>

    </RelativeLayout>

    <RelativeLayout
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_below="@+id/input_Layout"
        android:id="@+id/screen_value">

        <TextView
            android:id="@+id/rec_WH"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:textSize="15pt"
            android:text="width_height" />

        <TextView
            android:id="@+id/wheelStr"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:textSize="15pt"
            android:text="wheelStrongth"
            android:layout_below="@+id/rec_WH"/>

        <TextView
            android:id="@+id/ironStr"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:textSize="15pt"
            android:text="ironStrength"
            android:layout_below="@id/wheelStr"/>

    </RelativeLayout>

    <RelativeLayout
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_below="@+id/input_Layout"
        android:layout_toRightOf="@+id/screen_value">

        <Button
            android:id="@+id/btnCal"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="calculation" />

        <Button
            android:id="@+id/btnNext"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="next"
            android:layout_below="@+id/btnCal"/>

    </RelativeLayout>

</RelativeLayout>

Answer 1

所有都应该在onCreate（）..

中实例化

TextView recText ,wheelStr,ironStr ;
EditText editFck ,editFy ,edit_life_load,edit_dead_load,editL,editRatio;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

         recText = (TextView)findViewById(R.id.rec_WH);
    wheelStr = (TextView)findViewById(R.id.wheelStr);
    ironStr = (TextView)findViewById(R.id.ironStr);

    editFck = (EditText)findViewById(R.id.fck);
    editFy = (EditText)findViewById(R.id.fy);
    edit_life_load = (EditText)findViewById(R.id.life_load);
    edit_dead_load = (EditText)findViewById(R.id.dead_load);
    editL = (EditText)findViewById(R.id.l);
    editRatio = (EditText)findViewById(R.id.ratio);
    .....................
    ...................

Answer 2

您无法在onCreate()功能

之外初始化元素或控件

你必须在里面进行初始化。

public class MainActivity extends AppCompatActivity {

    Button btnCal;
    TextView recText, wheelStr, ironStr;
    EditText editFck, editFy, edit_life_load, edit_dead_load, editL, editRatio;

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

        /* OTHER CODE */
        recText = (TextView)findViewById(R.id.rec_WH);
        wheelStr = (TextView)findViewById(R.id.wheelStr);
        ironStr = (TextView)findViewById(R.id.ironStr);
        editFck = (EditText)findViewById(R.id.fck);
        editFy = (EditText)findViewById(R.id.fy);
        edit_life_load = (EditText)findViewById(R.id.life_load);
        edit_dead_load = (EditText)findViewById(R.id.dead_load);
        editL = (EditText)findViewById(R.id.l);
        editRatio = (EditText)findViewById(R.id.ratio);
        /* OTHER CODE */
    }
}

Answer 3

你需要在onCreate（）方法中为资源提供id：

protected void onCreate(Bundle savedInstanceState) {
     super.onCreate(savedInstanceState);
     setContentView(R.layout.activity_main);
     editFck = (EditText)findViewById(R.id.fck);
     ......
 }

Answer 4

而不是像

public class MainActivity extends AppCompatActivity {
Button btnCal;

TextView recText = (TextView)findViewById(R.id.rec_WH);
TextView wheelStr = (TextView)findViewById(R.id.wheelStr);
TextView ironStr = (TextView)findViewById(R.id.ironStr);

EditText editFck = (EditText)findViewById(R.id.fck);
EditText editFy = (EditText)findViewById(R.id.fy);
EditText edit_life_load = (EditText)findViewById(R.id.life_load);
EditText edit_dead_load = (EditText)findViewById(R.id.dead_load);
EditText editL = (EditText)findViewById(R.id.l);
EditText editRatio = (EditText)findViewById(R.id.ratio);

您已将所有这些内容放入 onCreate

TextView recText ,wheelStr,ironStr ;
EditText editFck ,editFy ,edit_life_load,edit_dead_load,editL,editRatio;
 @Override
 protected void onCreate(Bundle savedInstanceState) {
  super.onCreate(savedInstanceState);
  setContentView(R.layout.activity_main);

  recText = (TextView)findViewById(R.id.rec_WH);
  wheelStr = (TextView)findViewById(R.id.wheelStr);
  ironStr = (TextView)findViewById(R.id.ironStr);

  editFck = (EditText)findViewById(R.id.fck);
  editFy = (EditText)findViewById(R.id.fy);
  edit_life_load = (EditText)findViewById(R.id.life_load);

EditText和TextView等

4 个答案: