Question

这是我的应用程序中的fourthpage类。我收到了错误

遗憾的是，申请已停止工作

我不知道为什么我会这样做。

package student.a.a;

import android.app.Activity;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import android.widget.TextView;

import java.text.DecimalFormat;

public class fourthpage extends Activity {
    EditText txtb1, txtb2, txtb3, txtb4, txtb5;
    Button btnper;
    TextView lblgrade, lblper;

    DecimalFormat df = new DecimalFormat("##.##");

    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.fourthxml);

        // text boxes
        txtb1 = (EditText) findViewById(R.id.txtb1);
        txtb2 = (EditText) findViewById(R.id.txtb2);
        txtb3 = (EditText) findViewById(R.id.txtb3);
        txtb4 = (EditText) findViewById(R.id.txtb4);
        txtb5 = (EditText) findViewById(R.id.txtb5);

        // buttons
        btnper = (Button) findViewById(R.id.btnper);

        // labels/text view
        lblgrade = (TextView) findViewById(R.id.lblgrade);
        lblper = (TextView) findViewById(R.id.lblgrade);
    }

    String tb1 = txtb1.getText().toString();
    String tb2 = txtb2.getText().toString();
    String tb3 = txtb3.getText().toString();
    String tb4 = txtb4.getText().toString();
    String tb5 = txtb5.getText().toString();

    double txb1 = Double.parseDouble(tb1);
    double txb2 = Double.parseDouble(tb2);
    double txb3 = Double.parseDouble(tb3);
    double txb4 = Double.parseDouble(tb4);
    double txb5 = Double.parseDouble(tb5);

    double sum = 0;
    double total = 0;

    public void onClickper(View v) {
        sum = txb1 + txb2 + txb3 + txb4 + txb5;
        total = (sum / 500) * 100;
        String tot = df.format(total);
        lblper.setText(tot);

        if (total <= 100) {
            lblgrade.setText("Congratulations !! , Grade 'A+' ");
        } else if (total <= 80) {
            lblgrade.setText("Congratulations !! , Grade 'A'");
        } else if (total <= 70) {
            lblgrade.setText("Grade 'B'");
        } else if (total <= 60) {
            lblgrade.setText("Grade 'C'");
        } else
            lblgrade.setText("Failed");
    }
}

这是fourthpage的xml代码。它包含5个文本框，一个按钮和两个textview：

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical" >

    <TableLayout
        android:id="@+id/tableLayout1"
        android:layout_width="match_parent"
        android:layout_height="wrap_content" >

        <TableRow
            android:id="@+id/tableRow1"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content" >

            <GridLayout
                android:id="@+id/gridLayout1"
                android:layout_width="wrap_content"
                android:layout_height="wrap_content" >

                <TextView
                    android:id="@+id/textView1"
                    android:layout_gravity="left"
                    android:text="Calculate your marks"
                    android:textAppearance="?android:attr/textAppearanceMedium" />

            </GridLayout>

        </TableRow>

        <TableRow
            android:id="@+id/tableRow7"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content" >

            <GridLayout
                android:id="@+id/gridLayout3"
                android:layout_width="wrap_content"
                android:layout_height="wrap_content" >

                <Space android:layout_gravity="fill_horizontal" />

            </GridLayout>

        </TableRow>

        <TableRow
            android:id="@+id/tableRow2"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content" >

            <GridLayout
                android:id="@+id/gridLayout2"
                android:layout_width="wrap_content"
                android:layout_height="wrap_content" >

                <TextView
                    android:id="@+id/textView2"
                    android:layout_gravity="left"
                    android:text="Subject 1"
                    android:textAppearance="?android:attr/textAppearanceMedium" />

                <EditText
                    android:id="@+id/txtb1"
                    android:layout_width="162dp"
                    android:layout_gravity="fill_horizontal" >

                    <requestFocus />
                </EditText>

            </GridLayout>

        </TableRow>

        <TableRow
            android:id="@+id/tableRow3"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content" >

            <GridLayout
                android:id="@+id/GridLayout01"
                android:layout_width="wrap_content"
                android:layout_height="wrap_content" >

                <TextView
                    android:id="@+id/TextView01"
                    android:layout_gravity="left"
                    android:text="Subject 2"
                    android:textAppearance="?android:attr/textAppearanceMedium" />

                <EditText
                    android:id="@+id/txtb2"
                    android:layout_gravity="fill_horizontal" />

            </GridLayout>

        </TableRow>

        <TableRow
            android:id="@+id/tableRow4"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content" >

            <GridLayout
                android:id="@+id/GridLayout02"
                android:layout_width="wrap_content"
                android:layout_height="wrap_content" >

                <TextView
                    android:id="@+id/TextView02"
                    android:layout_gravity="left"
                    android:text="Subject 3"
                    android:textAppearance="?android:attr/textAppearanceMedium" />

                <EditText
                    android:id="@+id/txtb3"
                    android:layout_gravity="fill_horizontal" />

            </GridLayout>

        </TableRow>

        <TableRow
            android:id="@+id/tableRow5"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content" >

            <GridLayout
                android:id="@+id/GridLayout03"
                android:layout_width="wrap_content"
                android:layout_height="wrap_content" >

                <TextView
                    android:id="@+id/TextView03"
                    android:layout_gravity="left"
                    android:text="Subject 4"
                    android:textAppearance="?android:attr/textAppearanceMedium" />

                <EditText
                    android:id="@+id/txtb4"
                    android:layout_gravity="fill_horizontal" />

            </GridLayout>

        </TableRow>

        <TableRow
            android:id="@+id/tableRow6"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content" >

            <GridLayout
                android:id="@+id/GridLayout04"
                android:layout_width="wrap_content"
                android:layout_height="wrap_content" >

                <TextView
                    android:id="@+id/TextView04"
                    android:layout_gravity="left"
                    android:text="Subject 5"
                    android:textAppearance="?android:attr/textAppearanceMedium" />

                <EditText
                    android:id="@+id/txtb5"
                    android:layout_gravity="fill_horizontal" />

            </GridLayout>

        </TableRow>

        <TableRow
            android:id="@+id/tableRow8"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content" >

            <GridLayout
                android:id="@+id/gridLayout4"
                android:layout_width="wrap_content"
                android:layout_height="wrap_content" >



                <Button
                    android:id="@+id/btnper"
                    android:layout_gravity="left"
                    android:text="Button" android:onClick="onClickper"/>

                <Button
                    android:id="@+id/btngrade"
                    android:layout_gravity="left"
                    android:text="Button" />

            </GridLayout>

        </TableRow>

        <TableRow
            android:id="@+id/tableRow9"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content" >

            <GridLayout
                android:id="@+id/gridLayout5"
                android:layout_width="wrap_content"
                android:layout_height="wrap_content" >

                <TextView
                    android:id="@+id/textView3"
                    android:layout_gravity="left"
                    android:text="percentage is  "
                    android:textAppearance="?android:attr/textAppearanceSmall" />

                <TextView
                    android:id="@+id/lblper"
                    android:layout_gravity="left"
                    android:text="Large Text"
                    android:textAppearance="?android:attr/textAppearanceLarge" />

            </GridLayout>

        </TableRow>

        <TableRow
            android:id="@+id/tableRow10"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content" >

            <GridLayout
                android:id="@+id/gridLayout6"
                android:layout_width="wrap_content"
                android:layout_height="wrap_content" >

                <TextView
                    android:id="@+id/textView5"
                    android:layout_gravity="left"
                    android:text=" Grade is           "
                    android:textAppearance="?android:attr/textAppearanceSmall" />

                <TextView
                    android:id="@+id/lblgrade"
                    android:layout_gravity="left"
                    android:text="Large Text"
                    android:textAppearance="?android:attr/textAppearanceLarge" />

            </GridLayout>

        </TableRow>

    </TableLayout>

</LinearLayout>

这是androidmanifest.xml：

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="student.a.a"
    android:versionCode="1"
    android:versionName="1.0" >

    <uses-sdk android:minSdkVersion="14" />

    <application
        android:icon="@drawable/ic_launcher"
        android:label="@string/app_name" >
        <activity
            android:label="@string/app_name"
            android:name=".StudentsinfoActivity" >
            <intent-filter >
                <action android:name="android.intent.action.MAIN" />

                <category android:name="android.intent.category.DEFAULT" />
            </intent-filter>
        </activity>
        <activity
            android:label="@string/app_name"
            android:name=".secondpage" >
            <intent-filter >
                <action android:name="android.intent.action.MAIN" />

                <category android:name="android.intent.category.DEFAULT" />
            </intent-filter>
        </activity>
        <activity
            android:label="@string/app_name"
            android:name=".thirdpage" >
            <intent-filter >
                <action android:name="android.intent.action.MAIN" />

                <category android:name="android.intent.category.DEFAULT" />
            </intent-filter>
        </activity>
        <activity
            android:label="@string/app_name"
            android:name=".fourthpage" >
            <intent-filter >
                <action android:name="android.intent.action.MAIN" />

                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
        </activity>
    </application>
</manifest>

这是我的logcat：

08-09 16:32:00.970: W/dalvikvm(892): threadid=1: thread exiting with uncaught exception (group=0x409961f8)
08-09 16:32:00.980: E/AndroidRuntime(892): FATAL EXCEPTION: main
08-09 16:32:00.980: E/AndroidRuntime(892): java.lang.RuntimeException: Unable to start activity ComponentInfo{student.a.a/student.a.a.fourthpage}: java.lang.NumberFormatException: Invalid double: ""
08-09 16:32:00.980: E/AndroidRuntime(892):  at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1955)
08-09 16:32:00.980: E/AndroidRuntime(892):  at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:1980)
08-09 16:32:00.980: E/AndroidRuntime(892):  at android.app.ActivityThread.access$600(ActivityThread.java:122)
08-09 16:32:00.980: E/AndroidRuntime(892):  at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1146)
08-09 16:32:00.980: E/AndroidRuntime(892):  at android.os.Handler.dispatchMessage(Handler.java:99)
08-09 16:32:00.980: E/AndroidRuntime(892):  at android.os.Looper.loop(Looper.java:137)
08-09 16:32:00.980: E/AndroidRuntime(892):  at android.app.ActivityThread.main(ActivityThread.java:4340)
08-09 16:32:00.980: E/AndroidRuntime(892):  at java.lang.reflect.Method.invokeNative(Native Method)
08-09 16:32:00.980: E/AndroidRuntime(892):  at java.lang.reflect.Method.invoke(Method.java:511)
08-09 16:32:00.980: E/AndroidRuntime(892):  at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:784)
08-09 16:32:00.980: E/AndroidRuntime(892):  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:551)
08-09 16:32:00.980: E/AndroidRuntime(892):  at dalvik.system.NativeStart.main(Native Method)
08-09 16:32:00.980: E/AndroidRuntime(892): Caused by: java.lang.NumberFormatException: Invalid double: ""
08-09 16:32:00.980: E/AndroidRuntime(892):  at java.lang.StringToReal.invalidReal(StringToReal.java:63)
08-09 16:32:00.980: E/AndroidRuntime(892):  at java.lang.StringToReal.parseDouble(StringToReal.java:248)
08-09 16:32:00.980: E/AndroidRuntime(892):  at java.lang.Double.parseDouble(Double.java:295)
08-09 16:32:00.980: E/AndroidRuntime(892):  at student.a.a.fourthpage.onCreate(fourthpage.java:61)
08-09 16:32:00.980: E/AndroidRuntime(892):  at android.app.Activity.performCreate(Activity.java:4465)
08-09 16:32:00.980: E/AndroidRuntime(892):  at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1049)
08-09 16:32:00.980: E/AndroidRuntime(892):  at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1919)
08-09 16:32:00.980: E/AndroidRuntime(892):  ... 11 more

Answer 1

仅仅因为您在onCreate之后放置了变量声明，这并不意味着此代码将在onCreate之后执行。在调用String之前和onCreate成员初始化之前，您的所有EditText成员都将被初始化。您的double成员也一样。

String tb1 = txtb1.getText().toString();
String tb2 = txtb2.getText().toString();
String tb3 = txtb3.getText().toString();
String tb4 = txtb4.getText().toString();
String tb5 = txtb5.getText().toString();

double txb1= Double.parseDouble(tb1);
double txb2= Double.parseDouble(tb2);
double txb3= Double.parseDouble(tb3);
double txb4= Double.parseDouble(tb4);
double txb5= Double.parseDouble(tb5);

您必须将初始化置于onCreate之上，并分别声明String和double成员。

...
String tb1, tb2, tb3, tb4, tb5;    
double txb1, txb2, txb, txb4, txb5;

protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.fourthxml);

    //text boxes
    txtb1=(EditText)findViewById(R.id.txtb1);
    txtb2=(EditText)findViewById(R.id.txtb2);
    txtb3=(EditText)findViewById(R.id.txtb3);
    txtb4=(EditText)findViewById(R.id.txtb4);
    txtb5=(EditText)findViewById(R.id.txtb5);

    //buttons
    btnper=(Button)findViewById(R.id.btnper);

    //labels/text view
    lblgrade=(TextView)findViewById(R.id.lblgrade);
    lblper=(TextView)findViewById(R.id.lblgrade);

    tb1 = txtb1.getText().toString();
    tb2 = txtb2.getText().toString();
    tb3 = txtb3.getText().toString();
    tb4 = txtb4.getText().toString();
    tb5 = txtb5.getText().toString();

    txb1= Double.parseDouble(tb1);
    txb2= Double.parseDouble(tb2);
    txb3= Double.parseDouble(tb3);
    txb4= Double.parseDouble(tb4);
    txb5= Double.parseDouble(tb5);
}

您正在获取NumberFormatException，因为您正在解析空字符串。如果字符串不包含有效的double值，您可以使用以下方法安全地解析double或将其值设置为某个默认值。

public double getDoubleOrDefault(String value, double defValue)
{
    try
    {
        return Double.parseDouble(value);
    }
    catch (Exception ex)
    {
        return defValue;
    }
}

txb1 = getDoubleOrDefault(tb1, 0.0);

Double.parseDouble documentation

应用程序已停止在android中工作

1 个答案: