Question

我试图将double数据类型的变量转换为字符串，反之亦然，但我遇到了logcat生成的错误。请帮我找出并纠正错误。

JavaCode：

public class DataTypeConversion extends ActionBarActivity {

TextView stringValue;
TextView numericValue;
double var;
String text;

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

    stringValue = (TextView) findViewById(R.id.stringValue);
    numericValue = (TextView) findViewById(R.id.numericValue);

    stringValue.setText("0123.45");
    var = Double.valueOf((String) stringValue.getText());
    text = String.valueOf(var);

XML：

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:paddingBottom="@dimen/activity_vertical_margin"
android:paddingLeft="@dimen/activity_horizontal_margin"
android:paddingRight="@dimen/activity_horizontal_margin"
android:paddingTop="@dimen/activity_vertical_margin"
tools:context="com.example.datatypeconversion.DataTypeConversion$PlaceholderFragment" >

<TextView
    android:layout_width="wrap_content"
    android:layout_height="wrap_content" 
    android:id="@+id/stringValue"/>

<TextView
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:id="@+id/numericValue"/>

LOGCAT输出：

04-16 09:17:20.715: D/AndroidRuntime(1056): Shutting down VM
04-16 09:17:20.715: W/dalvikvm(1056): threadid=1: thread exiting with uncaught exception (group=0x41465700)
04-16 09:17:20.735: E/AndroidRuntime(1056): FATAL EXCEPTION: main
04-16 09:17:20.735: E/AndroidRuntime(1056): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.datatypeconversion/com.example.datatypeconversion.DataTypeConversion}: java.lang.NullPointerException
04-16 09:17:20.735: E/AndroidRuntime(1056):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2211)
04-16 09:17:20.735: E/AndroidRuntime(1056):     at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2261)
04-16 09:17:20.735: E/AndroidRuntime(1056):     at android.app.ActivityThread.access$600(ActivityThread.java:141)
04-16 09:17:20.735: E/AndroidRuntime(1056):     at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1256)
04-16 09:17:20.735: E/AndroidRuntime(1056):     at android.os.Handler.dispatchMessage(Handler.java:99)
04-16 09:17:20.735: E/AndroidRuntime(1056):     at android.os.Looper.loop(Looper.java:137)
04-16 09:17:20.735: E/AndroidRuntime(1056):     at android.app.ActivityThread.main(ActivityThread.java:5103)
04-16 09:17:20.735: E/AndroidRuntime(1056):     at java.lang.reflect.Method.invokeNative(Native Method)
04-16 09:17:20.735: E/AndroidRuntime(1056):     at java.lang.reflect.Method.invoke(Method.java:525)
04-16 09:17:20.735: E/AndroidRuntime(1056):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:737)
04-16 09:17:20.735: E/AndroidRuntime(1056):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:553)
04-16 09:17:20.735: E/AndroidRuntime(1056):     at dalvik.system.NativeStart.main(Native Method)
04-16 09:17:20.735: E/AndroidRuntime(1056): Caused by: java.lang.NullPointerException
04-16 09:17:20.735: E/AndroidRuntime(1056):     at com.example.datatypeconversion.DataTypeConversion.onCreate(DataTypeConversion.java:31)
04-16 09:17:20.735: E/AndroidRuntime(1056):     at android.app.Activity.performCreate(Activity.java:5133)
04-16 09:17:20.735: E/AndroidRuntime(1056):     at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1087)
04-16 09:17:20.735: E/AndroidRuntime(1056):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2175)
04-16 09:17:20.735: E/AndroidRuntime(1056):     ... 11 more
04-16 09:17:24.825: I/Process(1056): Sending signal. PID: 1056 SIG: 9

Answer 1

你的程序崩溃了：

stringValue.setText("0123.45");

这意味着此行返回null：

 stringValue = (TextView) findViewById(R.id.stringValue);

最可能的罪魁祸首是你没有activity_data_type_conversion.xml中带有id stringValue的TextView，这是你的布局。确保文本视图存在，并且具有正确的ID值，并且它应该有效。

Answer 2

请试试这个，我希望它可以帮到你

var = Double.valueOf(stringValue.getText().toString());

双到字符串转换错误

2 个答案: