这是一小段代码，但是我已经对其进行了很多次调整，我不知道它是否仍然明智。我正在尝试将String保存到持久的sharePreference存储中，并在应用启动时获取该字符串。
由于不保存字符串，因此每次尝试输入字符串时代码都会崩溃。
public class MainActivity extends AppCompatActivity {
TextView displayHours;
EditText userYears;
EditText userAge;
TextView outputText;
SharedPreferences sharedPref;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
displayHours = (TextView) findViewById(R.id.displayHours);
userYears = (EditText) findViewById(R.id.userYears);
userAge = (EditText) findViewById(R.id.userAge);
outputText = (TextView) findViewById(R.id.outputText);
sharedPref = getPreferences(Context.MODE_PRIVATE);
String defaultValue = getString(R.string.user_age);
String savedAge = sharedPref.getString("AgeData", defaultValue);
setAgeIfEmpty(savedAge);
Button calcButton = (Button) findViewById(R.id.calcButton);
calcButton.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
float range = 300;
if (Float.parseFloat(userYears.getText().toString()) <= range) {
float years = Float.parseFloat(userYears.getText().toString());
float totalHours = years*365*24;
String setHours = Float.toString(totalHours);
displayHours.setText(setHours);
}
}
});
EditText ageText = (EditText) findViewById(R.id.userAge);
ageText.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View view) {
String ageNumber = userAge.getText().toString();
userAge.setText(ageNumber);
sharedPref = getPreferences(Context.MODE_PRIVATE);
SharedPreferences.Editor editor = sharedPref.edit();
editor.putString("AgeData", ageNumber);
editor.apply();
Toast myToast = Toast.makeText(getApplicationContext(), "Age Saved!",
Toast.LENGTH_SHORT);
myToast.show();
}
});
ageText.addTextChangedListener(new TextWatcher() {
@Override
public void beforeTextChanged(CharSequence s, int start, int count, int after) {
}
@Override
public void onTextChanged(CharSequence s, int start, int before, int count) {
}
@SuppressLint("StringFormatMatches")
@Override
public void afterTextChanged(Editable s) {
int age = Integer.parseInt(userAge.getText().toString());
int intYears = Integer.parseInt(userYears.getText().toString());
String text;
if (age < intYears/3){
text = getString(R.string.Message_1, age);
outputText.setText(text);
}
else if (intYears < 8 || Integer.parseInt(displayHours.getText().toString()) < 40000){
text = getString(R.string.Message_3, displayHours.getText().toString());
outputText.setText(text);
}
else{
text = getString(R.string.Message_2, age);
outputText.setText(text);
}
}
});
}
public void setAgeIfEmpty(String data) {
if (!TextUtils.isEmpty(userAge.getText())) {
userAge.setText(data);
}
}
回溯；
I/zygote: at void com.android.internal.os.Zygote$MethodAndArgsCaller.run() (Zygote.java:240)
at void com.android.internal.os.ZygoteInit.main(java.lang.String[]) (ZygoteInit.java:767)
D/OpenGLRenderer: HWUI GL Pipeline
D/: HostConnection::get() New Host Connection established 0xa4ffbf40, tid 7284
I/OpenGLRenderer: Initialized EGL, version 1.4
D/OpenGLRenderer: Swap behavior 1
W/OpenGLRenderer: Failed to choose config with EGL_SWAP_BEHAVIOR_PRESERVED, retrying without...
D/OpenGLRenderer: Swap behavior 0
D/EGL_emulation: eglCreateContext: 0x994f6be0: maj 3 min 1 rcv 4
D/EGL_emulation: eglMakeCurrent: 0x994f6be0: ver 3 1 (tinfo 0x98f23590)
E/eglCodecCommon: glUtilsParamSize: unknow param 0x000082da
glUtilsParamSize: unknow param 0x000082da
I/Choreographer: Skipped 36 frames! The application may be doing too much work on its main thread.
D/EGL_emulation: eglMakeCurrent: 0x994f6be0: ver 3 1 (tinfo 0x98f23590)
W/View: dispatchProvideAutofillStructure(): not laid out, ignoring
I/AssistStructure: Flattened final assist data: 3872 bytes, containing 1 windows, 14 views
I/zygote: Background concurrent copying GC freed 3588(934KB) AllocSpace objects, 2(40KB) LOS objects, 67% free, 756KB/2MB, paused 4.816ms total 110.298ms
I/zygote: Do partial code cache collection, code=20KB, data=29KB
I/zygote: After code cache collection, code=20KB, data=29KB
Increasing code cache capacity to 128KB
I/zygote: Do partial code cache collection, code=49KB, data=51KB
After code cache collection, code=49KB, data=51KB
Increasing code cache capacity to 256KB
D/AndroidRuntime: Shutting down VM
E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.example.lifewirehours, PID: 7243
java.lang.NumberFormatException: For input string: ""
at java.lang.Integer.parseInt(Integer.java:620)
at java.lang.Integer.parseInt(Integer.java:643)
at com.example.lifewirehours.MainActivity$3.afterTextChanged(MainActivity.java:98)
at android.widget.TextView.sendAfterTextChanged(TextView.java:9375)
at android.widget.TextView$ChangeWatcher.afterTextChanged(TextView.java:11917)
at android.text.SpannableStringBuilder.sendAfterTextChanged(SpannableStringBuilder.java:1262)
at android.text.SpannableStringBuilder.replace(SpannableStringBuilder.java:574)
at android.text.SpannableStringBuilder.replace(SpannableStringBuilder.java:504)
at android.text.SpannableStringBuilder.replace(SpannableStringBuilder.java:502)
at android.text.method.NumberKeyListener.onKeyDown(NumberKeyListener.java:131)
at android.widget.TextView.doKeyDown(TextView.java:7316)
at android.widget.TextView.onKeyDown(TextView.java:7093)
at android.view.KeyEvent.dispatch(KeyEvent.java:2691)
at android.view.View.dispatchKeyEvent(View.java:11662)
at android.view.ViewGroup.dispatchKeyEvent(ViewGroup.java:1827)
at android.view.ViewGroup.dispatchKeyEvent(ViewGroup.java:1827)
at android.view.ViewGroup.dispatchKeyEvent(ViewGroup.java:1827)
at android.view.ViewGroup.dispatchKeyEvent(ViewGroup.java:1827)
at android.view.ViewGroup.dispatchKeyEvent(ViewGroup.java:1827)
at android.view.ViewGroup.dispatchKeyEvent(ViewGroup.java:1827)
at com.android.internal.policy.DecorView.superDispatchKeyEvent(DecorView.java:437)
at com.android.internal.policy.PhoneWindow.superDispatchKeyEvent(PhoneWindow.java:1818)
at androidx.core.view.KeyEventDispatcher.activitySuperDispatchKeyEventPre28(KeyEventDispatcher.java:130)
at androidx.core.view.KeyEventDispatcher.dispatchKeyEvent(KeyEventDispatcher.java:87)
at androidx.core.app.ComponentActivity.dispatchKeyEvent(ComponentActivity.java:133)
at androidx.appcompat.app.AppCompatActivity.dispatchKeyEvent(AppCompatActivity.java:558)
at androidx.appcompat.view.WindowCallbackWrapper.dispatchKeyEvent(WindowCallbackWrapper.java:59)
at androidx.appcompat.app.AppCompatDelegateImpl$AppCompatWindowCallback.dispatchKeyEvent(AppCompatDelegateImpl.java:2814)
at com.android.internal.policy.DecorView.dispatchKeyEvent(DecorView.java:351)
at android.view.ViewRootImpl$ViewPostImeInputStage.processKeyEvent(ViewRootImpl.java:4714)
at android.view.ViewRootImpl$ViewPostImeInputStage.onProcess(ViewRootImpl.java:4586)
at android.view.ViewRootImpl$InputStage.deliver(ViewRootImpl.java:4128)
at android.view.ViewRootImpl$InputStage.onDeliverToNext(ViewRootImpl.java:4181)
at android.view.ViewRootImpl$InputStage.forward(ViewRootImpl.java:4147)
at android.view.ViewRootImpl$AsyncInputStage.forward(ViewRootImpl.java:4274)
at android.view.ViewRootImpl$InputStage.apply(ViewRootImpl.java:4155)
at android.view.ViewRootImpl$AsyncInputStage.apply(ViewRootImpl.java:4331)
at android.view.ViewRootImpl$InputStage.deliver(ViewRootImpl.java:4128)
at android.view.ViewRootImpl$InputStage.onDeliverToNext(ViewRootImpl.java:4181)
at android.view.ViewRootImpl$InputStage.forward(ViewRootImpl.java:4147)
at android.view.ViewRootImpl$InputStage.apply(ViewRootImpl.java:4155)
at android.view.ViewRootImpl$InputStage.deliver(ViewRootImpl.java:4128)
at android.view.ViewRootImpl.deliverInputEvent(ViewRootImpl.java:6642)
at android.view.ViewRootImpl.doProcessInputEvents(ViewRootImpl.java:6616)
at android.view.ViewRootImpl.enqueueInputEvent(ViewRootImpl.java:6577)
at android.view.ViewRootImpl$ViewRootHandler.handleMessage(ViewRootImpl.java:3911)
at android.os.Handler.dispatchMessage(Handler.java:105)
at android.os.Looper.loop(Looper.java:164)
at android.app.ActivityThread.main(ActivityThread.java:6541)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.Zygote$MethodAndArgsCaller.run(Zygote.java:240)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:767)
Process 7243 terminated.
在此行：int age = Integer.parseInt(userAge.getText().toString());之所以会收到NumberFormatException，是因为userAge.getText().toString()返回了一个空字符串（“”），该字符串无法解析为Integer，因为它不是数字。您的日志显示：
java.lang.NumberFormatException: For input string: ""
at java.lang.Integer.parseInt(Integer.java:620)
at java.lang.Integer.parseInt(Integer.java:643)
at com.example.lifewirehours.MainActivity$3.afterTextChanged(MainActivity.java:98)
Udi Idan评论和Traendy回答指出了您的错误。您不能将空字符串或非“数字字符串”转换为数字，这将引发NumberFormatException。我认为您应该使用此问题中的函数：
[How can I parse String to int with the default value?
public static int parseWithDefault(String s, int defaultVal) {
return s.matches("-?\\d+") ? Integer.parseInt(s) : defaultVal;
}
此功能允许您在转换之前检查输入的字符串，并且如果该字符串不只包含数字，它还允许您使用defaultVal参数指定默认值。
然后您可以更改行
int age = Integer.parseInt(userAge.getText().toString());
收件人
int age = MainActivity.parseWithDefault(userAge.getText().toString(), 100);