[英]ANDROID - How to display value of database mysql php into textview in android studio
[英]How do I get Android Studio to display the value of a calculation in a textView
我是android编程的新手,但在编程基本应用程序时遇到问题。 该应用程序应该计算课程考试中需要的分数,以便在课程中获得一定的分数(这不是家庭作业问题,而我正在研究)。 具体来说,我在寻找一种在textView小部件中显示计算结果的方法时遇到了麻烦。 我已经在下面发布了我的代码。 附带一提,我的应用程序在启动时也会立即崩溃,因此,如果您发现任何可疑的内容,那将大有帮助。 谢谢!
更新:感谢hai hack,我的应用程序现在可以正常打开。 但是,单击按钮后它仍然崩溃。 我已经更新了我的代码和logcat以显示所做的更改
主要活动:
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.widget.EditText;
import android.widget.TextView;
import android.widget.Button;
import static com.managergmail.time.finite.finitemanager02.R.id.calculateButton;
import static com.managergmail.time.finite.finitemanager02.R.id.textViewExamMarkNeeded;
public class MainActivity extends AppCompatActivity {
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
Button buttonCalculate = (Button) findViewById(R.id.buttonCalculate);
buttonCalculate.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View view) {
EditText currentGradeInput = (EditText) findViewById(R.id.currentGradeInput);
float currentGradeValue = Float.valueOf(currentGradeInput.getText().toString());
//obtaining value of currentGrade inputted by the user and converting to float
EditText desiredGradeInput = (EditText) findViewById(R.id.desiredGradeInput);
float desiredGradeValue = Float.valueOf(desiredGradeInput.getText().toString());
//obtaining value of currentGrade inputted by the user and converting to float
EditText examWeightInput = (EditText) findViewById(R.id.examWeightInput);
float examWeightValue = Float.valueOf(examWeightInput.getText().toString());
//obtaining value of currentGrade inputted by the user and converting to float
float currentGradeWeight = 100-examWeightValue;
//calculating current grade weight
final float examMarkNeededValue;
examMarkNeededValue= ((100*desiredGradeValue)-currentGradeValue*currentGradeWeight)/examWeightValue;
textViewExamMarkNeeded.setText((Float.toString(examMarkNeededValue)));
}
});
}
}
xml代码:
<android.support.constraint.ConstraintLayout
android:layout_width="match_parent"
android:layout_height="match_parent"
<TextView
android:id="@+id/textView"
android:layout_width="180dp"
android:layout_height="45dp"
android:text="@string/input_the_weighting_of_your_exam"
app:layout_constraintBottom_toBottomOf="parent"
app:layout_constraintHorizontal_bias="0.078"
app:layout_constraintLeft_toLeftOf="parent"
app:layout_constraintRight_toRightOf="parent"
app:layout_constraintTop_toTopOf="parent"
app:layout_constraintVertical_bias="0.356" />
<TextView
android:id="@+id/textView2"
android:layout_width="180dp"
android:layout_height="45dp"
android:text="@string/input_your_desired_grade"
app:layout_constraintBottom_toBottomOf="parent"
app:layout_constraintHorizontal_bias="0.078"
app:layout_constraintLeft_toLeftOf="parent"
app:layout_constraintRight_toRightOf="parent"
app:layout_constraintTop_toTopOf="parent"
app:layout_constraintVertical_bias="0.19" />
<TextView
android:id="@+id/textViewExamMarkNeeded"
android:layout_width="265dp"
android:layout_height="64dp"
app:layout_constraintBottom_toBottomOf="parent"
app:layout_constraintLeft_toLeftOf="parent"
app:layout_constraintRight_toRightOf="parent"
app:layout_constraintTop_toTopOf="parent"
app:layout_constraintVertical_bias="0.662"
app:layout_constraintHorizontal_bias="0.378" />
<TextView
android:layout_width="180dp"
android:layout_height="45dp"
android:text="@string/input_your_current_grade"
app:layout_constraintBottom_toBottomOf="parent"
app:layout_constraintHorizontal_bias="0.073"
app:layout_constraintLeft_toLeftOf="parent"
app:layout_constraintRight_toRightOf="parent"
app:layout_constraintTop_toTopOf="parent"
app:layout_constraintVertical_bias="0.034"
android:id="@+id/textView3" />
<EditText
android:id="@+id/currentGradeInput"
android:layout_width="0dp"
android:layout_height="0dp"
android:ems="10"
android:inputType="numberDecimal"
tools:layout_constraintTop_creator="1"
tools:layout_constraintRight_creator="1"
tools:layout_constraintBottom_creator="1"
android:layout_marginStart="17dp"
app:layout_constraintBottom_toBottomOf="@+id/textView3"
android:layout_marginEnd="33dp"
app:layout_constraintRight_toRightOf="parent"
tools:layout_constraintLeft_creator="1"
app:layout_constraintTop_toTopOf="@+id/textView3"
app:layout_constraintLeft_toRightOf="@+id/textView3" />
<EditText
android:id="@+id/desiredGradeInput"
android:layout_width="133dp"
android:layout_height="31dp"
android:ems="10"
android:inputType="numberDecimal"
tools:layout_constraintTop_creator="1"
tools:layout_constraintRight_creator="1"
tools:layout_constraintBottom_creator="1"
app:layout_constraintBottom_toTopOf="@+id/examWeightInput"
android:layout_marginEnd="33dp"
app:layout_constraintRight_toRightOf="parent"
android:layout_marginTop="44dp"
app:layout_constraintTop_toBottomOf="@+id/currentGradeInput"
android:layout_marginBottom="42dp" />
<EditText
android:id="@+id/examWeightInput"
android:layout_width="0dp"
android:layout_height="33dp"
android:ems="10"
android:inputType="numberDecimal"
tools:layout_constraintTop_creator="1"
tools:layout_constraintRight_creator="1"
tools:layout_constraintBottom_creator="1"
app:layout_constraintBottom_toTopOf="@+id/calculateButton"
android:layout_marginStart="2dp"
android:layout_marginEnd="2dp"
app:layout_constraintRight_toRightOf="@+id/desiredGradeInput"
android:layout_marginTop="12dp"
tools:layout_constraintLeft_creator="1"
android:layout_marginBottom="19dp"
app:layout_constraintLeft_toLeftOf="@+id/desiredGradeInput"
app:layout_constraintTop_toTopOf="@+id/textView" />
<Button
android:id="@+id/buttonCalculate"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_marginBottom="17dp"
android:layout_marginEnd="7dp"
android:onClick="onButtonClick"
android:text="@string/calculate"
app:layout_constraintBottom_toTopOf="@+id/textViewExamMarkNeeded"
app:layout_constraintRight_toRightOf="@+id/textViewExamMarkNeeded"
tools:layout_constraintBottom_creator="1"
tools:layout_constraintRight_creator="1" />
logcat的
12-17 21:14:05.840 18312-18312/? E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.managergmail.time.finite.finitemanager02, PID: 18312
java.lang.RuntimeException: Unable to start activity ComponentInfo{com.managergmail.time.finite.finitemanager02/com.managergmail.time.finite.finitemanager02.MainActivity}: java.lang.NumberFormatException: Invalid float: ""
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2581)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2647)
at android.app.ActivityThread.-wrap11(ActivityThread.java)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1502)
at android.os.Handler.dispatchMessage(Handler.java:111)
at android.os.Looper.loop(Looper.java:207)
at android.app.ActivityThread.main(ActivityThread.java:5763)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:888)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:749)
Caused by: java.lang.NumberFormatException: Invalid float: ""
at java.lang.StringToReal.invalidReal(StringToReal.java:63)
at java.lang.StringToReal.parseFloat(StringToReal.java:308)
at java.lang.Float.parseFloat(Float.java:306)
at java.lang.Float.valueOf(Float.java:343)
at com.managergmail.time.finite.finitemanager02.MainActivity.onCreate(MainActivity.java:20)
at android.app.Activity.performCreate(Activity.java:6280)
at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1116)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2534)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2647)
at android.app.ActivityThread.-wrap11(ActivityThread.java)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1502)
at android.os.Handler.dispatchMessage(Handler.java:111)
at android.os.Looper.loop(Looper.java:207)
at android.app.ActivityThread.main(ActivityThread.java:5763)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:888)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:749)
尝试将其添加到您的editext
final EditText currentGradeInput = (EditText)findViewById(R.id.currentGradeInput);
currentGradeInput.addTextChangedListener(new TextWatcher() {
@Override
public void beforeTextChanged(CharSequence charSequence, int i, int i1, int i2) {
}
@Override
public void onTextChanged(CharSequence charSequence, int i, int i1, int i2) {
currentGradeValue = Float.valueOf(currentGradeInput.getText().toString());
}
@Override
public void afterTextChanged(Editable editable) {
}
});
上面的代码将完美运行,而不会引发任何数字格式异常。
看来examMarkNeededValue
计算为null
。 因此,我建议您使用:
String.valueOf(examMarkNeededValue)
代替
Float.toString(examMarkNeededValue)
因为在Float.toString
情况下,如果实例为null
,则抛出NullPointerException
,但是在这种情况下, String.valueOf
将返回字符串"null"
。 计算为空,因为您尚未在按钮上使用事件侦听器。
从一开始,您的EditTexts就没有值,因此在onCreate()方法中使用Float.valueOf(currentGradeInput.getText().toString())
意味着您将空字符串“”转换为浮点数。 这不可能使您的应用程序崩溃。
在这种情况下,您应在应用程序中具有一个“提交”按钮以获取输入值并进行转换。 在onCreate()中,添加:
Button btnSubmit = findViewById(R.id.btn_button);
btnSubmit.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View view) {
float desiredGradeValue = Float.valueOf(desiredGradeInput.getText().toString());
float examWeightValue = Float.valueOf(examWeightInput.getText().toString());
textViewExamMarkNeeded.setText((Float.toString(examMarkNeededValue)));
}
});
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