java Android EditText到int会话错误

1 周，5 日 Questions & Answers 164

这可能是问得最多的问题，但很难找到答案。首先我是新手。我想做一个简单的二次方程公式应用程序。这将使我们能够快速找到解决方案。我碰到一个问题，Android Studio说代码没问题，但在打开应用程序后设备崩溃了

private Button   mButton;
private EditText mEdit;
private EditText mEdit1;
private EditText mEdit2;
private TextView mText;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    mButton = (Button)findViewById(R.id.button2);
    mEdit   = (EditText)findViewById(R.id.editText);
    mEdit1   = (EditText)findViewById(R.id.editText2);
    mEdit2   = (EditText)findViewById(R.id.editText3);
    mText = (TextView)findViewById(R.id.textView4);

    //Int definēšana
    final int i1 = Integer.parseInt(mEdit.getText().toString());
    final int i2 = Integer.parseInt(mEdit1.getText().toString());
    final int i3 = Integer.parseInt(mEdit2.getText().toString());

    mButton.setOnClickListener(
            new View.OnClickListener()
            {
                public void onClick(View view)
                {
                    //Mainīgo ievade
                    int a = i1;
                    //Pārbauda vai a nav nulle
                    if (a == 0){
                        mText.setText(String.valueOf("Nav kvadrātvienādojums"));
                    } else {
                        int b = i2;
                        int c = i3;

                        //Diskriminanta aprēķināšana
                        double diskr = (b*b)-4*a*c;
                        //Kvadrātsakne no diskriminanta
                        double sd = (double) Math.sqrt(diskr);
                        //Sakņu aprēķināšana
                        double x1 = (-b+sd)/(2*a);
                        double x2 = (-b-sd)/(2*a);

                        //Rezultāta izvade
                        if (diskr < 0){
                            mText.setText(String.valueOf("Kvadrātvienādojumam nav sakņu"));
                        } else if (diskr == 0){
                            mText.setText(String.valueOf("Kvadrātvienādojumam ir viena sakne: " + x1));
                        } else {
                            mText.setText(String.valueOf("Kvadrātvienādojuma saknes: " + x1 + " un " + x2));
                        }
                    }
                }
            });
}

以及可能有助于检测问题的logcat

FATAL EXCEPTION: main
Process: com.homemade.prtbust.kvadratvienadojums, PID: 4552
java.lang.RuntimeException: Unable to start activity ComponentInfo{com.homem`enter code here`ade.prtbust.kvadratvienadojums/com.homemade.prtbust.kvadratvienadojums.MainActivity}: java.lang.NullPointerException: Attempt to invoke virtual method '安卓.text.Editable 安卓.widget.EditText.getText()' on a null object reference
at 安卓.app.ActivityThread.performLaunchActivity(ActivityThread.java:3133)
at 安卓.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3243)
at 安卓.app.ActivityThread.access$1000(ActivityThread.java:218)
at 安卓.app.ActivityThread$H.handleMessage(ActivityThread.java:1718)
at 安卓.os.Handler.dispatchMessage(Handler.java:102)
at 安卓.os.Looper.loop(Looper.java:145)
at 安卓.app.ActivityThread.main(ActivityThread.java:6917)
at java.lang.reflect.Method.invoke(Native Method)
at java.lang.reflect.Method.invoke(Method.java:372)
at com.安卓.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1404)
at com.安卓.internal.os.ZygoteInit.main(ZygoteInit.java:1199)
Caused by: java.lang.NullPointerException: Attempt to invoke virtual method '安卓.text.Editable 安卓.widget.EditText.getText()' on a null object reference
    at com.homemade.prtbust.kvadratvienadojums.MainActivity.onCreate(MainActivity.java:38)
    at 安卓.app.Activity.performCreate(Activity.java:6609)
    at 安卓.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1134)
    at 安卓.app.ActivityThread.performLaunchActivity(ActivityThread.java:3086)
    at 安卓.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3243)
    at 安卓.app.ActivityThread.access$1000(ActivityThread.java:218)
    at 安卓.app.ActivityThread$H.handleMessage(ActivityThread.java:1718)
    at 安卓.os.Handler.dispatchMessage(Handler.java:102)
    at 安卓.os.Looper.loop(Looper.java:145)
    at 安卓.app.ActivityThread.main(ActivityThread.java:6917)
    at java.lang.reflect.Method.invoke(Native Method)
    at java.lang.reflect.Method.invoke(Method.java:372)
    at com.安卓.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1404
    at com.安卓.internal.os.ZygoteInit.main(ZygoteInit.java:1199)

private Button mButton; private EditText mEdit; private EditText mEdit1; private EditText mEdit2; private TextView mText; @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.activity_main); mButton = (Button)findViewById(R.id.button2); mEdit = (EditText)findViewById(R.id.editText); mEdit1 = (EditText)findViewById(R.id.editText2); mEdit2 = (EditText)findViewById(R.id.editText3); mText = (TextView)findViewById(R.id.textView4); mButton.setOnClickListener( new View.OnClickListener() { public void onClick(View view) { //Int definēšana int i1 = Integer.parseInt(mEdit.getText().toString()); int i2 = Integer.parseInt(mEdit1.getText().toString()); int i3 = Integer.parseInt(mEdit2.getText().toString()); //Mainīgo ievade int a = i1; //Pārbauda vai a nav nulle if (a == 0){ mText.setText(String.valueOf("Nav kvadrātvienādojums")); } else { int b = i2; int c = i3; //Diskriminanta aprēķināšana double diskr = (b*b)-4*a*c; //Kvadrātsakne no diskriminanta double sd = (double) Math.sqrt(diskr); //Sakņu aprēķināšana double x1 = (-b+sd)/(2*a); double x2 = (-b-sd)/(2*a); //Rezultāta izvade if (diskr < 0){ mText.setText(String.valueOf("Kvadrātvienādojumam nav sakņu")); } else if (diskr == 0){ mText.setText(String.valueOf("Kvadrātvienādojumam ir viena sakne: " + x1)); } else { mText.setText(String.valueOf("Kvadrātvienādojuma saknes: " + x1 + " un " + x2)); } } } }); }

//load all the views from the xml file setContentView(R.layout.activity_main); mButton = (Button)findViewById(R.id.button2); mEdit = (EditText)findViewById(R.id.editText); mEdit1 = (EditText)findViewById(R.id.editText2); mEdit2 = (EditText)findViewById(R.id.editText3); mText = (TextView)findViewById(R.id.textView4); //Int definēšana final int i1 = Integer.parseInt(mEdit.getText().toString()); final int i2 = Integer.parseInt(mEdit1.getText().toString()); ... mButton.setOnClickListener(/*your code here*/);

@Override protected void onStart() { super.onStart(); final int i1 = Integer.parseInt(mEdit.getText().toString()); final int i2 = Integer.parseInt(mEdit1.getText().toString()); final int i3 = Integer.parseInt(mEdit2.getText().toString()); }

共 (3) 个答案

# 1 楼答案

您没有为活动分配任何布局，因此您的所有编辑文本、按钮和文本视图都不存在，当您试图通过代码访问其中任何一个时，程序将崩溃

其次，您应该在单击按钮时读取变量的值，而不是在oncreate中，因为这将导致另一个错误，因为您将尝试解析空字符串（除非您在xml中的android:text标记中设置了值）。我也不会宣布它们为最终版本（因为以后您将无法修改它们）

尝试使用以下代码：

# 2 楼答案

我想你错过了

setContentView(R.layout.activity_main);“activity_name是布局的名称，其中是编辑文本”

在使用findViewById之前必须调用setContentView

# 3 楼答案

在设置活动的内容视图后，请尝试编写此代码

在创建EditText视图之前，无法从EditText获取文本。如果这并没有解决你的问题，试着在onStart上写下你的i1/2/3变量

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java Android EditText到int会话错误

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