将settext添加到textview后运行android应用程序时出错

问题描述 投票:-1回答:2

它可能是问题的java文件,它根本与xml无关:

    package com.example.android.randomnumber;

import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.util.Log;
import android.view.View;
import android.widget.EditText;
import android.widget.TextView;
import android.widget.Toast;

import java.util.Random;

public class MainActivity extends AppCompatActivity {

    EditText from = (findViewById(R.id.editTextFrom));
    EditText to = (findViewById(R.id.editTextTo));
    TextView output =(findViewById(R.id.textViewOutput));

    String wfrom = from.getText().toString();
    int numberfrom=Integer.parseInt(wfrom);
    String wto = to.getText().toString();
    int numberto=Integer.parseInt(wto);
    Random randomNumberGenerator =new Random();
    int number = randomNumberGenerator.nextInt(numberto-numberfrom)+numberfrom;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        output.setText(number);
    }
    public void generate(View view){


        if (from.getText() == null || "".equals(from.getText().toString())){
            Toast.makeText(MainActivity.this, "the -From- value is empty!",
                    Toast.LENGTH_SHORT).show();
            return;
        }else if (to.getText() == null || "".equals(to.getText().toString())){
            Toast.makeText(MainActivity.this, "the -To- value is empty!",
                    Toast.LENGTH_SHORT).show();
            return;
        }else if(numberfrom >= numberto){
            Toast.makeText(MainActivity.this, "the -To- value must be greater than the -From- value",
                    Toast.LENGTH_SHORT).show();
            return;
        }
        Log.d("test", "it's from:"+numberfrom+" to this:"+numberto+"generatednumber"+number);


    }
}

Logcat中的错误提前谢谢:

02-24 14:16:33.865 23117-23117/com.example.android.randomnumber E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.example.android.randomnumber, PID: 23117
java.lang.RuntimeException: Unable to instantiate activity ComponentInfo{com.example.android.randomnumber/com.example.android.randomnumber.MainActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'android.view.Window$Callback android.view.Window.getCallback()' on a null object reference
    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2989)
    at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3260)
    at android.app.ActivityThread.access$1000(ActivityThread.java:218)
    at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1734)
    at android.os.Handler.dispatchMessage(Handler.java:102)
    at android.os.Looper.loop(Looper.java:145)
    at android.app.ActivityThread.main(ActivityThread.java:6934)
    at java.lang.reflect.Method.invoke(Native Method)
    at java.lang.reflect.Method.invoke(Method.java:372)
    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1404)
    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1199)
 Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'android.view.Window$Callback android.view.Window.getCallback()' on a null object reference
    at android.support.v7.app.AppCompatDelegateImpl.<init>(AppCompatDelegateImpl.java:249)
    at android.support.v7.app.AppCompatDelegate.create(AppCompatDelegate.java:182)
    at android.support.v7.app.AppCompatActivity.getDelegate(AppCompatActivity.java:520)
    at android.support.v7.app.AppCompatActivity.findViewById(AppCompatActivity.java:191)
    at com.example.android.randomnumber.MainActivity.<init>(MainActivity.java:15)
    at java.lang.reflect.Constructor.newInstance(Native Method)
    at java.lang.Class.newInstance(Class.java:1690)
    at android.app.Instrumentation.newActivity(Instrumentation.java:1094)
    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2979)
    at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3260) 
    at android.app.ActivityThread.access$1000(ActivityThread.java:218) 
    at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1734) 
    at android.os.Handler.dispatchMessage(Handler.java:102) 
    at android.os.Looper.loop(Looper.java:145) 
    at android.app.ActivityThread.main(ActivityThread.java:6934) 
    at java.lang.reflect.Method.invoke(Native Method) 
    at java.lang.reflect.Method.invoke(Method.java:372) 
    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1404) 
    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1199) 

我试图通过我的手机运行它问题是stil和问题开始toshow当我添加output.setText并再次感谢你...................... .................................................. ...

java android runtime
2个回答
0
投票

您的逻辑代码不正确,请将其更改为

public class MainActivity extends AppCompatActivity {
    EditText from;
    EditText to;
    TextView output;

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

        from = (findViewById(R.id.editTextFrom));
        to = (findViewById(R.id.editTextTo));
        output = (findViewById(R.id.textViewOutput));
    }

    public void generate(View view) {
        // Get values of from and to edit text
        String wfrom = from.getText().toString();
        String wto = to.getText().toString();

        // Validate from value
        if (TextUtils.isEmpty(wfrom)) {
            Toast.makeText(MainActivity.this, "the -From- value is empty!",
                    Toast.LENGTH_SHORT).show();
            return;
        }

        // Validate to value
        if (TextUtils.isEmpty(wto)) {
            Toast.makeText(MainActivity.this, "the -To- value is empty!",
                    Toast.LENGTH_SHORT).show();
            return;
        }

        int numberfrom = Integer.parseInt(wfrom);
        int numberto = Integer.parseInt(wto);
        // Check whether from larger or equal than to
        if (numberfrom >= numberto) {
            Toast.makeText(MainActivity.this, "the -To- value must be greater than the -From- value",
                    Toast.LENGTH_SHORT).show();
            return;
        }

        // Generate a random number in range [from - to]
        Random randomNumberGenerator = new Random();
        int number = randomNumberGenerator.nextInt(numberto - numberfrom) + numberfrom;

        // Display the random number on output text view
        output.setText(number + "");

        // Log for debug
        Log.d("test", "it's from:" + numberfrom + " to this:" + numberto + "generatednumber" + number);
    }
}
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