Android - 线程问题（按钮中的随机字符切换，直到单击按钮）

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我想在按钮中切换随机字符，直到按下停止按钮。当你按下停止按钮时，随机字符将显示为按钮文字。我设法做到的唯一方法是使用Threads。但我有问题，3-4次工作，但当我打开活动第三次或某些第四次应用程序崩溃。我不知道为什么会这样。我需要帮助来解决这个问题。如果有人知道如何在没有线程的情况下做到这一点，并希望帮助我会很感激。
这是app的图片：CLICK

public class NajduzaRec extends AppCompatActivity {private int brojac = 0; String randomLetters = "ABCDEFGHIJKLMNOPQRSTUVWXYZ"; //char[] randomLetters = { 'A', 'B', 'C', 'D', 'E', 'F', 'G', 'H', 'I', 'J', 'K', 'L', 'M', 'N', 'O', 'P', 'R', 'S', 'T', 'U', 'V', 'Z', '?', '?', '?', '?', '?'}; private boolean threadRunning=true; Random r = new Random(); private static ManualResetEvent mre = new ManualResetEvent(false); EditText unosReciTxt; Button stopBtn, slovo1Btn,slovo2Btn,slovo3Btn,slovo4Btn,slovo5Btn,slovo6Btn,slovo7Btn,slovo8Btn,slovo9Btn,slovo10Btn,slovo11Btn,slovo12Btn; @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.activity_najduza_rec); stopBtn = (Button)findViewById(R.id.stopBtn); slovo1Btn = (Button)findViewById(R.id.slovo1Btn); slovo2Btn = (Button)findViewById(R.id.slovo2Btn); slovo3Btn = (Button)findViewById(R.id.slovo3Btn); slovo4Btn = (Button)findViewById(R.id.slovo4Btn); slovo5Btn = (Button)findViewById(R.id.slovo5Btn); slovo6Btn = (Button)findViewById(R.id.slovo6Btn); slovo7Btn = (Button)findViewById(R.id.slovo7Btn); slovo8Btn = (Button)findViewById(R.id.slovo8Btn); slovo9Btn = (Button)findViewById(R.id.slovo9Btn); slovo10Btn = (Button)findViewById(R.id.slovo10Btn); slovo11Btn = (Button)findViewById(R.id.slovo11Btn); slovo12Btn = (Button)findViewById(R.id.slovo12Btn); unosReciTxt = (EditText)findViewById(R.id.unosReciTxt); /*while(brojac==0) { char randomChar = randomLetters.charAt(r.nextInt(randomLetters.length())); slovo1Btn.setText("" + randomChar); }*/Thread t = new Thread(new Runnable() {public void run() { while (threadRunning) { char randomChar = randomLetters.charAt(r.nextInt(randomLetters.length())); slovo1Btn.setText("" + randomChar); } } }); t.start(); }public void stopOnClick (View v){ switch (brojac){ case 0: threadRunning = false; Thread t = new Thread(new Runnable() { public void run() { while (!threadRunning) { char randomChar = randomLetters.charAt(r.nextInt(randomLetters.length())); slovo2Btn.setText("" + randomChar); } } }); t.start(); brojac++; break; case 1: threadRunning = true; Thread t1 = new Thread(new Runnable() { public void run() { while (threadRunning) { char randomChar = randomLetters.charAt(r.nextInt(randomLetters.length())); slovo3Btn.setText("" + randomChar); } } }); t1.start(); brojac++; break; case 2: threadRunning = false; Thread t2 = new Thread(new Runnable() { public void run() { while (!threadRunning) { char randomChar = randomLetters.charAt(r.nextInt(randomLetters.length())); slovo4Btn.setText("" + randomChar); } } }); t2.start(); brojac++; break; case 3: threadRunning = true; Thread t3 = new Thread(new Runnable() { public void run() { while (threadRunning) { char randomChar = randomLetters.charAt(r.nextInt(randomLetters.length())); slovo5Btn.setText("" + randomChar); } } }); t3.start(); brojac++; break; case 4: threadRunning = false; Thread t4 = new Thread(new Runnable() { public void run() { while (!threadRunning) { char randomChar = randomLetters.charAt(r.nextInt(randomLetters.length())); slovo6Btn.setText("" + randomChar); } } }); t4.start(); brojac++; break; case 5: threadRunning = true; Thread t5 = new Thread(new Runnable() { public void run() { while (threadRunning) { char randomChar = randomLetters.charAt(r.nextInt(randomLetters.length())); slovo7Btn.setText("" + randomChar); } } }); t5.start(); brojac++; break; case 6: threadRunning = false; Thread t6 = new Thread(new Runnable() { public void run() { while (!threadRunning) { char randomChar = randomLetters.charAt(r.nextInt(randomLetters.length())); slovo8Btn.setText("" + randomChar); } } }); t6.start(); brojac++; break; case 7: threadRunning = true; Thread t7 = new Thread(new Runnable() { public void run() { while (threadRunning) { char randomChar = randomLetters.charAt(r.nextInt(randomLetters.length())); slovo9Btn.setText("" + randomChar); } } }); t7.start(); brojac++; break; case 8: threadRunning = false; Thread t8 = new Thread(new Runnable() { public void run() { while (!threadRunning) { char randomChar = randomLetters.charAt(r.nextInt(randomLetters.length())); slovo10Btn.setText("" + randomChar); } } }); t8.start(); brojac++; break; case 9: threadRunning = true; Thread t9 = new Thread(new Runnable() { public void run() { while (threadRunning) { char randomChar = randomLetters.charAt(r.nextInt(randomLetters.length())); slovo11Btn.setText("" + randomChar); } } }); t9.start(); brojac++; break; case 10: threadRunning = false; Thread t10 = new Thread(new Runnable() { public void run() { while (!threadRunning) { char randomChar = randomLetters.charAt(r.nextInt(randomLetters.length())); slovo12Btn.setText("" + randomChar); } } }); t10.start(); brojac++; break; case 11: threadRunning = true; brojac++; stopBtn.setEnabled(false); unosReciTxt.setText(""+slovo1Btn.getText().toString()+""+slovo2Btn.getText().toString()); break; } } }

答案使用Handler对象从另一个线程更新UI元素。
请参阅此问题以获取示例How to textView.setText from Thread?
另一答案我想看看你的错误日志。通过阅读代码我会说你的问题是你正在尝试从不是UI线程的线程更新UI项。
要快速测试并解决您的问题，只需将button.setText放在runonUIThread块中即可。要与另一个线程的UI线程进行通信，您可以使用Handler。
【Android - 线程问题（按钮中的随机字符切换，直到单击按钮）】DOCS：https://developer.android.com/training/multiple-threads/communicate-ui https://developer.android.com/reference/android/app/Activity#runOnUiThread(java.lang.Runnable)