============问题描述============
private int i = 0;
private int x = 0;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.hello_world_layout);
Button b = (Button) findViewById(R.id.button);
final TextView v2 = (TextView) findViewById(R.id.t2);
new Thread() {
public void run() {
try {
Thread.sleep(1000);
} catch (InterruptedException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
v2.setText(x++ + "");
};
}.start();
初学者 写了一个线程 。这样会出错，求解
============解决方案1============
setText 需要对 view 重新绘制,显示文本 而在 android 里对 view 重新进行绘制的话,需要在主线程中调用,或者使消息进入 Looper 队列
============解决方案2============
UI控件的函数setText只能在UI线程里调用，否则会导致异常。
可以用AsyncTask来处理。
============解决方案3============
示例代码
public class MainActivity extends Activity {
private Button incButton;
private TextView msgTextView;
private int count = 0;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
msgTextView = (TextView)findViewById(R.id.msgTextView);
incButton = (Button)findViewById(R.id.incButton);
incButton.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
AsyncTask<Void, Void, String> thread = new AsyncTask<Void, Void, String>() {
@Override
public String doInBackground(Void... params) {
count++;
return String.format("%d", count);
}
@Override
public void onPostExecute(String msg) {
msgTextView.setText(msg);
}
};
thread.execute();
}
});
}
}
============解决方案4============
或者把线程封装成一个内部类，这样代码就会写得更简洁优雅：
public class MainActivity extends Activity {
private Button incButton;
private TextView msgTextView;
private int count = 0;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
msgTextView = (TextView)findViewById(R.id.msgTextView);
incButton = (Button)findViewById(R.id.incButton);
incButton.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
new MyTask().execute();
}
});
}
private class MyTask extends AsyncTask<Void, Void, String> {
@Override
public String doInBackground(Void... params) {
count++;
return String.format("%d", count);
}
@Override
public void onPostExecute(String msg) {
msgTextView.setText(msg);
}
}
}
时间： 2024-08-01 10:44:55