在线程中刷新 editText

Question

我已经制作了这段代码，我需要在屏幕上实时显示一些值，所以，我试图这样做，有人知道哪里出了问题吗？

public class Test extends AppCompatActivity {

    TextView lastValue;
    int i = 0;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_test);

        lastValue = (TextView) findViewById(R.id.textViewID);
        Thread t = new Thread(new Runnable() { 

            @Override
            public void run() {
                while(i<90000) {
                    i++;
                    lastValue.setText(String.valueOf(i));

                }
        }});       t.start();

    }
}

Android 监控：

java.lang.NullPointerException: Attempt to invoke virtual method 'int android.text.Layout.getLineCount()' on a null object reference at android.widget.TextView.onMeasure(TextView.java:7520) at android.view.View.measure(View.java:19917) at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:6139) at android.widget.LinearLayout.measureChildBeforeLayout(LinearLayout.java:1485) at android.widget.LinearLayout.measureVertical(LinearLayout.java:775) at android.widget.LinearLayout.onMeasure(LinearLayout.java:657) at android.view.View.measure(View.java:19917) at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:6139) at android.widget.FrameLayout.onMeasure(FrameLayout.java:185) at android.support.v7.widget.ContentFrameLayout.onMeasure(ContentFrameLayout.java:139) at android.view.View.measure(View.java:19917) at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:6139) at android.support.v7.widget.ActionBarOverlayLayout.onMeasure(ActionBarOverlayLayout.java:393) at android.view.View.measure(View.java:19917) at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:6139) at android.widget.FrameLayout.onMeasure(FrameLayout.java:185) at android.view.View.measure(View.java:19917) at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:6139) at android.widget.LinearLayout.measureChildBeforeLayout(LinearLayout.java:1485) at android.widget.LinearLayout.measureVertical(LinearLayout.java:775) at android.widget.LinearLayout.onMeasure(LinearLayout.java:657) at android.view.View.measure(View.java:19917) at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:6139) at android.widget.FrameLayout.onMeasure(FrameLayout.java:185) at com.android.internal.policy.DecorView.onMeasure(DecorView.java:729) at android.view.View.measure(View.java:19917) at android.view.ViewRootImpl.performMeasure(ViewRootImpl.java:2436) at android.view.ViewRootImpl.performTraversals(ViewRootImpl.java:2182) at android.view.ViewRootImpl.doTraversal(ViewRootImpl.java:1366) at android.view.ViewRootImpl$TraversalRunnable.run(ViewRootImpl.java:6768) at android.view.Choreographer$CallbackRecord.run(Choreographer.java:923) at android.view.Choreographer.doCallbacks(Choreographer.java:735) at android.view.Choreographer.doFrame(Choreographer.java:667) at android.view.Choreographer$FrameDisplayEventReceiver.run(Choreographer.java:909) at android.os.Handler.handleCallback(Handler.java:761) at android.os.Handler.dispatchMessage(Handler.java:98) at android.os.Looper.loop(Looper.java:156) at android.app.ActivityThread.main(ActivityThread.java:6523) at java.lang.reflect.Method.invoke(Native Method) at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:941) at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:831)

Answer 1

What you are trying to do is accessing a view from a thread. But the View is only available with UI Thread and hence null pointer exception is thrown. To achieve this you can try:

Thread t = new Thread(new Runnable() { 
    @Override
    public void run() {
        while(i<90000) {
            i++;
            runOnUiThread(new Runnable {
                lastValue.setText(String.valueOf(i));
            });
        }
    }
});       
t.start();

runOnUiThread causes thread to 运行 on UI Thread.

Answer 2

关于您的代码的第一点，您不能从 UI thread.Therefore 外部修改 View 对象，您应该使用各种处理程序或技术来完成它，就像@Embydextrous 的回答

第二点，如果你的代码因为 UI 线程的这个原因而失败，logchat 将是这样的

android.view.ViewRootImpl$CalledFromWrongThreadException: Only the original thread that created a view hierarchy can touch its views.
at android.view.ViewRootImpl.checkThread(ViewRootImpl.java:6566)
at android.view.ViewRootImpl.requestLayout(ViewRootImpl.java:911)

但是你的logchat很different.Problem会是别的东西，都是日志吗？可能错误的原因是你的布局，检查一下

Answer 3

在Android的开发中，所有显示在UI界面的控件都在一个单独的线程UI-Thread（或叫MainThread）；当你想在其他线程刷新界面时，必须跳转到UI线程，你可以使用Handler来实现这个操作。

public class Test extends AppCompatActivity {

private static final int REFRESH_LASTVALUE=0;
private Handler handler=new Handler(){
    @Override
    public void handleMessage(Message msg) {
        switch (msg.what){
            case REFRESH_LASTVALUE:
                lastValue.setText((String)msg.obj);
                break;
        }
    }
};
TextView lastValue;
int i = 0;
@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_test);

    lastValue = (TextView) findViewById(R.id.textViewID);
    new Thread(new Runnable() {
        @Override
        public void run() {
            while(i<90000) {
                i++;
                Message message=new Message();
                message.what=REFRESH_LASTVALUE;
                message.obj=String.valueOf(i);
            }
        }}).start();

}

}

或者你可以使用 runOnUiThread，这也是通过 Handler、Message 等实现的。

在线程中刷新 editText

Refresh editText in a thread

android

real-time

textview