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，有谁知道怎么回事？

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监视器：

java.lang.NullPointerException：尝试调用虚方法＆＃39; int android.text.Layout.getLineCount（）＆＃39;在null对象引用上在android.widget.TextView.onMeasure（TextView.java:7520）在android.view.View.measure（View.java:19917）在android.view.ViewGroup.measureChildWithMargins（ViewGroup.java:6139）在android.widget.LinearLayout.measureChildBeforeLayout（LinearLayout.java:1485）在android.widget.LinearLayout.measureVertical（LinearLayout.java:775）在android.widget.LinearLayout.onMeasure（LinearLayout.java:657）在android.view.View.measure（View.java:19917）在android.view.ViewGroup.measureChildWithMargins（ViewGroup.java:6139）在android.widget.FrameLayout.onMeasure（FrameLayout.java:185）在android.support.v7.widget.ContentFrameLayout.onMeasure（ContentFrameLayout.java:139）在android.view.View.measure（View.java:19917）在android.view.ViewGroup.measureChildWithMargins（ViewGroup.java:6139）在android.support.v7.widget.ActionBarOverlayLayout.onMeasure（ActionBarOverlayLayout.java:393）在android.view.View.measure（View.java:19917）在android.view.ViewGroup.measureChildWithMargins（ViewGroup.java:6139）在android.widget.FrameLayout.onMeasure（FrameLayout.java:185）在android.view.View.measure（View.java:19917）在android.view.ViewGroup.measureChildWithMargins（ViewGroup.java:6139）在android.widget.LinearLayout.measureChildBeforeLayout（LinearLayout.java:1485）在android.widget.LinearLayout.measureVertical（LinearLayout.java:775）在android.widget.LinearLayout.onMeasure（LinearLayout.java:657）在android.view.View.measure（View.java:19917）在android.view.ViewGroup.measureChildWithMargins（ViewGroup.java:6139）在android.widget.FrameLayout.onMeasure（FrameLayout.java:185）在com.android.internal.policy.DecorView.onMeasure（DecorView.java:729）在android.view.View.measure（View.java:19917）在android.view.ViewRootImpl.performMeasure（ViewRootImpl.java:2436）在android.view.ViewRootImpl.performTraversals（ViewRootImpl.java:2182）在android.view.ViewRootImpl.doTraversal（ViewRootImpl.java:1366）在android.view.ViewRootImpl $ TraversalRunnable.run（ViewRootImpl.java:6768）在android.view.Choreographer $ CallbackRecord.run（Choreographer.java:923）在android.view.Choreographer.doCallbacks（Choreographer.java:735）在android.view.Choreographer.doFrame（Choreographer.java:667）在android.view.Choreographer $ FrameDisplayEventReceiver.run（Choreographer.java:909）在android.os.Handler.handleCallback（Handler.java:761）在android.os.Handler.dispatchMessage（Handler.java:98）在android.os.Looper.loop（Looper.java:156）在android.app.ActivityThread.main（ActivityThread.java:6523） at java.lang.reflect.Method.invoke（Native Method）在com.android.internal.os.ZygoteInit $ MethodAndArgsCaller.run（ZygoteInit.java:941）在com.android.internal.os.ZygoteInit.main（ZygoteInit.java:831）

Answer 1

关于你的代码的第一点，你不能从UI线程之外修改View对象。因此你应该使用各种处理程序或技术来完成它，就像@Embydextrous答案一样

第二点，如果您的代码因为这个原因而失败，这是UI线程，则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是非常不同的。问题将是另一回事，是否都是日志？可能错误的原因是你的布局，检查它

Answer 2

您要做的是从线程访问视图。但View仅适用于UI线程，因此抛出空指针异常。为此，您可以尝试：

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导致线程在UI线程上运行。

Answer 3

在Android的开发中，UI界面控件中显示的所有内容都在一个单独的线程UI-Thread（或称为MainThread）;当你想刷新其他线程中的接口时，必须跳转到UIThread，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();

}

}

或者您可以使用runOnUiThread，也可以通过Handler，Message等实现。

在线程

3 个答案: