Question

我正在尝试创建一个基本应用程序，该应用程序只计算用户将方向从纵向更改为横向的次数，并在屏幕上显示计数。我有：

public class MainActivity extends Activity {
int count = 0;
private static boolean inLandscape = true;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    TextView tv = (TextView) findViewById(R.id.count);
    tv.setText(getResources().getString(R.string.count) + ' ' + count);
    if (!inLandscape && getResources().getConfiguration().orientation == Configuration.ORIENTATION_LANDSCAPE)
    {
        inLandscape = true;
        count++;
        Log.e("Debug","In Landscape " + count);
    }
    else if (inLandscape && getResources().getConfiguration().orientation == Configuration.ORIENTATION_PORTRAIT)
        inLandscape = false;
}

问题是，在我的调试语句中，count始终为1，并且文本永远不会在屏幕上更改。做一些研究，我认为这是因为每次方向改变时，活动都会被删除并重新创建。如何在整个方向变化中保持变量值？

我尝试将savedInstanceState与

一起使用

if (savedInstanceState.containsKey("count"))
            count = savedInstanceState.getInt("count");
savedInstanceState.putInt("count", count);

但是这会在containsKey行给出NullPointerException。

Answer 1

覆盖onSaveInstanceState以存储您的方向更改计数器。

@Override
public void onSaveInstanceState(Bundle savedInstanceState) {
    super.onSaveInstanceState(savedInstanceState);
    savedInstanceState.putInt("count", count)
}

并覆盖onRestoreInstanceState以便在更改后将其读回。

@Override
public void onRestoreInstanceState(Bundle savedInstanceState) {
    super.onRestoreInstanceState(savedInstanceState);
    count = savedInstanceState.getInt("count");
}

显然，您仍然可以将代码保存在'onCreate'中的相同位置，以便每次调用onCreate时根据方向有条件地添加到计数器。

Answer 2

它给你一个NullPointerException，因为saveInstanceState为null。您还需要将savedInstanceState.putInt("count", count)放在onRestoreInstanceState方法中。所以你的代码看起来像......

int mCount;    

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    TextView tv = (TextView) findViewById(R.id.count);
    mCount = 0;
    tv.setText(getResources().getString(R.string.count) + ' ' + mCount);
}

@Override
public void onConfigurationChanged(Configuration newConfig) {
    super.onConfigurationChanged(newConfig);
    mCount++;
    tv.setText(getResources().getString(R.string.count) + ' ' + count);
}

public void onRestoreInstanceState(Bundle savedInstanceState) {
    // Always call the superclass so it can restore the view hierarchy
    super.onRestoreInstanceState(savedInstanceState);
    mCount = savedInstanceState.getInt("count");
}

@Override
public void onSaveInstanceState(Bundle savedInstanceState) {
    savedInstanceState.putInt("count", mCount);

    // Always call the superclass so it can save the view hierarchy state
    super.onSaveInstanceState(savedInstanceState);
}

有关详细信息，请参阅http://developer.android.com/training/basics/activity-lifecycle/recreating.html和http://developer.android.com/guide/topics/resources/runtime-changes.html。

Android计数用户更改方向的次数

2 个答案: