是否有一种方法来迭代Java SparseArray (Android) ?我使用sparsearray很容易地按索引获取值。我找不到一个。
当前回答
对于使用Kotlin的人来说,老实说,到目前为止迭代SparseArray最简单的方法是:使用Anko或Android KTX的Kotlin扩展!(感谢Yazazzello指出Android KTX)
简单地调用forEach {i, item ->}
其他回答
对于使用Kotlin的人来说,老实说,到目前为止迭代SparseArray最简单的方法是:使用Anko或Android KTX的Kotlin扩展!(感谢Yazazzello指出Android KTX)
简单地调用forEach {i, item ->}
如果不关心键,则可以在遍历稀疏数组时使用valueAt(int)来直接访问值。
for(int i = 0, nsize = sparseArray.size(); i < nsize; i++) {
Object obj = sparseArray.valueAt(i);
}
或者你只需要创建你自己的ListIterator:
public final class SparseArrayIterator<E> implements ListIterator<E> {
private final SparseArray<E> array;
private int cursor;
private boolean cursorNowhere;
/**
* @param array
* to iterate over.
* @return A ListIterator on the elements of the SparseArray. The elements
* are iterated in the same order as they occur in the SparseArray.
* {@link #nextIndex()} and {@link #previousIndex()} return a
* SparseArray key, not an index! To get the index, call
* {@link android.util.SparseArray#indexOfKey(int)}.
*/
public static <E> ListIterator<E> iterate(SparseArray<E> array) {
return iterateAt(array, -1);
}
/**
* @param array
* to iterate over.
* @param key
* to start the iteration at. {@link android.util.SparseArray#indexOfKey(int)}
* < 0 results in the same call as {@link #iterate(android.util.SparseArray)}.
* @return A ListIterator on the elements of the SparseArray. The elements
* are iterated in the same order as they occur in the SparseArray.
* {@link #nextIndex()} and {@link #previousIndex()} return a
* SparseArray key, not an index! To get the index, call
* {@link android.util.SparseArray#indexOfKey(int)}.
*/
public static <E> ListIterator<E> iterateAtKey(SparseArray<E> array, int key) {
return iterateAt(array, array.indexOfKey(key));
}
/**
* @param array
* to iterate over.
* @param location
* to start the iteration at. Value < 0 results in the same call
* as {@link #iterate(android.util.SparseArray)}. Value >
* {@link android.util.SparseArray#size()} set to that size.
* @return A ListIterator on the elements of the SparseArray. The elements
* are iterated in the same order as they occur in the SparseArray.
* {@link #nextIndex()} and {@link #previousIndex()} return a
* SparseArray key, not an index! To get the index, call
* {@link android.util.SparseArray#indexOfKey(int)}.
*/
public static <E> ListIterator<E> iterateAt(SparseArray<E> array, int location) {
return new SparseArrayIterator<E>(array, location);
}
private SparseArrayIterator(SparseArray<E> array, int location) {
this.array = array;
if (location < 0) {
cursor = -1;
cursorNowhere = true;
} else if (location < array.size()) {
cursor = location;
cursorNowhere = false;
} else {
cursor = array.size() - 1;
cursorNowhere = true;
}
}
@Override
public boolean hasNext() {
return cursor < array.size() - 1;
}
@Override
public boolean hasPrevious() {
return cursorNowhere && cursor >= 0 || cursor > 0;
}
@Override
public int nextIndex() {
if (hasNext()) {
return array.keyAt(cursor + 1);
} else {
throw new NoSuchElementException();
}
}
@Override
public int previousIndex() {
if (hasPrevious()) {
if (cursorNowhere) {
return array.keyAt(cursor);
} else {
return array.keyAt(cursor - 1);
}
} else {
throw new NoSuchElementException();
}
}
@Override
public E next() {
if (hasNext()) {
if (cursorNowhere) {
cursorNowhere = false;
}
cursor++;
return array.valueAt(cursor);
} else {
throw new NoSuchElementException();
}
}
@Override
public E previous() {
if (hasPrevious()) {
if (cursorNowhere) {
cursorNowhere = false;
} else {
cursor--;
}
return array.valueAt(cursor);
} else {
throw new NoSuchElementException();
}
}
@Override
public void add(E object) {
throw new UnsupportedOperationException();
}
@Override
public void remove() {
if (!cursorNowhere) {
array.remove(array.keyAt(cursor));
cursorNowhere = true;
cursor--;
} else {
throw new IllegalStateException();
}
}
@Override
public void set(E object) {
if (!cursorNowhere) {
array.setValueAt(cursor, object);
} else {
throw new IllegalStateException();
}
}
}
看来我找到解决办法了。我没有正确地注意到keyAt(index)函数。
所以我会这样说:
for(int i = 0; i < sparseArray.size(); i++) {
int key = sparseArray.keyAt(i);
// get the object by the key.
Object obj = sparseArray.get(key);
}
简单得很。只是要确保在实际执行循环之前获取数组大小。
for(int i = 0, arraySize= mySparseArray.size(); i < arraySize; i++) {
Object obj = mySparseArray.get(/* int key = */ mySparseArray.keyAt(i));
}
希望这能有所帮助。
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